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Pilot-Scale Study of Integrated Membrane-Aerated Biofilm Reactor (MABR) System on the Urban River Remediation Mei Li, Peng Li, Chunyu Du, Linquan Sun, and Baoan Li Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b00143 • Publication Date (Web): 12 Jul 2016 Downloaded from http://pubs.acs.org on July 18, 2016

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Industrial & Engineering Chemistry Research

Pilot-Scale Study of Integrated Membrane-Aerated Biofilm Reactor (MABR) System on the Urban River Remediation Mei Li a,b,c,d, Peng Li a,b,c,d , Chunyu Du a,b,c,d, Linquan Sun a,b,c,d, Baoan Li a,b,c,d,* a

Chemical Engineering Research Center, School of Chemical Engineering and

Technology, Tianjin University, Tianjin 300072, PR China b

State Key Laboratory of Chemical Engineering, Tianjin University, Tianjin 300072,

PR China c

Tianjin Key Laboratory of Membrane Science and Desalination Technology, Tianjin

University, Tianjin 300072, PR China d

Collaborative Innovation Center of Chemical Science and Engineering (Tianjin),

Tianjin 300072, PR China Corresponding author Baoan Li Chemical Engineering Research Center, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, PR China. Tel.: +86 22 2740 7854, Fax: +86 22 2740 4496 E-mail: [email protected]

ACS Paragon Plus Environment


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ABSTRACT Coupled with the hydrolysis-acidification (H-A) process, two-stage continuous flow MABR system was designed for the urban river treatment and parameter optimization was investigated in accordance to the average effluent concentrations of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN) and suspended solids (SS). The optimal process parameters included temperature 19 °C, pH 8.0, the reflux ratio of 200% and hydraulic retention time (HRT) of 15 hours (h), based on which the operational feasibility of the integrated system was further evaluated during the 40 days pilot-study for the urban river treatment. Results indicated that the integrated system exhibited highly-effective performance for the urban river remediation with ~87% COD removed and >95% NH4+-N removed. Nitrification and denitrification were simultaneously achieved inside the system. The TN removal process was enhanced by the reflux system with the effluent TN concentration remained at ~1.8 mg/L. In conclusion, the systematic applicability for the water quality improvement of the urban river was effectually confirmed on the pilot-scale study, which was conducive to the technical engineering application. KEYWORDS: MABR; Hydrolysis-acidification Process; Urban River; Reflux; Enhanced nitrogen removal. HIGHLIGHTS: 1 Two-stage continuous flow MABR system, coupled with the H-A pretreatment, was integrated for the urban river treatment. 2 The nitrogen removal was enhanced by the relux system under shortened HRT.


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1. INTRODUCTION Urban rivers are of significant importance to economic development and ecological protection.1-3 In recent years, urbanization has been dramatically accelerated in China, where the industrial and domestic water consumption has skyrocketed inevitably4-6 and ecosystem degradation of the urban river has been widespread even with worsening tendency. It’s been investigated that the ecological degradation is closely associated with the excessive exploitation and utilization, and further intensified by the eutrophication due to the improper wastewater discharge. Generally, rivers are characterized by the diverse pollutants with high mobility and the extensive contaminated area. The centralized process and financial development of regions along the destructed ecology would be definitely stagnated and human survival might be severely threatened. Promotion of effective treatment and remediation technologies is urgent for the ecological city construction,7 yet which are evidently restrained at present. Conventional physic-chemical techniques (e.g. diversion/dredging, sediment dredging, filtration and coagulation/precipitation) and biological treatments (e.g. activated sludge) are generally inapplicable to the river remediation due to the high cost and/or low efficiency.8 Characterized by lower energy-consumption and investment, the enhanced microbial technology has been widely applied in the surface water for the water quality restoration and self-purification capacity remediation .9-11 Membrane-aerated biofilm reactor (MABR), an innovative wastewater treatment technology, utilizes the gas-permeable membrane as biofilm carrier12 and promotes



