Comparative study of two biological nitrogen removal processes:A/O process and step-feeding process

Two biological nitrogen removal processes are compared in the aspect of nitrogen removal, process operation and energy saving. Results show that when the returned sludge ratio is 50% of the inflow rate, the step-feeding process achieves over 80% total nitrogen （TN） removal efficiency, but the TN removal efficiency of the A/O process is only 40%. Moreover, filamentous sludge bulking can be well restrained in the step-feeding process. Given the conditions of a returned sludge ratio of 100% and a nitrifying liquor recycle ratio of 200%, the TN removal efficiency is 78.32% in the A/O process, but the sludge volume index （SVI） value increases to 143 mL/g. In the step-feeding process, the SVI is only 94.4 mL/g when the TN removal efficiency reaches 81. 1%. The step-feeding process has distinct advantages over the A/O process in the aspects of practicability, nitrogen removal and operating stability.

Simultaneous nitrification and denitrification in step feeding biological nitrogen removal process

The simultaneous nitrification and denitrification in step-feeding biological nitrogen removal process were investigated under different influent substrate concentrations and aeration flow rates. Biological occurrence of simultaneous nitrification and denitrification was verified in the aspect of nitrogen mass balance and alkalinity. The experimental results also showed that there was a distinct linear relationship between simultaneous nitrification and denitrification and DO concentration under the conditions of low and high aeration flow rate. In each experimental run the floc sizes of activated sludge were also measured and the results showed that simultaneous nitrification and denitrification could occur with very small size of floc.

Enhanced nitrogen removal at low temperature with mixed anoxic/oxic process

Different hydraulic retention times(HRTs)were tested in a mixed anoxic/oxic(A/O)system at 5C and 10C to investigate the effects of HRT and carrier on nitrogen removal in wastewater at low temperatures.The results showed that the addition of the fillers improved the treatment effect of each index in the system.With an optimal HRT of 7.5 h at 5C,the removal efficiencies of NHþ4-N and total nitrogen(TN)reached 91.2%and 75.6%,respectively.With an HRT of 6 h at 10C,the removal efficiencies of NHþ4-N and TN were 96.7%and 82.9%,respectively.The results of high-throughput sequencing showed that the addition of the suspended carriers in the aerobic zone could improve the treatment efficiency of nitrogen at low temperatures.The microbial analysis indicated that the addition of the suspended carriers enhanced the enrichment of nitrogen removal bacteria.Nitrospira,Nitrotoga,and Nitrosomonas were found to be the bacteria responsible for nitrification,and their relative concentrations on the biofilm at 5C and 10C accounted for 98.11%,92.79%,and 69.98%of all biological samples,respectively.

Nitrogen removal influence factors in A/O process and decision trees for nitrification/denitrification system

In order to improve nitrogen removal in anoxic/oxic(A/O) process effectively for treating domestic wastewaters, the influence factors, DO(dissolved oxygen), nitrate recirculation, sludge recycle, SRT(solids residence time), influent COD/TN and HRT(hydraulic retention time) were studied. Results indicated that it was possible to increase nitrogen removal by using corresponding control strategies, such as, adjusting the DO set point according to effluent ammonia concentration; manipulating nitrate recirculation flow according to nitrate concentration at the end of anoxic zone. Based on the experiments results, a knowledge-based approach for supervision of the nitrogen removal problems was considered, and decision trees for diagnosing nitrification and denitrification problems were built and successfully applied to A/O process.

