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Article Modified Septic Tank: Innovative Onsite Treatment System

Bassim E. Abbassi 1,* ID , Raihan Abuharb 2 ID , Bashaar Ammary 2 ID , Naser Almanaseer 2 and Christopher Kinsley 3

1 School of Engineering, University of Guelph, Guelph, ON N1G2W1, Canada 2 Department of Water Resources and Environmental Management, Al-Balqa Applied University, 19117 Al-Salt, Jordan; [email protected] (R.A.); [email protected] (B.A.); [email protected] (N.A.) 3 Civil Engineering Department, University of Ottawa, Ottawa, ON K1N 6N5, Canada; [email protected] * Correspondence: [email protected]

 Received: 13 February 2018; Accepted: 26 April 2018; Published: 29 April 2018 

Abstract: This research documents two innovative designs of septic tanks used for onsite . The designs were implemented and tested as part of a research project focused on innovative decentralized wastewater treatment solutions. The modified septic tanks were tested at different hydraulic loading rates for sufficient periods to effectively evaluate their performance. The two systems were designed with successive anaerobic and aerobic chambers and were differentiated between attached and suspended growth. The systems were operated at detention times of 4.3, 3.2, and 2.6 days. High removal of organic load was achieved under all loading criteria in both systems. Effluent BOD5 concentration at lower and higher loading rates were found to be less than 15 and 25 mg/L, respectively, representing a removal rate of more than 95%. was also removed but at a lower rate. The highest TN removal was achieved (59%) in the attached growth system at the lowest loading rate. Although two logs of E. coli removal (99%) were achieved in all systems, E. coli numbers were high enough to necessitate further tertiary treatment. The modified septic tanks proved to be a cost-effective technology with low energy and O&M requirements.

Keywords: onsite wastewater treatment; decentralized wastewater; septic tank; aerobic; anaerobic; attached growth; suspended growth

1. Introduction There is a growing need for the development of sustainable and cost-effective technologies to treat wastewater [1,2]. Within the context of adaptive water resources management, centralized wastewater treatment is an appropriate approach for large communities [3]. In small communities, however, centralized wastewater collection and treatment systems are not feasible because of the relatively high cost of capital investment and intensive operation and maintenance requirements [4–6]. Decentralized solutions in wastewater management are recognized as cost-effective alternatives to centralized systems, which could be effectively integrated into rural as as urban settings. This can significantly support future water resources management plans [7–9]. Moreover, extension of wastewater management services to small communities is essential to address serious concerns in , , and public health. Accordingly, decentralized wastewater treatment has been recognized as an effective solution allowing the requirements to be met [10–12]. In Ontario, Canada, about 10% of the population uses onsite systems for wastewater sanitation, where most of these systems are conventional septic systems (i.e., septic tank and leaching bed) [13]. Similarly, 12% of the population in Australia relies on septic systems [14]. In the , around

Water 2018, 10, 578; doi:10.3390/w10050578 www.mdpi.com/journal/water Water 2018, 10, 578 2 of 11 Water 2018, 10, x FOR PEER REVIEW 2 of 11

60 million people are connected to onsite wastewater treatment systems with the majority use of conventional onsite systems [15]. [15]. In In Germany, Germany, about 15% of the population use onsite wastewater treatment systems [[16].16]. In Jordan, 32% of the population is not connected to a sewer system. Most of them rely rely on on cesspits for for wastewater wastewater disposal disposal [9]. [9 Hence,]. Hence, onsite onsite wast wastewaterewater systems systems are common are common and andcan be can replicated be replicated to help to helpserve serve smaller smaller communities communities.. Meuler Meuler et al. et[16] al. described [16] described septic septic tanks tanks as a aspoor a poor pretreatment pretreatment system system and and a source a source of of , pollution, where where dissolved dissolved , nutrients and pathogens may remain in the effluenteffluent causing serious threat to human health and accelerated deterioration to the environment includingincluding air, water water and and . soil. One study has even reported a significantsignificant increase in Escherichia colicoli ((E.E. colicoli)) concentrationconcentration inin thethe septicseptic tanktank effluenteffluent [[17].17]. It is is evident evident that that there there is a is need a need for more for efficient more efficient and reliable and decentralized reliable decentralized wastewater wastewater treatment solutions.treatment solutions. Modifications Modifications of septic of tank septic design tank havedesign been have proposed been proposed in different in different studies studies in order in toorder improve to improve onsite onsite wastewater wastewater system system performance. performance. For For example, example, changing changing septic septic tanktank retention times and including packing materials have been suggested [[6,18,19].6,18,19]. Other studies investigated the effects of bafflesbaffles on the treatment process and the results showed that increased number of baffles baffles resulted in enhanced treatment per performanceformance [6,20,21]. [6,20,21]. Generally, Generally, most septic tank modifications modifications were suggested to enhance the performance of the septic system. However, However, if a septic tank is recognized as a stand-alone stand-alone treatment unit, unit, rational rational modification modification should should be be considered. considered. This paper aiaimsms at evaluating the the performance performance of of two two modified modified septic septic tanks tanks (MSTs) (MST designeds) designed as onsite as systems onsite systems for treating for domestictreating domestic wastewater. wastewater. This project This demonstrates project demonstrates a modern a low-cost modern onsite low-cost wastewater onsite wastewater treatment technologytreatment technology tested at varying tested hydraulic at varying loading hydraulic rates with loading both ratesattached with growth both and attached suspended growth growth and biologicalsuspended treatment. growth biological treatment.

