Ultraviolet Disinfection System for Constructed Wetlands

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ULTRAVIOLET DISINFECTION SYSTEM FOR CONSTRUCTED WETLANDS

HUMBOLDT STATE UNIVERSITY

Jong Chan Ly

A Thesis

Presented to

The Faculty of Humboldt State University

In Partial Fulﬁllment

Of the Requirements for the Degree

Master of Science

In Environmental Systems: Environmental Resources Engineering

December, 2008 ULTRAVIOLET DISINFECTION SYSTEM FOR CONSTRUCTED WETLANDS

HUMBOLDT STATE UNIVERSITY

Jong Chan Ly

Approved by the Master’s Thesis Committee:

Dr. Brad A. Finney, Major Professor Date

Dr. Robert A. Gearheart, Committee Member Date

Dr. Margaret Lang, Committee Member Date

Dr. Christopher Dugaw, Graduate Coordinator Date

Chris A. Hopper, Interim Dean Date Research, Graduate Studies & International Programs ABSTRACT

ULTRAVIOLET DISINFECTION SYSTEM FOR CONSTRUCTED WETLANDS Jong Chan Ly

Disinfection processes in wastewater treatment systems have been playing a vital role in protecting water resources from pathogenic microorganisms for decades. Currently the leading disinfection process is chlorination, which has contributed significantly to public health protection. However, ultraviolet (UV) disinfection systems have been recently adopted for wastewater treatment due to advantages over chlorination such as not creating Trihalomethanes (THMs), no odor, no danger of overdosing, not creating volatile organic compounds (VOC), and very little contact time. Although UV disinfection has been widely applied to conventional wastewater treatment, it is not common for constructed wetland wastewater treatment due to concerns of high effluent turbidity. This research was conducted to estimate the potential for UV disinfection technology in constructed wetland wastewater treatment. The Arcata Wastewater Treatment Plant (AWTP) was selected for this study because it is a wetland treatment system widely recognized for stable conditions and high quality effluent. The majority of samples were collected from the Pilot Marsh and samples from other treatment marshes were utilized for additional tests. During the research period, no fecal coliform was found after UV disinfection. This study also investigated possible concerns associated with UV disinfection: the effect of high UV dosage on algae population, the interfering substances of UV transmittance, physical characterization of particles in the effluent of the marshes, and the potential for fecal coliform re-growth. This research found that algae death by UV light does not significantly contribute to effluent BOD. Also, the UV interfering substances (lignite and silt) in the Pilot Marsh do not influence the effectiveness of UV disinfection. Less than 1% of the iii suspended particles in the wastewater had diameters exceeding 50µm which UV can not penetrate, and over 90% of particles are smaller than 10 µm. In addition, UV disinfected samples showed no re-growing fecal coliform bacteria by photoreactivation or dark repair. Results of this research demonstrate that UV disinfection would be a highly viable option for AWTP. Further research is needed to estimate the applicable range of UV disinfection in different locations and environments.

iv ACKNOWLEDGEMENTS

My sincere appreciation goes to the many people who offered tremendous support and invaluable advice throughout this study. I would like to express my gratitude to my committee members: Dr. Brad A. Finney, Dr. Robert A. Gearheart, and Dr. Margaret Lang. My main advisor, Brad, has been greatly supportive and has provided the remarkable guidance. I also thank Bob for his encouragement and excellent advice. My thesis would not be complete without Margarets contributions. I also would like to thank all the ERE faculty and staff, especially Collin Wingﬁeld, Marty Reed and Mary Jo Sweeters. The Arcata Marsh Research Members deserve special thanks: Mary C. Burke, who has been greatly inspirational, as well as Lucas Siegfried, Timothy Welgand, Gabriel Rossi, Jeff Woodke and Karen Wetherow. I would like to express my deep appreciation to my beloved family, my parents and my sister, for their endless devotion, patience, and love. Finally, I thank and praise God for all His work and love in my life. To them I dedicate this thesis.

v TABLE OF CONTENTS

ABSTRACT ...... iii

ACKNOWLEDGEMENTS ...... v

TABLE OF CONTENTS ...... vi

LIST OF FIGURES ...... viii

LIST OF TABLES ...... x

INTRODUCTION ...... 1 Wetlands and Disinfection ...... 1 Wastewater Treatment System in Arcata ...... 2

LITERATURE REVIEW ...... 4 Disinfection of wastewater ...... 4 Chlorination ...... 5 Ultraviolet disinfection ...... 6 Constructed Wetlands ...... 9 The Effect of Particulate Matter on UV disinfection ...... 10 Coliform Re-growth ...... 13 The Effect of UV disinfection on Algae ...... 13 Humic Acid and UV transmittance ...... 15 Dose and Response of UV disinfection ...... 15 Design Factors of UV disinfection System ...... 18 Hydraulic properties of the reactor ...... 18 Intensity of the UV radiation ...... 20 Wastewater characteristics ...... 20 Main Parameters and Regulations ...... 21 Fecal Coliform ...... 21 Total Suspended Solids ...... 22 pH...... 22 Biological Oxygen Demand ...... 22 Regulations ...... 23

METHODS ...... 24 Study Site Description ...... 24 UV Disinfection Unit ...... 25 Sampling ...... 26

vi Water Quality Analysis ...... 26 Biochemical Oxygen Demand (BOD) ...... 26 Algae Survival ...... 27 Total Suspended Solids ...... 27 Fecal Coliform MF Method ...... 28 Ultraviolet Absorption Method ...... 28 Fecal Coliform Re-growth Test ...... 29

RESULTS AND DISCUSSION ...... 30 The Effect of UV Disinfection on Algae ...... 32 Algae Survival ...... 32 5-Day BOD ...... 33 Ultimate BOD ...... 35 UV Transmittance ...... 35 Particle counting test ...... 37 Fecal Coliform Re-growth Test ...... 38

CONCLUSION ...... 39

BIBLIOGRAPHY ...... 40

APPENDIX I ...... 45

vii LIST OF FIGURES

Figure Page

1 Location of Arcata wastewater treatment plant (Roberts et al., 2008). . . . . 2

2 Arcata wastewater treatment plant with Arcata Marsh and Wildlife Sanctuary. 3

3 UV light in the electromagnetic spectrum (Washington State Department of Ecology, 2006)...... 7

4 Illustration of the effect of UV ray on DNA (Herring, 2006)...... 8

5 Effects of particles on UV disinfection (Blume and Neis, 2001)...... 11

6 Blue green algae (Anabaena) (Mount Allison University, 2000)...... 14

7 Examples of UV reactors : (a) Closed-channel and (b) Open-channel (US EPA, 2006)...... 19

8 Escherichia coli bacteria (Erbe, 2006)...... 21

9 Sampling Sites at Arcata Wastewater Treatment Plant...... 24

10 Pilot UV disinfection unit (Double Helix UV sterilizer)...... 25

11 Fecal coliform counts from the Pilot Marsh (August 22, 2007 - December 20, 2007)...... 30

12 Total suspended solids from the Pilot Marsh (August 22, 2007 - December 20, 2007)...... 31

13 Dissolved oxygen results of Test I with sample Group A (R1: non-disinfected, A: 94.4 mJ/cm2, B: 121.9 mJ/cm2, C: 196.0 mJ/cm2)...... 32

