Control of COD/N ratio for nutrient removal in a modified membrane bioreactor (MBR) treating high strength wastewater

A modified membrane bioreactor (MBR) system has been developed to evaluate the efficiency of nutrient removal in treating synthetic high strength water. This study examined the effect of influent COD/N ratio on this system. Results showed that above 95.0% removal efficiencies of organic matter were achieved; indicating COD removal was irrespective of COD/N ratio. The average removal efficiencies of total nitrogen (TN) and phosphate (PO(4)(3-)-P) with a COD/N ratio of 9.3 were the highest at 90.6% and 90.5%, respectively. Furthermore, TN removal was primarily based on simultaneous nitrification and denitrification (SND) process occurred in the aerobic zone. Decreased COD/N ratios to 7.0 and 5.3, TN removal efficiencies in steady-states were 69.3% and 71.2%, respectively. Both aerobic SND and conventional biological nitrification/denitrification contributed to nitrogen removal and the latter played dominant effect. PO(4)(3-)-P-release and uptake process ceased in steady-states of COD/N 7.0 and 5.3, which decreased its removal efficiency significantly.     

Characterization of microbial community in an aerobic moving bed biofilm reactor applied for simultaneous nitrification and denitrification

A continuous-flow moving bed biofilm reactor (MBBR) under aerobic conditions was established for simultaneous nitrification and denitrification (SND), and microbial communities were investigated by a combination of denaturing gel gradient electrophoresis (DGGE) and fluorescence in situ hybridization (FISH). DGGE analysis has revealed more similar microbial community structures formed in the biofilms with more similar carbon nitrogen (C/N) ratios. FISH analysis shows that the dominance of both Betaproteobacteria ammonia-oxidizing bacteria and Nitrospira-like nitrite-oxidizing bacteria were negatively correlated to C/N ratios. Sequence analysis of DGGE bands has indicated the presence of anoxic denitrifying bacteria Agrobacterium tumefaciens and Rhizobium sp., suggesting that the oxygen gradient inside the biofilm may be responsible for the mechanism of SND in aerobic MBBRs. The study confirms that appropriate control of microbial community structure resulting from optimal C/N ratio is beneficial in improving SND, thus optimizing nitrogen removal in aerobic MBBR. The established SND-based MBBR can save operation space and time in comparison to the traditional nitrogen removal process, and might be very attractive for future practical applications.     

进水碳氮比对CANON型人工湿地脱氮性能的影响

通过逐步提高进水中的有机碳源浓度,探讨进水碳氮比(C/N)对基于亚硝化的全程自养脱氮(CANON)型潮汐流人工湿地(TFCW)脱氮效能及其微生物特性的影响.结果表明: 进水C/N可显著影响CANON型TFCW中脱氮功能微生物的数量与活性,进而影响其氮素转化速率.当进水C/N由0.0增至6.0时,TFCW中反硝化功能基因的丰度随之增加,系统反硝化性能提高,TFCW中逐渐形成同步亚硝化、厌氧氨氧化与反硝化(SNAD)耦合反应体系,其脱氮效果得以强化.当进水C/N＞6.0时,好氧氨氧化菌活性受到抑制,数量逐渐减少,TFCW中的厌氧氨氧化作用与反硝化作用受阻,系统脱氮性能恶化.当进水C/N为6.0时,TFCW中的SNAD作用可得到最大限度的强化,其总氮(TN)去除率和去除负荷分别达(93.3±2.3)%和(149.30±8.00) mg·L^-1·d^-1,高于CANON系统中TN去除率的理论值.     

Impact of carbon to nitrogen ratio on nutrient removal in a liquid–solid circulating fluidized bed bioreactor (LSCFB)

The performance of a liquid–solid circulating fluidized bed bioreactor (LSCFB) with anoxic and aerobic beds and lava rock as a biofilm carrier media was used to investigate the impact of the COD/N ratio on the process performance, with particular focus on total nitrogen removal. Three different COD/N ratios of 10:1, 6:1 and 4:1 were tested at an empty bed contact time of 0.82 h. More than 90% of the influent organic matter was removed throughout the study with 58% removal in the anoxic column in Phase III. Total nitrogen removal efficiencies in Phases I–III were 91%, 82% and 71% and simultaneous nitrification–denitrification (SND) occurred in the aerobic downer. The LSCFB demonstrated tertiary effluent quality at COD/N ratio of 10:1 and 6:1 with soluble biochemical oxygen demand (SBOD) <10 mg l^?1 and total nitrogen (TN) <10 mg l^?1.     