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the microbial growth through membrane aeration13. Consequently, pollutants in the water can be removed by the active biofilm for proliferation and metabolism. Mass transfer of oxygen molecules and substrates inside the heterogenous biofilm is in counter-direction, the independence between which stabilizes the aeration and degradation process. By penetrating through the membrane, molecular oxygen can be directly consumed by the attached biofilm with the theoretical utilization rate up to 100%,14 which avoids the observable biofilm detachment caused by sloughing and/or scraping and enhances the ammonia oxidization by nitrifying bacteria.15 Due to the biofilm stratification relevant with the counter-diffusion and reaction of oxygen molecules and substrates,16 MABR is typically appropriate for TN removal.17, 18 It’s been confirmed that the simultaneous nitrification and denitrification (SND) and organic pollutants removal synchronize during the MABR process, making it distinct from the conventional TN removal technologies.19, 20 In laboratory scale, MABR feasibility has been extensively conducted on the treatment of municipal sewage21 and refractory industrial wastewater22-25. Furthermore, reports are available on the industrial wastewater treatment by the pilot-scale MABR system.26-29 But few researches are performed on the applicability of up-scaling MABR system in the treatment and remediation of urban river and process parameter optimization. In this paper, the two-stage MABR system coupled with the H-A pretreatment has been designed and constructed for the river remediation. The Shiwuli River, with length of ~27.2 km and basin area of ~111.25 km2, belongs to the principal ecological


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river of Hefei City (Anhui Province, China) as the important flood discharge channel and landscape river. In recent years, the water deterioration has appeared due to the improper discharge of industrial and domestic wastewater and the deficient water supplement. Continuous-flow single-stage MABR has been previously applied in the river for a long term. COD and NH4+-N could be substantially removed (data unshown). Effluent TN, however, was higher than the demand of the Chinese National Standard for surface water (GB3838-2002). And the overall treatment performance was greatly affected by the influent SS. With membrane module improved, the integrated pilot-scale system was introduced in the paper to enhance the removal of carbon and nitrogen and SS. Processing parameters, including the temperature, the pH value, the reflux ratio and the hydraulic retention time (HRT), were optimized and determined according to the removal effects and the systematic performance. Furthermore, stability and feasibility of the integrated system was examined under the optimal parameters. This research was aimed to optimize the MABR process and promote the urban river treatment and remediation with theoretical and applicable foundation. 2. MATERIALS AND METHODS 2.1. Characteristics of Membrane and Membrane Module Polymer composite hollow-fiber membrane dedicated to the MABR process was obtained from Hydroking Sci & Tech Ltd. (Tianjin, China). The membrane is characterized by high mechanical strength for the tensile strength and elongation rate at break determined as 49.9 MPa and 168.5%, respectively and rupture or distortion



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are efficiently avoided under higher hydraulic shock. Great biocompatibility has been detected, indicating excellent biofouling resistibility. The hollow-fiber membrane dedicated for the MABR is validated suitable for long-term operation under greater stability, maintaining higher aeration flux and anti-fouling ability besides the great pollutant removal performance. Main technical parameters of the membrane are specified in Table 1. Totally, 3600 membranes were regularly sealed into the acrylonitrile-butadiene-styrene valves by epoxy resin adhesive to be configured as one membrane module in the cross-flow pattern, effective membrane area of which was ~175m2. 17 membrane modules, paralleled to the main aerated conduit, were assembled inside the stainless steel bracket to be configured as one module unit (Figure 1). Packing density of each module unit was maintained at 66%, which was appropriate to control and avoid excessive microbial growth and/or biofilm detachment. Then ten module units were installed inside the MABR system, the total membrane area of which was ~1775m2. The flow-through aeration mode was selected during the research to inhibit the efficiency drop caused by vapor permeation towards the membrane lumen. 2.2. Configuration of the Integrated System Schematic flow chart and assembly diagram of the system are shown in Figure 1. Design capacity of the system was 50 m3/d. The system mainly included two tanks (three reactors), i.e. the H-A pool, MABR-1, and MABR-2, respectively, all of which were internally applied by the rust-proof treatment and externally installed with insulation layer. Each tank was segmented into three flow channels and width of each