2. Materials and Methods This paperpaper reflectsreflects actual actual experimental experimental work work ranging ranging from from developing developing the the idea, idea, to designing to designing and constructingand constructing onsite onsite systems, systems, to testing to testing and analyzing and analyzing the performance the performa ofnce these of systems.these systems. The two The onsite two treatmentonsite treatment units were units designed were designedand constructed and constructed within the Competence within the FacilityCompetence for Decentralized Facility for WastewaterDecentralized Management—SMART Wastewater Management Project—SMART in Jordan Project [22]. Thein Jordan two units [22] were. The builttwo usingunits were reinforced built concreteusing reinforced with proper mechanical with proper and electrical mechanica connections.l and electrical Each unitconnections. has a total Each working unit has volume a total of 5700working L and volume consists of of5700 four L and equally consists sized of chambers four equally connected sized chambers in series; withconnected the first in threeseries; chambers with the operatedfirst three underchambers anaerobic operated conditions under anaerobic with a total conditions volume with of 4275 a total L. volume The fourth of 4275 chamber L. The consists fourth ofchambe an aerationr consists chamber of an aeration and settling chamber tank and with settling working tank volumeswith working of 950 volumes and 475 of L,950 respectively. and 475 L, Waterrespectively. depth inWater all chambers depth in wasall chambers 1.5 m. Air was is supplied 1.5 m. Air for is 15supplied min intermittently for 15 min intermittently (every other 15 (every min) toother the 15 aeration min) to chamber the aeration via a chamber plate diffuser via a usingplate diffuser a 0.18 KW usin blower.g a 0.18 Figure KW 1blower shows. Figure the general 1 shows layout the ofgeneral the MST layout system. of the MST system.

Figure 1. Schematic diagram of the modified modified septic tank (MST) system.

The MST is designed to allowallow gravitygravity flowflow betweenbetween thethe compartments.compartments. The treatment in one MST was designed designed as as a a suspended suspended growth growth system system (MST (MST-S),-S), while while the the other other one one was was designed designed as an as anattached attached growth growth system system (MST (MST-A).-A). In the In MST the MST-A-A system, system, all chambers all chambers (except (except the first the one) first were one) filled were with fixed bed media (corrugated plastic media with a specific area of 100 m2/m3) filled to 2/3 of the

Water 2018, 10, 578 3 of 11

filled with fixed bed media (corrugated plastic media with a specific area of 100 m2/m3) filled to 2/3 of the tank working capacity. Both of these MSTs were operated in parallel, so that their performances can be compared. The MST systems were initially designed to receive an average wastewater flow of 1.2 m3/d. Raw wastewater was obtained from the forebay of a nearby centralized domestic wastewater treatment after bar screening and grit removal. The wastewater dosing was controlled by an electromagnetic flowmeter connected to programmable logic controller (PLC) SIEMENS-SIMATIC S7-200. Within the MST, the water flow pattern between the chambers resembles the plug flow pattern to minimize short circuiting. While oxygen is limited in the anaerobic chambers, oxygen concentration in the aeration chamber was set to remain above 2 mg/L during the aeration period to ensure that oxygen is not a limiting factor in the treatment process. The aerated chamber is equipped with an integrated settling tank, so that the mixed liquor suspended solids are settled and the supernatant (effluent) is flowing free of solid downstream to the tank. The configuration of aeration and settling tank was designed such that the settled is returned continuously to the aeration tank. The were equipped with several by-passes, fittings, and valves, so that the mode of operation can be easily changed and adjusted. Initially, the MST systems were operated with a hydraulic loading of 1.2 m3/d (Phase 1). However, the systems were further investigated under higher loading rates of 1.6 and 2.0 m3/d (Phases 2 and 3, respectively). At each loading rate, the investigation was carried out for a period of 26 weeks. Between any two loading phases MSTs were not sampled for a period of four weeks in order to allow the systems to develop a steady state condition. Table1 shows the summary of the hydraulic loading rates and the detention times in the MST chambers for each investigation phase.

Table 1. Wastewater loading at different investigation phases.

