Treating High Salt Content Wastewater with Sand Bioreactors

THESIS

Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University

Kristen Conroy

Graduate Program in Food, Agricultural & Biological Engineering

The Ohio State University

2017

Master's Examination Committee:

Karen M. Mancl, Advisor

Olli H. Tuovinen

Zhongtang Yu

Copyrighted by

Kristen Monica Conroy

2017

Abstract

The ability to treat high salt content wastewater in a cost-effect and environmentally sustainable manner is important to the food processing industry. Processing foods such as meat and fish often produces wastewater with a high salt content, which can interfere with treatment systems. Demand for meat and fish products are increasing rapidly as both population and GDP rise globally. At the same time, many small-scale food producers are facing increased wastewater treatment costs and more stringent environmental regulation.

The objective of the present study was to determine the feasibility of treating high salt, high organic matter content wastewater with sand bioreactors. Sand bioreactors are fixed film systems consisting of pea gravel, coarse sand and fine sand. Bioreactors were dosed with turkey processing wastewater as control. The three treatments consisted of adding 6 g/L table salt, 13 g/L table salt and 35 g/L sea salt to the wastewater. Organic matter removal (COD, TOC) and ammonia removal were measured. Organic matter removal by sand bioreactors at all treatment levels was >90% from week 4-49. Acclimation periods for ammonia removal in the filters increased with increased salt content in the wastewater, ranging from 4 to 7 weeks and steady state ammonia removal was >99%.

Clogging was observed in all salt treatment levels and was treated with resting and intermittent loading. Best practices for mitigating and alleviating clogging should be further explored. This low cost, non-sludge-forming technology could offer a potential alternative to conventional systems for high salt, high fat content wastewater treatment.

Acknowledgments

I would like to acknowledge my advisor, Dr. Karen Mancl, for her openness and for sharing her wealth of knowledge. I would like to thank all of my committee members for assisting me in my pursuit and offering advice and guidance. I would like to thank

Lingling Wang for her expertise, endless patience and positive attitude. Thank you to everyone at Whitewater Processing Co. for the crucial contribution of wastewater for this study and always bringing deliveries with a smile. I would like to thank Chris Geccik for his assistance. Thank you also to Kun Liu and Charlotte Bucy for their willingness to help with various tasks and for their comradery.

I am also grateful for fellowships and funding from the Ohio State University, the Ohio

Agricultural Research and Development Center and the Baas Memorial Endowment

Fund.

iii

Vita

2013...... B.S. Ecological Science, Elon University

2015 to present ...... Graduate Fellow, Department of Food

Agriculture and Biological Engineering, The

Ohio State University

Fields of Study

Major Field: Food, Agricultural & Biological Engineering

Table of Contents

Abstract ...... ii Acknowledgments...... iii Vita ...... iv Table of Contents ...... v List of Tables ...... vii List of Figures ...... viii Chapter 1: Introduction ...... 1 Chapter 2: Treating High Salt Content Wastewater with Sand Bioreactors ...... 7 Introduction ...... 7 Methods ...... 11 Experimental Design ...... 11 Wastewater Characteristics ...... 13 Analytical Methods...... 14 Results ...... 14 Organic Matter Removal ...... 14 Ammonia Removal ...... 15 Discussion ...... 20 Acclimation Period ...... 20 Steady State Period ...... 21 Clogging and Clogging Treatment ...... 23 Conclusions ...... 25 Chapter 3: Treating Saline Wastewater with Marine Sediment Inoculated Sand Bioreactors: A Feasibility Study ...... 26 Introduction ...... 26 Organic Matter Removal ...... 28 - Nitrogen Removal – NH3 and NO2 ...... 32 Inoculation ...... 34 Fixed Film Systems ...... 36

Research Applications and Objective ...... 37 Methods ...... 37 Experimental Design ...... 37 Wastewater Characteristics ...... 39 Inoculant ...... 39 Analytical Methods...... 40 Results ...... 40 Acclimation Phase ...... 40 Steady State Period and Overall Treatment ...... 41 Clogging Period ...... 42 Treatment of Clogged Filters ...... 43 Discussion ...... 48 Acclimation period ...... 48 Steady State Period and Clogging Period ...... 50 Intermittent Loading ...... 51 Resting Period...... 52 Post Rest Period ...... 53 Conclusions ...... 54 Chapter 4: Overall Conclusions and Recommendations for Future Work ...... 56 Conclusions ...... 56 Recommendations for Future Work ...... 58 Operations and Maintenance Approaches to Clogging ...... 58 Acclimation Period ...... 63 Microbial Community ...... 63 Scaling Up ...... 64 Other Wastewaters and Reuse ...... 65 REFERENCES ...... 66 Appendix A: Table of Acronyms ...... 73

List of Tables

Table 1. Effective size and uniformity coefficient of sand and gravel ...... 12 Table 2. COD removal during the entire study period for controls, 6 g/L and 13 g/L added table salt (Average ± Standard Deviation) ...... 15 Table 3. Average ammonia and COD removal for control, 6 g/L and 13 g/L added table salt throughout steady state period (Average ± S.D.) ...... 17 Table 4. Impacts of salt content on organic matter removal in the literature ...... 31 Table 5. Parameters of raw turkey processing wastewater ...... 39 Table 6. Variation in ammonia and TOC removal from steady state through clogging period ...... 51 Table 7. Frequently used acronyms ...... 73

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List of Figures

Figure 1. International Panel of Climate Change diagram of wastewater treatment and discharge pathways (Doorn et al., 2006) ...... 4 Figure 2. International Panel on Climate Change diagram edited to include sand bioreactors ...... 5 Figure 3. Experimental design showing columns and treatments...... 13 Figure 4. COD removal for control, 6 g/L and 13 g/L added table salt before and after resting period ...... 15 Figure 5. Ammonia removal during acclimation period for control, 6 g/L and 13 g/L added table salt filters ...... 16 Figure 6. Ammonia removal for control, 6 g/L and individual 13 g/L added table salt filters during steady state period and clogging ...... 18 Figure 7. The 13 g/L added table salt filters a) and c) before resting period and b) and d) after resting period, respectively. e) Ponding on top of gravel layer of 13 g/L filters prior to resting...... 19 Figure 8. Ammonia removal for 6 g/L and 13 g/L added table salt filters after a 5 week resting period ...... 20 Figure 9. Experimental design and column structure ...... 38 Figure 10. Ammonia removal by control and filters treating 35 g/L sea salt wastewater 41 Figure 11. TOC and ammonia removal by control and filters treating 35 g/L sea salt wastewater...... 42 Figure 12. TOC and ammonia removal by control and 35 g/L added sea salt filter (a in Figure 14) ...... 43 Figure 13. TOC and ammonia removal by control at full loading rate and 35 g/L filter (b in Figure 14) receiving intermittent loading ...... 44 Figure 14. Filters treating 35 g/L sea salt wastewater on day 255 of study. a) Filter with reduced effluent quality due to breakthrough and b) Intermittently loaded filter with high quality effluent ...... 45 Figure 15. a) Raw wastewater b) control effluent and post-clogging effluent from c) and d) 35 g/L filter experiencing breakthrough and intermittently loaded 35 g/L filter, respectively ...... 45 Figure 16. 35 g/L sea salt filters a) on intial day of resting period and after b) 2, c)4 and d) 5 weeks ...... 46 Figure 17. Ammonia removal for 35 g/L sea salt filters with continuous original loading rate and intermittent loading beginning 6.5 weeks after resting period...... 47 Figure 18. TOC removal for 35 g/L sea salt filters with continuous original loading rate and intermittent loading beginning 6.5 weeks after resting period ...... 48

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Chapter 1: Introduction

The food processing industry is large and growing around the world. Food processing

includes any system that takes food from raw material to processed good. This includes industries such as slaughtering, canning and curing. Wastewater from slaughterhouses can contain blood, manure, feathers and fat (USEPA, 2012). These wastewaters are challenging to treat due to their high organic matter and fat content. Another compound that is present in several food processing wastewaters and increases the complexity of treatment is salt. Salt is present in the wastewaters of industries such as fish processing, meat curing and pickling. Wastewater from these processes therefore contains not only high loads of organic matter and nutrients, but also a high salt content. Knowing how to effectively treat wastewaters from these industries in a cost effective manner is crucial to the sustainability of food processing plants.

Wastewater treatment can be accomplished through many avenues. Chemical, physical and biological process all play a part in wastewater treatment. In most cases several of these processes are used in conjunction to reach the desired level of treatment. The first step is often a physical process to remove large solids. The second step usually uses biological processes for treatment of remaining pollutants and nutrients (Doorn, 2006).

Biological systems create appropriate environmental conditions for naturally occurring

1 organisms to degrade or consume pollutants. Microbial consortia grow in the system and are used to treat the wastewater.

Biological treatment systems can be anaerobic or aerobic. Anaerobic systems are devoid of oxygen and cultivate a microbial community that can survive in these conditions.

Aerobic systems, alternatively, operate in the presence of oxygen. Some popular aerobic systems include sequencing batch reactors (SBR) and membrane bioreactors (MBR).

These systems are both considered suspended film systems. Suspended film systems rely on microbes growing in flocs within the water itself to treat the wastewater as it passes through various tanks. Aerobic treatment plants are the most commonly used form of wastewater treatment in developed countries (Doorn, 2006).