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flow channel was 0.7 m. Water temperature monitored throughout the research ranged between 4°C and 8 °C. Hence the electrical heater was supplemented to maintain the biofilm activity and stabilize the treatment process. Influent from the Shiwuli River was pumped and homogeneously distributed into the H-A pool, the effluent of which, overflowed consecutively into the MABR-1, the MABR-2 and then the river. The H-A pool (Volume

Effective=5

m3) was filled with 30 combined rows of

bio-carriers. Adequate activated sludge was inoculated at the start-up phase and the anaerobic biofilm was cultivated to hydrolyze and acidify the river water to improve the degradability. Flow-aid devices were mounted at the end to enhance mass transfer efficiency. Furthermore, SS could be effectively absorbed by the bio-carriers of the H-A pool, facilitating the bio-degradation process of the subsequent MABR system. For the MABR-1 (Volume

Effective=10

m3), four module units were equally divided

into the 2nd and 3rd channels to eliminate short flow. Annular reactor, similar to the oxidation ditch, formed between the connected ends of the 1st and 2nd channels. Impellers were installed to inhibit locally-excessive biofilm growth. Flow meters and valves were mounted to regulate effluent from the MABR-1 into the 1st channel of the MABR-2. For the MABR-2 (Volume

Effective=15

m3), six module units were

equally immobilized inside the three channels. Effluent from the 3rd channel was re-circulated into the 1st channel to improve the flow rate. Excess sludge was periodically removed through the sludge-discharge system at the bottom of each tank. Aeration equipment could provide the MABR system with compressed air of 0.01-0.8 MPa .The main aerated conduit were divided to individually aerate the MABR-1 and



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the MABR-2 and to regulate the pressure and airflow rate. Throughout the research, the overall aeration pressure remained at 0.30 MPa. 2.3. Biofilm Acclimation and Startup of the Pilot-Scale System After the activated sludge was inoculated, nutrient solution, mainly containing carbohydrates, ammonium sulfate, potassium dihydrogen phosphate (C: N: P=100:5:1) and other microelements etc., was daily supplemented into the integrated system to promote the biofilm formation. Results of microscopic examination (Data unshown) indicated that tawny biofilm with sufficient microflora, protozoa and metazoa was visible on the membrane of the MABR, and local thickness of the biofilm was higher than 500 µm. Then river water was periodically pumped to replace the nutrient solution and to acclimate the attached biofilm. During the replacement, the influent flowrate was simultaneously regulated in accordance with the water quality and biofilm stability, which was maintained at 1.2m3/h during the acclimation under the water temperature of 18 °C and pH 7.0. 2.4. Optimization of the Process Parameters The research was conducted from Dec., 2013 to Mar., 2014 and the water quality was successively monitored and recorded, which was characterized by the high COD and NH4+-N concentration (Table 2). Effects of process parameters on the removal of COD, NH4+-N and TN was investigated, which included the temperature (10 °C, 13 °C, 16 °C, 19 °C and 22 °C, respectively), pH value (5.5, 6.0, 7.0, 8.0 and 9.0, respectively), the reflux ratio (0%, 100%, 200%, 100% and 400%, respectively) and HRT (10h, 12h, 15h, 20h and 25h, respectively). Systematic performance was


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validated by the 40-day operation under the combination of the optimum parameters. 2.5. Determination of the Water Quality Effluent was daily sampled and examined throughout the research. Water temperature was monitored and recorded. COD, NH4+-N, TN, and SS were detected by the spectrophotometry using Multiparameter Bench Photometer for Laboratoris (2800, Hach Instruments Inc., USA). BOD was determined by the BOD analyzer (BODTrak™, Hach Instruments Inc., USA) according to the instruction. the dissolved oxygen (DO) profile and pH value were measured using DO probe (JPBJ-608, Shanghai Precision & Scientific Instrument Co. Ltd., China) and pH probe (Delta320, Mettler Toledo, USA), respectively. All determinations were carried out in triplicate and the mean value was reported. 3. RESULTS AND DISCUSSION 3.1. Startup of the Pilot-Scale System During the sludge inoculation, impellers of the H-A pool and MABR-1 and circulating pump of the MABR-2 were opened to substantially enhance microorganism attachment on the membrane surface by improving the flowrate and blending the nutrient solution. Homogeneous biofilm with thickness ~200 µm appeared on the membrane surface at the third day and gradually thickened to ~400 µm at the tenth day. Biofilm immobilized on the bio-carriers inside the H-A pool became acclimated to the anaerobic environment, and biodegradability of certain refractory organics was largely improved after the hydrolysis and acidification process. With the accomplishment of acclimation, the effluent ratio of BOD to COD