Detention Time in Anaerobic Detention Time in the Phase Loading Rate (m3/d) Chambers (d) Aerobic Chamber (d) 1 1.2 3.56 0.79 2 1.6 2.67 0.59 3 2.0 2.14 0.47

Inflow and outflow of MST-S and MST-A were monitored weekly and evaluated for a number of parameters. A wastewater sample volume of 500 mL from each system was collected and analyzed for temperature, pH, electrical conductivity (EC), dissolved oxygen (DO), and Oxidation Reduction Potential (ORP). A WTW multi-meter was used to measure ORP and DO, while a WTW ProfiLine-Cond 3110 (Xylem Analytics, Weilheim, Germany) probe was used to measure the EC, pH and temperature. Subsequently, 25 mL of wastewater samples were filtered (using a 0.45 µm membrane filter) for further + − analysis of (COD), (NH4 ), (NO3 ), and orthophosphate 3− (PO4 ) using LCK test kits and HACH spectrophotometer model 2800. Biochemical oxygen demand ® (BOD5) was measured using OxiTop manometric OC 100, following the German standard DIN 38 409 H52. Total suspended solid (TSS) concentration was analyzed according to the Standard Methods for Examination of Water and Wastewater [23]. Finally, E. coli was measured using the IDEXXTM Colilert-18 Quanti-tray method according to the manufacturer’s specifications.

3. Results and Discussion The analysis results of pH, EC, DO, ORP, , and TSS for the three phases are summarized in Table2. Each value in this table represents an average of 26 weeks of investigation. Under all loading conditions, pH values were found to be in an acceptable range for wastewater effluent (pH values of 6–9) [24]. It was also observed that no significant changes in pH values during the treatment process were noted compared with raw wastewater pH values, indicating a good buffering capacity of the wastewater. Effluent EC values also showed no reduction during treatment but consistently remained Water 2018, 10, 578 4 of 11 below the Jordanian Standards No. JS893/2006, for reclaimed domestic wastewater; indicating acceptable salt content in the wastewater for reuse purposes (EC < 3000 µS/cm) [25]. Table2 shows also the development and change of the ORP at the different phases. The higher negative ORP values of raw wastewater indicate clearly the anaerobic character of the influent water. Due to the aeration in the last chamber, ORP values in both systems were significantly increased indicating a well aerated effluent. However, a slightly higher ORP values in MST-A compared to MST-S indicates a higher treatment efficiency of MST-A [26]. Table2 shows the temperature of wastewater over the entire phases of investigation. The average temperature of raw wastewater during the three phases (78 weeks) was 19.8 ± 3.8 ◦C. The location where the systems were installed and tested exhibits moderate climate with low inter-annual variability in temperature. Thus, temperature had minimal influence on the tested parameters. The results in Table2 also show that both systems were able to produce clear water based on low TSS concentrations and turbidity as opposed to the conventional septic tank, where high effluent solids represent the main cause for most dysfunctional septic systems [7]. The results show two trends of solid concentration in the effluent. TSS concentrations and turbidity were significantly lower in MST-A than in MST-S effluents, suggesting that the attached growth media plays a significant role in either filtering or trapping suspended solids. Lower TSS concentrations were observed as hydraulic loading increased for MST-A, but remained almost constant for MST-S. There was no clear correlation between turbidity and hydraulic loading, however. One of the main objectives of this investigation was to evaluate the MST systems for their capacity to reduce the organic loading. Accordingly, the pilot plants were monitored for carbonaceous oxygen demand in the effluents. Figures2 and3 show the results of BOD 5 and COD concentrations for MST-A and MST-S under a hydraulic loading rate of 1.2 m3/d over the entire investigation period. It is clearly observed that both systems were able to significantly reduce carbonaceous content of wastewater (BOD5 and COD) to a level [27]. The wastewater effluent quality even meets the strict Jordanian Reuse Standards for Irrigation (JS893/2006) [25] of BOD5 and COD concentrations of 30 and 100 mg/L, respectively.

Table 2. Results of physical wastewater parameters for all treatment systems and phases.

Phase Parameter Raw Wastewater MST-A Effluent MST-S Effluent pH 7.9 ± 0.1 8.0 ± 0.1 8.1 ± 0.2 EC (µS/cm) 1864 ± 516 1798 ± 588 1917 ± 542 DO (mg/L) 0.1 ± 0.1 3.7 ± 0.6 2.1 ± 1.0 1 ORP (mV) −236 ± 27 −57 ± 73 149 ± 65 TSS (mg/L) 314 ± 168 7 ± 4 18 ± 8 Turbidity (NTU) 997 ± 225 9 ± 6 59 ± 10 Temperature (◦C) 19.9 ± 3.3 19.5 ± 3.9 19.4 ± 3.7 pH 7.5 ± 0.2 7.7 ± 0.2 7.5 ± 0.3 EC (µS/cm) 2470 ± 399 2357 ± 578 2468 ± 389 DO (mg/L) 1.0 ± 1.3 3.6 ± 1.9 3.3 ± 1.3 2 ORP (mV) −208 ± 49 −1 ± 108 −107 ± 98 TSS (mg/L) 239 ± 107 13 ± 6 18 ± 10 Turbidity (NTU) 317 ± 161 30 ± 26 43 ± 61 Temperature (◦C) 18.2 ± 2.8 17.8 ± 3.5 17.6 ± 3.2 pH 7.2 ± 0.2 7.7 ± 0.2 7.5 ± 0.2 EC (µS/cm) 2016 ± 513 2125 ± 624 2011 ± 680 DO (mg/L) 0.8 ± 0.3 3.2 ± 1.5 3.5 ± 2.9 3 ORP (mV) −239 ± 31 −39 ± 126 −120 ± 110 TSS (mg/L) 267 ± 360 16 ± 4 19 ± 6 Turbidity (NTU) 283 ± 76 22 ± 17 34 ± 24 Temperature (◦C) 21.4 ± 3.3 21.4 ± 3.5 21.3 ± 3.3 Water 2018, 10, 578 5 of 11