14 Dissolved oxygen results of Test I with sample Group B (R1: non-disinfected, A: 94.4 mJ/cm2, B: 121.9 mJ/cm2, C: 196.0 mJ/cm2)...... 33

15 5-Day BOD and 10-Day BOD after UV radiation of Test I (R1: sample before UV radiation without seed, R2: sample before UV radiation with seed)...... 34

viii 16 Ultimate BOD results of Test I (A: 106.5 mJ/cm2, B: 126.6 mJ/cm2, C: 216.3 mJ/cm2)...... 36

17 Particle size distribution in percentage (Treatment marsh 3)...... 37

18 5-Day BOD and 10-Day BOD after UV radiation. (R1: sample before UV radiation without seed, R2: sample before UV radiation with seed)...... 45

19 Ultimate BOD results of Test II (A: 96.9 mJ/cm2, B: 125 mJ/cm2, C: 171.7 mJ/cm2)...... 46

20 Dissolved oxygen results of Test II with sample Group A (R1: non-disinfected, A: 106.5 mJ/cm2, B: 126.6 mJ/cm2, C: 216.3 mJ/cm2)...... 46

21 Dissolved oxygen results of Test II with sample Group B (R1: non-disinfected, A: 106.5 mJ/cm2, B: 126.6 mJ/cm2, C: 216.3 mJ/cm2)...... 47

ix LIST OF TABLES

Table Page

1 Health effects of some by-products of chlorine disinfection (Bull, 1982). . 5

2 Typical Mercury Vapor Lamp Characteristics (US EPA, 2006) ...... 8

3 Mercury Vapor Lamp Operational Advantages (US EPA, 2006)...... 9

4 Energy Requirements for UV Treatment Systems on Selected Organisms (The Northeast Midwest Institute, 2001)...... 16

5 Efﬂuent limits for discharge to Humboldt Bay, Arcata Marsh and Wildlife Santuary (Kuhlman, 2007)...... 23

6 UV disinfection test results from the Pilot Marsh (August 22, 2007 - De- cember 20, 2007)...... 31

7 Dosage summary for effect of UV radiation on 5-Day BOD and 10-Day BOD...... 34

8 Summary of average ultimate BOD results with various doses...... 35

9 Summary of UV transmittance test results...... 36

10 Summary of particle counting test results for each samples sites (TM2 : Treatment marsh 2, TM3 : Treatment marsh 3, EM : Enhancement marsh). . 37

11 Summary of UV 10 day fecal coliform re-growth test results...... 38

x INTRODUCTION

Wetlands and Disinfection

For decades environmental engineers have been concerned with the impact of treated waste discharges to natural water bodies to protect wildlife and public health. In particular, the level of bacterial contamination from wastewater on beaches and other recreational waters has become critical. Every year thousands of shellfish beds are closed due to excessive levels of fecal coliform bacteria (McDonald et al., 2006). These issues have brought more attention to the need for disinfection of pathogenic organisms in wastewater treatment. Dis- infection processes generally use physiochemical treatment or chemical reagents. Chlorine is currently the most common disinfection chemical because of its high effectiveness in destroying pathogenic organisms and its economic feasibility. Over the last decade, the use of ultraviolet (UV) disinfection in wastewater treatment systems has rapidly increased due to cost competitiveness and advantages over chlorination including no by-product, no odor, no dechlorination needed, and safe and easy operations. Although UV disinfection has been widely used as an alternative disinfection process over the last decade, it is still generally limited to conventional treatment systems. UV disinfection is still not common for ponds and constructed wetlands due to a major concern that the high turbidity and total suspended solids of the wetland effluent would result in inadequate disinfection. Because of the significant concerns related to chlorination by-products and the large number of constructed wetland systems, it would be worthwhile to study a UV disinfection system in a well-established constructed wetland treatment system. The Pilot Marsh in Arcata Waste- water Treatment Plant was found to be a good candidate due to proven long-term stability and effective wastewater treatment.

1 2

Wastewater Treatment System in Arcata

The Arcata Wastewater Treatment Plant (AWTP), located on Arcata Bay in Arcata, Cal- ifornia (Figure 1), consists of primary treatment, oxidation ponds, treatment marshes and constructed polishing marshes.

Idaho Oregon

Wyoming

Mad River n a e c O

c Arcata i f P i AWTF

a California Nevada c Utah

c a Humboldt Bay i P

e Eureka

Arizona µ 0 01.5 1 3 2 6 M4 Mileiless

0 85 170 340 Miles

Figure 1: Location of Arcata wastewater treatment plant (Roberts et al., 2008).

The primary treatment plant was designed to treat up to 5 million gallons per day (MGD). The primary mechanical plant can be bypassed during high flows with up to 14 MGD by flowing directly to the oxidation ponds. Oxidation pond effluent flows through treatment marshes and is then disinfected with chlorine prior to discharge to Arcata Bay or to polishing marshes (Figure 2). The oxidation ponds were built as a part of the Arcata water treatment system in 1957. The system was modified with the addition of a chlorination process in 1966. From 1979 to 3

1982, the Pilot Marsh Project demonstrated the natural processes of a wetland ecosystem as a possible wastewater treatment system in Arcata. The experiments were completed in 1982 and the full scale wetland marsh treatment system has been operating since 1986. The average ﬂows are 1.8 MGD and 6 MGD for summers and winters, respectively. Since this treatment system utilizes a natural process to treat wastewater, the performance depends on environmental conditions. Under normal conditions, the Arcata Wastewater Treatment Plant does not violate permits with average BOD and TSS less than 30 mg/L. Arcata Marsh & Wildlife Sanctuary

➤ Arcata uth So S 1 o 10 Salt Marsh u Wastewater y t wa h gh G Hi o Str Treatment Plant T eet Arcata Marsh H Street Interpretive Center

Oxidation Ponds

Butcher’s Wastewater Slough Aquaculture Reclaimed Logpond Project

I S tre et

Allen Marsh

Arcata Bay Gearheart Marsh Klopp Lake

Hauser Marsh Marsh

E Foot Trails

N S Railroad Bird Blind

W Boat Ramp 1" = Approx. 800'

Figure 2: Arcata wastewater treatment plant with Arcata Marsh and Wildlife Sanctuary. LITERATURE REVIEW

Disinfection of wastewater

Since the industrial revolution, human activities have produced a wide range of water- borne waste products that have to be controlled and treated before being released into the environment. Especially important for public health is the control or destruction of any microorganisms causing water-born diseases. Disinfection is an important process where a significant amount of pathogenic microorganisms are eliminated. Disinfection, the last process of wastewater treatment, provides a level of protection against pathogens causing water-born diseases such as polio, cholera, hepatitis, typhoid, and a number of other bacterial diseases (US EPA, 1986). Detecting individual pathogenic organisms in a large volume of wastewater is almost impossible and economically not feasible. Therefore disinfection efficiency is normally expressed as a number of indicator organisms that coexist in significant quantities where pathogenic organisms are present (McDonald et al., 2006). Fecal and total coliform bacteria are currently the most common indicator organisms. This study, as well as water quality regulations resulting from shellfish harvesting in Humboldt Bay, use the test for fecal coliform bacteria. Also, fecal coliform are generally found in smaller population than that of total coliform in the same condition (Shen et al., 2008). Therefore, the degree of severity in contamination may be studied by the more sensitive of fecal coliform population. A number of disinfectants are being utilized in disinfection systems, including chlorine dioxide, chloramines, ozone, and ultraviolet radiation. Each disinfection technology has different benefits and limitations, but economical feasibility drives the use of chlorination and UV radiation.