Suspended film biological systems are used by many meat producers that have on-site wastewater treatment plants (O’Keefe, 2002, 2003; Laginestra, 2015). These on-site systems can be a large economic burden for small food processors due to wastewater treatment regulations put in place by the EPA and individual states (Brinfield and

Phillips, 1977). Suspended film systems have several economic concerns. Electric costs associated with constant aeration of the system and the production of a sludge byproduct are two important economic considerations when treating meat industry wastewater

(Laginestra, 2015). Sludge is considered its own waste stream and these solids must be treated or reused in addition to treating the water portion of the waste (Doorn, 2006). The

noise and olfactory pollution associated with some large-scale wastewater treatment plants are also a public concern (O’Keefe, 2002; O’Keefe, 2003).

Another type of treatment system that appears appropriate for high strength, high fat content wastewater is a sand bioreactor. Sand bioreactors are fixed film systems meaning they have media on which biofilms, congregations of bacteria that grow on the media in a film, can grow. A biofilm is a group of cells that immobilize on a surface and form

colonies with protective, secreted coatings (Costerton, 1995). Fixed film systems are a

relatively underexplored sector of aerobic biological treatment for high salt content

wastewater. Media for fixed film systems can include textiles, ceramics, sand, wetland soils, Pall rings and more. The sand bioreactors used in this study are a fixed film system using various sizes of sand ranging from pea gravel to fine sand. These systems have been successfully used to treat food processing wastewater specifically from the poultry industry (Kang et al., 2007a).

Fixed film systems offer many benefits but sand bioreactors are not always considered, as

shown in Figure 1. This image by the International Panel on Climate Change shows all

the potential pathways for wastewater. Once the wastewater has been collected to a plant,

the options become Aerobic, Anaerobic or Wetland. The benefit of the wetland system,

as shown, is the entire process of sludge management is removed. Sand bioreactors can

also fill this same space and offer an aerobic treatment alternative to conventional

activated sludge systems currently used by many meat producers (Mancl et al., 2016)

(Figure 2). Sand bioreactor do not require mechanical aeration and do not produce sludge, two potential economic benefits for industries using their own on-site wastewater treatment.

Figure 1. International Panel of Climate Change diagram of wastewater treatment and discharge pathways (Doorn et al., 2006)

Figure 2. International Panel on Climate Change diagram edited to include sand bioreactors Salt can have a negative impact on biological wastewater treatment (Kargi and Dincer,

1996; Hashad et al., 2006). Microbial consortia must adapt to their surrounding environment and salt represents a stress to these communities. When a solute imbalance occurs in the environment, the cells will try to balance the osmotic pressure. In environments with high salt content, water will move out of the bacterial cells and the cells will lose functionality. This means that any bacteria that do not have salt-tolerant adaptations will not be able to survive in the environment.

With respect to wastewater treatment, this means that the microbial community treating the wastewater will likely be changed by the addition of salt to the wastewater stream. 5

The ability of microbes to adapt to additional salts varies widely among species and the amount of salt in a wastewater will partially dictate which microbes are present. To know if sand bioreactors can still provide treatment for food processing wastewaters with high salt content, three different salt levels were utilized in this study.

Understanding sand bioreactors limitation in addressing high salt content wastewater has the potential to open up new opportunities to implement this environmentally friendly, low cost, passive treatment system. A full-scale sand bioreactor system has already been put into operation at a turkey processing plant (Mancl et al., 2016). Therefore, understanding which other food industries may be able to use this technology is a step toward sustainable, cost-effective high salt content wastewater treatment.

Chapter 2: Treating High Salt Content Wastewater with Sand Bioreactors

Introduction

Finding a sustainable solution to treating high salt content wastewater is a pressing issue in industrial waste management. High salt content wastewater is produced from industries as varied as tanning, chemical production, pickling, oil refining, tomato canning, precious metal recovery, soap manufacturing, meat curing, shellfish processing and fisheries

(Yoshie et al., 2004; Lefebvre, 2006; Riffat and Krongthamchat, 2007). Production and consumption of meat and fish around the world is projected to continue growing rapidly over the coming decade, particularly in developing nations, leading to increased wastewater streams from these industries (Rene, 2008; Hansen, 2014; OECD/FAO,

2015). This will lead to increases in high salt content wastewater, furthering the need to find a biological alternative to the current expensive and technologically demanding physiochemical treatment processes (Lefebvre, 2006; Khengaoui et al., 2015; Shi et al.,

2015).

High salt content impacts biological treatment by causing bacteria that are involved in the treatment of pollutants to plasmolyze. Plasmolysis is a process by which microbes move water outside of the cell membrane in an attempt to balance an increased solute concentration in the surrounding environment, leading to death (Oparka, 1994). Increased

sodium in the water will cause this solute imbalance and can impact cells ability to grow

in the high salt environment. Even prior to plasmolysis, the increased solute

concentration in the environment can lead to decreased enzyme functionality in the

microbial cells. If a bacterial population can be selected for or acclimated to handle this

stress, biological treatment can be used. Biological treatment is both less expensive and

has fewer environmental concerns relative to physiochemical treatment (Woolard and

Irvine, 1994).

Many studies have examined the biological treatment of high salt content wastewaters

over the past two decades. Large variations in the level of salinity were used in these

studies and they have found biological treatment was inhibited. It is generally agreed that

organic matter removal inhibition becomes evident at 30 g/L NaCl. Sequencing batch

reactors (SBR) and anaerobic treatment systems are the most commonly studied

technologies in this category. Kokabian et al. (2013) treated high salt content, azo-dye

containing wastewater using a lab scale anaerobic-aerobic system. They reported roughly

70% removal of COD when treating 0-20 g/L NaCl wastewater with a lab scale aerated

activated sludge system (Kokabian et al., 2013). Riffat and Krongthamchat (2007) used

lab scale upflow anaerobic filter reactors, which used plastic Pall rings as media, with and

without halophilic cultures to treat synthetic wastewater. They found that a stepwise

increase from 10 g/L NaCl to 20 g/L NaCl led to a short-term drop of COD removal to

60%, with a long term efficiency of 80%. Furthermore, the lab scale systems were able to

maintain >75% COD removal at 35 g/L NaCl (Riffat and Krongthamchat, 2007).

Uygur (2006) used a lab scale sequencing batch reactor (SBR) treating synthetic wastewater to test organic matter removal from high salt content wastewater. Results showed a drop in COD removal above 10g/L NaCl using an SBR. Rene et al. (2008) studied benchtop SBR systems treating synthetic wastewater and found that the systems maintained a 95% removal up to 20g/L NaCl. Similarly, Deorsola et al. (2013) studied treatment of synthetic wastewater in a lab study of an SBR system. COD removal was found to decrease at 2% mass/volume NaCl, but remained above 80% even at 6% mass/volume NaCl (Deorsola et al. 2013). Yogalakshmi and Joseph (2010) used high salt content wastewater to shock an MBR submerged in an aerated tank. They found COD removal of 95% when the system was fed wastewater without salt and subsequently 83-

87% removal when 5, 10, 20 and 30 g/L NaCl were added to the wastewater

(Yogalkshmi and Joseph, 2010). All studies found inhibition of treatment due to the presence of excess salt in the system, but maintained some level of biological treatment.

Sand bioreactors offer another biological treatment option for wastewater. Sand bioreactors require fewer mechanical parts and less energy input than anaerobic treatment systems and sequencing batch reactors. The system consists of layers of sand that allow wastewater to pass through slowly and rely upon biofilms produced on the media to treat the water. Sand filters have been effectively used to treat sewage wastewater, winery wastewater and turkey processing wastewater (Tao et al., 2011; Welz, 2014; Kang et al.,

2007a). This technology requires minimal operations and maintenance and is particularly

suited to onsite wastewater treatment.

Treatment of high salt content wastewater by sand bioreactors in an underexplored area

of biological treatment. Khengaoui et al. (2015) studied bench top fine sand filters to treat synthetic wastewater with total salinity of .06-0.265% using CaCl2. COD removal was

maintained at 80% (Khengaoui et al., 2015). Jurš e et al. (2015) conducted a pilot scale study of fine grain sand filters planted with Poplar. The study tested a combination of groundwater and municipal sludge with 11 g/L NaCl and reported a 15% reduction in

COD removal compared with systems where no salt was added (Jurse et al., 2015). Thus, this technology is relatively unexplored in regards to the impacts of high salt content wastewater.

The salinity of the wastewater from the many industries mentioned varied widely from

<1% to 15%. Some meat curing plants produce wastewater with a salinity of 0.4%

(Carawan et al., 1979). Wastewater from tanneries were shown to have salinities around

1.7% (Sivaprakasam et al., 2008). On the higher end, concentrated wastewater from the

fisheries industry will often have salinities as high as 15%, and it is necessary to dilute

these before beginning biological treatment (Corsino, 2016). Cui et al. (2009) calculated

that based on the amount of wastewater produced by flush toilets in China, if the country

were to begin using sea water for flush toilets and to segregate domestic wastewater from

other sources, the resulting water would have a salinity of 1.3%.

The present study proposes novel research into sand bioreactor technology differentiated

by the use of turkey processing wastewater, a higher salinity level than has been

previously tested and a three-layer, unplanted sand filter. The sand bioreactor system

used in this study has been shown to effectively treat turkey processing wastewater at 0.3

and 0.6 % (weight/volume) salt, indicating that some microbial species were able to

effectively adapt to the conditions in the filter (Chen, 2016).

The objective of the present study was to test sand bioreactors’ ability to treat high salt

content wastewater. The criteria for treatment performance was removal of organic

matter and ammonia. Salt levels of 6 g/L table salt and 13 g/L table salt were evaluated in

high strength, high fat content wastewater. These treatments will be referred to

throughout this paper as the 6g/L and 13 g/L filters.