Moreover, Figures2 and3 show also that in spite of highly fluctuating quality of the influent wastewater,Water 2018 the, 10, effluentx FOR PEER quality REVIEW remained stable over the period of investigation. This shows5 of 11 the capacityWater of 2018 the, 10, MST x FOR PEER systems REVIEW to absorb the normal shock loading usually experienced in5 of onsite11 systemscapacity [28]. It of is the also MST clearly systems seen to that absorb the the MST-A normal produced shock loading a slightly usually better experienced quality effluent in onsite than MST-S,systemscapacity which [28]. of is the attributed It is MST also systemsclearly to the seen to robustness absorb that the the MST ofnormal attached-A produced shock growth loading a slightly systems usually better [ experienced29 quality]. As opposed in onsite than to the MSTsystems-S, which[28]. It is is attributed also clearly to seenthe robustnessthat the MST of -attachedA produced growth a slightly systems better [29]. quality As opposed effluent to than the conclusion of Meuler et al. [16], who stated that only about 40% of the BOD5 is removed in septic tanks, conclusion of Meuler et al. [16], who stated that only about 40% of the BOD5 is removed in septic both ofMST MST-S, systemswhich is haveattributed gone to much the robustness further and of achievedattached growth removal systems rates of[29]. more As opposed than 95%. to the tanks,conclus bothion of MSTMeuler systems et al. have[16], whogone statedmuch furtherthat only and about achieved 40% ofremoval the BOD rates5 is of removed more than in 95%.septic tanks, both of MST systems have gone much further and achieved removal rates of more than 95%. 800 Raw WW 700800 MST-ARaw WW effluent 600700 MST-SMST-A effluenteffluent MST-S effluent 500600

400500 400

BOD (mg/L) BOD 300

BOD (mg/L) BOD 200300

100200

1000 0 0 5 10 15 20 25 30 Week 0 5 10 15 20 25 30 Week Figure 2. BOD5 concentration with time in attached growth system (MST-A) and suspended growth Figure 2. BOD5 concentration with time in attached3 growth system (MST-A) and suspended growth systemFigure 2.(MST BOD-S)5 concentrationat hydraulic loading with time of 1.2 in mattached/d. growth system (MST-A) and suspended growth system (MST-S) at hydraulic loading of 1.2 m3/d. system (MST-S) at hydraulic loading of 1.2 m3/d. 1600 Raw WW 14001600 MST-ARaw WW effluent 1400 1200 MST-SMST-A effluenteffluent

10001200 MST-S effluent

1000800 800

COD COD (mg/L) 600

COD COD (mg/L) 400600

200400

2000 0 0 5 10 15 20 25 30 Week 0 5 10 15 20 25 30 Week Figure 3. Chemical oxygen demand (COD) concentration with time in MST-A and MST-S at hydraulic 3 loadingFigure 3. of Chemical 1.2 m /d. oxygen demand (COD) concentration with time in MST-A and MST-S at hydraulic Figure 3. Chemical oxygen demand (COD) concentration with time in MST-A and MST-S at hydraulic 3 loading of 1.23 m /d. loadingAs of a 1.2result m of/d. increased interest in nutrient concentrations in wastewater effluent, the monitoring includedAs a resultboth nitrogen of increased and interest phosphorous in nutrient constituents. concentrations Nitrate in iswastewater a very important effluent, parameterthe monitoring that Asindicatesincluded a result theboth of efficiency increased nitrogen ofand interest a treatmentphosphorous in nutrient system constituents. concentrationsto remove Nitrate nitrogenous in is wastewater a very compounds important effluent, from parameter thewastewater monitoring that included[3indicates0]. bothThe resultsthe nitrogen efficiency of nitrate and of phosphorous (NOa treatment3-N) concentration system constituents. to remove for both Nitrate nitrogenous systems is under a verycompounds a importanthydraulic from loading parameterwastewater of 1.2 that m3/d over the entire investigation period are shown in Figure 4. The very low nitrate concentration indicates[30]. the The efficiency results of ofnitrate a treatment (NO3-N) system concentration to remove for both nitrogenous systems under compounds a hydraulic from loading wastewater of 1.2 [30]. inm 3the/d over influent the entire wastewater investigation is expected period in aredomestic shown wastew in Figureater 4. as The most very of lowthe nitrogennitrate concentration compounds 3 The results of nitrate (NO3-N) concentration for both systems under a hydraulic loading of 1.2 m /d arein the present influent as organic wastewater nitrogen is expected or ammonia in domestic nitrogen wastew [30]. Theater increase as most in of the the nitrate nitrogen concentration compounds in over the entire investigation period are shown in Figure4. The very low nitrate concentration in theare presenteffluents as reflects organic the nitrogen nitrification or ammonia capacity nitrogen of both [30]. systems. The increase Nitrification in the innitrate the attached concentration growth in the influentsystemthe wastewater is, however, reflects isthe more expected nitrification stable in than domestic capacity in the of suspended wastewater both systems. growth as Nitrification most system. of the This in nitrogen the is attributedattached compounds growth to the are presentnumeroussystem as organic is, nitrifyinghowever, nitrogen bacteria more or ammonia stable in the than nitrogen in thein the suspended [30 attached]. The increase growth systems system. in the nitratecompared This is concentration attributed to those toin the in the numerous nitrifying bacteria in the biofilm in the attached growth systems compared to those in the

