Effects of acetate and nitrite addition on fraction of denitrifying phosphate-accumulating organisms and nutrient removal efficiency in anaerobic/aerobic/anoxic process

The effects of acetate and nitrite on the performance of sequencing batch reactors (SBRs) employing an anaerobic/aerobic/anoxic (AOA) process were investigated. Three types of SBR operations were used: sodium acetate addition at the start of anoxic condition for heterotrophic denitrification (Type 1); sodium acetate addition at the start of aerobic condition for anoxic phosphate removal by denitrifying phosphate-accumulating organisms (DNPAOs) (Type 2: conventional AOA process); and nitrite addition at the start of aerobic condition for inhibition of phosphate-accumulating organisms (PAOs) (Type 3). A track experiment shows that Type 2 led to the best performance of SBRs among the three types. An analysis by fluorescence in situ hybridization (FISH) revealed that nitrite addition decreased the ratio of PAOs with a decrease in phosphorus removal efficiency. The fraction of DNPAOs in Type 2 was the highest at 13%, indicating that Type 2 is suitable for the simultaneous nitrogen and phosphorus removal in the AOA process.     

Nitrate removal in closed-system aquaculture by columnar denitrification.

The columnar denitrification method of nitrate-nitrogen removal from high-density, closed system, salmonid aquaculture was investigated and found to be feasible. However, adequate chemical monitoring was found to be necessary for the optimization and quality control of this method. When methanol-carbon was not balanced with inlet nitrate-nitrogen, the column effluent became unsatisfactory for closed-system fish culture due to the presence of excess amounts of nitrite, ammonia, sulfide, and dissolved organic carbon. Sulfide production was also influenced by column maturity and residence time. Methane-carbon was found to be unsatisfactory as an exogenous carbon source. Endogenous carbon could not support high removal efficiencies. Freshwater columns adpated readily to an artificial seawater with a salinity of 18% without observable inhibition. Scanning electron microscopy revealed that the bacterial flora was mainly rod forms with the Peritricha (protozoa) dominating as the primary consumers. Denitrifying bacteria isolated from freshwater columns were tentatively identified as species of Pseudomonas and Alcaligenes. A pilot plant column was found to behave in a manner similar to the laboratory columns except that nitrite production was never observed.     

Horizontal subsurface flow constructed wetlands for tertiary treatment of dairy wastewater

The aim of this work was to evaluate the efficiency of horizontal subsurface flow constructed wetlands (HSFCWs) planted with Typha domingensis and Phragmites australis in the final treatment of dairy wastewater. Ten microcosms-scale reactors simulating HSFCWs were arranged outdoors under a semi-transparent plastic roof. Five replicates were planted with T. domingensis and five with P. australis. In both cases, light expanded clay aggregate (LECA) 10/20 was used as a substrate. Real effluent with previous treatment was used. In order to evaluate contaminant removal efficiencies in each reactor, pH, electrical conductivity, suspended solids, ammonium, nitrate, nitrite, total phosphorus, and chemical oxygen demand (COD) were analyzed before and after treatment. HSFCWs planted with T. domingensis and P. australis were efficient for the final treatment of dairy wastewater. Removal efficiencies obtained in microcosms planted with both macrophytes were over 96% for ammonium and nitrite. Nitrate removal efficiency was 39%. COD decreased along the experiment near 75% for both treatments. High removal percentages for suspended solids (78.4–81.1%) were also achieved. However, systems planted with T. domingensis were significantly more efficient for total phosphorus removal (88.5%) than those planted with P. australis (71.6%).     

Nitrogen removal via nitrite in a sequencing batch reactor treating sanitary landfill leachate

The present paper reports the results of the application of a control system, based on artificial intelligence concepts, for the automation of a bench-scale SBR treating leachate generated in old landfills. Attention was given to the nitritation and denitritation processes in order to enhance the nitrogen removal efficiency. Nitrification and nitrogen removal were usually higher than 98% and 95%, respectively, whereas COD removal was approximately 20-30% due to the low biodegradability of organic matter in the leachate from old landfills; therefore, external COD was added to accomplish the denitrification process. Adjusting the length of the oxic phase, almost complete inhibition of the nitrite oxidizing organisms was observed. The results confirm the effectiveness of the nitrite route for nitrogen removal optimisation in leachate treatment. A significant saving of approximately 35% in external COD addition was achieved.     

