Anoxic Filter Research Articles

A sustainable integrated anoxic/aerobic bio-contactor process for simultaneously in-situ deodorization and pollutants removal from decentralized domestic sewage

The integration of anoxic filter and aerobic rotating biological contactor shows promise in treating rural domestic sewage. It offers high efficiency, low sludge production, and strong shock resistance. However, further optimization is needed for odor control, pollutant removal, and power consumption. In this study, the investigation on a one-pump-drive lab-scale device of retention anoxic filter (RAF) integrated with hydraulic rotating bio-contactor (HRBC) and its optimal operation mode were conducted. During the 50-day operation, optimal operation parameters were investigated. These parameters included a 175 % reflux ratio (RR), 5-h hydraulic retention time in the RAF (HRTRAF), and 2.5-h hydraulic retention time in the HRBC (HRTHRBC). Those conditions characterized a micro-aerobic environment (DO: 0.6–0.8 mg/L) in RAF, inducing improved deodorization (89.3 % sulfide removal) and denitrification (85.9 % nitrate removal) simultaneously. During the operation period, 84.79 ± 3.87 % COD, 82.71± 2.06 % NH4+-N, 74.83 ± 2.06 % TN, 91.68± 2.12 % S2−, and 89.04 ± 1.68 % TON were removed in RAF-HRBC. Based on large amount of operational data, organic loading rate curves of RAF-HRBC were validated and calibrated as a crucial reference to aid in full-scale designs and applications. The richness of microbial community was improved in both RAF and HRBC. In the RAF, the autotrophic sulfide-oxidizing nitrate-reducing bacteria (a-son) and heterotrophic sulfide-oxidizing nitrate-reducing bacteria (h-son) were selectively enriched, which intensified the sulfide removal and denitrification process. In the two-stage HRBC system, the 1st stage RBC was primarily composed of organics degraders, while the 2nd stage RBC consisted mainly of ammonium oxidizers. Overall, the integrated RAF-HRBC process holds significant potential for simultaneously improving pollutant removal and in-situ odor mitigation in decentralized domestic sewage treatment. This process specifically contributes to enhancing environmental sustainability and operational efficiency.

An anoxic-aerobic system combined with integrated vertical-flow constructed wetland to highly enhance simultaneous organics and nutrients removal in rural China

The biggest problem in the treatment of rural domestic sewage is that the existing treatment projects require the big investment and the high operation and maintenance costs. To overcome this problem, cost-effective, low-consuming, resource-recovering and easy-maintenance technologies are urgently demanded. To this end, a novel anoxic-aerobic system combined with integrated vertical-flow constructed wetland (IVFCW) with source separation was proposed for treating rural sewage in this study. The anoxic-aerobic system contained the anoxic filter (ANF), two-stage waterwheel driving rotating biological contactors (ts-WDRBCs). Key parameters of ts-WDRBCs were identified to be 0.6 m drop height and 4 r/min rotational speed found on oxygenated clean water experiments. Then, the optimal operating parameters were determined to be 200% reflux ratio and 3 h hydraulic retention time of ts-WDRBCs. During the 80-day operation, 91.58 ± 1.86% COD, 96.17 ± 0.92% NH4+-N, 82.71 ± 3.92% TN and 92.28 ± 2.78% TP were removed under the optimal operating parameters. Compared with other treatment technologies, this combined bio-ecological system could achieve the higher simultaneous organics and nutrients removal. The effluent NO3−-N/NH4+-N concentration ratio of ts-WDRBCs was 2.15 ± 0.54, which was proved to be beneficial for plants growth. The microbial communities coexisted in each section ensured the desired removal performance of combined bio-ecological system. Summarily, high performance together with low investment costs and cheap operation costs are characteristics that make this system a promising and competitive alternative for rural sewage treatment.