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(B/C ratio) increased from 0.17 to 0.31 (Figure 2-a), indicating the degradation of long-chain organics and gradually-improved biodegradability of effluent from H-A pool. SS were substantially removed, about ~75% to 80%, by the filler interception and anaerobic biofilm absorption. The turbidity was reduced observably, which was conducive to the immobilized biofilm in the subsequent MABR system. Impellers of the MABR were operated to enhance the flowrate under the plug-flow pattern and promote mass transfer inside the biofilm, avoiding locally-excessive microbial growth. The DO concentration of each MABR steadily decreased during the biofilm acclimation (Figure 2-b). As indicated, anaerobic environment formed inside the MABR-1 for the DO below 0.5 mg/L at the end while aerobic biofilm matured better inside the MABR-2. Effluent from the H-A pool flowed into the MABR-1, where the macromolecular organics were further degraded to strengthen the biofilm activity of the MABR-2. Influent of the MABR-1 contained sufficient readily-biodegradable COD and NH4+-N. Heterotrophs outperformed the autotrophic ammonia oxidation bacteria (AOB) for oxygen consumption. DO was substantially utilized for the COD degradation. Hence organic loading of the MABR-2 was effectually controlled. Effluent from the MABR-2 was circulated back into the MABR-1 to supplement DO and ammonia oxidation products and facilitate denitrification inside the MABR-1. Total COD removal efficiency increased from 40% to ~80% with effluent COD concentration measured lower than 30 mg/L. Nitrogen substance of the Shiwuli River water mainly included NH4+-N (≥80%) and organic nitrogen. As monitored, the NH4+-N removal efficiency fluctuated provisionally, which might be associated with


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the effects of water quality fluctuation on the biofilm system. With the nitrifying bacteria gradually enriched on the membrane surface, the NH4+-N removal efficiency correspondingly improved to 90% with effluent NH4+-N concentration under 1.6 mg/L. TN removal efficiency increased from 15% to 59% during the acclimation. Unsteady TN removal efficiencies might be related with the tendency of denitrifying bacteria assembling outside the biofilm, which was affected by the river water replacement. 3.2. Investigation on the Process Parameters 3.2.1. Temperature This research was conducted in winter and lower temperatures would affect the biofilm activity. Hence the electrical heater was moderately applied to improve the systematic performance. In this paper, 10°C, 13°C, 16°C, 19°C and 22 °C were selected to observe the treatment efficiency of major pollutant in terms with the overall energy consumption. Applicability of the system under lower environmental temperatures was evaluated. Significant effects of temperatures on the COD removal efficiency were detected (Figure 3-a). For 10 °C, the COD removal efficiency was 54% (6% by the H-A pool). Subsequently, the COD removal efficiency was elevated about 10% with the temperature ranging from 10°C to 19°C. For 19°C and 22°C, total COD removal efficiencies were within minor differences, which were 81% and 83%, respectively. Results indicated that temperature positively affected the biofilm activity on COD degradation. COD removal efficiency in the MABR-1 under 22 °C improved 8% and that in the MABR-2 reduced 9%. COD was substantially degraded in the