Methods

Experimental Design

Clear, plastic columns of 14.5 cm interior diameter, 0.3 cm wall thickness and 92 cm

height were filled in layers of 15 cm gravel, 15 cm coarse sand, 46 cm fine sand and 5 cm

gravel from top to bottom. Sand was analyzed using sieve analysis for effective size and uniformity coefficient (Table 1) (Mancl and Tao, 2011).

Table 1. Effective size and uniformity coefficient of sand and gravel

Sand Type Uniformity Coefficient Effective Size

Gravel 1.3 3.5 mm

Coarse Sand 2.9 1.3 mm

Fine Sand 3.3 0.26 mm

Six columns were utilized in this study (Figure 3). Two each were used to treat turkey processing wastewater with no added salt, 6 g/L of added table salt and 13 g/L of added table salt. Filters were operated for 12 months. Wastewater was dosed into the system at

6 hour intervals at a rate of 4 cm /day or approximately 700 mL/day.

Figure 3. Experimental design showing columns and treatments

Wastewater Characteristics

The wastewater used throughout the experiment was turkey processing wastewater provided by Whitewater Processing Co (Harrison, OH). Average COD and ammonia of the wastewater were 2,770 ± 1450 mg/L and 68 ± 27 mg/L, respectively. The water was collected in 19 L containers after passing through a grease trap, but before any further treatment. The containers were then transported to the laboratory and maintained at 4 °C.

Wastewater was mixed to suspend solids and set out of the refrigerator for at least 30-60 min before being dosed onto the filters. The table salt consisted primarily of NaCl with calcium silicate as an anticaking agent. Table salt was manually added to 2 L batches of wastewater to obtain the desired concentrations.

Analytical Methods

Ammonia nitrogen was tested using an ammonia test kit (HACH 5870040, Loveland,

CO). Ammonia was tested three times per week for the first six weeks, weekly for the

next two weeks, bi-weekly for the next four weeks and then monthly for the remainder of

the study. Chemical oxygen demand (COD) was tested in accordance with the Standard

Method (APHA, 1998). COD was tested weekly from weeks 4-7 and then monthly for the remainder of the study. One-way analysis of variance (ANOVA) was used to compare ammonia and COD removal across groups (Minitab 17, State College, PA).

Results

Organic Matter Removal

Organic matter removal for all treatments, as measured by COD removal, had an average

of >91% over the entire study period (Table 2). COD removal for the 6 g/L and 13 g/L

treatments during steady state operations was 94.1 ± 2.7 and 93.8 ± 5.5. After 255 days of operation, the 13 g/L filters COD removal was 70.9% and all filters were rested for 5 weeks (Figure 4). Following the rest, average percent COD removal for the 6 g/L and 13 g/L filters from day 302-340 of the study were, respectively, 98.2 ± 0.5 and 93.5 ± 6.8.

Table 2. COD removal during the entire study period for controls, 6 g/L and 13 g/L added table salt (Average ± Standard Deviation)

Control 6 g/L 13 g/L 98.5 ± 0.8 94.1 ± 2.7 91.6 ± 8.2

Figure 4. COD removal for control, 6 g/L and 13 g/L added table salt before and after resting period

COD removal was statistically significantly different between the control and both the 6 g/L and 13 g/L filters (p < 0.05). The 6 g/L and 13 g/L filters COD removal was not statistically significantly different from one another in COD removal (p < 0.05).

Ammonia Removal

Ammonia removal fluctuated throughout the study. The ammonia removal could be categorized into four distinct periods. The ammonia removal decreased during the first

11-17 days and then began to increase. A steady state followed in which ammonia

removal was >99% and COD removal was >93%. Clogging then commenced in several filters and a decrease in ammonia removal was observed for the 13 g/L filters. The filters were then rested for 5 weeks and a post-rest period was observed where ammonia removal was >99% for the final 7 weeks of the study.

Acclimation Period

The acclimation period for ammonia removal in each filter was defined as beginning on

the first day of system operation and ending on the day on which measured ammonia

removal was greater than 95% in both replicates for a given treatment. Acclimation for

each treatment took several days longer than for the control (Figure 5). The 6 g/L and 13

g/L filters took 5 and 12 days, respectively, longer than the control filter to reach steady

state.

Figure 5. Ammonia removal during acclimation period for control, 6 g/L and 13 g/L added table salt filters 16

Steady State Period

The control filters achieved ammonia and COD removal of 99.8 and 98.6% removal, respectively, during steady state operations. During steady state operations, the ammonia removal showed no significant difference among the control, 6 g/L or 13 g/L treatments

(p < 0.05). Ammonia and COD removal for the 6 g/L and 13 g/L treatments were not statistically significantly different from one another throughout steady state operations.

Average ammonia removal was 99.8 and 99.0% for each treatment, respectively (Table

3).

Table 3. Average ammonia and COD removal for control, 6 g/L and 13 g/L added table salt throughout steady state period (Average ± S.D.)

Control 6 g/L 13 g/L

Ammonia Removal (%) 99.7 ± 0.7 99.8 ± 0.3 99.0 ± 1.2

COD Removal (%) 98.6 ± 0.9 94.1 ± 32.7 93.8 ± 5.5

Days from commencement of 231 179-226* 144 steady state to Clogging * One filter clogged after 179 days of steady state and the other did not clog at all.

Clogging

One impact of increased salt content in the wastewater was filter clogging. Clogging was seen in only one of the 6 g/L filters and began on day 208. Clogging was observed in both 13 g/L filters, commencing on day 180. Ponding on the gravel layer occurred for a brief period for the 13 g/L filters. By day 234, clogging had impacted ammonia removal for the 13 g/L treatment (Figure 6).

Figure 6. Ammonia removal for control, 6 g/L and individual 13 g/L added table salt filters during steady state period and clogging

As a measure to assist the filters in recovering from clogging, a 5 week resting period

was implemented. No wastewater was added to the sand bioreactors for 5 weeks. As a

result, all the discoloration was eliminated (Figure 7).

a) b) c) d)

Figure 7. The 13 g/L added table salt filters a) and c) before resting period and b) and d) after resting period, respectively. e) Ponding on top of gravel layer of 13 g/L filters prior to resting

Post Rest

Following the resting period, the filters were doesed with wastewater for another 7 weeks. The ammonia removal in the 13 g/L filters recovered after the resting period and remained at >99% throughout the remainder of the study (Figure 8). Ammonia removal for the 6 g/L filter also remained >99% (Figure 8).

Figure 8. Ammonia removal for 6 g/L and 13 g/L added table salt filters after a 5 week resting period

Discussion

Acclimation Period

This study found that increasing the salt content of wastewater increased the amount of time it took for the filters to acclimate and reach steady state for ammonia removal.

Increasing salinity from 0 to 6 g/L added table salt added 5 days to the acclimation period. An additional 12 days were needed for acclimation of the 13 g/L filter compared 20

with the control. The finding that extended acclimation time is needed with increased

salinity is in agreement with a study done by Chen et al. (2015) who found that when the

salinity of mustard wastewater increased from 0 g/L to 1.5 g/L added NaCl, the treatment

system needed three weeks to acclimate but when going from 1.5 to 3.0 g/L NaCl, four to

five weeks were needed for acclimation.

The total time to steady state for the 6 g/L filter was 29 days and for the 13 g/L filter was

36 days, compared with 24 days for the control filter. Mannina et al. (2016) found a

similar time to steady state when the salt concentration was increased from 0-8 g/L NaCl

at 2 g/L intervals weekly. Recovery to pre-salt COD removal was not observed until week four and another 26 days were needed for acclimation when salt level increased

from 8 g/L to 10 g/L NaCl (Mannina et al., 2016). Shi et al. (2014) tested treatment of 23

g/L total dissolved solids wastewater in both an SBR and MBR system and found that 43

and 29 days were needed for full ammonia treatment acclimation. The need for a 4+ week

acclimation period when working with high salt content wastewater as seen in the

literature is supported by the findings of the present study that 4-5 weeks were needed

for acclimation.

Steady State Period

This study found that adding 6 g/L table salt versus 13 g/L of table salt did not have

statistically significantly different impacts on COD and ammonia removal. In both

treatments ammonia removal remained above 99% and COD removal remained above

93% during the steady state period. These removal efficiencies are higher than those found in studies of other fixed media technologies at comparable salt levels. Klomjek and

Nitisoravut (2005) studied the ability of planted constructed wetlands to treat wastewater with NaCl added to obtain conductivity of 4 mS/cm and found maximum ammonia removal was 65.3%. In their study of planted horizontal flow wetlands for polishing tannery wastewater with conductivity of 16.7 mS/cm, findings by Calheiros et al. (2012) showed 51-80% COD removal and 40-93% ammonia removal. Sand bioreactors appear to have better treatment at these salt levels than constructed wetlands.

Activated sludge systems treating wastewater with salt content similar to those used in this study had varying results. Corsino et al. (2016) studied SBR treatment of synthetic wastewater and found >90% COD removal at 5 g/L NaCl. Kargi et al. (2002) studied an un-inoculated fed batch aeration tank system treating 1% NaCl wastewater and found

COD removal efficiency ranging from 70% to 80%, varying with loading rate. At 10 g/L

NaCl, Mannina et al. (2016) found 93% COD removal with a sequential batch membrane bio-reactor. Bassin et al. (2011) tested both a moving bed biological reactor and an SBR system to treat a mixture of sewage and industrial wastewater with 8,000 mg/L Cl-. They found that ammonia removal reached a high of 90% over the study period in each technology (Bassin et al., 2011). COD removal of 95% was maintained in an SBR systems with 20 g/L NaCl wastewater in a study by Rene et al. (2008). Similarly, when using SBR and MBR as post-treatment for pharmaceutical wastewater with 23 g/L total dissolved solids, Shi et al. (2014) found 86 and 90% ammonia removal, respectively.