4 5

Chlorination

The most common disinfectant for wastewater treatment is chlorine because of its effectiveness against a wide range of pathogenic organisms and its relatively low cost (Pol- prasert and Rajput, 1984). Chlorine gas is a powerful oxidizing and disinfecting chemical. However, because of the discovery of a couple of major issues, the practicality and safety of this disinfection system is debatable. When chlorine reacts with organic material, the concentration of chlorine gets reduced and disinfection-by-products (DBPs) including Trihalomethanes (THMs) are often formed. DBPs include chloroform, bromodichloromethane, chlorodibromomethane, bromoform and Dihloroacetic Acid that may cause kidney, liver, and central nervous system damage. The most prevalent is chloroform also known as a member of THMs which are considered highly carcinogenic materials (Bull, 1982) (Table 1).

Table 1: Health effects of some by-products of chlorine disinfection (Bull, 1982). By-product Health Effects Chloroform Animal carcinogen which can induce liver tumors in mice and kidney tumors in rats. Bromodichloromethane Produces liver and kidney damage in both mice and rats. Carcinogenic in mice and rats, producing renal, liver, and intestinal tumors. Chlorodibromomethane Produces liver and kidney damage in both mice and rats. Induces tumors in the liver of mice. Bromoform Low incidence of intestinal tumors in rats. Chloroacetic Acid Neurologic effects in animals. No increased tumors. Dichloroacetic Acid Major toxicities are damage to the nervous system and liver. Induces liver tumors in mice. Trichloroacetic Acid Potent inducer of liver tumors in male mice. Dichloroacetonitrile No speciﬁc toxicological effects reported, only nonspeciﬁc effects on body weight and some organ weights and some reproductive effects. 6

Since the US EPA started to limit the allowable amount of THMs in waste discharges, wastewater utilities have been trying to reduce THMs. However, more fundamental solutions are needed for this issue. Also, the cost of chlorination has been increasing due to the high security requirements of the transportation of chlorine and special operators based on the EPA Risk Management Program (RMP). Moreover, dechlorination is generally re- quired before discharging treated wastewater into water bodies, which makes this method more complicated and expensive (Ying, 2008). The common chemical for the dechlorination is sulphur dioxide, which is corrosive and hazardous to handle. Dechlorination may cause high hazard liability insurance and increase initial capital costs with special stor- age and handling equipment (US EPA, 2006). All of these issues have been motivation to investigate other disinfection alternatives.

Ultraviolet disinfection

Ultraviolet disinfection has been determined as an effective alternative to chlorination. Although UV technology has been shown to be a highly effective disinfectant, the low cost of chlorine and operational problems with early UV disinfection equipment contributed to its slow growth (Nelsone, 2000). However, a number of UV-relative technologies have reduced the cost of the UV disinfection process, while stronger regulations of the chlorination system have made UV disinfection economically compatible with chlorination(Koehler, 2006). Ultra-violet disinfection technology has been developing since Downes and Blunt discovered the germicidal properties of sunlight in 1877. The use of UV disinfection systems for potable water started in 1916 in the U.S., and these systems have been applied to both water and wastewater treatment plants for decades. The mechanisms of UV disinfection are 7

Figure 3: UV light in the electromagnetic spectrum (Washington State Department of Ecol- ogy, 2006). relatively simple. An Ultraviolet disinfection system uses a mercury lamp to produce electromagnetic energy or UV radiation, which lies between visible light and X-Rays (Figure 3). The electromagnetic energy penetrates the cell wall of a microorganism and damages RNA and DNA, interfering with the reproduction process (Figure 4). The most effective wavelength to inactivate microorganisms is in the range of 250 to 270nm (Andreadakis et al., 1999). One of the common UV lamps is a low-pressure lamp that produces monochromatic light at a wavelength of 253.7 nm. Medium-pressure lamps are normally used in large facilities. They have stronger germicidal UV intensity than low-pressure lamps. However, these lamps require higher temperatures with a higher energy consumption (US EPA, 2006). General characteristics and operational advantages are summarized in Table 2 and 3. Although UV disinfection is not economically ideal for all wastewater treatment systems, there are some signiﬁcant advantages over other disinfection systems. UV disinfec- 8

Figure 4: Illustration of the effect of UV ray on DNA (Herring, 2006).

Table 2: Typical Mercury Vapor Lamp Characteristics (US EPA, 2006) Parameter Low-pressure Low-pressure Medium-pressure High-output Mercury vapor 0.93 0.18 - 1.6 4 ×104 - 4 ×106 pressure (Pa) Operating 40 60 - 100 600 - 900 temperature (oC) Electrical 0.5 1.5 - 10 50 - 250 input (W/cm) Germicidal UV 0.2 0.5 - 3.5 5 - 30 output (W/cm) Electrical to UV conversion 35 - 38 30 - 35 10 - 20 efﬁciency (%) Relative number of High Intermediate Low lamps for a given dose Germicidal Monochromatic Monochromatic Polychromatic & UV light at 254 nm at 254 nm germicidal range Arc length (cm) 10 - 150 10 - 150 5 - 120 Lifetime (hr) 8,000 - 10,000 8,000 - 12,000 4,000 - 8,000 9

Table 3: Mercury Vapor Lamp Operational Advantages (US EPA, 2006). Low-pressure and Low-pressure Hight-output Medium-pressure Higher germicidal efﬁciency Higher power output Smaller power draw per lamp Fewer lamps for a given application Longer lamp life tion is highly effective at inactivating most viruses, spores, and cysts (US EPA, 1999). The contact time of this disinfection is approximately from 20 to 30 seconds with low-pressure lamps which is shorter than other conventional disinfectants (Solomon et al., 1998). There are no known residual effects that may be harmful to humans and aquatic life. The equipment and units of this system require less space than other methods. Also, this system is relatively easy and simple to operate. UV disinfection is a physical process rather than a chemical disinfectant, which normally deals with toxic chemicals (Richter and Weaver, 2003). When all of these advantages have been evaluated and qualiﬁed in conventional wastewater treatment systems, UV disinfection system for constructed wetlands needs more attention with adequate and active research.