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MABR-1. Then the effluent with lower BOD and COD loading flowed into the MABR-2, which decreased the COD removal efficiency. Temperature effects on the NH4+-N removal were more significant than on the COD removal (Figure 3-a). In this research, the nitrification activity increased with the temperature ranging from 10°C to 19 °C and the total removal efficiency reached to ~98%, which was similar to that under 22°C. Results indicated that the AOB activity was enhanced under higher temperature. Denitrification was facilitated by abundant nitrification products. As indicated in Figure 3-b, TN was mainly removed in the MABR-1. The removal tendency of NH4+-N and TN were similar, indicating the simultaneous nitrification and denitrification (SND) occurred in the MABR-1. About 15.6% TN was removed under 10°C. Then the TN removal efficiency remarkably increased to 71.3% under 19°C. Only 3% TN was further removed at 22°C (Figure 3-c). In combination of the systematic performance with the electrical consumption, the water temperature maintained at 19 °C was considered the optimum for conducting the subsequent research. 3.2.2. pH The pH value of Shiwuli River water ranged from 5.5 to 7.5. pH buffer solution was added to regulate the influent pH value, effects of which on the H-A process and the MABR performance were evaluated under 19 °C and influent flowrate of 1.2m3/h. From Figure 4-a, the COD removal efficiency was increased with the influent pH value (7.0, more NH4+-N were transformed into free ammonia (FA), which would decrease the ammonia bio-utilizability. Excessive FA would inhibit the Nitrosomas spp. activity. Based on the systematic performance, pH8.0 was optimum for the integrated system. 3.2.3. The reflux ratio Effluent from the MABR-2 was circulated back into the 1st channel of MABR-1 and effects of the reflux ratio (i.e. 0%, 100%, 200%, 300% and 400%, respectively)



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on the pollutant removal were evaluated under 19 °C, pH8.0 and influent flowrate of 1.2m3/h. It’s of great importance to control the effluent reflux to enhance pollutants removal with the operational cost economized. As shown in Figure 5-a, COD was substantially removed under the reflux ratio of 200% (82.6%) and only more 0.5% was further degraded at 300% (83.1%). The removal efficiency reduced to 78.7% under the reflux ratio of 400%. The influent organic loading was increased with the the reflux ratio, affecting the activity of heterotrophic bacteria. From Figure 5-b, the DO difference between the MABR-1 and the MABR-2 minimized with the increase of the reflux ratio. Indirect changes of biofilm in the MABR-1 adversely affected on the COD removal. Biofilm stratification inside the biofilm caused by the counter-transfer of oxygen and substrates creates advantageous conditions for simultaneous carbon and nitrogen removal.34-36 The nitrifying bacteria have enriched around the membrane surface, i.e. the inner region of biofilm. Hence, detachment and/or sloughing resulted from the hydraulic impact can be effectively avoided.37 As indicated in the Figure 5-b, the carbon substance was substantially removed in the MABR-1, and activity of the heterotrophic bacteria were inhibited with the increase of reflux ratio. The reflux ratio had insignificant effects on the NH4+-N removal (Figure 5-c) for the NH4+-N removal efficiency were all above 96% under different ratios. Besides the nitrification under aerobic environment, the ammonia nitrogen substance might be further removed by biofilm assimilation. Nitrification and denitrification would be


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preferably connected by coordinating the reflux ratio, which was available to the TN removal.38 TN removal efficiencies were 93.4% and 92.8% for the reflux ratios of 100% and 200%, respectively (Figure 5-c). And the effluent nitrate concentrations were similar (~ 2.0 mg/L). TN removal efficiencies dramatically reduced to 83.5% and 68.8% at 300% and 400%, respectively. With the reflux system, HRT of the MABR-1 was relatively shortened, lowering the denitrification efficiency. Incomplete denitrification in MABR-1 was detected under lower reflux ratios, and the DO profile was relatively increased in the MABR-2. Effluent from the MABR-2 with higher DO concentration was circulated back into the MABR-1, which affected the microbial ecology of the denitrification. And dissolved oxygen was mainly consumed by the biodegradable carbon source, not the nitrate, which might decrease the TN removal in the MABR-2. Comprehensively, the reflux ratio of 200% was optimal for the integrated MABR system to achieve better carbon and nitrogen removal performance. 3.2.4. HRT It’s of practical significance to evaluate effects of HRT on the processing performance of the integrated system. With the reflux system closed, HRT was monitored by regulating the influent flowrate under temperature of 19°C and influent pH8.0 (Table 3). Results showed that the COD removal efficiency were reduced with the HRT decreased (Figure 6-a). Under moderate HRT, the carbon substance were sufficiently consumed by the anaerobic microbes inside the H-A pool. Abundant BOD was advantageous to the subsequent MABR process. Minor differences were detected