Performance of a combined low-consumption biotreatment system with cost-effective ecological treatment technology for rural domestic sewage treatment

Treating rural domestic sewage has always been a hard task for rural vitalization in China. To overcome this problem, high-efficiency, easy-maintenance and low-consumption treatment technologies are urgently needed. To meet the requirements of rural sewage treatment, a new combined bio-ecological system was proposed in this study, including the anoxic filter (ANF), novel integrated guide-plate rotating biological contactors (NIGPRBC) and constructed wetland (CW). Key parameters of “ANF-NIGPRBC” system including hydraulic residence time (HRT), reflux ratio (RR) and rotational speed (RS) were identified founded on the organic matter and nitrogen removal performance for further application. In addition, the combined bio-ecological system was lasted for the 90 days at optimal operating parameters to confirm its performance on pollutant removal. The optimal operating parameters were determined to be 5 h HRTNIGPRBC, 100 % RR and 3 r/min RS. Under the optimal operating parameters, average 95.14 ± 1.31 % COD, 79.07 ± 4.32 % TN, 93.42 ± 2.16 % NH4+-N and 83.39 ± 3.46 % TP were removed during the 90-day operation. The operating results of the combined bio-ecological system indicate that the effluent meet local rural domestic wastewater pollution discharge standard. The microbial community results also helped to better explain the process performance of the whole system by high-throughput sequencing analysis. Proteobacteria and Bacteroidetes were the dominant phylum existing widely in this system. Denitrification-related genera were abundant both in ANF and CW. Overall, the new combined bio-ecological system is one of the priority choices for treating rural wastewater owing to its economic benefits, integrated design concept and convenient operation.

A Fixed-Film Bio-Media Process Used for Biological Nitrogen Removal from Sewage Treatment Plant

In this study, a lab-scale fixed-film bio-media process was developed and operated to evaluate nitrogen removal from domestic sewage treatment plants. For nitrogen removal, the fixed-film bio-media process was applied in series with anaerobic, anoxic, and aerobic units in three separate reactors that were operated continuously at the same loading rates and hydraulic retention time. A biofilm separation bioreactor was developed for on-site domestic wastewater treatment and the bioreactor employed synthetic fiber modules so that the biomass could be completely attached to the media. In this paper, the performance of the fixed-film bio-media process with an average flow rate was evaluated before and after stabilization of the treatment system for nitrogen removal. The results show that the fixed-film bio-media process was successful for improved nitrogen removal from secondary and tertiary treated wastewater, with a 77% decrease in the total nitrogen discharge. Rapid nitrification could be achieved, and denitrification was performed in the anoxic filter with external carbon supplements during tertiary treated sewage wastewater. However, aeration was supplied after the stabilization process to achieve the nitrification and denitrification reaction for nitrogen removal. However, stable aeration supply could enhance nitrification at moderate temperature with benefits from complete retention of nitrifying bacteria within the system due to bio-media separation.

Full-scale application and performance of a low-consuming system for decentralized village domestic wastewater treatment

Rural domestic wastewater (RDW) management has always been challenging due to the vast range and decentralized household distribution. This study constructed a full-scale system combined with source-separated pretreatment and terminal bio-eco treatment for a village RDW treating. The process of the application was designed from the perspective of low consumption in energy and device. The performance of the biological units consisted of an anoxic filter (ANF) and multi-stage waterwheel driving rotating biological contactors (ms-wdRBCs) was investigated. ANF/ms-wdRBCs with HRTANF 12 h and HRTms-wdRBCs 1.5 h performed best in pollutants' removal at 200% reflux ratio (RR). The maximum flow rate (FR) that the system could burden is 0.6 m3/h with a 42% increase from the designed FR 0.42 m3/h, which shows the potential in coping with the future increase of individual RDW generation. Meanwhile, the source separation and primary treatment could effectively reduce the pollutant load entering the biologic units. In the four consecutive seasons' operating, 84.9 ± 3.1% COD, 87.6 ± 3.5% NH4+-N, 44.2 ± 3.1% TN, and 28.2 ± 2.0% TP are removed, respectively. Seasonal water temperature (WT) variation is found to have a remarkable effect on biological treatment. NH4+-N removal is found the most sensitive index of pollutant removal to RR, FR, and WT variating. The system has shown the reliability of the year-round running. The full-scale application could serve as a sustainable prototype for the village RDW treatment.