Constructed Wetlands

Constructed wetlands are artificial marshes that are utilized as secondary wastewater treatment units by mimicking the biochemical and physical treatment processes of natural marshes. Since the late 1960’s, over 200 constructed wetlands have been developed and recognized as effective wastewater treatment systems (US EPA, 2000). Research on this wastewater treatment technology has been growing rapidly, resulting in a variety of designs and modified technologies of the wetlands. Successful implementations of those designs and technologies, as well as general characterization of the performance of constructed wetlands, have been accumulated in the web accessible Treatment Wetlands Database (Finney 10 and Gearheart, 2008). This database has opened up the possibility of application to different types and sizes of communities and facilities. Constructed wetlands have been found to provide Nitrogen and Carbon removal capacities as well as coliform removal (Tchobanoglous and Stensel, 2003). Microorganisms have a major role in this removal by degrading organic materials as they grow and generate bio-film on the roots and stems of vegetation in a wetland (US EPA, 2000). Although constructed wetlands are considerably effective in reducing biological oxygen demand (BOD) and total suspended solids (TSS), they generally do not eliminate fecal pathogens completely and often fail to meet fecal coliform regulations (Borup and Adams, 1985). Though the fecal coliform regulations varies region to region, generally the range of fecal coliform regulation is from 100 to 200 CPU/100mL. However, the Arcata Wastewater Treatment Plant must meet 14 CPU/100mL average each month 90% of the time before discharge into the Humboldt Bay due to shellfish farming in the bay (Gearheart, 1999; Wilson, 1996). The AWTP currently utilizes chlorination disinfection along with dechlorination by using sulfur dioxide (US EPA, 1987). Since AWTP discharges the treated wastewater into Arcata Bay where shellfish farms exist, UV radiation disinfection may be more appropriate than chlorination. Prior to the application of this technology, it is necessary to evaluate relevant water quality parameters to assess the practicality.

The Effect of Particulate Matter on UV disinfection

Since UV disinfection utilizes radiation, particulates in wastewater may affect its disinfection efﬁciency. Suspended particles can increase optical pathway by scattering (Mass- chelein, 2002) and generate shields for microorganisms. In addition, pores in the particulates can result in occlusion of microorganisms into the particles (Figure 5). 11

Figure 5: Effects of particles on UV disinfection (Blume and Neis, 2001).

To optimize the performance of UV disinfection, it is crucial to characterize and evaluate the particulates in wastewater. There are four major methods to estimate particles in a water sample: turbidity, total suspended solids, particle counting and UV absorption. Turbidity is an optical characteristic, which refers to water clarity. Turbidity relates the decrease of transparency to suspended particulate and colloidal material. The equipment for measuring turbidity is normally an optical instrument called a nephelometric turbidime- ter. The term nephelometric indicates the estimated degree of light scattering caused by particulate material in the water. The units are Nephelometric Turbidity Units (NTUs); lower NTU numbers are equated with clearer water. Since this property of liquid is not color related, but rather to suspended materials, turbidity may be affected by temperature, pH, or any factors that are related to the materials. In addition, protein-based constituents may increase turbidity as these compounds react with other dissolved components. Total suspended solids (TSS) are commonly related to turbidity because water with high turbidity appears cloudier and typically has high TSS level. TSS is a measure of the mass of particles that cannot pass through a standard glass-fiber filter. The common sources of TSS 12 are clay, sand, and silt from solids, algae, and organic materials from decaying vegetation, sewage and industrial waste. Particle counters can be used to measure all particles in a sample including fibers, dirt, microorganisms, any other kind of debris. Light extinction or light blockage is a common principle applied to counting instruments to detect particles (Xu, 2000). This test is a useful method to characterize the distribution of particle size and numbers in a water sample. UV absorption or UV transmittance is a more practical method to evaluate the effect of particulates on UV radiation. The theory behind this technique is based on the fact that materials in a sample absorb UV light in proportion to their concentration (APHA, 2005). Although UV radiation is mainly scattered and absorbed by colloidal particles, any organic and inorganic substances such as ferrous iron, nitrate, nitrite and bromide may result in high UV absorption. Also, certain oxidants and reducing agents, such as chlorate, chlorite, thiosulfate and ozone are known as UV-absorbing substances (APHA, 2005). There is a common assumption that high turbidity and TSS absolutely causes the failure of UV 99% inactivating effectiveness. However, this assumption may not be appropriate for all wastewater. It is a well known fact that large particles (> 50µm) are very difficult to penetrate (Sakamoto and Zimmer, 1997). However, according to recent research, the effectiveness of UV disinfection does not necessarily depend on simply the total amount of particles, but the actual sizes of particles (Madge and Jensen, 2006). It was demonstrated that all particles greater than 10 micrometers (µm) in diameter are significantly related to residual coliform bacteria concentration after high doses of UV light (Emerick et al., 1999). Also, Madge and Jensen (2006) discovered that the smaller size particles (< 5µm) do not provide significant shielding for free floating bacteria. Since the green algae in constructed wetlands are between 5 and 10 micrometers, it is possible that UV disinfection is viable with a high TSS condition. 13

Coliform Re-growth

The major inactivating effect of UV radiation on pathogens is the formation of photoproducts in DNA (Kulms et al., 1999). Of these photoproducts, the pyrimidine dimer inter- rupts both the transcription and replication of DNA by forming between adjacent pyrimidine molecules (Alonso et al., 2004). This formation of the dimer can be reversed by two repair processes: photoreactivation and dark repair (Salcedo et al., 2007). Photoreactiva- tion may occur when a damaged cell is exposed to a relatively intense source of visible or UV-A light. In a condition of no light, dark repair can occur by producing a different dimer (Shin et al., 2001). These self-repair mechanisms may results in failing to meet water quality disinfection standards. In particular, photoreactivation may be a serious concern when wastewater treated by UV radiation is discharged into any open-surface systems such as reservoirs and rivers where damaged pathogens can be exposed to light energy sources. There are well-developed tests for coliform re-growth, but a standardized method is not available. Due to the effects of various water quality parameters on microorganisms for both photoreactivation and dark repair, it is very difﬁcult to obtain results representing the actual re-growth process. Whitby and Palmateer (1993) found that photoreactivation tests cannot accurately demonstrate the actual re-growth phenomenon in a natural system due to the limitation and artiﬁcial settings of the laboratory. However, these tests can be useful in determining the potential for re-growth and the effect that might have on the success of a disinfection strategy.

The Effect of UV disinfection on Algae

Algae are a relatively simple form of aquatic organism (Figure 6). They are classified as non-flowering plants since they have similar biological systems to convert inorganic 14 substance into organic materials by using photosynthesis. They are normally found near shallow ocean coasts and any fresh water bodies that have relatively slow or no flow. Vari- ous kinds of algae play significant roles in wetland function.

Figure 6: Blue green algae (Anabaena) (Mount Allison University, 2000).