Aloui et al. (2009) observed 85% COD removal and 70% ammonia removal when using

an activated sludge system to treat fish processing wastewater with 25 g/L NaCl. All of these removal efficiencies are comparable to the results found in the present study and indicate that during steady state operations sand bioreactors are a sufficient aerobic treatment system comparable to activated sludge systems during their steady state operations.

Clogging and Clogging Treatment

Clogging of sand bioreactors and other fixed media filters can arise when the systems are

stressed. Kang et al. (2007b) found that when sand bioreactors were consistently loaded

at three times the loading rate used in the present study, the systems clogged and ponded

after 49 days of operation. The present study found that when 13 g/L table salt was added

to turkey processing wastewater, the sand bioreactors began clogging on day 180. The 13

g/L filters also experienced some ponding on top of the gravel layer after 6 months of

operation. When 6 g/L table salt was added to the wastewater, only one of the filters

clogged and this began after 208 days of operation. Therefore, clogging may be a concern

but only after 6-7 months of operating the sand bioreactors and very minimally at 6 g/L

added table salt.

Clogging is often attributed to the growth of biofilms that impact the areas where the

effective size of the sand changes. During a more than 800 day study of sand filters

Rodgers et al. (2004) found that clogging was due mainly to biomass accumulation in the

23 top 1 cm of a 25 cm coarse sand layer below a 10 cm gravel layer of the filter, which led to ponding during the study (Rodgers et al., 2004). In the present study, the clogging layer first formed in the coarse sand directly above the fine sand layer. The concept of media layer changes being primary sites for clogging is supported by observations by

Kristiansen (1981) that sand filter clogging occurred at the interface between the gravel and find sand layers only. Wang and Banks (2006) observed that clogging due to growth of biofilms will occur in fine sand but not coarse sand when various media sizes were used in anaerobic sand filters.

Biofilm accumulation can be the cause of clogging, but clogging can be exacerbated by the anaerobic conditions caused as water is trapped in the filter behind the clogging layer.

A decrease in oxygen in aerobic systems previously achieving high ammonia removal at high salinity can lead to inhibition of ammonia oxidizing bacteria and an accumulation of ammonia in the effluent (Ramos et al., 2015). Clogging layers were observed in the filters in this study when a dark color appeared at the bottom of the coarse sand layer. A blackening of the sand particle surfaces was observed in Wang and Bank’s (2006) study of an anaerobic sand filter system, further supporting that anaerobic conditions may have arisen in the 6 g/L and 13 g/L filters after clogging commenced.

In the present study the filters were not dosed with wastewater during a 5 week resting period. A 5 week resting period was previously shown to have a restorative effect on sand bioreactors in a lab scale study by Kang et al. (2007b). Resting restored ammonia

treatment to steady state conditions for both 6 g/L and 13 g/L filters once dosing resumed and alleviated the clogging issues for the remaining 7 weeks of the study.

Conclusions

In this study, the ability of sand bioreactors to treat high salt content wastewater was studied. The sand bioreactors removed >93% of COD and >99% of ammonia when salt

levels were increased to 13 g/L table salt. Adding 13 g/L rather than 6 g/L table salt did

not statistically significantly change mean removal of COD and ammonia.. The

acclimation period of the filters increased as salt level increased, indicating that increased

salinity in wastewater will require a longer acclimation period for sand bioreactors.

Time to clogging decreased as salt levels increased, but clogging was not observed in any

filters until the end of the 6th month of operation. Clogging was alleviated for the

remainder of the study period by discontinuing dosing for 5 weeks. This study shows that

sand bioreactors can feasibly treat high salt content wastewater. Clogging is a concern

and more research into the best ways to mitigate clogging and ideal rest periods is

recommended. Research on additional salt levels is also recommended to find the limits

of the sand bioreactor systems in terms of treatment and clogging.

Chapter 3: Treating Saline Wastewater with Marine Sediment Inoculated Sand

Bioreactors: A Feasibility Study

Introduction

Throughout the world fisheries and aquaculture are on the rise, coastal cities are becoming more vulnerable to seawater infiltration and seawater is replacing fresh water in various applications (Yue and Tang, 2011, World Bank, 2013, WWAP, 2015). All of these lead to a growing need to treat high salt content wastewater. New technologies and approaches are emerging that use seawater in place of fresh water. These systems have been designed to address the need to conserve and best utilize limited fresh water resources in dry areas. Using seawater for toilet flushing is a growing trend in some coastal areas, with 80% of residences in Hong Kong now using seawater in toilets (Cui et al., 2009; Yue and Tang, 2011; Guan et al., 2014). In Chile, an entire mining site has been developed to use seawater in place of fresh water to ensure long-term water security in a dry region (WWAP, 2015). High salt content wastewater from aquaculture, fish farming, and coastal wastewater treatment plants susceptible to seawater intrusion are predicted to grow globally in coming years (WWAP, 2015). Finding a way to effectively treat wastewaters containing sea level salt content in a sustainable manner is thus crucial to the global water use of the future.

Seawater poses a unique challenge to wastewater treatment due to the high salt content of

this wastewater. Salinity has negative impacts on wastewater treatment systems ranging

from corrosion of mechanical parts to inhibition of bacterial growth (Oparka, 1994;

Ericsson and Hallmans, 1996). Microbial consortia used for traditional wastewater treatment are not always able to adapt to high salt environments, which can decrease treatment efficiency in biological systems when wastewater salt content is high (Shi et al., 2015). Removing salt from these waste streams is an economic concern because of the energy requirements for desalination. For this reason prospective applications where seawater can directly be substituted for fresh water, without having to desalinize, are being increasingly explored world-wide.

Treating high salt content wastewater with biological systems has gained growing interest over the past fifteen years. The technologies studied span both anaerobic and aerobic treatments, with the most common aerobic systems being sequencing batch reactors

(SBR) and membrane bioreactors (MBR). A wide variety of salinity levels have been tested, from 0.5-10% salt content and the impacts of salinity on wastewater treatment efficiency vary widely across studies. Nearly all studies showed at least some inhibition in organic matter and nutrient removal at a threshold of 3% salinity (Uygur and Kargi,

2004; Uygur, 2006; Osaka et al., 2008; Shi et al., 2012).

Organic Matter Removal

Salt appears to effect treatment of different constituents in different ways, including

organic matter and nitrogen. One of the most important parameters for regulatory

permitting and pollution control in wastewater treatment is the removal of organic matter.

When shock loading a lab scale MBR system treating synthetic wastewater with various

NaCl concentrations, Yogalakshmi and Joseph (2010) found that COD removal was not

severely impacted even at 30 g/L NaCl. The steady state conditions without added NaCl

were 95% removal and reduced to 87% at 5 g/L NaCl and 83% at 30 g/L NaCl. Wang et

al. (2015a) tested the treatment of synthetic wastewater with 30 g/L added seawater

crystals, corresponded to 3% salinity by an SBR. The SBR was seeded with sludge previously acclimated to the 30 g/L seawater crystal concentration and 90% COD

removal was observed (Wang et al., 2015a). Corsino et al. (2016) studied a sequencing

batch airlift reactor with granules that was acclimated to a mixture of synthetic and fish

canning wastewater at 25 g/L NaCl prior to the experiment. The NaCl concentration

increased to 30 g/L and diluted fish canning wastewater without being mixed with

synthetic wastewater was used. COD removal dropped to ~60%, but gradually increased

to ~90% (Corsino et al., 2016). When organic loading rate was increased by 1 kg

COD/m3/day and NaCl concentration increased from 30 g/L to 38 g/L, the systems

highest COD removal rate was ~85%. Deorsola et al. (2013) studied an SBR system and

observed 81% COD removal from a synthetic wastewater even at NaCl levels of 6%

weight/volume. They did, however, see a continuous decrease in organic matter removal

28 as salt levels increased from negligible in the control to 6% weight/volume NaCl in increments of 2% NaCl (Deorsola et al., 2013).

Figueroa et al. (2015) found increased salinity impacted their study of fishmeal wastewater treatment more than in the previously mentioned studies. Fishmeal wastewater was made using seawater and treated in constantly aerated flasks inoculated with eight known halotolerant microbial species (Figueroa et al., 2015). At a salinity of

3.4%, the removal of COD was 59% after 80 hours. This system lacked activated sludge and operated at an elevated temperature of 45 °C (Figueroa et al., 2015). Uygur and Kargi

(2004) also noted a greater salinity impact than studies by Wang et al. (2015a) or

Yogalakshmi and Joseph (2010), finding that COD removal reduced to 60% at 3% weight to volume NaCl when treating synthetic wastewater in an SBR system.

Osaka et al. (2008) and Aloui et al. (2009) used 2 and 4% salinity levels, using NaCl, and found that at 2% little impact on organic matter removal occurred, but at 4% inhibition was notable. In a study testing synthetic methanol wastewater in a continuously stirred tank reactor removal of TOC decreased steadily with increase in salinity levels up to 4%

(Osaka, 2008). Aloui et al. (2009) used a lab scale activated sludge system with an acclimatized consortium of bacteria to treat fisheries wastewater adjusted to up to 20, 40 and 60 g/L NaCl content. At 2% NaCl almost complete removal of COD was possible, but treatment decreased when NaCl was increased to 4% (Aloui et al., 2009). A summary

of the literature on organic matter removal from high salt content wastewater is presented

in Table 4.