Water 2018, 10, 578 6 of 11 effluents reflects the nitrification capacity of both systems. Nitrification in the attached growth system is, however, more stable than in the suspended growth system. This is attributed to the numerous nitrifyingWater bacteria 2018, 10, inx FOR the PEER biofilm REVIEW in the attached growth systems compared to those in the6bioflocs of 11 of 3 the suspendedbioflocs growth of the suspended system [11 growth]. Under system a hydraulic [11]. Under loading a hydraulic of 1.2 loading m /d, of the 1.2 average m3/d, the effluent average nitrate concentrationseffluent fornitrate MST-A concentrations and MST-S for areMST 14.9-A and and MST 8.2- mg/L,S are 14.9 respectively. and 8.2 mg/L, Though respectively. these Though values seem to be relativelythese values low, seem some to nitrate-vulnerable be relatively low, some areas nitrate requires-vulnerable certain areas measures requires certain to further measure decreases to the nitrate concentrationfurther decrease (i.e., the denitrification). nitrate concentration In many (i.e., denitrification). areas around theIn many world, areas where around water the is world, scarce and wastewaterwhere is deemed water is to scarce be a and resource wastewater for irrigation, is deemed high to be nitrate a resource concentrations for irrigation, can high be beneficial nitrate for concentrations can be beneficial for agriculture and reduce the dependence on chemical fertilizers agriculture and reduce the dependence on chemical fertilizers [30]. [30].

30 Raw WW 25 MST-A effluent MST-S effluent 20

15

N (mg/L)

- 3

NO 10

5

0 0 5 10 15 20 25 30 Week

3 Figure 4. NO3-N concentration with time in MST-A and MST-S at hydraulic loading of 1.2 m /d. 3 Figure 4. NO3-N concentration with time in MST-A and MST-S at hydraulic loading of 1.2 m /d. Total nitrogen (TN) concentrations were also monitored and the results for the two systems Totaloperated nitrogen at hydraulic (TN) concentrations loading of 1.2 m were3/d are alsoshown monitored in Figure 5. and The theresults results clearly for show the that two both systems Water 2018, 10, x FOR PEER REVIEW 7 of 11 operatedsystems at hydraulic were able loading to reduce of the 1.2 total m3 /dnitrogen are shown concentration in Figure with5 higher. The results(better) performance clearly show for thatthe both MST-A. Nevertheless, if more TN reduction is required, measures to enhance denitrification should Similarly, phosphorous concentration was monitored and the results of total phosphorous (TP) systems werebe considered. able to reduceAs previously the total mentioned, nitrogen each concentration MST is equipped with with higher a return (better) line performanceconnecting the for the for both systems operated at hydraulic loading of 1.2 m3/d are shown in Figure 6. The results show MST-A. Nevertheless,aerobic chamber if with more the TN first reduction anaerobic compartment. is required, measuresThis line was to not enhance utilized denitrification in this investigation should be that there were small decreases in TP concentration in both systems. This can be seen by comparing considered.and Asshould previously be used in mentioned, future research each work. MST is equipped with a return line connecting the aerobic the average TP concentration in raw wastewater (12.9 ± 3.1 mg/L) with the effluent average of MST- chamberA with and MST the- firstB (9.7 anaerobic± 6.7 and 9.4 compartment. ± 1.9 mg/L, respectively This line). The was 24–2 not7% average utilized reduction in this in investigation TP is likely and should be used in future250 research work. due to the settling of organic phosphorus associated with TSS. Raw WW MST-A effluent 20030 MST-S effluent Raw WW 15025 MST-A effluent MST-S effluent

10020 TN TN (mg/L)

1550 TP (mg/L) TP 10 0 0 5 10 15 20 25 30 5 Week

Figure 5. Total0 nitrogen (TN) concentration with time in MST-A and MST-S at hydraulic loading of 1.2 m3/d. 0 5 10 15 20 25 30 Week

Figure 6. Total phosphorous (TP) concentration with time in MST-A and MST-S at hydraulic loading