Algae provide a food source for small aquatic living organisms (Sullivan and Moncreif, 1990). Algal photosynthesis generates significant amount of Oxygen for any living organisms in wetlands, greatly influencing water-column dynamics (McCormick and Cairns, 1994). These organisms are also an important part of the purification process and biofilter- ation of wetland treatment systems. Algae incorporate the nutrients from wastewater into new cellular matter as they reproduce. A potential problem may arise when using UV to disinfect wastewater from wetlands that contains high concentration of algae since above a certain dose, UV radiation may start to destroy the algae. It is found that Ultraviolet-B (UV-B) irradiation on algae results in DNA damage, interruption of photosynthesis, pig- ment synthesis (Hader et al., 1998) and disturbance of growth. UV sterilization is one of the common techniques that actually utilize this phenomenon to eliminate or control algae population in outdoor ponds. However, in wetlands of wastewater treatment systems, a sudden 15 rise of destroyed algal populations may result in high biological oxygen demand (BOD), violating water quality standards. In addition, due to humic and conjugated compounds in BOD, the UV transmittance may be decreased.

Humic Acid and UV transmittance

Humic acid (HA) is a type of compound resulting from decomposition of organic matter. Humic acid is generally dark brown and is a major constituent of soil and lignite (Islam et al., 2005). Although humic acid inhibits bacterial and fungal growth, it has a negative effect on the efficiency of UV disinfection due to its UV absorbing characteristic. This may be a concern for the application of UV disinfection systems to constructed wetlands since the effluent of the wetlands often has a relatively high amount of humic acid. A recent study demonstrated that humic water has an effect on UV radiation, resulting in more bacteria survivals (Alkan et al., 2006). Bitton et al. (1972) investigated the effect of humic acid and clay on UV irradiation. They found that humic acid has a more negative effect on the efficiency of UV disinfection than clay. In addition, the research demonstrated that the absorption of UV radiation by humic acid at high pH (7.2) was significantly higher than that at low pH (5.7).

Dose and Response of UV disinfection

The choice of the disinfecting UV dosage is crucial for both economic and public health aspects. Theoretically, UV dose is calculated as the integral of UV intensity during the exposure time (Lindenauer and Darby, 1994). Assuming the intensity is consistent, UV dose will be the product of the UV intensity and exposure time and is deﬁned as follows: 16

Table 4: Energy Requirements for UV Treatment Systems on Selected Organisms (The Northeast Midwest Institute, 2001). Continuous Continuous Plused Organism UV 90% (1log)a UV 99% (2log)b UV 90% (1log)c Effectiveness Effectiveness Effectiveness (mW-s/cm2) (mW-s/cm2) (mW-s/cm2) Cryptosporidium1 110 330 > 16 Escherichia coli 1 3 - 6 7 - 16 > 13 Staphylococcus aureus1 2 - 5 7 > 10 Vibrio cholerae 2 6 - 7 7- 13 NA Infectious hepatitis2 5 - 8 8 - 15 NA Poliovirus2 3 -12 6 - 13 NA Nematode eggs3 31 - 51 92 NA Chlorella vulgaris 4 12 - 14 22 NA Blue-green algae 4 300 - 600 NA NA Infectious pancreatic necrosis5 40 60 NA a: Aquionics, Inc., and Safe Water Solutions Inc. b: Aquaﬁne Corporation and Safe Water Solutions Inc. c: Innovatech Inc. 1: Bacteria. 2: Viruses. 3: Protozoan. 4: Algae. 5: Fish Related Disease.

D = I × t

where D = dose (mWs/cm2 ) I = average intensity applied to the efﬂuent (mW/cm2 ) t = exposure time (seconds) Common units for UV dose are milliJoules per square centimeters (mj/cm2) or the equivalent milliwatt seconds per square centimeters (mWs/cm2). Both irradiance and exposure time are complicated factors that normally need to be evaluated carefully. UV doses must be adequate to inactivate targeted microorganisms (Table 4). 17

There are a number of methods to measure UV dose directly for bench and full-scale reactor systems. Those techniques are classiﬁed into physical, chemical, biological, and mathematical approaches.

• Physical techniques Physical methods use radiometry, a measure of narrow and broadband spectral re- sponses. The technique unfortunately provides only UV irradiance for one point in a reactor and does not provide any information on hydraulic retention time. Due to the limitation that most sensors can precisely measure radiation irradiance perpendicular to the board of the detector, this method is generally used for relative UV measurements. In a practical way, this technique has been applied to UV output monitoring in UV disinfection system to indicate any decrease of irradiance due to fouling or aging of the UV lamps (Linden and Moﬁdi, 2004).

• Chemical techniques Chemical methods involve chemical actinometry. This technique can provide a single UV dose value to the whole complex system with the bulk liquid ﬂow in the reactor. Chemical actinometry determines the radiation dose by measuring the reaction of a compound the UV dose. Chemical actinometry is not practical since it would require continuous injection of a compound such as Potassium Ferrioxalate into the waste stream (Linden and Moﬁdi, 2004).

• Biological techniques Biodosimetry is the most common measurement of a radiation dose for biological systems. This technique assesses the effective germicidal dose meaning that it will provide the proper dose for any targeted pathogenic microorganisms. This method is not a comprehensive measurement for different ﬂow rates and clumped organisms. 18

Since this test is based on the assumption that all disinfection is only from UV radiation, actual UV dose from this technique may be miscalculated due to any synergistic reactions (Linden and Moﬁdi, 2004).

• Mathematical techniques The Point Source Summation (PSS) method has been commonly used for estimating UV irradiance in low-pressure UV systems. There are concerns about the accuracy and relevance of this method. Like actinometry, this technique provides only single averaged UV dose, whereas actual dose normally depends on the ﬂow path of targeted particles. In order to estimate accurate UV dose with this method, measurement of UV absorbance must be considered for particle scattering and absorption (Linden and Moﬁdi, 2004).

Design Factors of UV disinfection System

The design of a UV disinfection system is generally site-speciﬁc. Three factors listed below are critical for design parameters.

Hydraulic properties of the reactor

A UV disinfection system ideally needs to have steady-state flow with enough radial mixing to maximize exposure to UV radiation. Generally, UV facilities have multiple UV chambers of the same capacity. Upstream and downstream processes must be considered for the hydraulic evaluation. The path of targeted particles in UV reactors determines the amount of UV radiation. Any short-circuiting or dead zones must be avoided in the design to prevent any ineffectiveness of energy and contact time. UV disinfection systems may be classified as either open or closed channel systems. A typical open channel UV system 19 used for the disinfection of wastewater is illustrated on Figure 7-a. Lamps can be placed either horizontal and parallel to the flow or vertical and perpendicular to the flow. The design flow rate can be evenly distributed along a number of open channels. A typical channel contains more than two banks of UV lamps in series, and each bank consists of a specified number of modules (Metcalf and Eddy, 2003). A common design of a closed channel UV system is shown on Figure 7-b. The flow direction for this type of channel is often perpendicular to the placement of the lamps rather than parallel to the UV lamps. The closed channel system is becoming more preferred due to the following advantages:

• No danger of personnel being exposed to UV light.

• No growth of algae in the channel.

• Better hydraulic mixing than in open channel systems.

a. b.