Within studies, it is observed that increased salt content in the wastewater leads to

decreased organic matter treatment efficiency. It is more difficult to compare reported

percent removal efficiencies for salt levels across studies. Variation in the type of

wastewater, salt and technology used may contribute to variability in actual percent

results between studies. Yet, as seen in the Table 4, the trend of decreased performance with increased salinity is observed within each of the studies. The control in each study is a wastewater with no added salt, unless otherwise noted. For Corsino et al. (2016) Table

4 shows only the difference in % COD removal when the salt concentration increased from 30 g/L to 38 g/L NaCl. In the case of Aloui et al. (2009) the original fish processing wastewater was treated as the control and contained 10 g/L NaCl. The controls serve as a benchmark to highlight the impact of each salt level used within a study. The present study tested turkey processing wastewater with 35 g/L added sea salt, contributing to the knowledge of more specifically which salinity level causes treatment inhibition to the point of infeasibility.

Table 4. Impacts of salt content on organic matter removal in the literature 31

- Nitrogen Removal – NH3 and NO2

Several studies in the literature note relatively successful treatment of ammonia when treating high salt content wastewater. Values of < 2.0% NaCl content wastewater resulted in ammonia removal >80% (Chen et al., 2015; Aloui et al., 2009; Yogalakshmi and

Joseph, 2010). Chen et al. (2015) in their study of an SBR as secondary treatment for mustard processing wastewater found that at 16.1 g/L NaCl, ammonia removal stabilized around 90%. Uygur (2006) studied SBR systems with and without Halobacter halobium added to the initial microbial consortium. Ammonia removal rate in both SBR systems decreased a salinity increased from 0 to 6% NaCl (Uygur, 2006). Aloui et al. (2009) found that 2% NaCl did not significantly impact ammonia removal. At 4% NaCl ammonia removal decreased to about 75% (Aloui et al., 2009). Yogalakshmi and Joseph

(2010) tested the ability of an aerated membrane bioreactor (MBR) to handle shock loads of various NaCl concentrations in a lab study. Steady state conditions of 95% removal were transiently decreased to 84% when 5g/L NaCl was added to the wastewater and

64% at 30 g/L added NaCl (Yogalaskshmi and Joseph, 2010).

Two studies noted that high salt content led to more ammonia in the effluent than influent

(Ng et al., 2014; Deorsola et al., 2013). Ng et al. (2014) found more ammonia in the effluent than influent when studying two different MBR systems treating high salt content pharmaceutical wastewater characterized by 20,000 mg/L Cl-. One system had a container of biocarriers submerged in the activated sludge system and the second was

seeded with salt marsh sediment. The authors concluded that the inhibition of nitrification could be partially attributed to the salt content of the pharmaceutical wastewater (Ng et al., 2014). Deorsola et al. (2013) studied an SBR and found that ammonia was present at about the same level at the beginning and end of the 1 day aeration period for 0, 2 and 4% mass/volume added NaCl. However, at 6% mass/volume added NaCl, the ammonoia level was higher in the effluent than influent (Deorsola et al., 2013).

An increase in nitrite accumulation in relation to increased wastewater salinity has been noted in the literature. Yogalakshmi and Joseph (2010) found that when shocking an

MBR system with 5 to 60 g/L NaCl, the highest nitrite levels were found when the system was shocked with 20 and 30 g/L NaCl. Findings by Corsino et al. (2016) indicated that ammonia oxidizing bacteria were not inhibited at NaCl levels up to 3%, whereas nitrite oxidizing bacteria were inhibited. Zhu et al. (2016) also concluded that nitrite oxidizing bacteria could not acclimate as well as ammonia oxidizing bacteria in their lab scale study treating marine aquaculture water. Moving bed biofilm reactors had

300 carriers submerged in the treatment tank with varying number of carriers inoculated with mature biofilms from another treatment system. The inoculated systems showed a greater ammonia removal at first but all systems equalized at around 95% removal by day

32 (Zhu, 2016). Nitrification rates were higher in systems inoculated with greater amounts of mature biofilm. This indicates that ammonia oxidizers were more able to form new biofilms on carriers over time than nitrite oxidizers.

Inoculation

One approach to dealing with the inhibition of bacteria community growth due to the high salt content is to inoculate systems with salt tolerant bacteria. Studies have tested the

impacts of inoculating treatment systems with halotolerant bacteria to improve treatment

efficiency for high salt content wastewater (Kargi and Uygur 1996; Shi et al., 2012).

These studies showed that inoculation with salt tolerant organisms will not make a large

difference at low salt concentrations (i.e. 1% NaCl) but will be beneficial to treatment of

wastewater with greater than 4% NaCl. Kargi and Uygur (1996) noted that an activated

sludge system inoculated with Halobacter halobium had decreased treatment

performance at 3% weight/volume NaCl, but that performance improved again at 4% weight/volume NaCl. A microbial consortium was used for startup of the activated sludge systems, but Halobacter halobium were introduced in only half of the systems. The fact that inoculated systems showed decreased performance up to 3% NaCl and improved at

4% was attributed to the idea that several species of other microorganisms were not completely inhibited at 3% salinity and Halobacter was not in its optimal salinity environment. At 4% NaCl, Halobacter thrived and many other organisms could not tolerate the high salinity, leading to increased organic matter removal in the Halobacter systems but continued decline in systems not inoculated with Halobacter.

Ng et al.(2014) used a 10 L MBR with sediment from a salt marsh to treat pharmaceutical wastewater with approximately 20,000 mg/L Cl- and 26 g/L total dissolved solids in a

bench scale study. This MBR was compared with a bio-entrapped membrane reactor with

34 sludge from a local wastewater treatment plant (Ng et al., 2014). The bio-entrapped MBR had a submerged container of biocarriers, but did not have salt marsh sediment.

Conversely, the salt marsh sediment MBR had salt marsh sediment but no biocarriers.

Both systems had more ammonia in the effluent than the influent throughout the study period, indicating that ammonia oxidation was inhibited regardless of inoculation with salt marsh sediment. However, the salt marsh sediment system attained 26% more TOC removal than the bio-entrapped membrane reactor (Ng et al., 2014). Shi et al. (2012) used four marine halophilic bacteria to inoculate an intermittently aerated biological filter.

They found that TN and COD removal were better in the inoculated system at salt ranges above 5-8 and 4-10% NaCl, respectively (Shi et al., 2012). At 3% salinity COD and TN removal in the inoculated filters were 85% and 54% compared with 95% and 73% in control systems treating wastewatwer with less than 1% NaCl. This shows that 3% NaCl had a stronger impact on nitrogen removal than organic matter removal, even with inoculation (Shi et al., 2012). In a study using intertidal wetland sediment to inoculate an anaerobic system, Shi et al. (2015) found up to 10 times the bacterial community richness and significantly better organic matter removal in the inoculated vs. non-inoculated anaerobic systems treating high salt content pharmaceutical wastewater. These studies show that inoculation may have some positive effects on treatment, but cannot entirely resolve the impacts of salt in the wastewater.

Fixed Film Systems

Another proposed solution for high salt content wastewater treatment is to use a fixed

film system. Fixed film systems consist of media within a system that promote

immobilized growth of bacteria. Constructed wetlands and filters using sand as media are

two varieties of fixed film systems. Jurš e et al. (2015) studied the treatment of wastewater using planted constructed wetlands. When wastewater salinity increased to 30 g/L NaCl a

25% decrease in COD removal was observed (Jurse et al., 2015). Fixed film systems do

appear to increase treatment performance when directly compared to suspended film

systems of the same type in two studies doing direct comparisons and using high salt

content wastewater. Zhou et al. (2015) tested the ability of graphene oxide modified

polyvinyl alcohol particles to improve bacterial immobilization and wastewater

treatment. At 3-5% weight/volume NaCl, the increased immobilization of microbes

associated with the graphene oxide modified polyvinyl alcohol showed lower effluent

COD than the system without media (Zhou et al., 2015). Wang et al. (2015b) tested the

ability of microbes from diesel oil contaminated seawater to degrade oil in the water both

in suspension and when adhered to media. Three bacteria isolates were found to

successfully treat for diesel oil in a seawater suspension of 3.38% sea salt. When the microbes were in a suspended film system with salinity of 3.38% 40-60% of the diesel

was degraded, whereas 80-100% of diesel was degraded when bacteria were immobilized

(Wang et al., 2015b). These results indicate that fixed film systems may allow biofilms to

adapt to salt stress more easily than suspended film systems.

Research Applications and Objective

The present study combines the ideas of using a fixed film, sand media filter with the

concept of marine sediment inoculation. Sand bioreactors are a low-tech wastewater treatment system that can be constructed with local materials and treat sewage or food processing wastewater (Kang et al., 2007a; Tao et al., 2011). The wastewater in this study was from a full-scale food processing plant and the ability of sand bioreactors to treat this wastewater is well-documented (Kang et al., 2007a; Mancl, 2016). The present study goes further by adding sea salt to this raw wastewater and observing the impacts.

Treatment filters were dosed with 35 g/L added sea salt wastewater and will be referred to as 35 g/L filters throughout this paper. The objective of this study was to determine the feasibility of using sand bioreactors inoculated with marine sediment to treat high salt, high organic matter content wastewater.