Enhanced aerobic granulation and nitrogen removal by the addition of zeolite powder in a sequencing batch reactor

The aim of this study was to evaluate the impact of zeolite powders on feasibility of rapid aerobic granulation in the column-type sequencing batch reactors. After 90 days' operation, aerobic granular sludge was formed in both reactors by altering influent chemical oxygen demand/nitrogen (COD/N) ratios. R1 with zeolite powders had better removal capabilities of COD and total nitrogen than R2, which was without zeolite powders. Mixed liquor volatile suspended solid concentrations of the two reactors were 7.36 and 5.45 g/L, while sludge volume index (SVI₃₀) values were 34.9 and 47.9 mg/L, respectively. The mean diameters of aerobic granular sludge in the above two reactors were 2.5 and 1.5 mm, respectively. Both reactors achieved the largest simultaneous nitrification and denitrification (SND) efficiency at an influent COD/N ratio of 8; however, R1 exhibited more excellent SND efficiency than R2. The obtained results could provide a novel technique for rapid aerobic granulation and N removal simultaneously, especially when treating nitrogen-rich industrial wastewater.     

Control of carbon and ammonium ratio for simultaneous nitrification and denitrification in a sequencing batch bioreactor

This study shows how the carbon and nitrogen (C/N) ratio controls the simultaneous occurrence of nitrification and denitrification in a sequencing batch reactor (SBR). Data demonstrated that a low C/N ratio resulted in a rapid carbon deficit, causing an unbalanced simultaneous nitrification–denitrification (SND) process in SBR. When the initial COD/NH₄⁺-N ratio was adjusted to 11.1, the SND-based SBR achieved complete removal of NH₄-N and COD without leaving any NO₂⁻-N in the effluent. The nitrogen removal efficiency decreases gradually with increasing ammonium-loading rate to the SND–SBR system. Altogether, data showed that appropriate controls of carbon and nitrogen input are required to achieve an efficient SND–SBR. An established SND technology can save operation time and energy, and might replace the traditional two-stage biological nitrification and denitrification process.     

Nitrogen removal performance in a novel combined biofilm reactor

Experiments have been performed to investigate the nitrogen removal performance in a novel combined biofilm reactor using synthetic wastewater. In the reactor, one cubic box was separated by two baffles into three zones: aerobic zone, buffering zone and anoxic zone. Nitrification and denitrification were supposed to be mainly accomplished in the aerobic and anoxic zones, respectively. When the influent total nitrogen (TN) and organic carbon loadings were averaged at 0.093 and 0.40 kg/m³/d, 84% TN removal efficiency was achieved by adjusting the aeration rate and the configuration of the reactor. Continuous experimental results demonstrated that NH₃-N removal efficiency increased by adjusting the clapboards of the reactor at a certain aeration rate. Energy produced by aeration was used for liquid recycle, so TN could be more efficiently removed at lower cost in this reactor.     

Study of operational conditions of simultaneous nitrification and denitrification in a Carrousel oxidation ditch for domestic wastewater treatment

The study on the operational conditions of simultaneous nitrification and denitrification (SND) in the channel of oxidation ditch (OD) without the need for a special anoxic tank was carried out based on lab-scale and pilot-scale experiments using real domestic wastewater. The influence of sludge loading and component proportion in influent, temperature, hydraulic retention time (HRT), dissolved oxygen (DO) and operational mode on SND was investigated. The result indicated that the optimal DO (ODO) of SND occurrence was confirmed majorly by the sludge loading of influent and temperature, the high TCOD/NH₃–N and short HRT can enhance the occurrence of SND. A new operational mode was proposed that achieved a higher removal efficiency of 60–70% for total nitrogen by SND with HRT of 4–6 h, and the concentrations of NH₃–N and TN in effluent are less than 5 and 15 mg/L, respectively.     

Enhanced denitrifying phosphorous removal in a novel anaerobic/aerobic/anoxic (AOA) process with the diversion of internal carbon source

A novel anaerobic/aerobic/anoxic (AOA) process is proposed to realize denitrifying phosphorous removal in this study, and the characteristic of the AOA process is transferring part of the anaerobic mixed liquor to the post-anoxic zone for providing the carbon source needed for denitrification. The AOA process was operated for 3 months, and the average removal efficiencies of NH4+-N, TN and PO4(3-)-P were 93.0±3.1%, 70.3±2.9% and 87.3±11.8%, respectively. A mass balance analysis indicated that 0.49±0.02 g VSS(-1) d(-1) of PO4(3-)-P and 0.23±0.04 g VSS(-1) d(-1) of NO3--N were simultaneously removed in the anoxic zone, and it is speculated that denitrifying phosphorous removal occurred in the AOA process. Furthermore, 0.24±0.06 g VSS(-1) d(-1) of TN was removed in the aerobic zone via simultaneous nitrification and denitrification (SND). The results demonstrate that the multi-zone structure of the AOA process favors the enhancement of denitrifying phosphorous removal and SND for municipal wastewater treatment.     