The Influence of Different Operation Conditions on the Treatment of Mariculture Wastewater by the Combined System of Anoxic Filter and Membrane Bioreactor.

The mariculture wastewater treatment performance for the combined system of anoxic filter and membrane bioreactor (AF-MBR) was investigated under different hydraulic retention times (HRTs), influent alkalinity, and influent ammonia nitrogen load. The results showed that the removal efficiencies of TOC and total nitrogen were slightly better at the HRT of 8 h than at other HRTs, and the phosphate removal efficiency decreased with the increase of HRT. With the increase of influent alkalinity, the removal of TOC and phosphate did not change significantly. With the increase of influent alkalinity from 300 mg/L to 500 mg/L, the total nitrogen removal efficiency of AF-MBR was improved, but the change of the removal efficiency was not obvious when the alkalinity increased from 500 mg/L to 600 mg/L. When the influent concentration of ammonia nitrogen varied from 20 mg/L to 50 mg/L, the removal efficiencies of TOC, phosphate, and total nitrogen by AF-MBR were stable. An interesting finding was that in all the different operation conditions examined, the treatment efficiency of AF-MBR was always better than that of the control MBR. The concentrations of NO3−-N in AF-MBR were relatively low, whereas NO3−-N accumulated in the control MBR. The reason was that the microorganisms attached to the carrier and remained fixed in the aerobic and anoxic spaces, so that there was a gradual enrichment of bacteria characterized by slow growth in a high-salt environment. In addition, the microorganisms could gather and grow on the carrier forming a biofilm with higher activity, a richer and more stable population, and enhanced ability to resist a load impact.

Use of a low-cost and energy-efficient device for treating low-strength wastewater at low temperatures focusing on nitrogen removal and microbial community

Treating wastewater at low temperatures has always been challenging. In this study, an anoxic filter (ANF)/multi-stage waterwheel driving rotating biological contactors (ms-wdRBCs) device was investigated as a potential solution for treatment of low-strength domestic wastewater at low temperatures (6–18 °C). Parameters, including the recirculation ratio (RR) and hydraulic retention time (HRT), were regulated to identify the optimum operating conditions. Using the optimum parameters of 200% RR, 10.67 h HRTANF, and 1.33 h HRTwdRBC, 75.37% ± 4.43% COD, 44.81% ± 3.67% TN, 75.05% ±1.86% NH4+-N, and 35.46% ± 4.87% TP were removed. The microbial communities in eight different sections of the device were investigated through the 16s rRNA analysis. The microbial results helped to explain the device performance. Denitrification-related bacteria were present in great abundance in both the ANF and the ms-wdRBCs. Anammox-related bacteria were also in significant abundance in ANF and some parts of ms-wdRBCs, which suggested a potential solution for improving the device performance by expanding the role of these anammox bacteria. Considering both the pollutant removal efficiency and investment costs, this device is acceptable as part of a low-strength domestic wastewater treatment solution at low temperatures.

Pilot-scale anoxic/aerobic biofilter system combined with chemical precipitation for tertiary treatment of wastewater

In this study, a pilot-scale anoxic/aerobic biofilter system combined with chemical precipitation was devised and applied for the tertiary treatment of nitrogen, and post-treatment of phosphorus and residual organics in effluent from existing wastewater treatment facilities. When the system operated under a system hydraulic retention time (HRT) of 5.98 h, nitrified effluent recirculation ratio of 0.5, average methanol-supplement concentration of 23.2 mg/L, and average aluminum-sulfate concentration of 2.37 mg/L, the average concentration of BOD5, COD, SS, TN, and TP in the system effluent were 3.3, 10.4, 4.2, 6.1, and 0.43 mg/L, respectively. Despite the shorter HRT of 1.35 h in the anoxic filter packed with media, noticeable denitrification was achieved rapidly. A perfect nitrification rate was achieved and no clear deterioration in performance by chemical addition was observed. Thus, the system achieved not only outstanding nitrogen-removal performance, but also the additional removal of residual organics and phosphorus.