Figure 7: Examples of UV reactors : (a) Closed-channel and (b) Open-channel (US EPA, 2006). 20

Intensity of the UV radiation

The most common factors affecting the intensity of UV radiation are fouling, aging, and the conﬁguration and placement of lamps in the reactor. Water quality may cause the fouling of lamp sleeves. The degree of fouling depends on hardness, alkalinity, lamp temperature, pH and concentration of calcium and iron. Fouling is normally not a major issue for most treatment plants. However, adequate monitoring for these factors is necessary for proper design and operation. The decrease of UV radiation can occur from aged UV lamps. Each type of UV lamp has different operation-hours (Table 2).

Wastewater characteristics

Analyzing wastewater characteristics plays a crucial role as a decision making tool for the UV facility design. The characteristics include the ﬂow rate, particle content, initial coliform population and other physical and chemical parameters. For proper design, characteristics affecting UV transmittance (UVT) must be analyzed. Typical sources affecting UVT are soluble and particulate forms of humic and fulvic acid, including phenols, iron, nitrates and sulﬁtes (Yip and Konasewich, 1972; DeMers and Renner, 1992). Also upstream treatment processes must be considered because any chemical addition from prior processes may affect the performance of UV reactors. For example, UV transmittance may increase by introducing chlorine or ozone, resulting reduction of soluble constituents, precipitating metals, and degrading organic materials (APHA, 2005). 21

Main Parameters and Regulations

Fecal Coliform

Coliform bacteria are a typical bacterial indicator for water resources, especially for surface water bodies. Fecal coliform bacteria are microscopic organisms that normally live in the intestines of warm-blooded animals and are introduced into surface water in the form of waste material, or feces. Fecal coliform bacteria have a short life span and are categorized into pathogenic and non-pathogenic bacteria. Escherichia coli is an example of fecal coliform bacteria (Figure 8). Fecal coliform bacteria are good indicators of a potential fecal contamination. When fecal coliform bacteria are present in high numbers in a water sample, there is a high possibility of the presence of disease-carrying organisms, which live in the same environment as the fecal coliform bacteria.

Figure 8: Escherichia coli bacteria (Erbe, 2006). 22

Total Suspended Solids

Total suspended solids (TSS) affects the effectiveness of UV disinfection by scattering, reﬂecting and absorbing the UV irradiation. In addition, TSS can carry nutrients to support microbial growth in water and provide coliform space to attach on and shelter them from UV radiation (Qualls and Johnson, 1983).

Fecal coliform concentrations generally are negatively correlated with pH, so lower pH values would be associated with higher concentration of coliform. pH affects solubility of metals and carbonates that can absorb UV light and can cause the fouling of carbonates on quartz tubes (US EPA, 2006).

Biological Oxygen Demand

Biochemical oxygen demand is a measure of the quantity of oxygen consumed by microorganisms to degrade organic materials. The sources of organic matter are from nature and human activities. Natural sources of organic material are generally from degraded plants and dead aquatic organisms. Human sources of organic material are classified as non-point sources and point sources. The level of BOD is significantly linked to aquatic organisms. High BOD usually results in less dissolved oxygen and favors microorganisms that are more tolerant of lower dissolved oxygen than fish and bigger aquatic organisms. A study proved that BOD has a minor effect on the effectiveness of UV disinfection (Darby et al., 1995). 23

Table 5: Efﬂuent limits for discharge to Humboldt Bay, Arcata Marsh and Wildlife Santu- ary (Kuhlman, 2007). Constituent Unit 30-Day Average 7-Day Average Daily Max BOD (20◦C, 5-day) mg/L 30 30 60 lb/day 575 863 1151 Suspended Solids mg/L 30 45 60 lb/day 575 863 1151 Settleable Solids mg/L 0.1 0.2 pH Standard Unit Within limits of 6.0 and 9.0 at all times Total Coliform CPU/100mL 14 43

Regulations

The Arcata wastewater treatment plant is under various regulations because the treated efﬂuent goes into the enhancement marshes where are a part of recreational areas and into the Arcata Bay where shellﬁsh are being cultivated. The regulations are summarized in Table 5. METHODS

Study Site Description

This study was conducted to evaluate the disinfecting efficiency of a pilot UV unit for the effluent from a constructed wetland. The samples for this study were collected from the Arcata Wastewater Treatment Plant in Arcata California. This plant has a treatment capacity of an average daily flow of 2.3 MGD. The wastewater treatment facility consists of primary treatment plant, three oxidation ponds (45.14 acres), four treatment marshes (6.4 acres) and four enhancement marshes (31 acres).

Treatment Marsh 3

Oxidation Pond 3

Treatment Marsh 2 Pilot Marsh (Treatment Marsh 4)

Oxidation Pond 2 Treatment Marsh 1

Figure 9: Sampling Sites at Arcata Wastewater Treatment Plant.

The primary sampling site for this experiment was the efﬂuent of the Pilot Marsh; now known as Treatment Marsh 4. The Pilot Marsh was built in 1979 to demonstrate the

24 25 effectiveness of wetlands for treating wastewater. The Pilot Marsh has ten 20 ft by 200 ft cells and treats the efﬂuent from Oxidation Pond 2 and discharges the treated water near the exit of Treatment Marsh 1. Other marshes and ponds in the wastewater treatment system were selected as sampling sites for a particle size characterization study (Figure 9).

UV Disinfection Unit

The UV disinfection unit is a manufactured product called the Double Helix UV sterilizer. This unit has a 5.3 watt UV lamp manufactured by GE company with 51 mW/cm2 output. The water jacket in the unit has a double helix shape to maximize the effectiveness of UV radiation (Figure 10). This design minimizes the size of the unit but maximizes the contact time in the unit. Also this unit has reﬂecting material on the inside of the chamber to enhance the UV irradiation. The contact time was controlled by varying the ﬂow rate. The range of UV doses with this unit was from 96 to 153 mJ/cm2 which is relatively higher than a typical design range (20-140 mJ/cm2) for the industry norms (US EPA, 2006).

Figure 10: Pilot UV disinfection unit (Double Helix UV sterilizer). 26

Sampling

The samples were collected from the efﬂuent of the Pilot Marsh, stored into containers and transferred in coolers. The sample volume was approximately 10 gallons each time and the lab analyses were begun in 20 mins of sampling. The sampling period began August 22, 2007 and ended December 20, 2007. This sample period was selected because fecal coliform counts were expected to high between August and December due to migrating birds using the oxidation ponds as a resting area. For particle counting tests, samples were collected from Oxidation Pond 2 and 3, Treatment Marsh 2 and 3, as well as the efﬂuent from the enhancement marshes.

Water Quality Analysis

Five water quality analyses were conducted on water samples from the marsh. Five-day biochemical oxygen demand, ultimate biochemical oxygen demand, total suspended solids, and MF fecal coliform counts were performed following procedures given in Standard Methods for the Examination of Water and Wastewater (APHA, 2005). The analysis of the impact of UV on algal survival did not have a corresponding Standard Method for the Examination of Water and Wastewater. Speciﬁc details on each analytic method are provided below.