Influence of wastewater composition on nitrogen and phosphorus removal and process control in A2O process

A bench-scale anaerobic–anoxic–oxic (A²O) bioreactor with steady denitrifying phosphorus removal performance was tested to determine the influence of influent C/N ratio (SCOD/TN) and C/P ratio (SCOD/TP) on biological nutrient removal for treating synthetic brewage wastewater; meanwhile, the spatial profiles of DO, pH and ORP sensors in such systems were investigated. The results showed that influent C/N ratio had significant effect on the TN, TP removal efficiencies and the ratio of anoxic to aerobic P uptake amount. The maximal TN and TP removal efficiencies could be achieved when influent C/N ratio was kept at about 7.1 and 5, respectively. Besides, the ratio of anoxic to aerobic P uptake amount was found to be linearly dependent on the influent C/N ratio with coefficient R ² of 0.685 when total recirculation ratio was constant at 3.5. Influent C/P ratio had an important effect on the TP removal efficiency, while it hardly affected TN removal efficiency. In addition, the TP removal efficiency reached the maximum for influent C/P ratio of 42. On the other hand, it was also found that the typical profiles of DO, pH and ORP sensors could be observed, and they have similar trends at the different influent C/N ratio and C/P ratio. It was suggested that the operational state could be well known according to the changes of simple on-line sensors.     

Comparison between a moving bed membrane bioreactor and a conventional membrane bioreactor on organic carbon and nitrogen removal

A membrane bioreactor filled with carriers instead of activated sludge named a moving bed membrane bioreactor (MBMBR) was investigated for simultaneously removing organic carbon and nitrogen in wastewater. Its performance was compared with a conventional membrane bioreactor (CMBR) at various influent COD/TN ratios of 8.9–22.1. The operational parameters were optimized to increase the treatment efficiency. COD removal efficiency averaged at 95.6% and 96.2%, respectively, for MBMBR and CMBR during the 4 months experimental period. The MBMBR system demonstrated good performance on nitrogen removal at different COD/TN ratios. When COD/TN was 8.9 and the total nitrogen (TN) load was 7.58 mg/l h, the TN and ammonium nitrogen removal efficiencies of the MBMBR were maintained over 70.0% and 80.0%, respectively, and the removed total nitrogen (TN) load reached to 5.31 mg/l h. Multifunctional microbial reactions in the carrier, such as simultaneous nitrification and denitrification (SND), play important roles in nitrogen removal. In comparison, the CMBR did not perform so well. Its TN removal was not stable, and the removed total nitrogen (TN) load was only 1.02 mg/l h at COD/TN ratio 8.9. The specific oxygen utilization rate (SOUR) showed that the biofilm has a better microbial activity than an activated sludge. Nevertheless, the membrane fouling behavior was more severe in the MBMBR than in the CMBR due to a thick and dense cake layer formed on the membrane surface, which was speculated to be caused by the filamentous bacteria in the MBMBR.     

Organics and nitrogen removal and sludge stability in aerobic granular sludge membrane bioreactor

Novel aerobic granular sludge membrane bioreactor (GMBR) was established by combining aerobic granular sludge technology with membrane bioreactor (MBR). GMBR showed good organics removal and simultaneous nitrification and denitrification (SND) performances for synthesized wastewater. When influent total organic carbon (TOC) was 56.8-132.6 mg/L, the TOC removal of GMBR was 84.7-91.9%. When influent ammonia nitrogen was 28.1-38.4 mg/L, the ammonia nitrogen removal was 85.4-99.7%, and the total nitrogen removal was 41.7-78.4%. Moreover, batch experiments of sludge with different particle size demonstrated that: (1) flocculent sludge under aerobic condition almost have no denitrification capacity, (2) SND capacity was caused by the granular sludge, and (3) the denitrification rate and total nitrogen removal efficiency were enhanced with the increased particle size. In addition, study on the sludge morphology stability in GMBR showed that, although some granular sludge larger than 0.9 mm disaggregated at the beginning of operation, the granular sludge was able to maintain the stability of its granular morphology, and at the end of operation, the amount of granular sludge (larger than 0.18 mm) stabilized in GMBR was more than 56-62% of the total sludge concentration. The partial disaggregation of large granules is closely associated with the change of operating mode from sequencing batch reactor (SBR) system to MBR system.     