Performance of a coupling device combined energy-efficient rotating biological contactors with anoxic filter for low-strength rural wastewater treatment

Abstract In order to meet the requirements of decentralized sewage treatment in rural China, a source-sorted treating method was proposed, including a black water pre-treating anaerobic baffled reactor (ABR), an anoxic filter (ANF), a novel multi-stair waterwheel driving rotating biological contactors (ms-wdRBCs) and constructed wetlands (CW). The ms-wdRBCs were utilized to post-treat mixture of digested black water and raw grey water with the ANF. Key parameters of ANF/ms-wdRBCS were identified founded on the nutrient removal performance, especially nitrogen removal, for further application in the project. Besides, the ANF/ms-wdRBCs coupling device was operated 10 weeks at the optimum parameters to confirm its performance on contamination removal. The coupling device performed well on chemical oxygen demand (COD), total nitrogen (TN), and ammonia (NH4+-) removal. When running under 150% reflux ratio, 1 h HRT of each-stair wdRBC and 7.11 h HRT of ANF, the removal efficiency of COD, TN, NH4+- and total phosphorus (RTP) were 88.40 ± 2.16%, 52.33 ± 3.80%, 88.14 ± 2.30% and 34.11 ± 7.00%, respectively. The NH4+-/ NO3−- concentration ratio of effluent was approximately 3 which was certificated to be beneficial to plants growth in CW. Although the removal efficiency of TP was only 34.11 ± 7.00%, the phosphorus was partly retained to contribute to plants growth in CWs. Overall, the entire four-part system achieved outstanding pollutant removal efficiencies, while the selected plants in CW also gained benefits back. Low construction and operating cost, simple management and easy maintenance of the system ensure the application in rural areas.

Optimization of a full‐scale site to achieve total nitrogen removal through implementation of a denitrification‐submerged anoxic filter

AbstractA full‐scale wastewater treatment plant with a 5500 population equivalent was retrofitted with a pre‐denitrification‐submerged anoxic filter (SAnoF) in order to achieve new total nitrogen (TN) consent of 35 mg/L. A 36 m3 SAnoF was installed downstream the primary settling tanks. The optimal operation of the anoxic SAnoF was investigated by varying the recirculation ratio, the carbon‐to‐nitrate ratio, and the hydraulic retention time. After stable operation was achieved, nitrate was removed by 80% at a loading of 0.5 kg NO3/m3 day and a retention time of 60 min. The SAnoF presented a number of advantages, including the use of internal carbon for denitrification, decrease of carbon load to the trickling filter by 30%, and production of alkalinity required for nitrification in the trickling filter (11 mg CaCO3/mg NH4 removed). Overall, the SAnoF was satisfactory and the effluent TN concentration reached 20–25 mg TN/L.

Performance and Microbial Diversity in a Low-Energy ANF-WDSRBC System for the Post-Treatment of Decentralized Domestic Wastewater

Recently, more decentralized wastewater treatments are of great interest for rural regions. In this work, a novel ANF-WDSRBC system combined with an anoxic filter (ANF) and a four-stage water-dropping-self-rotating biological contactor (WDSRBC) was designed as a post-treatment option. With a total hydraulic retention time (HRT) of 8.8 h and reflux ratio of 1:1, the ANF-WDSRBC system was operated 160 days. The results showed the ANF-WDSRBC system had better performance without mechanical aeration devices, the removal efficiencies of chemical oxygen demand (COD), ammonia (NH4+–N) and total nitrogen (TN) were 61.4% ± 4.3%, 86.1% ± 3.7%, and 54.5% ± 3.9%, respectively. By means of high-throughput MiSeq sequencing, the results suggested that Proteobacteria, Bacteroidetes, Firmicutes, and Chloroflexi were the predominant phyla in the system. In the WDSRBC units, Nitrosomonas, Nitrosospira, Bacillus, and Nitrospira were the main genera to take part in nitrification. Longilinea, Bellilinea, Thiobacillus, and Thauera in the ANF unit were the main genera to participate in denitrification and organic matters degradation. The novel ANF-WDSRBC system had great potential in the post-treatment of decentralized domestic wastewater.