Biochemical Oxygen Demand (BOD)

Two types of BOD tests were conducted for this study: the 5-Day BOD test and the Ul- timate BOD test (Procedure 5210 B and 5210 C) in Standard Methods for the Examination of Water and Wastewater (APHA, 2005). The scientiﬁc methodology for this test measures consumed oxygen by biochemical degradation of organic material in samples. The 5-Day 27

BOD test and Ultimate BOD test measure oxygen consumed for 5 days and for 60 to 90 days, respectively. Six 300mL BOD bottles were utilized instead of one 2L BOD bottle for Ultimate BOD; 40mL samples were used for both tests. Since there is a possibility that a signiﬁcant amount of microorganisms are inactivated after UV disinfection, there are controlled tests with bacterial seed. Polyseed manufactured by InterLab Supply was used for the test.

Algae Survival

An alternative way to evaluate the effect of UV radiation on algae population is to measure dissolved oxygen produced by algae for a certain period of time. This test is based on the assumption that the population of algae is directly proportional to the amount of dissolved oxygen produced by algae. After UV radiation, samples in BOD bottles were set in a light incubator for 60 hours with GE T5 HO ﬂuorescent lamps that are specialized for growing plants. Since there is a potential measurement error with resealing after each measurement in the same bottle, a separate group of bottles was used for each measurement. The samples in Group A were prepared in groups for each measurement date, and after each measurement, the samples were discarded. The samples in Group B were resealed after each measurement for the following measurements.

Total Suspended Solids

Total suspended solids Dried at 103-105oC (Procedure 2540 D: Standard Methods for the Examination of Water and Wastewater) was used for this analysis.The basic principle is to filter a well-mixed sample through a standard glass-fiber filter and dry the sample to examine weight difference between before and after filtering. The volume of the samples 28 were 100 mL with one replicate. Distilled water (1000 mL) was used for the blanks to iden- tify possible errors in procedure. Glass fiber filters (2.5 cm) produced by Fisher Scientific and a scale manufactured by GMBH Gottingen¨ were utilized for this test.

Fecal Coliform MF Method

The MF method in Standard Methods for the Examination of Water and Wastewater (APHA, 2005) was used for this study. Only fecal coliform was tested for this study since research demonstrated that inactivation rate of total coliform and fecal coliform are very similar after exposure to UV irradiation (Darby et al., 1993). The membrane filter (MF) method is the most common technique for fecal and total coliform due to the capacity of large sample volume and relatively rapid results. The fundamental procedure for the MF method is to filter samples through a membrane and culture them with a broth in an incubator with a proper temperature. Two replicates of 4mL raw sample (before UV disinfection) were filtered through a 0.45 µm membrane filter. For samples after disinfection, there were five replicates with 15 mL samples. All the samples were diluted with distilled water and made into 100 mL samples for each test to get proper colony counts (Procedure 9222: Stan- dard Methods for the Examination of Water and Wastewater).

Ultraviolet Absorption Method

The UV transmittance was measured instead of UV absorption since the Hitachi Model 100-50 Double Beam Spectrophotometer provides both measurements. To compare the effect of organic and inorganic materials on UV disinfection efﬁciency, lignite and silt were added to samples and fecal coliform was enumerated before and after UV radiation. 29

Also UV transmittance with the range from 200 to 500 µm was measured to determine the presence of interfering substances.

Fecal Coliform Re-growth Test

A fecal coliform re-growth test was conducted along with the algae survival test. After UV radiation, one group of samples in BOD bottles were set in a light incubator and one group of samples in a dark incubator to evaluate photoreactivation and dark repair. Fecal coliform were measured every two days over a 10 day period. RESULTS AND DISCUSSION

The fecal coliform in the efﬂuent of the Pilot Marsh varied between 600 and 11200 CPU/100mL over the ﬁfteen different sample periods (Figure 11). UV dose ranged from 96 to 153 mJ/cm2. Fecal coliform counts gradually increased from September and reached over 10000 CPU/100mL. This trend may be explained by feces from migrating birds using the oxidation ponds as a staging ground during winter.

Figure 11: Fecal coliform counts from the Pilot Marsh (August 22, 2007 - December 20, 2007).

During this approximately 4 month measuring period, TSS ranged between 17 and 35 mg/L (Figure 12). The average UV transmittance during the measurement period varied between 44.8 to 54.7 %; pH ranged between 6.0 and 6.3. In all samples and at all doses, no fecal coliform were detected in the disinfected efﬂuent (Table 6).

30 31

Table 6: UV disinfection test results from the Pilot Marsh (August 22, 2007 - December 20, 2007). Date Avg. TSS Avg. Inﬂuent Fecal UV dose Fecal Coliform after (mg/L) Coliform (CPU/100mL) (mJ/cm2) disinfection (CPU/100mL) 8/22/07 17 863 96 0 8/25/07 25 1500 108 0 9/3/07 27.5 650 105 0 9/6/07 23 662 123 0 9/18/07 35 700 121 0 9/26/07 24.5 2150 115 0 10/3/07 33 2217 118 0 10/9/07 30 2383 117 0 10/17/07 28 2308 111 0 10/25/07 23.5 2433 121 0 11/2/07 27.5 3208 120 0 11/10/07 31.5 2992 111 0 11/15/07 24 5300 113 0 11/21/07 27 5333 117 0 12/20/07 22.5 10942 153 0

Figure 12: Total suspended solids from the Pilot Marsh (August 22, 2007 - December 20, 2007). 32

Figure 13: Dissolved oxygen results of Test I with sample Group A (R1: non-disinfected, A: 94.4 mJ/cm2, B: 121.9 mJ/cm2, C: 196.0 mJ/cm2).

The Effect of UV Disinfection on Algae

Excessive dosage of UV radiation might degrade the efﬂuent quality by killing algae causing an increase in BOD. Three different doses were applied to evaluate the relationship between UV dosage and increase in BOD.

Algae Survival

The algae survival test demonstrated the effect of UV radiation on algae population. The higher UV doses on the samples resulted in lower dissolved oxygen in the sample bottles (Figure 13). This would indicate the UV radiation was adversely effecting the survival. The two different measurement methods for measuring dissolved oxygen produced relatively similar results (Figure 14). This result indicates that in case a similar test is needed, measuring from the same bottles is desirable in terms of cost and time efﬁciency. The repli- 33

Figure 14: Dissolved oxygen results of Test I with sample Group B (R1: non-disinfected, A: 94.4 mJ/cm2, B: 121.9 mJ/cm2, C: 196.0 mJ/cm2). cate test (Test II) results are summarized in Figure 20 and 21 in Appendix I. Although this test illustrated the relationship between UV dosage and algae population indirectly, a more speciﬁc test was still needed to further quantify the potential impact of UV disinfection resulting in an increase of BOD due to algal death.

5-Day BOD

Five-Day BOD and 10-Day BOD tests were conducted twice with three different UV doses (Table 7). Since UV radiation has the potential effect not only on terminating algae but also on inactivating microorganisms that are necessary for the BOD test, BOD seeds were added to compensate for the possible effect of UV radiation on BOD results. All of the BOD samples were seeded except R1(non disinfected) and Blank 1. The average 5-Day BOD was approximately 29 mg/L. The effect of UV radiation on BOD was insigniﬁcant 34

Figure 15: 5-Day BOD and 10-Day BOD after UV radiation of Test I (R1: sample before UV radiation without seed, R2: sample before UV radiation with seed).