Fuzzy Control of Nitrate Recirculation and External Carbon Addition in A/O Nitrogen Removal Process

Nitrogen and phosphorous concentrations of effluent water must be taken into account for the design and operation of wastewater treatment plants. In addition, the requirement for effluent quality is becoming strict. Therefore, intelligent control approaches are recently required in removing biological nutrient. In this study, fuzzy control has been successfully applied to improve the nitrogen removal. Experimental results showed that a close relationship between nitrate concentration and oxidation-reduction potential (ORP) at the end of anoxic zone was found for anoxic/oxic (A/O) nitrogen removal process treating synthetic wastewater. ORP can be used as online fuzzy control parameter of nitrate recirculation and external carbon addition. The established fuzzy logic controller that includes two inputs and one output can maintain ORP value at - 86 mV and - 90 mV by adjusting the nitrate recirculation flow and external carbon dosage respectively to realize the optimal control of nitrogen removal, improving the effluent quality and reducing the operating cost.

Theoretical evaluation on nitrogen removal of step-feed anoxic/oxic activated sludge process

Evaluation on nitrogen removal of step-feed anoxic/oxic activated sludge process at the standpoint of reaction kinetics and process kinetics was conducted. Theoretical biological nitrogen removal efficiency was deduced based on the mass balance of nitrate in the last stage. The comparison of pre-denitrification process and step feed process in the aspects of nitrogen removal efficiency, volume of reactor and building investment was studied, and the results indicated that step-feed anoxic/oxic activated sludge process was superior to pre-denitrification process in these aspects.

Nitrogen removal for low-carbon wastewater in reversed A^2/O process by regulation technology

Full scale experimental study on nitrogen removal for low-carbon wastewater was conducted in reversed A2/O process in Jiguanshi waste water treatment plant in Chongqing,in order to aid the operation and maintenance of similar WWTP. When the proposed measures,such as using 0.1% (volume fraction of wastewater) landfill leachate,shortening HRT by 2/3 in the primary sedimentation tank and controlling DO at 0.5 mg/L in the 3rd section of aerobic zone,are applied,15% of the carbon source can be complemented,the favorable property of activated sludge is achieved,and the nitrogen removal effect is significantly improved. The effluent NH3-N is 2 mg/L and the removal rate is 90%. The effluent TN is 17 mg/L and the removal rate is 54%. The up-to-standard discharge of the effluent is achieved. And after the optimization,the unit electricity consumption also reaches 0.21 kW/h and saves 20%.

Development and Study on Nitrogen Removal Controller in A/O Process

In this paper three controllers for A/O process are developed, including a DO cascade controller, an external carbon flow rate controller and an internal recycling flow rate controller. The objective of the different controllers is to control the nitrate and ammonia concentration. Simulation study demonstrated that these controllers could efficiently control nitrogen removal and meet stricter effluent quality standards at a minimum cost.

Removal of nitrogen and phosphorus in a combined A^2/O-BAF system with a short aerobic SRT

A bench-scale anaerobic/anoxic/aerobic process-biological aerated filter （A^2/O-BAF） combined system was carded out to treat wastewater with lower C/N and C/P ratios. The A^2/O process was operated in a short aerobic sludge retention time （SRT） for organic pollutants and phosphorus removal, and denitrification. The subsequent BAF process was mainly used for nitrification. The BAF effluent was partially returned to anoxic zone of the A^2/O process to provide electron acceptors for denitrification and anoxic P uptake. This unique system formed an environment for reproducing the denitdfying phosphate-accumulating organisms （DPAOs）. The ratio of DPAOs to phosphorus accumulating organisms （PAOs） could be maintained at 28% by optimizing the organic loads in the anaerobic zone and the nitrate loads into the anoxic zone in the A^2/O process. The aerobic phosphorus over-uptake and discharge of excess activated sludge was the main mechanism of phosphorus removal in the combined system. The aerobic SRT of the A^2/O process should meet the demands for the development of aerobic PAOs and the restraint on the nitrifiers growth, and the contact time in the aerobic zone of the A^2/O process should be longer than 30 min, which ensured efficient phosphorus removal in the combined system. The adequate BAF effluent return rates should be controlled with 1--4 mg/L nitrate nitrogen in the anoxic zone effluent of A^2/O process to achieve the optimal nitrogen and phosphorus removal efficiencies.