Figure 5.ofTotal 1.2 m nitrogen3/d. (TN) concentration with time in MST-A and MST-S at hydraulic loading of 1.2 m3/d. Bacteriological load in the form of E. coli was another parameter used to evaluate the system’s performance. The results of E. coli monitoring for both systems operated at 1.2 m3/d are shown in Figure 7. Logarithmic values were plotted in order to graphically show the log reduction in E. coli concentrations. The results show clearly that both MST systems were able to significantly decrease the E. coli concentration. Two logs of E. coli reduction was achieved by MST-S, while only approximately one log was achieved for MST-A. The higher E. coli reduction in MST-S could be attributed to the formation of bioflocs that can agglomerate the free swimming bacteria, including E. coli, and settle them out in the sedimentation tank. Though the MST-S showed higher performance compared to the MST-A, E. coli concentrations in both effluents were very high and thus tertiary treatment is required. The investigations in Phases 2 and 3 are similar to those carried out in Phase 1 and were designed to examine the capability of the treatment systems to operate under elevated hydraulic loadings (1.6 and 2.0 m3/d). The purpose of this investigation was to reveal the upper limits of the system at which wastewater can be properly treated. This can significantly affect the construction cost and energy consumption for the treatment systems.

Water 2018, 10, 578 7 of 11

Water 2018, 10, x FOR PEER REVIEW 7 of 11 Similarly, phosphorous concentration was monitored and the results of total phosphorous (TP) for both systemsSimilarly, operated phosphorous at hydraulic concentration loading was of monitored 1.2 m3/d and are the shown results inof Figuretotal phosphorous6. The results (TP) show that therefor were both smallsystems decreases operated at in hydraulic TP concentration loading of 1.2 in m both3/d are systems. shown in This Figure can 6. be The seen results by show comparing the averagethat TPthere concentration were small decreases in raw in wastewater TP concentration (12.9 ±in both3.1 mg/L) systems. with This thecan effluentbe seen by average comparing of MST-A the average TP concentration in raw wastewater (12.9 ± 3.1 mg/L) with the effluent average of MST- and MST-B (9.7 ± 6.7 and 9.4 ± 1.9 mg/L, respectively). The 24–27% average reduction in TP is likely A and MST-B (9.7 ± 6.7 and 9.4 ± 1.9 mg/L, respectively). The 24–27% average reduction in TP is likely due to thedue settling to the settling of organic of organic phosphorus phosphorus associated associated with with TSS.

30 Raw WW 25 MST-A effluent MST-S effluent 20

15 TP (mg/L) TP 10

5

0 0 5 10 15 20 25 30 Week

Figure 6. Total phosphorous (TP) concentration with time in MST-A and MST-S at hydraulic loading Figure 6.ofTotal 1.2 m phosphorous3/d. (TP) concentration with time in MST-A and MST-S at hydraulic loading of 1.2 m3/d. Bacteriological load in the form of E. coli was another parameter used to evaluate the system’s Bacteriologicalperformance. loadThe results in the of form E. coli of monitoringE. coli was for another both systems parameter operated used at 1.2 to m evaluate3/d are shown the system’sin Figure 7. Logarithmic values were plotted in order to graphically show the log reduction in E. coli performance. The results of E. coli monitoring for both systems operated at 1.2 m3/d are shown in concentrations. The results show clearly that both MST systems were able to significantly decrease Figure7.the Logarithmic E. coli concentration. values were Two plotted logs of inE. order coli reduction to graphically was achieved show the by MSTlog reduction-S, while only in E. coli concentrations.approximately The results one log show was clearlyachieved that for both MST- MSTA. The systems higher E. were coli reduction able to significantly in MST-S could decrease be the E. coli concentration.attributed to the Two formation logs of ofE. bioflocs coli reduction that can agglomerate was achieved the free by swimming MST-S, while bacteria, only including approximately E. one log wascoli, and achieved settle them for out MST-A. in the Thesedimentation higher E. tank. coli Thoughreduction the MST in MST-S-S showed could higher be perfo attributedrmance to the formationcompared of bioflocs to the that MST can-A, agglomerateE. coli concentrations the free in swimmingboth effluents bacteria, were very including high and thusE. coli tertiary, and settle treatment is required. them out in the sedimentation tank. Though the MST-S showed higher performance compared to the The investigations in Phases 2 and 3 are similar to those carried out in Phase 1 and were designed MST-A, E. coli concentrations in both effluents were very high and thus tertiary treatment is required. Waterto examine 2018, 10 ,the x FOR capability PEER REVIEW of the treatment systems to operate under elevated hydraulic loadings8 of(1.6 11 and 2.0 m3/d). The purpose of this investigation was to reveal the upper limits of the system at which wastewater can100,000,000 be properly treated. This can significantly affect the construction cost and energy consumption for the treatment systems. 10,000,000