Effects of nitrite inhibition on anaerobic ammonium oxidation

In order to assess the stability of nitrogen removal systems utilizing anaerobic ammonium oxidation (anammox), it is necessary to study the toxic effects of nitrite on these biochemical reactions. In this study, the effects of nitrite on anammox bacteria entrapped in gel carriers were investigated using batch and continuous feeding tests. The results showed that the nitrite concentration in a reactor must be less than 274-mg N/L in order to prevent a decrease in the anammox activity, which occurred when the gel carriers were soaked in nitrite solutions with concentrations greater than 274-mg N/L in a batch test. In a continuous feeding test, nitrite inhibition was not observed at low concentrations of nitrite. However, the anammox activity decreased to 10% when the nitrite concentration increased to 750-mg N/L over a 7-day period in the reactor. In addition, it was shown that the effects of nitrogen on the anammox reaction were reversible because the anammox activity completely recovered within 3 days when the influent nitrite concentration was decreased to less than 274-mg N/L.     

一株养殖水体中亚硝酸盐去除菌的鉴定及其去除条件

【目的】从养殖污泥中分离筛选优良亚硝酸盐去除菌,并对其去除条件进行研究。【方法】从养殖污泥中分离亚硝酸盐去除菌,进一步通过测定比较分离菌株对亚硝酸盐的去除率,筛选优良的亚硝酸盐去除菌,通过API ID32GN细菌鉴定系统以及16S rDNA序列分析法对其进行鉴定,并采用单因子法研究其去除亚硝酸盐的条件。【结果】从养殖污泥中分离筛选了一株优良的亚硝酸盐去除菌AQ-3,其对50 mg/L亚硝酸盐的去除率高达99.47%。菌株AQ-3被鉴定为鲍曼氏不动杆菌(Acinetobacter baumannii)(GenBank登录号:JF751054.1),其16S rDNA序列与基因库中不动杆菌属菌株的16S rDNA序列有99%?100%的同源性,而且与鲍曼氏不动杆菌KF714株(GenBank登录号:AB109775)的亲缘关系最近。菌株AQ-3去除亚硝酸盐的最适初始pH范围为7?9,最佳碳源为乙酸钠和丁二酸钠,而且随着初始菌浓度的不断增大,菌株AQ-3对亚硝酸盐的去除率显著升高;随着亚硝酸盐浓度的不断增大,菌株AQ-3对亚硝酸盐的去除率逐渐降低。【结论】在丰富亚硝酸盐去除菌种质资源的同时,为该菌在养殖水体中的实际应用提供了理论基础。     

沼泽红假单胞菌(Rhodopseudomonas palustris)CQV97对无机三态氮共存水体中氮素的去除效率及其影响因素

研究水体环境因素(温度、光照和pH)、小分子有机碳和有机氮化合物对一株具有高效脱氮潜力的沼泽红假单胞菌(Rhodopseudomonas palustris)CQV97在无机三态氮共存体系中脱除无机三态氮的影响规律。结果显示,该菌株在20~40℃,500~5 000lux,pH 6.0~9.0环境条件下,能够脱除高浓度无机三态氮(其中亚硝氮不低于40mg·L-1),表明该菌株具有较强的适应复杂环境的能力;以乙酸钠/乙醇为唯一碳源时,该菌株能有效地去除无机三态氮,而以葡萄糖为唯一碳源时,能有效去除硝氮,但不能去除氨氮,亚硝氮明显积累,表明环境中小分子有机碳源影响菌体对无机三态氮的去除能力;体系中添加高浓度(120mg·L-1)蛋白胨或尿素时,由于有机氮降解的释氨作用,菌体对氨氮的去除能力受到明显抑制,氨氮积累明显,13d时氨氮去除率仅分别为16%(蛋白胨)和6%(尿素),但硝氮和亚硝氮的去除能力并没有受到明显影响。异位处理实际水体结果表明,菌株可使水体中氨氮含量明显降低、硝氮和亚硝氮被完全去除。综上,沼泽红假单胞菌CQV97菌株环境适应能力强,具有高效脱除水体无机三态氮的应用潜力,这为进一步开发高效脱氮微生物制剂及其合理使用奠定了基础。     

Performance of a membrane bioreactor used for the treatment of wastewater contaminated with heavy metals

In this work the performance of a Membrane bioreactor (MBR) was assessed for the removal of 3-15 mg/l of copper, lead, nickel and zinc from wastewater. The average removal efficiencies accomplished by the MBR system were 80% for Cu(II), 98% for Pb(II), 50% for Ni(II) and 77% for Zn(II). The addition of 5 g/l vermiculite into the biological reactor enhanced metal removal to 88% for copper, 85% for zinc and 60% for nickel due to adsorption of metal ions on the mineral, while it reduced biomass inhibition and increased biomass growth. The metal ions remaining in soluble form penetrated into the permeate, while those attached to sludge flocs were effectively retained by the ultrafiltration membranes. The average heterotrophic biomass inhibition was 50%, while it reduced to 29% when lower metal concentrations were fed into the reactor in the presence of vermiculite. The respective autotrophic biomass inhibition was 70% and 36%. The presence of heavy metals and vermiculite in the mixed liquor adversely impacted on membrane fouling.     