Integrated nitrogen removal biofilter system with ceramic membrane for advanced post-treatment of municipal wastewater

ABSTRACTThe pre-denitrification biofilm process for nitrogen removal was combined with ceramic membrane with pore sizes of 0.05–0.1 µm as a system for advanced post-treatment of municipal wastewater. The system was operated under an empty bed hydraulic retention time of 7.8 h, recirculation ratio of 3, and transmembrane pressure of 0.47 bar. The system showed average removals of organics, total nitrogen, and solids as high as 93%, 80%, and 100%, respectively. Rapid nitrification could be achieved and denitrification was performed in the anoxic filter without external carbon supplements. The residual particulate organics and nitrogen in effluent from biofilm process could be also removed successfully through membrane filtration and the removal of total coliform was noticeably improved after membrane filtration. Thus, a system composed of the pre-denitrification biofilm process with ceramic membrane would be a compact and flexible option for advanced post-treatment of municipal wastewater.

A novel approach to realize SANI process in freshwater sewage treatment – Use of wet flue gas desulfurization waste streams as sulfur source

SANI (Sulfate reduction, Autotrophic denitrification and Nitrification Integrated) process has been approved to be a sludge-minimized sewage treatment process in warm and coastal cities with seawater supply. In order to apply this sulfur-based process in inland cold areas, wet flue gas desulfurization (FGD) can be simplified and integrated with SANI process, to provide sulfite as electron carrier for sulfur cycle in sewage treatment. In this study, a lab-scale system of the proposed novel process was developed and run for over 200 days while temperature varied between 30 and 5 °C, fed with synthetic FGD wastewaters and sewage. The sulfite-reducing upflow anaerobic sludge bed (SrUASB) reactor, as the major bioreactor of the system, removed 86.9% of organics while the whole system removed 94% of organics even when water temperature decreased to around 10 °C. The bactericidal effect of sulfite was not observed in the SrUASB reactor, while thiosulfate was found accumulated under psychrophilic conditions. The sludge yield of the SrUASB reactor was determined to be 0.095 kg VSS/kg COD, higher than of sulfate reduction process but still much lower than of conventional activated sludge processes. The dominant microbes in the SrUASB reactor were determined as Lactococcus spp. rather than sulfate-reducing bacteria, but sulfite reduction still contributed 85.5% to the organic carbon mineralization in this reactor. Ammonia and nitrate were effectively removed in the aerobic and anoxic filters, respectively. This study confirms the proposed process was promising to achieve sludge-minimized sewage treatment integrating with flue gas desulfurization in inland and cold areas.

Enhanced denitrification with external carbon sources in a biological anoxic filter

Three parallel biological anoxic filters (BaFs) were operated to investigate the denitrification kinetics of methanol, brewery wastewater and bakery wastewater. The experiment was conducted within the temperature range of 15-20 °C, with an influent nitrate and carbon dosage of 30 mg/L and 150 mg COD/L (COD: chemical oxygen demand). The denitrification efficiencies of brewery wastewater, bakery wastewater and methanol were 84, 66 and 74%, specific denitrification rates were 1.44, 1.11 and 1.24 kg NO(3)-N/m(3) d, and total nitrogen (TN) removal rates were 74, 62 and 66%, respectively. The volatile attached solid (VAS) tests reveal that methanol has the minimum net biomass yield, so it needs the least carbon to nitrogen (expressed in COD to nitrate, C/N) ratio for complete denitrification. While the brewery wastewater and bakery wastewater need higher C/N ratio to remove all nitrate nitrogen, and they both may need pretreatment to remove phosphate when used as external carbon sources.

Internal Behavior of Biological Nutrient Removal System for Advanced Wastewater Treatment