Methods

Experimental Design

Sand bioreactors consist of three layers of sand with varying effective size in a column to which wastewater is applied from the top and allowed to passively flow through. The sand bioreactors used to treat 35 g/L sea salt content wastewater were inoculated with marine sediment. Four columns were used in this study. The influent for control columns consisted of turkey processing wastewater with no added salt. The influent for the remaining two filters was turkey-processing wastewater with 35 grams of sea salt per liter

(Figure 9). Plexiglass columns 92 cm tall with an internal diameter of 14.5 cm and wall

37 thickness of 0.3 cm were filled with four layers of substrate. Starting from the bottom: 5 cm gravel, 46 cm fine sand, 15 cm coarse sand and 15 cm gravel. The effective size of the three sand types were 3.5, 1.3 and 0.26 mm with uniformity coefficients of 1.3, 2.9 and 3.3, respectively. Sand analysis was conducted using sieve analysis (Mancl and Tao,

2011).

Figure 9. Experimental design and column structure

Wastewater was stored at 4 °C. The inflow rate was 40 L/m2/day, divided into four doses at six-hour intervals. Wastewater was temperature equilibrated in the laboratory for at least 30 minutes prior to dosing. To moisten the sand, each filter was dosed with tap water for four days prior to the study.

Wastewater Characteristics

Wastewater in this study was from a turkey processing plant in Harrison, OH. The wastewater passed through a grease trap only, with no further pretreatment. The wastewater was collected monthly and kept at 4 °C. Wastewater characteristics are described in Table 5. 35 g/L sea salt was added to the raw wastewater and is considered to be 3.5% salinity in this study due to the negligible salt content prior to addition of sea salt.

Table 5. Parameters of raw turkey processing wastewater

Parameter Average ± Standard Deviation

TOC mg/L 620 ± 290

COD mg/L 2,770 ± 1450

Ammonia mg/L 68 ± 27

Conductivity µS/cm 1,480 ± 250

Inoculant

Two cultivation systems were used to acclimate marine microbes to high strength wastewater. The filters being dosed with 35 g/L sea salt were inoculated with marine sediment from Marshfield, MA. Marine sediment was placed in containers with a combination of BOD dilution water, turkey processing wastewater, and 35 g/L sea salt. In one cultivation system, three containers were aerated by manual mixing twice per week.

A second cultivation system was created from the same marine sediment. The sediment was placed in an angled container and covered half way with turkey processing 39

wastewater with 35 g/L added sea salt. This system was continually aerated by an

aeration pump and the sediment was mixed daily. During the first three weeks of column

operation for wastewater treatment, 75-150 mL of inoculant water was added to each 2 L batch of wastewater and salinity was adjusted to 35 g/L sea salt.

Analytical Methods

Total organic carbon (TOC) was measured by a TOC analyzer (Shimadzu, Japan). TOC

of the treatment effluent was measured weekly during weeks 4-10. Effluent TOC was

measured at least every 10 days for weeks 11-15. After week 15, effluent TOC was

measured monthly. Control columns were sampled and TOC measured weekly for weeks

4-7 and monthly thereafter. Ammonia nitrogen was measured using the Ammonia

Nitrogen Test Kit (HACH 5870040, CO, USA). Ammonia nitrogen for treatment filters

was measured three times per week for weeks 1-7, weekly for weeks 8-10, biweekly

weeks 11-15 and then monthly thereafter. Control filters effluent was sampled and

ammonia nitrogen measured three times a week for weeks 1-6 and monthly thereafter.

For treatment filters ammonia nitrogen was measured biweekly weeks 9-14 and then

monthly thereafter. Nitrite nitrogen was measured using the Nitrite Test Kit (HACH

2182000, Loveland, CO) four times during weeks 42-49.

Results

Acclimation Phase

During the acclimation phase, the lowest ammonia removal for the filters treating 35 g/L

sea salt wastewater was 24%. This level of ammonia removal was observed during week

4. In contrast, the control filters reached steady state ammonia removal by week 4. It was not until week 7 that the 35 g/L filters reached steady state conditions, increasing beginning in week 6 (Figure 10).

Figure 10. Ammonia removal by control and filters treating 35 g/L sea salt wastewater

Steady State Period and Overall Treatment

Filters treating wastewater with 35 g/L of added sea salt achieved >97% ammonia removal from weeks 7-10 (Figure 11). Throughout the study period large fluctuations in influent ammonia were observed, ranging from 20-92 mg/L. The fluctuation in influent ammonia levels did not appear to directly impact treatment efficiency. From weeks 4-15

TOC removal of >93% was observed in all filters (Figure 11).

Figure 11. TOC and ammonia removal by control and filters treating 35 g/L sea salt wastewater

Clogging Period

Clogging occurred in both treatment filters. Discoloration within the coarse sand layer was observed beginning in weeks 13-15 and continued to increase until all of the coarse sand and most of the gravel layers were black. At week 20 one filter clogged completely.

As the other filter began clogging at about week 20, the effluent that did flow out of the filter had a light yellow to medium brown color and offensive odor, illustrating breakthrough (Figure 12). Ammonia removal for this filter decreased after week 11. On day 172, more ammonia was observed in the effluent than the influent. TOC removal of

>80% was maintained for all filters throughout the entire study period (Figure 12).

Figure 12. TOC and ammonia removal by control and 35 g/L added sea salt filter (a in Figure 14)

Treatment of Clogged Filters

Intermittent Loading

Clogging to the point of near overflow occurred in one filter during week 20 (Figure 14).

To treat the clogged filter, the dosing was reduced to one fourth of the original loading

rate. The original loading rate was 40 L/m2/day. The filter would be dosed for 2.5 days at

40 L/m2/day and then rested for 7.5 days. This allowed water that was ponding on top of

the filter enough time to pass through before more wastewater was added.

This loading pattern resulted in clear effluent from the filter for the remainder of the

study period (Figure 15). Removal efficiency reached 99.7 ± 0.5% ammonia removal and

97.6 ± 1.5% TOC removal with intermittent loading (Figure 13). Without altering the

loading pattern, average ammonia removal for the same period was 12.8 ± 25.3% and

TOC removal was 86.2 ± 3.9% (Figure 12). However, the discoloration remained with

the intermittent loading (Figure 14).

Figure 13. TOC and ammonia removal by control at full loading rate and 35 g/L filter (b in Figure 14) receiving intermittent loading

a) b)

Figure 14. Filters treating 35 g/L sea salt wastewater on day 255 of study. a) Filter with reduced effluent quality due to breakthrough and b) Intermittently loaded filter with high quality effluent

Figure 15. a) Raw wastewater b) control effluent and post-clogging effluent from c) and d) 35 g/L filter experiencing breakthrough and intermittently loaded 35 g/L filter, respectively 45

Resting Period After 36 weeks, no wastewater was added to the filters for a 5 week resting period. The discoloration in the filters gradually reduced over the 5 week period (Figure 16).

a) b) c) d)

Figure 16. 35 g/L sea salt filters a) on intial day of resting period and after b) 2, c)4 and d) 5 weeks 46

Post-Rest Period

After the resting period, both 35 g/L filters were loaded at the original loading rate of 40

L/m2/day. Clogging was seen in both filters within 18 days. Clogging lead to water

backup into the gravel layer by the end of the third week post-rest for the 35 g/L filter

being intermittently loading before the resting period. After 6.5 weeks the filter ponding

to the point of near overflow was observed and intermittent loading pattern of 2.5 days of

dosing and 7.5 days of rest was resumed.

The ammonia removal decreased over time when the original loading rate was

maintained, indicating that breakthrough re-occurred (Figure 17). The intermittently

loaded filter maintained >99% ammonia removal throughout the post-rest period (Figure

17). Both filters had >93% TOC removal throughout the post-rest period (Figure 18).

Figure 17. Ammonia removal for 35 g/L sea salt filters with continuous original loading rate and intermittent loading beginning 6.5 weeks after resting period.

Figure 18. TOC removal for 35 g/L sea salt filters with continuous original loading rate and intermittent loading beginning 6.5 weeks after resting period

During the post-rest period, nitrite did not show accumulation in the intermittently loaded filter. At the end of the study, nitrite levels were 0.02 in the intermittently loaded filter and 19 mg/L for the filter loaded at the original loading rate. The filter that was intermittently loaded again 6.5 weeks after the rest had all nitrite measurements for this filter were > 0.04 mg/L.

Discussion

Acclimation period

Across studies, it is shown that acclimation and recovery from salt shock can take from a few days to several weeks, but systems eventually exhibit acceptable treatment at steady state. MBR as a secondary treatment took 46 days to reach steady state removal for COD and 29 days for ammonia (Shi et al., 2014). Guan et al. (2014) studied the ability of an

MBR system modified with increased pore size of 55 micrometers to treat wastewater partially consisting of sewage resulting from sea water for toilet flushing. In a pilot study

28 days were needed for COD removal to reach steady state (Guan et al., 2014). A one month acclimation period was given when Ng et al. (2014) studied MBR systems treating pharmaceutical wastewater. Acclimation was accomplished by slowly increasing the percent of raw wastewater being added to the influent solution for each MBR. These studies indicate that anywhere from 4-7 weeks should be allowed for MBR to reach maximum organic matter removal.