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among the systematic performance on the COD removal (Figure 6-b). For the MABR-1, the COD removal efficiency gradually decreased with the reduced HRT. According to Figure 6-c, the DO profile of the MABR-1 and the MABR-2 decreased correspondingly. Substantial carbon substances were transported to the MABR-2, improving the COD removal efficiency with the DO concentration in the MABR-1 greatly reduced to 0.76 mg/L. The NH4+-N removal efficiency were relatively stable (~98%) for HRT ≥ 15h, which commenced to decrease under HRT < 15h, e.g. 84.2% for HRT of 10h (Figure 6-d). For MABR-2, reduce of the NH4+-N removal efficiency might be associated with the DO consumption increased by the organic loading shock. Among most of the conventional methods, HRT was insufficient for the nitrifying bacteria to compete with the heterotrophic bacteria for oxygen39. COD removal performance of the MABR-2 (Figure 6-b) indicated that the heterotrophic bacteria outperformed the nitrifying bacteria for oxygen utilization, i.e. the ammonia oxidation was affected (Figure 6-c). Insignificant differences were noticed among the NH4+-N removal efficiency among HRT of 15h, 20h and 25h, suggesting the various nitrogen removal processes might appear, e.g. the ANAMMOX (Data on the changes of biofilm microecology was not further summarized). TN removal tendency was similar to that of NH4+-N (Figure 6-e). For HRT ≥15h, the TN removal efficiency maintained ~72%. And the TN removal efficiency was decreased with the HRT shortened, e.g. 59% for HRT of 10h. Nitrification is the rate-limiting step of the TN removal process. And the nitrogen substance won’t be


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thoroughly bio-converted under insufficient HRT.40 The biofilm detachment was observed since the HRT was regulated to 12h. Scrapped biofilm in the MABR-1 was more distinct than the MABR-2 due to the strengthened hydraulic stress41, 42. Certain amount of the denitrifying bacteria on the biofilm external might be washed away with the effluent; and then the nitrifying bacteria on the biofilm internal would be further influenced. Hence the nitrification process might be inhibited. HRT maintained at 15h was considered the optimum for steady COD and nitrogen removal and economical operational cost. 3.3. Performance of the Integrated System under Optimal Process Parameters As described above, the process parameters optimal for the integrated MABR system included temperature 19°C, pH 8.0, the reflux ratio 200% and HRT 15h. The systematic performance and stability on the treatment and remediation of the Shiwuli River was further evaluated for 40 days. To determine the system capacity, the HRT was minimized to 12h, i.e. the influent flowrate was 2.5m3/h, since the 31st day. Water quality were monitored and profiled in the Figure 7. Results validated that the integrated system was indispensable for the efficient COD and nitrogen removal. The overall removal efficiencies of COD, NH4+-N, TN and SS were above 80% throughout the study with certain fluctuations. The effluent COD concentration was lower than 20mg/L under HRT 15h, in conformance to the requirements of Type-3 surface water stipulated in the national environmental quality standards for surface water (GB3838-2002). When the HRT was settled at 12h, the effluent concentration was slightly increased to ~30 mg/L due to certain detached biofilm. HRT impact on