1,000,000

100,000

10,000

(MPN/100mL) 1,000

E.coli 100 Raw WW MST-A effluent 10 MST-S effluent 1 0 5 10 15 20 25 30

Week

Figure 7. (E. coli) concentration with time in MST-A and MST-S at hydraulic loading of Figure 7. Escherichia coli E. coli 1.2 m3/d. ( ) concentration with time in MST-A and MST-S at hydraulic loading of 1.2 m3/d. The results of the three investigation phases for both systems are summarized in Table 3. Each value in this table represents an average of 26 weeks of investigation. The results show that both MST systems were able to operate under elevated hydraulic loadings with almost double the design capacity. The quality of the wastewater effluent was found to comply with the Jordanian standards except for E. coli [27]. This nonconformity is expected in most decentralized systems and, therefore, tertiary treatment is usually suggested (ex. UV, hypochlorite or chlorine disinfection) whenever reuse is required [31]. Table 3 also shows that the effluent quality of the MST-A system was better than the MST-S system. The difference in the system performance can be clearly seen in the nitrate and total nitrogen concentrations. Under a hydraulic loading of 1.2 m3/d (Phase 1), the total nitrogen concentration was almost 50% less in the attached growth system than in the suspended growth one. The enhanced nitrogen removal suggests both nitrifying and denitrifying biofilm on the media [32].

Table 3. Results of chemical and biological wastewater parameters for all treatment systems and phases.

Phase Parameter Raw Wastewater MST-A Effluent MST-S Effluent BOD5 (mg/L) 481 ± 83 8 ± 3 14 ± 6 COD (mg/L) 918 ± 314 55± 18 84 ± 30 TN (mg/L) 114.0 ± 29.6 46.6 ± 26.5 81.1 ± 21.9 NH4-N (mg/L) 69.9 ± 32.3 8.8 ± 31.9 6.7 ± 18.7 1 NO3-N (mg/L) 0.7 ± 0.3 14.9 ± 6.7 8.2 ± 7.0 TP (mg/L) 12.9 ± 3.1 9.7 ± 6.7 9.4 ± 1.9 PO4-P (mg/L) 7.7 ± 3.7 8.1 ± 3.3 7.4 ± 2.7 E. coli (MPN/100 mL) 1.3 × 107 ± 5.6 × 106 2.6 × 105 ± 1.3 × 105 1.3 × 104 ± 1.2 × 103 BOD5 (mg/L) 336 ± 64 18 ± 15 14 ± 11 COD (mg/L) 627 ± 158 58 ± 20 70 ± 26 TN (mg/L) 64.7 ± 14.8 43.5 ± 15.4 73.9 ± 34.1 NH4-N (mg/L) 52.2 ± 14.0 23.2 ± 15.1 13.4 ± 11.7 2 NO3-N (mg/L) 0.4 ± 0.2 7.2 ± 5.1 13.1 ± 15.2 TP (mg/L) 7.1 ± 2.0 6.7 ± 1.5 6.6 ± 1.4 PO4-P (mg/L) 5.7 ± 2.2 6.8 ± 1.6 6.6 ± 1.4 E. coli (MPN/100 mL) 1.3 × 107 ± 3.0 × 105 4.2 × 105 ± 3.3 × 105 3.2 × 104 ± 4.3 × 104 3 BOD5 (mg/L) 469 ± 62 25 ± 5 23 ± 36

Water 2018, 10, 578 8 of 11

The investigations in Phases 2 and 3 are similar to those carried out in Phase 1 and were designed to examine the capability of the treatment systems to operate under elevated hydraulic loadings (1.6 and 2.0 m3/d). The purpose of this investigation was to reveal the upper limits of the system at which wastewater can be properly treated. This can significantly affect the construction cost and energy consumption for the treatment systems. The results of the three investigation phases for both systems are summarized in Table3. Each value in this table represents an average of 26 weeks of investigation. The results show that both MST systems were able to operate under elevated hydraulic loadings with almost double the design capacity. The quality of the wastewater effluent was found to comply with the Jordanian standards except for E. coli [27]. This nonconformity is expected in most decentralized systems and, therefore, tertiary treatment is usually suggested (ex. UV, hypochlorite or chlorine disinfection) whenever reuse is required [31].

Table 3. Results of chemical and biological wastewater parameters for all treatment systems and phases.

Phase Parameter Raw Wastewater MST-A Effluent MST-S Effluent

BOD5 (mg/L) 481 ± 83 8 ± 3 14 ± 6 COD (mg/L) 918 ± 314 55± 18 84 ± 30 TN (mg/L) 114.0 ± 29.6 46.6 ± 26.5 81.1 ± 21.9 NH -N (mg/L) 69.9 ± 32.3 8.8 ± 31.9 6.7 ± 18.7 1 4 NO3-N (mg/L) 0.7 ± 0.3 14.9 ± 6.7 8.2 ± 7.0 TP (mg/L) 12.9 ± 3.1 9.7 ± 6.7 9.4 ± 1.9 PO4-P (mg/L) 7.7 ± 3.7 8.1 ± 3.3 7.4 ± 2.7 E. coli (MPN/100 mL) 1.3 × 107 ± 5.6 × 106 2.6 × 105 ± 1.3 × 105 1.3 × 104 ± 1.2 × 103