Similar acclimation trends are seen in other aerobic treatment systems, but necessary and ideal acclimation times still seems unclear in the literature. Even at the moderate salt level of 3.2 g/L, maximum recovery in an SBR system was not observed until day 27

(Chen et al., 2015). Cui et al. (2009) studied a modified University of Capetown system consisting of several tanks each with anaerobic, anoxic and aerobic conditions, three points of recirculation and a secondary clarifier. Each time the salinity level was increased in the bench scale modified University of Capetown system, they waited 4-5 weeks for full recovery (Cui et al., 2009). Before beginning their study of the ability of an aerobic granular sludge sequencing batch airlift reactor to treat wastewater from the fisheries industry, Corsino et al. (2016) acclimated the system to 30 g/L NaCl wastewater and worked through five levels to 75 g/L salinity over 78 days, noting that each salt level took at least 15 days to reach steady state.

The variation of acclimation periods cluster around 4-5 weeks (Cui et al., 2009; Chen et

al., 2015). In the present study, TOC was measured beginning on day 26 and very little

variation was seen in TOC removal during the first weeks of measurement. This indicates

that organic matter removal acclimation was complete before the end of week 4,

consistent with the commonly observed time frames in the literature. The present study found that it took almost 7 weeks for ammonia removal to reach maximum levels in the sand bioreactors. This may be due to the fact that a gradual acclimation was not used, but instead the systems were started immediately at 35 g/L sea salt content wastewater. The acclimation period for ammonia treatment in the fixed film system in the present study was longer than the more extensively studied suspended film systems.

Steady State Period and Clogging Period

The 35 g/L filters showed high removal of ammonia and TOC for 3 weeks after the initial

7 week acclimation period (Table 6). The 35 g/L filters showed average TOC removal of greater than 92% following acclimation until the resting period (Table 6). Some impact in organic matter removal due to salinity was noted as the 35 g/L filters had 5% less TOC removal than the control sand bioreactors. Yogalakshmi and Joseph (2010), in their study of salinity shock on MBR systems, similarly noted that COD removal was less sensitive to NaCl shock than ammonia removal. The COD removal dropped transiently to 83% when NaCl content increased from 20 g/L to 30 g/L (Yogalakshmi and Joseph, 2010).

Wang et al. (2015a) and Corsino et al. (2016) both found 90% COD removal in SBR systems at 3.0% salinity, produced with seawater crystals and NaCl, respectively. The

50 presently studied sand bioreactor systems therefore perform at similar levels to other treatment methods for percent organic matter removal.

Two studies saw a greater impact in ammonia than noted in the present study (Deorsola et al., 2013; Ng et al., 2014). Ng et al. (2014) and Deorsola et al. (2013) both noted increases in the ammonia content of effluent when treating high salt content wastewater versus controls. Only one sample showed higher ammonia in the effluent than influent in the present study. Average ammonia removal at 35 g/L of sea salt in the present study study from weeks 7-10 was 98.7 ± 0.7%.

Table 6. Variation in ammonia and TOC removal from steady state through clogging period

Time Period Ammonia TOC Removal (%) Removal (%) Steady State 98.7 ± 0.7 94.3 ± 0.6

Clogging Period 65.3 ± 45.3 91.7 ± 6.9

Steady State through Clogging Period 77.7 ± 35.5 92.7 ± 4.7

Intermittent Loading

Clogging occurred in the treatment filters following steady state. Due to ponding, the one filter was intermittently loaded at 40 L/m2/day for 2.5 days and then rested for 7.5 days.

Though clogged, the effluent eventually passed through the filter, just at a reduced rate.

Changing to intermittent loading led to ammonia removal >99% and TOC removal

>97%. Adjusting the loading rate may have helped preserve treatment efficiency. This is 51

supported by a study on effects of loading rate on high salt content wastewater treatment

by Aloui et al. (2009). To test the impacts of organic loading rate on an activated sludge

system treating wastewater with a salt content of 25 g/L NaCl, Aloui et al. (2009)

increased organic loading rate. As the organic lading rate increased and hydraulic

retention time decreased, overall treatment efficiency decreased, even when the NaCl

content of the wastewater remained contstant at 2.5%. In the present study of sand

bioreactors, clogging occurred in the filters and may be attributable to a loading rate that

was too high.

Torrens et al. (2009) studied the impacts of loading patterns on plant scale intermittent

sand filters using river bed sand with an effective size similar to that used in the present

study (0.26 and 0.25 mm, respectively). The filters were used to polish waste stabilization

pond effluent. The study concluded that the best loading pattern was to have 3 to 4 days

of dosing followed by 7 days of rest (Torrens et al., 2009). This supports the findings in

the present study that intermittent loading of 2.5 days followed by 7.5 days of rest

allowed for improved treatment compared to constant loading.

Resting Period

A resting period was implemented when both systems experienced discoloration

throughout the gravel and coarse sand layers and intense clogging. The resting period

consisted of 5 weeks with no wastewater being applied to the filters. As seen in Figure

16, this led to a decrease in the discoloration. Anaerobic conditions within the filter layers

may have been the cause of the discoloration. Once dosing ceased, increasingly aerobic

conditions returned the filters to pre-clogging conditions. The fact that resting helps alleviate anaerobic conditions produced by clogging in filters is supported by a study of

lab scale media filters using volcanic ash soil, sawdust and granular iron metal as media

(Masunaga et al., 2007). The study found that increased hydraulic loading rate and

wastewater strength caused clogging earlier, ranging from 4 months to 10 months into

operation. Therefore, the authors recommended dosing to resting ratios ranging from 4:2

to 7:2 months (Masunaga et al., 2007). A loading period followed by a resting period has

been commonly used to reduce clogging in vertical flow constructed wetlands and has

been successful when the clogging is caused by organics (Nivala et al., 2012). Resting clogged lab scale sand bioreactors treating turkey processing wastewater for 5 weeks lead to improved treatment (Kang et al., 2007b).

Post Rest Period

By the third week of reloading the filters at a rate of 40 L/m2/day, clogging resumed. The

resting period offered only temporary increases in treatment efficiency. Song et al. (2015)

in a lab scale study of vertical flow constructed wetlands using quartz sand found that

resting filters for 7 days did reduce the accumulation of biomass in clogged filters. The

study showed that a week of resting did reduce biofilm accumulation in the filters, but did

not alleviate the clogging symptoms once loading resumed for the decreasing-size filter

(Song et al., 2015). In the present study, the intermittently loaded filter maintained >99% ammonia removal until the end of the study. This shows that resting can help return

filters to pre-clogging conditions, but that this can only be maintained if a decreased

loading rate or intermittent loading is implemented.

High nitrite levels were observed in the filter with original loading rate after the resting

period. Equally high levels were not observed in the filter with intermittent loading rate.

This indicates that nitrite oxidizing bacteria were able to adapt to the 35 g/L sea salt

filters, but that the loading rate of 40 L/m2/day may have overwhelmed the systems. The

35 g/L filter with nitrite accumulation also had lower ammonia removal and the 35 g/L filter with low nitrite levels had high ammonia removal. This does not agree with findings by Corsino et al. (2016) that nitrite oxidizing bacteria were more inhibited by salt than ammonia oxidizing bacteria. Low treatment by the filter loaded at the full loading rate is likely attributable to breakthrough of untreated wastewater and not indicative of adaptation patterns by bacteria. The successful treatment of ammonia without nitrite accumulation in the intermittently loaded filter shows that salt was not the main contributor to decreased ammonia or nitrite removal.

Conclusions

The objective of this study was to determine the feasibility of using marine sediment inoculated sand bioreactors to treat seawater level salinity turkey processing wastewater.

The study results showed that marine sediment inoculated sand bioreactors are a feasible treatment option for high salt content wastewater. An acclimation period of 7 weeks was necessary for the filters to effectively treat high salt content wastewater for ammonia.

This acclimation period was several weeks longer than the control and should be taken into consideration when using sand bioreactors for treating high salt content wastewater.

Clogging was an issue that arose in the filters. Intermittent loading in a pattern of 2.5 days of dosing followed by 7.5 days of rest led to improved treatment performance.

Resting the filters and then continuing to load without intermittent loading led to clogging within 3 weeks of restarting the filters and was a less effective solution to clogging. Further research into the effects of decreased loading rate and intermittent loading on clogging of sand bioreactors treating 35 g/L sea salt wastewater is recommended.

Chapter 4: Overall Conclusions and Recommendations for Future Work

Conclusions

Previous studies showed that high strength, high fat content wastewater from a turkey

processing plant could be treated by sand bioreactors (Kang 2007a; Gaur, 2015). The sand bioreactors also showed consistent organic matter and ammonia removal in a lab scale study when 3 and 6 g/L table salt were added to the turkey processing wastewater

(Chen, 2016). Salt is known to be an important stressor for biological systems (Woolard and Irvine, 1995). To test the boundaries of this technology in relation to salt content, the objective of this study was to determine if sand bioreactors could treat high strength wastewater with much higher levels of salt.

1) Treatment of high salt content wastewater with sand bioreactors is feasible.

Carbon removal and ammonia removal varied by salt concentration. Sand

bioreactors removed >90% COD and ammonia from high salt content wastewater.

Adding 6 g/L and 13 g/L table salt to the wastewater did not significantly impact

ammonia treatment, but did significantly impact COD treatment. COD treatment

remained above 94% and 93% during steady state, respectively, making sand

bioreactors a feasible treatment system. The 6 g/L and 13 g/L NaCl wastewater

were not significantly different in the percent removal of ammonia or COD.

Inoculated sand bioreactors treated high strength wastewater with 35 g/L of added

sea salt at >97% ammonia removal and >92% TOC removal for three weeks.

2) The acclimation period of treatment is extended when salt is added to the wastewater.

The period needed for a biological wastewater treatment system to reach steady

state after startup is referred to as the acclimation period. In this study,

acclimation was considered complete when both replicates removed >95%

ammonia. The acclimation period extended with wastewater salt concentration.