(Figure 15). This result demonstrated that UV dose less than approximately 190 mJ/cm2 will not increase BOD since the range of UV dose for this test was between 96.0 mJ/cm2 and 190.2 mJ/cm2. High BODs of R2 may be explained simply by additional microorganisms from the seed. The results of another replicate test are summarized in Figure 18 and 19 in Appendix I.

Table 7: Dosage summary for effect of UV radiation on 5-Day BOD and 10-Day BOD. Test number Sampling Contact time Contact volume Detention time Dose and date group (sec) (mL) (sec) (mJ/cm2) Test I A 2.56 238 1.88 96 (Aug. 22) B 3.56 236 2.64 134.6 C 5.03 236 3.73 190.2 Test II A 2.33 249 1.64 83.5 (Oct. 26) B 3.01 243 2.17 110.6 C 4.87 247 3.45 176.0 35

Table 8: Summary of average ultimate BOD results with various doses. Test number and Sampling Dose BOD 5 BOD 10 BOD 15 BOD 20 date group (mJ/cm2) (mg/L) (mg/L) (mg/L) (mg/L) Test I A 106.5 36.80 68.35 84.66 86.36 (Sep. 06) B 126.6 34.74 64.91 81.80 83.50 C 216.3 33.39 62.44 79.90 81.49 Test II A 96.9 35.41 62.25 79.65 81.15 (Nov. 05) B 125 34.39 61.2 78.59 79.84 C 171.7 33.21 59.75 76.63 77.78

Ultimate BOD

All of the samples were seeded and measured for 20 days with 7 measurements for each sample. Comparing the Ultimate BOD with different UV doses, the effect of UV radiation on the Ultimate BOD was found to be insigniﬁcant, as were the 5-Day BOD results (Table 8). The average of ﬁnal BOD was 79.59 mg/L and BOD difference between the 15 day and the 20 day was approximately 1.3 mg/L.

UV Transmittance

Two tests were performed to determine the effect of humic acid and silt on UV trans- mitance. The average transmittances of the background sample were 54.7% and 44.8%. After introducing ether lignite, which is a common humic acid or silt representing inorganic material, the transmittance of samples were lower by approximately 20%. In the test, the average doses of UV radiation were 126 and 150.2 mJ/cm2. Fecal coliform were found in samples with lignite after UV disinfection. In contrast, no coliform was found in the sample with silt. Despite the fact that the doses were lower and transmittance was higher than the samples with silt, fecal coliform were found in the samples with lignite (Table 9). This result indicates that lignite has a negative effect on the efﬁciency of UV disinfection. 36

Figure 16: Ultimate BOD results of Test I (A: 106.5 mJ/cm2, B: 126.6 mJ/cm2, C: 216.3 mJ/cm2).

Table 9: Summary of UV transmittance test results. Test Samples Dose Transmittance Average Fecal Coliform Number (mJ/cm2) (%) (CPU/100mL) Test I Blank 0 54.7 2383 (Oct. 25) With Lignite 124.1 19 46.7 With Silt 127.8 9.8 0 Test II Blank 0 44.8 10941 (Dec. 20) With Lignite 152.9 23 13.3 With Silt 147.5 25.5 0 37

Figure 17: Particle size distribution in percentage (Treatment marsh 3).

Particle counting test

Over 80% of the particles found at each sampling point in the wetland treatment system were smaller than 10 µm (Table 10). In particular, over 90% of particles are smaller than 4µm in the treatment marsh efﬂuent (Figure 17). As mentioned in the literature review, this result supports that the UV disinfection system may be viable for constructed wetlands.

Table 10: Summary of particle counting test results for each samples sites (TM2 : Treat- ment marsh 2, TM3 : Treatment marsh 3, EM : Enhancement marsh). Particle Pond 1 Effluent TM2 Effluent TM3 Influent TM3 Effluent EM Effluent size (%) (%) (%) (%) (%) 2 µm 39.0 47.8 40.3 59.0 54.1 4 µm 44.6 47.3 50.0 38.3 36.7 7 µm 9.1 3.8 7.7 2.0 4.5 10 µm 4.9 0.9 1.8 0.5 2.6 15 µm 2.0 0.1 0.3 0.1 2.0 30 µm 0.2 0.0 0.0 0.0 0.1 50 µm 0.1 0.0 0.0 0.0 0.0 38

Table 11: Summary of UV 10 day fecal coliform re-growth test results. Test Type of Incubator Group Dose (mJ/cm2) Fecal Coliform (CPU/100mL) Test I Light A 96 0 (Aug. 22) incubator B 134.6 0 C 190.2 0 Dark A 96 0 incubator B 134.6 0 C 190.2 0 Test II Light A 83.5 0 (Oct. 26) incubator B 110.6 0 C 176.0 0 Dark A 83.5 0 incubator B 110.6 0 C 176.0 0

Fecal Coliform Re-growth Test

After UV radiation with a dose ranging from 83.5 to 190.2 mJ/cm2, no fecal coliform were found during a 10-day period in samples from either the light or dark incubator (Table 11). This suggests that fecal coliform were not able to successfully restore themselves by photoreactivation nor dark repair processes over a 10-day period. CONCLUSION

This study focused on the feasibility of UV disinfection systems for wetland wastewater treatment. Through the period of study from August 2007 to December 2007, the pilot UV reactor demonstrated a highly stable and effective performance for inactivating fecal coliform in different conditions. The following conclusions were made from the results of this study:

• The fecal coliform were terminated completely after UV disinfection with varied conditions during the period of this study. This is signiﬁcantly lower than 14 CPU/100mL, which is the fecal coliform permit standard for the Arcata Wastewater Treatment Plant.

• Although UV radiation did affect the algae population, its dosage, which was lower than approximately 190 mJ/cm2, did not have a signiﬁcant effect on algae population in terms of BOD. In other words, the actual doses for wastewater treatment plants that are normally lower than 100 mJ/cm2 will be less likely to cause the violation of BOD permits.

• Average transmittance of the efﬂuent of the Pilot Marsh did not have an effect on the performance of the pilot UV reactor. Although the transmittance of the samples were lower than the typical transmittance of efﬂuent from conventional wastewater treatment plants, which is approximately 65%, all of the fecal coliform were inactivated. The research demonstrated that lignite has a more negative effect on UV radiation than silt.

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Figure 18: 5-Day BOD and 10-Day BOD after UV radiation. (R1: sample before UV radiation without seed, R2: sample before UV radiation with seed).

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Figure 19: Ultimate BOD results of Test II (A: 96.9 mJ/cm2, B: 125 mJ/cm2, C: 171.7 mJ/cm2).

Figure 20: Dissolved oxygen results of Test II with sample Group A (R1: non-disinfected, A: 106.5 mJ/cm2, B: 126.6 mJ/cm2, C: 216.3 mJ/cm2). 47

Figure 21: Dissolved oxygen results of Test II with sample Group B (R1: non-disinfected, A: 106.5 mJ/cm2, B: 126.6 mJ/cm2, C: 216.3 mJ/cm2).