Enhanced biological nutrient removal using MUCT-MBR system

Biological nutrient removal was investigated in a combined modified University of Cape Town and membrane bioreactor system. When the influent nutrient mass ratio (COD/TN/TP) was 28.5/5.1/1 to 28.5/7.2/1, average removal efficiencies of COD, TN and TP were 90%, 81.6%, 75.2%. Obvious denitrifying phosphorus removal occurred with C/N ratio 3.98. When nitrite was the main electron acceptor, the ratio of denitrifying phosphate uptake to the total phosphate uptake were 99.8% and the sludge yield was 0.28kg VSS/kg COD; when nitrate was the main electron acceptor, the ratio was 92% and the yield was 0.32kg VSS/kg COD. In case of nitrite, the system not only kept TP and TN removal at 89.1% and 82.2%, but also ensured less sludge production. Batch tests showed that the proportion of denitrifying phosphorus-accumulating organisms in the total phosphorus-accumulating organisms in the system was higher than 80%.     

Packed cage rotating biological contactor system for treatment of cyanide wastewater

The aim of this work was to study the efficiency of the packed cage rotating biological contactor (RBC) system with synthetic wastewater (SWW) containing 800 mg/l BOD(5) with various cyanide residue concentrations and hydraulic loading time. The results showed that cyanide had a negative effect to both the system's efficiency and bio-film quality. An increase in cyanide concentration led to a decrease in bio-film growth and the consequent reduction in the removal efficiency of the system. Also, the effluent suspended solids (SS) of the system was increased with increasing cyanide concentrations because the bio-film detached from the media due to the toxicity of the cyanide residue. The system showed the highest COD, BOD(5), TKN and cyanide removal efficiencies of 94.0 +/- 1.6%, 94.8 +/- 0.9%, 59.1 +/- 2.8% and 95.5 +/- 0.6%, respectively, with SWW containing 5 mg/l cyanide under HRT of 8 days, while they were only 88.8 +/- 0.7%, 89.5 +/- 0.5%, 40.3 +/- 1.1% and 93.60 +/- 0.09%, respectively, with SWW containing 40 mg/l cyanide. In addition, the effluent ammonia, nitrite and nitrate were increased with increases in cyanide concentration or loading. However, the system with SWW containing the highest cyanide concentration of 40 mg/l showed almost constant COD and BOD(5) removal efficiencies of 89% and 90%, even when the system was controlled under the lowest HRT of 8 h.     

Effect of nitrate on anaerobic azo dye reduction

The aim of the study was to investigate the effect of nitrate on anaerobic color removal efficiencies. For this aim, anaerobic–aerobic sequencing batch reactor (SBR) fed with a simulated textile effluent including Remazol Brilliant Violet 5R azo dye was operated with a total cycle time of 12 h, including anaerobic (6 h) and aerobic cycles (6 h). Microorganism grown under anaerobic phase of the reactor was exposed to different amounts of competitive electron acceptor (nitrate) and performance of the system was determined by monitoring color removal efficiency, nitrate removal, nitrite formation and removal, oxidation reduction potential, color removal rate, chemical oxygen demand (COD), specific anaerobic enzyme (azo reductase) and aerobic enzyme (catechol 1,2 dioxygenase), and formation and removal of aromatic amines. Variations of population dynamics of microorganisms exposed to various amount of nitrate were identified by denaturing gradient gel electrophoresis (DGGE). It was found that nitrate has adverse effect on anaerobic color removal efficiency and color removal was achieved after denitrification process was completed. It was found that nitrate stimulates the COD removal efficiency and accelerates the COD removal in the first hour of anaerobic phase. About 90 % total COD removal efficiencies were achieved in which microorganism exposed to increasing amount of nitrate. Population dynamics of microorganisms exposed to various amount of nitrate were changed and diversity was increased.     

Rapid Retting of Kôzo (Paper Mulberry) Bast with Erwinia carotovora

The degradation of nitrite and the inhibition towards formation of carcinogenic nitrosamines by melanoidins, produced from the glucose-glycine system were investigated at various conditions. The degradation of nitrite was highest at pH 1.2 (29%), when the ratio of melanoidins to nitrite was 1: 3. The inhibition towards formation of nitrosamines by melanoidins had the same tendency as the degradation of nitrite, the inhibition also being highest at pH 1.2 (99%). In addition, melanoidins after nitrite treatment exhibited a little higher mutagenicity and much stronger desmutagenicity than those of the original melanoidins. The change of the structure of melanoidins after treating with nitrite was also investigated by HPLC and CP-MAS NMR.     