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the nitrogen (NH4+-N and TN) removal was distinct, the possible reason for which has been discussed in the above context. The simultaneous nitrification and denitrification (SND) process formed inside the MABR-2 and the nitrogen removal was affected after the HRT had just been increased. But the nitrifying bacteria enriched around the membrane surface, where the hydraulic impact and pH effects were virtually buffered. The nitrogen removal process became stable with the reflux system, revealing the SND circumstance formed in the MABR-2 and resistance of biofilm towards the hydraulic impact. With the reflux ratio regulated at 200%, effluent from the MABR-2 containing insufficiently-oxidized ammonia and nitrification products (nitrite and nitrate) was circulated back into the MABR-1 to implement the nitrogen removal (Figure 7-b and Figure 7-c) through denitrification. Then the removal efficiencies were gradually improved. Effluent NH4+-N concentration was lower than 1 mg/L, which indicated that ~95% NH4+-N was removed after the 40 days treatment. As for the TN, the removal efficiency was maintained at ~85%; the effluent concentration was examined ~1.8mg/L. Correspondingly, the effluent nitrate was relatively high (Data unshown), implying the incomplete denitrification. The effluent nitrogen concentration achieved the basic requirement for the surface water by the Chinese National Standard (GB3838-2002). Then the relux system was conducive to relieving the shortened HRT effects on the nitrogen removal and maintaining the systematic performance. The SS removal effect was profiled in Figure 7-d. As observed, effluent of the H-A pool was clearer than the influent, indicating that SS was substantially removed in the H-A pool by the precipitation and interception of the composite fillers.


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Besides, the biofilm inside the MABR might enhance the SS removal efficiency through absorption and/or interception. Throughout the operation, DO of the MABR-1 maintained lower than 0.5 mg/L, which was particularly feasible for nitrogen removal via denitrification under the reflux system. DO of the MABR-2 was ~ 1.5mg/L, where the nitrification was mainly involved. Then the ammonia was substantially oxidized into the nitrate through the reflux system to be thoroughly denitrified in the MABR-1. From this perspective, the integrated system in this research was similar to the conventional activated sludge system: the H-A pool as the “anoxic process” to reduce the COD via hydrolysis and acidification, the MABR-1 as the “aerobic/anaerobic process” to remove nitrogen mainly via nitrification and the MABR-2 as the “aerobic process” to remove ammonia via oxidization. But the MABR was characterized by the simplified treatment and maintenance process. Furthermore, the SND process formed inside the MABR biofilm, which would enhance the nitrogen substance removal. Comprehensively, it’s more economic to construct and manipulate the pilot-scale MABR systems than to operate the conventional technology on the major pollutants removal. 4. CONCLUSIONS Two-stage MABR integrated with the H-A pretreatment process was successfully constructed for the urban river treatment. Parameters for optimal processing performance were investigated in details, including temperature 19°C, pH 8.0, the reflux ratio 200% and HRT 15h. The systematic feasibility and capacity was further analyzed through the 40-day operation under the optimal process parameters.



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Nitrogen removal process was enhanced by the relux system under shortened HRT. The overall COD, ammonia and total nitrogen removal efficiencies were ≥85%, and the effluent concentrations basically achieved the requirements of the Chinese National Standard for the surface water (GB3838-2002). Configuration of the integrated system and relevant process operation in this paper was supposed to provide useful technical thinking for the urban river improvement and process regulation. ACKNOWLEDGMENTS This work was supported by Tianjin Scientific and Technological Planning Project, China (No.13ZCZDSF00500). There is no competing financial interest.


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TABLES Table 1. Parameters of the membrane and membrane module Hollow fiber membrane

Unit

Value

Effective length

m

1.3

Outer diameter

µm

700–780

Wall thickness

µm

70–90

2

Specific urface area

m

10.28

amount

10

Membrane module Unit number

2

Total surface area

m

Oxygen supply rate (theoretical

1775 2

g O2 / m d

value)

10 kPa

137.44

20 kPa

291.13

30 kPa

459.05

40 kPa

807.70

Table 2. Water quality index of Shiwuli River during the research from Dec., 2013 to Mar., 2014 Water quality indexes

Unit

Range

COD BOD5 TN NH4+-N pH SS Temperature

mg/L mg/L mg/L mg/L mg/L °C

90-190 20-50 12-18 11-17 5.5-7.5 380-610 4-8

Table 3. HRT of the integrated system under different influent flowrate (m3/h) Influent flowrate (m3/h)