 Abstract—The purpose of this research was develop a biological nutrient removal (BNR) system which has low energy consumption, sludge production, and land usage. These indicate that BNR system could be a alternative of future wastewater treatment in ubiquitous city(U-city). Organics and nitrogen compounds could be removed by this system so that secondary or tertiary stages of wastewater treatment satisfy their standards. This system was composed of oxic and anoxic filter filed with PVDC and POM media. Anoxic/oxic filter system operated under empty bed contact time of 4 hours by increasing recirculation ratio from 0 to 100 %. The system removals of total nitrogen and COD were 76.3% and 93%, respectively. To be observed internal behavior in this system SCOD, NH3-N, and NO3-N were conducted and removal shows range of 25~100%, 59~99%, and 70~100%, respectively. Keywords—BNR, nitrification, denitrification, organics removal, anoxic, oxic, advanced treatment. I. INTRODUCTION ATER/SEWAGE facility, one of the urban base facilities constituting a city, is an important infrastructure, and to manage it the nation has a systematic system established for a long time. In the mean time, recently the nation has recognized the importance of an ubiquitous environment to lead the future society and established 'u-Korea ' plan, and each local government is expanding the promotion of u-city construction projects connected to the ubiquitous environment (1). At the same time, low-carbon green growth, a national project, and water quality standards of discharged water(2) continuously reinforced to improve the water quality of rivers has presented a new paradigm trend composed of improvement of existing wastewater treatment plants, application of advanced treatment technology and distributed wastewater treatment for tertiary treatment. Thus, cases for application of the biological nutrient removal system (BNR) have been on the rise to reduce the installation site, produce high quality treated water, and save labor and operating costs with automated operation (3). The BNR system which has been developed mainly in Europe not only can maintain SRT (4) for a long time without separate operation and make free load changes but also does not require the secondary sedimentation tank and can secure high-concentration microbes, providing due to the shorter reaction time a higher degree of intensity for site requirement than the existing suspended growth process. Thus, the BNR system is advantageous in application to wastewater treatment

Textiles wastewater treatment using anoxic filter bed and biological wriggle bed-ozone biological aerated filter

In this study, the performance of the anoxic filter bed and biological wriggle bed-ozone biological aerated filter (AFB-BWB-O3-BAF) process treating real textile dyeing wastewater was investigated. After more than 2month process operation, the average effluent COD concentration of the AFB, BWB, O3-BAF were 704.8mg/L, 294.6mg/L and 128.8mg/L, with HRT being 8.1–7.7h, 9.2h and 5.45h, respectively. Results showed that the effluent COD concentration of the AFB decreased with new carriers added and the average removal COD efficiency was 20.2%. During operation conditions, HRT of the BWB and O3-BAF was increased, resulting in a decrease in the effluent COD concentration. However, on increasing the HRT, the COD reduction capability expressed by the unit carrier COD removal loading of the BWB reactor increased, while that of the O3-BAF reactor decreased. This study is a beneficial attempt to utilize the AFB-BWB-O3-BAF combine process for textile wastewater treatment.

Biological nutrient and organic removal from meat packing wastewater with a unique sequence of suspended growth and fixed-film reactors

A unique sequence of anaerobic filter/suspended anaerobic/aerobic (AO) reactor/aerobic filter system was developed to alleviate the drawbacks of conventional suspended growth and fixed growth systems. An anaerobic filter (AF) was used to efficiently produce volatile fatty acids (VFAs) prior to the aerobic suspended growth. A second anaerobic reactor was installed in the A/O return activated sludge line to improve phosphorus uptake by potentially controlling glycogen accumulating organisms (GAOs). One biological aerobic filter (BAF) was used for nitrification followed by an anoxic filter for denitrification and a second BAF was used for effluent polishing. The meat packing wastewater had a biochemical oxygen demand (BOD) of 853 mg/L and total nitrogen (T-N) and total phosphorus (T-P) concentrations of 61.1 mg/L and 5.8 mg/L, respectively. The BOD removal efficiency was 99.0-99.7% and the suspended solids (SS) concentration in the effluent was below 10 mg/L. The T-N removal efficiency was maintained at greater than 75.0% except at low C/N ratios. A high T-P removal efficiency, 74.7-83.9%, was also obtained when the system was operated at a hydraulic retention time of 15.7 hrs. The AF successfully produced VFAs that aided in phosphorus removal. Additionally, recycled concrete aggregate used as attachment media in the biological filters continuously provided micronutrients and stabilized the pH.