Optimization of free ammonia concentration for nitrite accumulation in shortcut biological nitrogen removal process

A shortcut biological nitrogen removal (SBNR) utilizes the concept of a direct conversion of ammonium to nitrite and then to nitrogen gas. A successful SBNR requires accumulation of nitrite in the system and inhibition of the activity of nitrite oxidizers. A high concentration of free ammonia (FA) inhibits nitrite oxidizers, but unfortunately decreases the ammonium removal rate as well. Therefore, the optimal range of FA concentration is necessary not only to stabilize nitrite accumulation but also to achieve maximum ammonium removal. In order to derive such optimal FA concentrations, the specific substrate utilization rates of ammonium and nitrite oxidizers were measured. The optimal FA concentration range appeared to be 5–10 mg/L for the adapted sludge. The simulated results from the modified inhibition model expressed by FA and ammonium/nitrite concentrations were shown very similar to the experimental results.     

Modeling kinetics of ammonium oxidation and nitrite oxidation under simultaneous inhibition by free ammonia and free nitrous acid

Inhibition of ammonium oxidation and nitrite oxidation by free ammonia (FA) and free nitrous acid (FNA) was studied using three different sludges. An uncompetitive inhibition model fit the experimental data well when the reactions were under FA inhibition, whereas a noncompetitive model fit well under FNA inhibition. The estimates of the inhibition constant (K_I) of nitrite oxidation were 46 μM for FA and 1.7–6.8 μM for FNA, each of which was significantly smaller than that of ammonium oxidation, which were 290–1600 μM for FA and 12 μM for FNA. The much smaller values of K_I for nitrite oxidation reflected the susceptibility of that reaction to inhibition by FA and FNA, which could lead to accumulation of nitrite during nitrification. A kinetic model for simultaneous inhibition by FA and FNA was derived. The model predicted that nitrite oxidation should be affected more seriously than ammonium oxidation by the simultaneous inhibition, which would accelerate the accumulation of nitrite in a strong nitrogenous wastewater treatment. It also indicated that a complete removal of ammonia could be achieved with high accumulation of nitrite in a sequencing batch reactor, which is impossible in a continuous-flow reactor.     

Long-term stability of partial nitritation of swine wastewater digester liquor and its subsequent treatment by Anammox

Partial nitritation using inhibition of free ammonia and free nitric acid is an effective technique for the treatment of high concentrations of ammonium in wastewaters. This technique was applied to the digester liquor of swine wastewater and the stability of its long-term operation was investigated. Partial nitritation was successfully maintained at a nitrogen loading rate (NLR) of 1.0 kg N m(-3)d(-1) for 120 days without acclimatization of nitrite oxidizing bacteria (NOB) to the inhibitory compounds (free ammonia and free nitric acid). The conversion efficiencies of NH(4)-N to NO(2)-N and to NO(3)-N were determined to be around 58% and <5%, respectively. After the establishment of partial nitritation, the influence of swine wastewater on the Anammox reaction was examined using continuous flow treatment experiments. Consistent nitrogen removal was achieved for 70 days at a nitrogen removal rate (NRR) of 0.22 kg N m(-3)d(-1) and the color of Anammox bacteria changed from red to greyish black. The NO(2)-N consumption and the NO(3)-N production increased concurrently and the Anammox reaction ratio was estimated to be 1:1.67:0.53, which is different from that reported previously (1:1.32:0.26).     

Short-cut nitrification of domestic wastewater in a pilot-scale A/O nitrogen removal plant

The feasibility of nitrite accumulation in a pilot-scale A/O (anoxic/oxic) nitrogen removal plant treating domestic wastewater was investigated at various dissolved oxygen (DO) concentrations and pH levels. The results showed that the pH was not a useful operational parameter to realize nitrite accumulation. Significant nitrite accumulation was observed at the low DO concentration range of 0.3–0.8 mg/l and the maximum nitrite accumulation ratio of about 90% occurred at a DO concentration of 0.6 mg/l. This suggests a reduction of 22% in the oxygen consumption, and therefore a considerable saving in aeration. However, the nitrite accumulation was destroyed at the high DO concentration and the resumption was very slow. In addition, the average ammonia removal efficiency reached as high as 93% at the low DO level. Moreover, experimental results indicated that nitrogen could be removed by simultaneous nitrification and denitrification (SND) via nitrite in the aerobic zones at the low DO concentration, with the efficiency of 6–12%.     