BOD5 (mg/L) 336 ± 64 18 ± 15 14 ± 11 COD (mg/L) 627 ± 158 58 ± 20 70 ± 26 TN (mg/L) 64.7 ± 14.8 43.5 ± 15.4 73.9 ± 34.1 NH -N (mg/L) 52.2 ± 14.0 23.2 ± 15.1 13.4 ± 11.7 2 4 NO3-N (mg/L) 0.4 ± 0.2 7.2 ± 5.1 13.1 ± 15.2 TP (mg/L) 7.1 ± 2.0 6.7 ± 1.5 6.6 ± 1.4 PO4-P (mg/L) 5.7 ± 2.2 6.8 ± 1.6 6.6 ± 1.4 E. coli (MPN/100 mL) 1.3 × 107 ± 3.0 × 105 4.2 × 105 ± 3.3 × 105 3.2 × 104 ± 4.3 × 104

BOD5 (mg/L) 469 ± 62 25 ± 5 23 ± 36 COD (mg/L) 770 ± 183 88 ± 35 95 ± 36 TN (mg/L) 84.6 ± 24.5 62.8 ± 17.1 66.1 ± 15.9 NH -N (mg/L) 70.8 ± 15.6 39.8 ± 22.2 39.2 ± 19.6 3 4 NO3-N (mg/L) 0.5 ± 0.1 7.4 ± 6.7 9.3 ± 11.2 TP (mg/L) 9.8 ± 2.8 9.5 ± 2.5 9.0 ± 2.2 PO4-P (mg/L) 8.0 ± 2.9 8.3 ± 2.7 8.2 ± 2.3 E. coli (MPN/100 mL) 3.0 × 107 ± 3.0 × 106 2.2 × 105 ± 8.4 × 104 2.7 × 104 ± 1.5 × 104

Table3 also shows that the effluent quality of the MST-A system was better than the MST-S system. The difference in the system performance can be clearly seen in the nitrate and total nitrogen concentrations. Under a hydraulic loading of 1.2 m3/d (Phase 1), the total nitrogen concentration was almost 50% less in the attached growth system than in the suspended growth one. The enhanced nitrogen removal suggests both nitrifying and denitrifying biofilm on the media [32]. The MSTs were also analyzed for their energy requirements. As wastewater flows by gravity in and out of the systems, the only energy-consuming part in both tanks are the blowers. Equation (1) is used to calculate the specific power consumption based on the capacity of the blowers and the served population equivalent. P ·N sPC = B (1) PE where sPC is the specific power consumption per capita per year (KW/c.y), PB is the power capacity of the blower (kW), N is the number of operational hours in a year (h), and PE is the population equivalent. The energy consumption in the different phases described as kilowatt hours per person per year (kWh/c.y) was calculated using Equation (1) based on the blower capacity, time of operation, Water 2018, 10, 578 9 of 11 and population equivalent. The results are shown in Table4. As clearly observed, energy requirement for the modified septic system operated at elevated hydraulic loading can be notably reduced making this system a low cost technology. The energy consumption of the MST under a hydraulic loading rate of 2 m3/d is very well matched with accepted values in modern wastewater treatment facilities [33]. Beside the advantage of low energy requirement, the MST systems demonstrated less operation and maintenance requirements and lower construction and operation costs than more mechanized systems.

Table 4. Comparison of energy requirements under different hydraulic loadings.

Hydraulic Loading, m3/d Energy Requirement, kWh/c.y 1.2 65 1.6 49 2.0 39

4. Conclusions Two innovative modified septic tank systems were designed as stand-alone technologies to treat domestic wastewater. Configurations with and without attached growth media were evaluated and demonstrated significant treatment capacities with 95–98% BOD and 92–98% TSS removal observed at hydraulic retention times ranging from 2.6 to 4.4 days. Significant nitrogen removal of 59% was observed in the attached growth system at 2.6 d HRT, while results varied between 26–33% removal at higher loading rates and between 0–29% in the suspended growth configuration. Effluent quality met secondary wastewater quality criteria as well as the Jordanian standard for wastewater reuse for all parameters except for E. coli, where further disinfection is required. Corrugated plastic fixed growth media showed a slight improvement in system performance over the suspended growth alternative. This study revealed that the modified septic tank system can be used as a low cost system due to its low energy requirement.

Author Contributions: Bassim E. Abbassi developed the MST system as well as conceived and designed the experiments; Raihan Abuharb performed the experiments; Bassim E. Abbassi and Naser Almanaseer supervised the field experiments; Bassim E. Abbassi, Bashaar Ammary, and Christopher Kinsley analyzed the data; all authors wrote the paper. Acknowledgments: This work was funded by the Research Plan of the Deanship of Scientific Research at Al-Balqa’ Applied University through a MSc contract to Raihan Abuharb and the German Federal Ministry of Education and Research (BMBF) through the Dead Sea 02WM0845 and SMART 02WM1080 research projects. Conflicts of Interest: The authors declare no conflict of interest.

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