The amounts of time needed to reach steady state were 5, 12 and 22 days longer

than when no salt was added for 6, 13 and 35 g/L added salt, respectively. This

general relationship of increased acclimation period with increased salt content of

wastewater should be explored further.

3) The onset of clogging is related to salt level.

At a constant loading rate and pattern, clogging occurs when salt is added to the

wastewater and time to clogging has a relationship to salt level. Clogging was

observed at all salt levels. Clogging was least severe in the 6 g/L filters, appearing

only in one filter and not covering the entire coarse and gravel area. Clogging

occurred in the 6 and 13 g/L table salt filters after 6-9 months of operation.

Clogging was most severe in the 35 g/L filters, leading to near overflow of one

filter and breakthrough of poorly treated wastewater in the duplicate filter. It is

important to note that in several filters clogging did not negatively impact the

quality of effluent.

4) Multiple approaches can be used to restore treatment by clogged filters.

The sand bioreactors were rested for 5 weeks after 8.5 months of operation. The 6

and 13 g/L added salt filters showed no clogging post-rest until the end of the

study. The filters treating wastewater with 35 g/L added salt began clogging again

within 3 weeks after the rest period. When intermittent loading in a pattern of 2.5

days at 40 L/m2/day followed by 7.5 days of no dosing was used, one sand

bioreactor maintained >97% TOC removal and >99% ammonia removal for more

than 16 weeks until a resting period began.

Recommendations for Future Work

Operations and Maintenance Approaches to Clogging

The addition of salt to high strength wastewater can present additional operations and maintenance (O&M) challenges when operating sand bioreactors. Sand bioreactors are difficult to clog. Gunarathna et al. (2016) found that different loading rates with high strength wastewater did not result in clogging. However, salt is a known stressor and

filters began to clog when loaded with high salt content wastewater. This O&M concern

was treated in a variety of ways based on variability in the extent and type of clogging

observed. Three different methods were tried.

1) “Resting” was one method used. Resting the filters consisted of a 5 week period during

which no wastewater was dosed onto the bioreactors. This rest began in the 8th month of

treatment when all treatment filters were clogged to some extent with the exception of

one filter treating 6 g/L added salt wastewater. Kang et al. (2007b) found that resting

clogged sand bioreactors for 5 weeks led to performance similar to pre-clogged conditions.

2) Intermittent loading was used as a method for managing ponding on top of the filter.

The clogged filter was loaded for 2.5 days at 40 L/m2/day and then not loaded for 7.5

days. This cycle was continued during 3.5 months of operation for one of the 35 g/L

added salt filters. Gunarathna et al. (2016) found that sand bioreactors were able to treat

wastewater even when hydraulic loading rates were dramatically increased 2 days of each

7-day cycle.

3) The final method used was to “rod” the filter. This is a practice that has been adopted

at the full scale sand bioreactor plant at Whitewater Processing in Harrison, OH. This

involved taking a ¼ inch diameter metal rod and inserting it through the gravel, coarse

sand and top inch of fine sand. The rod was then moved within the sand layers with the

59 objective of breaking up channeling. This was done for one of the 35 g/L added salt filters that experienced breakthrough.

Clogging can come in a variety of forms and the best approach to solving the problem may depend on a) effluent quality and b) severity. Three different combinations of these parameters were observed in the present study. Ideas on how to further study O&M approaches to these different clogging forms include:

1. High effluent quality, low severity:

Clogging within the coarse sand and lower portion of the gravel layers of a

sand bioreactor that does not lead to ponding may not be an issue that

needs addressing. This issue would be invisible to operators of a full scale

system where the bioreactors are in the ground and the top of the gravel

layer is not impacted.

In lab-scale studies, where clogging can be observed, resting of the

systems should be further tested. Resting was seen in this study to not only

arrest, but reverse clogging in all clogged filters. The ideal resting time

needed could be better understood if a variety of timeframes and a variety

of clogging levels were used.

2. High effluent quality, high severity (ponding):

Clogging is not always a problem. Clogging slows the passage of

wastewater through the media, increasing contact time. In these cases,

high quality effluent slowly emerges from the bioreactor. If ponding is

occurring but the effluent is still of high quality, then intermittent loading

is recommended based on observations of the present study. Intermittent

loading did not eliminate the clogging, but maintained the objective of

treating the effluent. Further research comparing the impacts of

intermittent loading vs. a steady but reduced loading rate is recommended.

This would allow more insight into whether or not the time with no dosing

is important to the systems functionality or if the issue is simply that the

initial loading rate was too high but consistent dosing is feasible.

Research into the effective hydraulic retention time of the clogged system

could be helpful in determining optimal hydraulic retention time and

loading rates for a sand bioreactor treating wastewater at 35 g/L sea salt.

This research, along with that on reduced loading rates, could also help

determine feasible loading rates at 35 g/L added salt and therefore

influence potential plant sizing.

3. Low effluent quality, low severity,:

Breakthrough of poorly treated wastewater can be caused by clogging and

channeling. Low severity clogging conditions that lead to reduced effluent

quality were addressed in two different ways in this study. One approach

was to rest the filters. This eliminated clogging and regained effluent

quality in two filters. A second approach was to take a rod and disturb the

media through the top one inch of fine sand. Channelling was evident in

the system that was rodded, but may also have been present in the rested

systems.

Future research in which channeling in sand bioreactors is induced and then treated with

these two approaches is recommended. Channeling did not occur in the majority of

filters, so the drip design of the lab-scale system itself does not appear to be the cause.

Further research into the causes of channeling themselves would be useful in avoiding

this issue. One hypothesis to test is that the filters dry out during resting causing sand to

shift and fill in spaces that were previously channels in the sand. Rodding on the other

hand physically moves the sand particles and could reduce channeling.

Rodding vs. resting presents important O&M considerations because the two methods

have trade-offs with respect to time and manpower. Rodding offers a faster solution, but also requires more man power. Resting, conversely, would take longer but would require less active management. Resting effectiveness may also depend on the amount of stress

62 on the system because it was ineffective at 35 g/L added sea salt, but effective at 6 and 13 g/L added table salt. Research prior to pilot plant would need to include a study of how long after resting the filters clog.

Acclimation Period

Further research into the extended acclimation period observed in relation to increased salt level is recommended. One interesting aspect of this observation is that the acclimation period for 35 g/L added salt was much longer than for the control, 6 g/L or

13 g/L added salt despite these sand bioreactors being inoculated with marine sediment.

Salt interferes with carbon measurements and this created challenges in obtaining carbon removal data in the present study for the first month of filter operations. In future research it would be useful to have COD data for trends because by the end of the 4th week the removal rates were already high.

Microbial Community

Understanding the different microbial communities that develop in filters treating wastewater with different salinity levels would be beneficial. Understanding differences in the level of diversity within each community could help indicate the resilience of the filters to additional stresses. This information could also be used to isolate microbes that are beneficial to high salt treatment and could potentially be used as an inoculant to attempt to mitigate the extended acclimation periods observed with high salt content.

This data could also potentially give insights into the causes of clogging.

Another future research study could identify the microbial community in the full scale wastewater treatment plant in Harrison, OH. This system treats turkey processing wastewater with no added salt. Taking samples from various filters could provide data on many aspects, including natural diversity under the same environmental conditions and which microbes are most abundant within the sand bioreactors. Relationships between microbial community composition and treatment or weather conditions could also be explored.

Scaling Up

It seems feasible that sand bioreactors can treat meat processing wastewater at 6 and 13 g/L added table salt. A pilot scale study of these systems treating 6 g/L salt wastewater would be beneficial to understanding how the systems operate on a larger scale and if clogging would be an issue. The O&M plan for such a plant would include a resting period every 6 months for 3 + weeks.

Testing additional salt levels and wastewaters in accordance with industry needs would be useful. Testing 20 g/L added salt would help to see what occurs in the range between

13 g/L and 35 g/L added salt. Treating wastewater with 35 g/L added salt without inoculation would help to understand whether or not the marine sediment inoculation had an impact. Salt fluctuation could also cause addition stress and should be studied to see if increases and decreases impact the systems more than a steady salt content.

Other Wastewaters and Reuse

The fact that sand bioreactors have shown the ability to treat poultry processing wastewater and sewage indicates the breadth of wastewaters for which this technology could be applied (Kang, 2007a; Gaur, 2015). The present study shows that salt stress can impact treatment performance, but that treatment is still feasible with additional salt content. Other wastewaters that could be tested include wastewaters from breweries, aquaculture, canning and more.

Seawater is being used in Hong Kong to flush toilets, which results in a 1.3% sea salt content in sewage for that city (Cui et al., 2009). Sand bioreactors could thus be feasibly applied as a wastewater treatment system in contexts where municipal wastewater treatment plants are dealing with high salt content wastewater. Research into the impacts of sewage with seawater incorporated on sand bioreactors is recommended. On a household scale, high salt content wastewater treatment by sand bioreactors presents opportunities for reuse. If coastal homes want to use seawater in toilet applications, an on-site enclosed sand bioreactor followed by disinfection could be used to recycle the water back into the homes toilet system. Understanding the impacts of salinity on various disinfection processes would be necessary to move this forward.

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Appendix A: Table of Acronyms

Table 7. Frequently used acronyms

Acronym Phrase TOC Total organic carbon COD Chemical oxygen demand SBR Sequencing batch reactor MBR Membrane bioreactor TN Total nitrogen O&M Operations and Maintenance