Steady-state model-based evaluation of sulfate reduction, autotrophic denitrification and nitrification integrated (SANI) process

Recently we developed a process for wastewater treatment in places where part of the fresh water usage is replaced by seawater usage. The treatment of this saline sewage consists of sulfate reduction, autotrophic denitrification and nitrification integrated (SANI) process. The process consists of an up-flow anaerobic sludge bed (UASB) for sulfate reduction, an anoxic filter for autotrophic denitrification using dissolved sulfide produced in the UASB and an aerobic filter for nitrification. The system was operated for 500 days with 97% COD removal and 74% total nitrogen removal without withdrawal of sludge. To verify these results and to understand this novel process, a steady-state model was developed from the COD, nitrogen and sulfur mass and charge balances based on the stoichiometries of the sulfate reduction, the autotrophic denitrification and the autotrophic nitrification. The model predictions agreed well with measured data on COD, nitrate and sulfate removal, sulfide production, effluent TSS, and mass balances of COD, sulfur and nitrogen in the three reactors. The model explains why withdrawal of sludge from the SANI system is not needed through comparisons of the predictions and measurements of effluent TSS and phosphorus concentrations.

A novel sludge minimized biological nitrogen removal process for saline sewage treatment

This study reports a lab-scale evaluation of a new biological nitrogen removal process for saline sewage treatment, namely a SANI process (Sulfate reduction, Autotrophic denitrification and Nitrification Integrated process). The experimental system consisted of an up-flow anaerobic bed for sulfate reduction, an anoxic filter for autotrophic denitrification using dissolved sulfide produced in the up-flow anaerobic bed and an aerobic filter for nitrification. The system successfully operated for more than 180 days with an overall organic carbon removal efficiency of 95%, in which, 82% removal was contributed by the up-flow anaerobic bed operating at a HRT of 6 h, and 13% removal by the anoxic filter. An average COD removed /sulfate removed ratio was found to be 0.76 gCOD/gSO(4) or 2.28 COD/gSO(4)-S further confirming that the organic removal was mainly achieved by the sulfate reduction. In terms of nitrogen removal efficiency, the SANI system was found sensitive to the recirculation rate between the anoxic filter and the aerobic filter. A recirculation rate of 3Q was found to be optimal for achieving 74% of the total nitrogen removal. It was confirmed that the autotrophic denitrification was a major contributor to the total nitrogen removal in the SANI system. Sulfur balance analysis indicated that both the accumulation of elementary sulfur in the biomass and the loss of hydrogen sulfide were trivial. During the entire operation period (330 days to date), no sludge was wasted from any reactors in this system. This was further confirmed by the biomass balance simulation results that low biomass yields of sulfate reducing bacteria, autotrophic denitrifiers and nitrifiers contribute to the zero excess sludge discharge.

A novel sulfate reduction, autotrophic denitrification, nitrification integrated (SANI) process for saline wastewater treatment

This paper reports on a lab-scale evaluation of a novel and integrated biological nitrogen removal process: the sulfate reduction, autotrophic denitrification and nitrification integrated (SANI) process that was recently proposed for saline sewage treatment. The process consisted of an up-flow anaerobic sludge bed (UASB) for sulfate reduction, an anoxic filter for autotrophic denitrification and an aerobic filter for nitrification. The experiments were conducted to evaluate the performance of the lab-scale SANI system with synthetic saline wastewater at various hydraulic retention times, nitrate concentrations, dissolved oxygen levels and recirculation ratios for over 500 days. The system successfully demonstrated 95% chemical oxygen demand (COD) and 74% nitrogen removal efficiency without excess sludge withdrawal throughout the 500 days of operation. The organic removal efficiency was dependent on the hydraulic retention time, up-flow velocity, and mixing conditions in the UASB. Maintaining a sufficient mixing condition in the UASB is important for achieving effective sulfate reduction. For a typical Hong Kong wastewater composition 80% of COD can be removed through sulfate reduction. A minimum sulfide sulfur to nitrate nitrogen ratio of 1.6 in the influent of the anoxic filter is necessary for achieving over 90% nitrate removal through autotrophic denitrifiers which forms the major contribution to the total nitrogen removal in the SANI system. Sulfur balance analyses confirmed that accumulation of elementary sulfur and loss of hydrogen sulfide in the system were negligible.