HRT (h) H-A pool

MABR-1

MABR-2

Total

1.2

4.2

8.3

12.5

25

1.5

3.3

6.7

10

20

2.0

2.5

5

7.5

15

2.5

2

4

6

12

3.0

1.7

3.3

5

10



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FIGURE CAPTIONS Figure 1. Schematic of the technological process in the designed MABR system. A, image of the pilot-scale system; B, Flow chart of the integrated two-stage MABR system, where ‐ air compressor, ‐ gas-filled stabilizer, ‐ air blower, ‐ reservoir, ‐ lifting pump, ‐ Tank 1, ‐ Tank 2, ‐ circulating pump. C, Detailed profile of the combined Tank1 and Tank2, where Tank 1 was composed of the H/A pool (c) with bio-carriers and MABR-1 (e) ; Tank 2 was the MABR-2 (f). a , water inlet; b, water distribution; c, the H/A pool; d, the impeller; e, MABR-Ⅰ;f, MABR-2; g, the flowmeter; h, the ater outlet. The assembled MABR module unit was shown below. A total of 17 curtain-like membrane modules were integrated in the stainless steel frame and paralleled to the principal aerated course to form one module unit. Figure 2. Variations of the influent and effluent B/C ratio of the H/A pool and the DO concentration profile of MABR during the system startup.

Figure 2-a,

variations of the influent and effluent B/C ratio of the H/A pool at the startup of the integrated system. Figure 2-b, variations of the DO concentration profile of the two MABR reactors during the biofilm acclimation. Figure 3. Effects of temperature on the removal efficiencies of COD and nitrogen. Figure 3-a, variations of COD removal efficiency. Figure 3-b, variations of NH4+-N removal efficiency in MABR process. Figure 5-c, variations of TN removal efficiency in MABR process. Figure 4. Effects of influent pH value on the performance of the integrated


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MABR system. Figure 4-a, variations of COD removal efficiency of the H/A pool and the MABR and effluent B/C of the H/A pool with pH. Figure 4-b, variations of NH4+-N and TN removal efficiencies of the MABR process with pH. Figure 5. Effects of the reflux ratio on the performance of the integrated MABR system. Figure 5-a, effects of the reflux ratio on the COD removal efficiency in MABRs process; Figure 5-b, variations of DO concentration in two MABRs under different reflux ratios; Figure 5-c, effects of the reflux ratio on the nitrogen removal in the MABRs process. Figure 6. Effects of HRT on the performance of the integrated MABR system. Figure 6-a, effects of HRT on the COD removal efficiency and effluent B/C ratio from HA pool; Figure 6-b, effects of HRT on the COD removal efficiency; Figure 6-c, variations of DO concentrations in the two MABRs under different HRT; Figure 6-d, variations of NH4+-N removal efficiency in MABRs process under different HRT; Figure 6-e, variations of TN removal efficiency in MABRs process under different HRT. Figure 7. Systematic performance under the optimal process parameters. Figure 7-a, COD removal of the integrated system; Figure 7-b, NH4+-N removal of the integrated systems; Figure 7-c, TN removal of the integrated system; Figure 7-d, SS removal of the integrated system.



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FIGURES

Figure 1. Schematic diagram of the technological process: A, Image of the pilot-scale system; B, Flow chart of the integrated two-stage MABR system; C, Detailed profile of the combined Tank 1 and Tank 2.


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Figure 2-a

Figure 2-b Figure 2. Variations of the influent and effluent B/C ratio of the H/A pool and the DO concentration profile of MABR during the system startup.



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Figure 3-a

Figure 3-b

Figure 3-c Figure 3. Effects of temperature on the removal efficiencies of COD and nitrogen


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Figure 4-a

Figure 4-b Figure 4. Effects of influent pH value on the performance of the integrated MABR system.



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Figure 5-a

Figure 5-b

Figure 5-c Figure 5. Effects of the reflux ratio on the performance of the integrated MABR system.


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Figure 6-a

Figure 6-b

Figure 6-c

Figure 6-d

Figure 6-e Figure 6. Effects of HRT on the performance of the integrated MABR system.



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Figure 7-a

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Figure 7-b

Figure 7-c Figure 7-d Figure 7. Systematic performance under the optimal process parameters.


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