Air-lift internal loop biofilm reactor for realized simultaneous nitrification and denitrification

Simultaneous nitrification and denitrification (SND) was realized by means of a novel air-lift internal loop biofilm reactor, in which aeration was set in middle of the reactor. During operation, the aeration was adjusted to get appropriate dissolve oxygen (DO) in bulk solution and let aerobic and anoxic zone coexist in one reactor. When aeration was at 0.6 and 0.2 L/min, corresponding to DO of 5.8 and 2.5 mg/L in bulk solution, ammonia nitrogen removal percentage reached about 80 and 90 %, but total nitrogen removal percentage was lower than 25 %. While the aeration was reduced to 0.1 L/min, aerobic and anoxic zones existed simultaneously in one reactor to get 75 % of ammonia nitrogen and 50 % of total nitrogen removal percentage. Biofilms were, respectively, taken from aerobic and anoxic zone to verify their function of nitrification and denitrification in two flasks, in which ammonia nitrogen was transferred into nitrate completely by aerobic biofilm, and nitrate was removed more than 80 % by anoxic biofilm. Microelectrode was used to measure the DO distribution inside biofilms in anoxic zone corresponding to different aerations. When aeration was at 0.6 and 0.2 L/min, DO inside biofilm was more than 1.5 mg/L, but the DO inside biofilm decreased to anoxic status with depth of biofilm increasing corresponding to aeration of 0.1 L/min. The experimental results indicated that SND could be realized because of simultaneous existence of aerobic and anoxic biofilms in one reactor.     

Effects of temperature on simultaneous nitrification and denitrification via nitrite in a sequencing batch biofilm reactor

A laboratory scale experiment was described in this paper to enhance biological nitrogen removal by simultaneous nitrification and denitrification (SND) via nitrite with a sequencing batch biofilm reactor (SBBR). Under conditions of total nitrogen (TN) about 30 mg/L and pH ranged 7.15–7.62, synthetic wastewater was cyclically operated within the reactor for 110 days. Optimal operation conditions were established to obtain consistently high TN removal rate and nitrite accumulation ratio, which included an optimal temperature of 31 °C and an aeration time of 5 h under the air flow of 50 L/h. Stable nitrite accumulation could be realized under different temperatures and the nitrite accumulation ratio increased with an increase of temperature from 15 to 35 °C. The highest TN removal rate (91.9%) was at 31 °C with DO ranged 3–4 mg/L. Process control could be achieved by observing changes in DO and pH to judge the end-point of oxidation of ammonia and SND.     

Performance and Microbial Structure of a Combined Biofilm Reactor

A novel combined biofilm reactor was established and applied as a single treatment unit for carbon and nitrogen removal of wastewater. The nitrogen removal performance of the reactor at different levels of organic carbon (COD) loading was investigated when the influent total nitrogen (TN) loading was 0.74 g TN/m² day. Continuous experimental results demonstrated that 80% nitrogen was eliminated when the influent COD loading ranged between 2.06 g and 3.92 g COD/m² day. Microbial composition in the reactor was analyzed using fluorescent in situ hybridization (FISH) and conventional batch tests. The relative abundance of ammonia-oxidizing bacteria in the aerobic zone of the reactor measured by FISH was consistent with the result from conventional batch tests.     

Nitrogen removal in moving bed sequencing batch reactor using polyurethane foam cubes of various sizes as carrier materials

The performance of moving bed sequencing batch reactors (MBSBRs) added with 8 % (v/v) of polyurethane (PU) foam cubes as carrier media in nitrogen removal was investigated in treating low COD/N wastewater. The results indicate that MBSBR with 8-mL cubes achieved the highest total nitrogen (TN) removal efficiency of 37% during the aeration period, followed by 31%, 24% and 19 % for MBSBRs with 27-, 64- and 125-mL cubes, respectively. The increased TN removal in MBSBRs was mainly due to simultaneous nitrification and denitrification (SND) process which was verified by batch studies. The relatively lower TN removal in MBSBR with larger PU foam cubes was attributed to the observation that larger PU foam cubes were not fully attached by biomass. Higher concentrations of 8-mL PU foam cubes in batch reactors yielded higher TN removal.     