Effect of stabilization on biomass activity

The study aimed to compare aerobic and aerobic/anoxic stabilization processes in terms of organic matter and the biomass removal efficiencies using a municipal sludge sample. The efficiency of stabilization process was assessed monitoring suspended solids (SS), volatile suspended solids (VSS), total and dissolved organic carbon (TOC, DOC), nitrate, nitrite, and phosphate parameters. The oxygen uptake rate (OUR) measurements were conducted to determine active biomass concentration. On the 30th day of the aerobic stabilization, the SS, VSS and TOC removal efficiencies were 22%, 28% and 55%, respectively. Under aerobic/anoxic conditions, removal efficiencies for SS, VSS and TOC were 25%, 27% and 67%. On the 17th day of the stabilization, SS and VSS removal rates were 60 mg SS/L day and 47 mg VSS/L day for aerobic and 102 mg SS/L day and 63 mg VSS/L day for aerobic/anoxic conditions, respectively. These findings reflected the higher stabilization performance of the aerobic/anoxic conditions. Based on respirometric results, the ratios of the active biomass were decreased to 30% and 24% for the 17th and 30th day of the aerobic stabilization, respectively. Such results have significant implications relative to the activity decrease quantification of the biomass as well as its further application potentials after aerobic or aerobic/anoxic sludge stabilization.     

亚硝酸盐对污水生物除磷影响的研究进展

亚硝酸盐作为生物硝化和反硝化的中间产物, 存在于污水生物脱氮除磷系统中。对于生物强化除磷工艺亚硝酸盐既是电子受体用于反硝化除磷, 同时又是抑制剂影响生物除磷过程。本文综述了聚磷菌在厌氧、好氧和缺氧环境中的代谢机理, 在此基础上分别从好氧除磷和反硝化除磷两方面介绍了亚硝酸盐对污水生物除磷影响的研究, 同时概述了亚硝酸盐对生物除磷的抑制机理, 并对该领域的研究提出了个人见解。     

Effect of pH on anoxic sulfide oxidizing reactor performance

The effects of pH on the performance of anoxic sulfide oxidizing (ASO) reactor were evaluated. Performance was investigated under various operational conditions at influent pH range of 4-11. At the influent pH of 7-7.5 during loading tests and HRT tests, the sulfide oxidation was partial. In general, the amount of sulfate formed decreased with the increasing sulfide and nitrite loadings. The bacterial communities in ASO reactors were more sensitive to acidic pH compared with alkaline pH, as nitrite and sulfide removal rates dropped significantly when exposed to acidic pH 3. High dissolved bisulfide ions, nitrite and excess of sulfate (>300 mg/L) might have inhibited the sulfide oxidation under highly acidic and alkaline conditions in the ASO reactor. Based on sulfide and nitrite removal efficiencies, the ASO reactor can be operated in a wide range of pH, i.e. 5-11.     

Sequencing batch membrane biofilm reactor for simultaneous nitrogen and phosphorus removal: novel application of membrane-aerated biofilm

A sequencing batch membrane biofilm reactor (SBMBfR) was developed for simultaneous carbon, nitrogen, and phosphorus removal from wastewater. This reactor was composed of two functional parts: (1) a gas-permeable membrane on which a nitrifying biofilm formed and (2) a bulk solution in which bacteria, mainly denitrifying polyphosphate-accumulating organisms (DNPAOs), were suspended. The reactor was operated sequentially under anaerobic condition and then under membrane aeration condition in one cycle. During the anaerobic period, organic carbon was consumed by DNPAOs; this was accompanied by phosphate release. During the subsequent membrane aeration period, nitrifying bacteria utilized oxygen supplied directly to them from the inside of the membrane. Consequently, the nitrite and nitrate products diffused into the bulk solution, where they were used by DNPAOs as electron acceptors for phosphate uptake. In a long-term sequencing batch operation, the mean removal efficiencies of total organic carbon (TOC), total nitrogen (T-N), and total phosphorus (T-P) under steady-state condition were 99%, 96%, and 90%, respectively. In addition, fluorescence in situ hybridization (FISH) clearly demonstrated the difference in bacterial community structure between the membrane biofilm and the suspended sludge: ammonia-oxidizing bacteria belonging to the Nitrosomonas group were dominant in the region adjacent to the membrane throughout the operation, and the occupation ratio of the well-known polyphosphate-accumulating organism (PAO) Candidatus "Accumulibacter phosphates" in the suspended sludge gradually increased to a maximum of 37%.