Development of model simulation based on BioWin and dynamic analyses on advanced nitrate nitrogen removal in deep bed denitrification filter

A pilot-scale deep bed denitrification filter using quartz sand as the filter media was operated under filtration velocity of 5.23 m/h. Nitrate, nitrite, ammonia, and total nitrogen removal rates were relatively high at influent C/N ratios of 4:1 and 5:1. A model was developed using software to simulate the processes operating in the filter and improve the related parameters in the actual operations. The normalized sensitivity coefficient and the mean square sensitivity measure were used for the sensitivity analysis. Results showed that the stoichiometric parameters were the most sensitive, which were related to methylotrophs and biofilm. Measured data were consistent with the simulations. Moreover, the order of significance of factors affecting nitrate nitrogen removal was as follows: influent chemical oxygen demand, influent nitrate nitrogen, and hydraulic retention time. Last, the denitrification dynamic model was obtained at influent C/N ratio of 5:1.

     

An effective way to select slow-growing nitrifying bacteria by providing a dynamic environment

In this study, two laboratory scale sequencing batch reactors (SBRs) were conducted to study the stability of aerobic granules. The strategy was involved in stepwise increase in ammonium (NH4⁺-N) concentration in the influent. Results showed that the activity of nitrifying bacteria and diameter of the aerobic granules significantly increased with gradually increasing NH4⁺-N, which reached persistently new balances by homeostasis. As a result, the stability of aerobic granules was remarkably enhanced. The value of sludge volume index (SVI) was below 25 ml/g, the mean settling velocity was excellent up to 107 m/h. The NH4⁺-N removal efficiency averaged above 99% and total nitrogen (TN) removal was greatly enhanced and could reach 68%. Besides dissolved oxygen, the granules size was also a dominant factor to influence denitrification, which could gradually increase in variable conditions through homeostasis. Stable, dense and well-settling nitrifying granules can be developed for simultaneous nitrification and denitrification removal.     

Simultaneous nitrification,denitrification, and phosphorus removal in a lab-scale sequencing batch reactor

Simultaneous nitrification and denitrification (SND) via the nitrite pathway and anaerobic-anoxic-enhanced biological phosphorus removal (EBPR) are two processes that can significantly reduce the energy and COD demand for nitrogen and phosphorus removal. The combination of these two processes has the potential of achieving simultaneous nitrogen and phosphorus removal with a minimal requirement for COD. A lab-scale sequencing batch reactor (SBR) was operated in alternating anaerobic-aerobic mode with a low dissolved oxygen (DO) concentration (0.5 mg/L) during the aerobic period, and was demonstrated to accomplish nitrification, denitrification, and phosphorus removal. Under anaerobic conditions, COD was taken up and converted to polyhydroxyalkanoates (PHAs), accompanied by phosphorus release. In the subsequent aerobic stage, PHA was oxidized and phosphorus was taken up to <0.5 mg/L by the end of the cycle. Ammonia was also oxidized during the aerobic period, but without accumulation of nitrite or nitrate in the system, indicating the occurrence of simultaneous nitrification and denitrification. However, off-gas analysis showed that the final denitrification product was mainly nitrous oxide (N(2)O), not N(2). Further experimental results demonstrated that nitrogen removal was via nitrite, not nitrate. These experiments also showed that denitrifying glycogen-accumulating organisms (DGAOs), rather than denitrifying polyphosphate-accumulating organisms (DPAOs), were responsible for the denitrification activity.     

Performance and optimization of biological nitrogen removal process enhanced by anoxic/oxic step feeding

The aim of this paper is to investigate the performance and optimization of an biological nitrogen removal process enhanced by the anoxic/oxic four stages step-feeding process under sufficient/insufficient influent carbon source. The concept of influent flow distribution ratio (λ) was introduced according to the performance of the step-feed process for inflow splitting and volume distribution. Under the condition of sufficient carbon, the uniform influent flow distribution ratio was proposed from the standpoint of which is easy for process control, operation optimization and management. Under the condition of different influent C/N ratios, the optimal influent flow distribution ratios (λ_opt) were determined, by trial-and-error method. The results showed that more than 95.81% of the total nitrogen removal efficiency could be achieved by step-feeding process with a fixed influent C/N ratio. A model was introduced to derive the relationships of total nitrogen removal efficiency with λ and influent C/N ratio. When the influent carbon source was insufficient, however, the λ_opt between two adjacent stages should not be uniform. The results also showed that the four-stage step-feeding process with λ_opt of 2.0:2.1:2.5:3.4 could significantly improve the total nitrogen removal efficiency. The results obtained in this study will help to optimize the design and the operation of BNR systems.