Anoxic Biological Phosphorus Uptake in A^2O Process

A lab-scale anaerobic-anoxic-oxic (A2O) process used to treat a synthetic brewage wastewater was investigated. The objectives of the study were to identify the existence of denitrifying phosphorus removing bacteria (DPB), evaluate the contribution of DPB to biological nutrient removal and enhance the denitrifying phosphorus removal in A2O bioreactors. Sludge analysis confirmed that the average anoxic P uptake accounted for approximately 70% the total amount of P uptake, and the ratio of anoxic P uptake rate to aerobic P uptake rate was 69%. In addition, nitrate concentration in the anoxic phase and different organic substrate introduced into the anaerobic phase had significant effect on the anoxic P uptake. Compared with conventional A2O processes, good removal efficiencies of COD, phosphorus, ammonia and total nitrogen (92.3%, 95.5%, 96% and 79.5%, respectively) could be achieved in the anoxic P uptake system, and aeration energy consumption was saved 25%. By controlling the nitrate recirculation flow in the anoxic zone, anoxic P uptake could be enhanced, which solved the competition for organic substrates among poly-P organisms and denitrifiers successfully under the COD limiting conditions. Therefore, in wastewater treatment plants the control system should be applied according to the practical situation to optimize the operation.

结晶磷回收联合A/O工艺处理猪场沼液工艺特性

厌氧发酵广泛用于猪场废水的前端处理,该过程将产生大量沼液。在中国受土地消纳能力限制,相当一部分猪场沼液不得不经处理后达标排放。猪场沼液含有高浓度污染物,目前仍缺少高效的处理工艺。化学磷回收与A/O工艺均已有较好应用基础,该研究尝试联合结晶磷回收与A/O系统设计了一套具有工程可行性的猪场沼液处理工艺,并以实际猪场沼液为处理对象,探究了该工艺的污染物去除效能与机制。A/O系统缺氧、好氧反应器水力停留时间(HRT,hydraulic retention time)分别为3.4、8.6 h,硝化液回流比为200%,结晶反应器HRT为15min。试验结果表明,所设计工艺获得了较好的污染物去除效果,TP(总磷)、NH_(4)^(+)-N、TN(总氮)、COD(化学需氧量)的去除率分别达到91.20%、94.67%、83.28%和96.18%;工艺同时实现了磷的高效回收,磷回收率(结晶单元对TP去除的贡献率)达到93.44%。缺氧、好氧单元对COD、TN、NH_(4)^(+)-N的去除贡献率分别为75.24%、47.66%、17.30%与24.76%、30.92%、62.75%;该工艺条件下,缺氧单元发生了明显的厌氧氨氧化过程,好氧单元可能通过同步硝化反硝化、厌氧氨氧化等过程实现了部分TN的去除。结晶单元主要结晶产物为MgNH_(4)PO_(4),同步去除了部分TN、NH_(4)^(+)-N,去除贡献率分别为21.39%、19.92%。该研究可为猪场沼液处理及资源回收提供参考。

一体式A^(2)O-MBR系统处理高速公路服务区污水的研究

为解决高速公路服务区污水中污染物浓度高、处理设施普遍存在效能低下等问题,采用一体式A^(2)O-MBR反应器处理该目标污水。在反应器启动成功的基础上,研究了不同溶解氧(DO)、硝化液回流比和C/N下A^(2)O-MBR工艺对污染物的去除性能。结果表明,在控制DO为4 mg/L,硝化液回流比为300%,C/N为6时,A^(2)O-MBR获得了最佳污染物去除效果,A^(2)O-MBR工艺的COD、BOD_5和TP去除率分别为90.57%、93.75%和93.00%。反应器稳定运行时,出水NH_(4)^(+)-N和SS分别为4.2 mg/L和4.5 mg/L,出水指标均达到了《城市污水再生利用城市杂用水水质》(GB/T 18920—2020)中冲厕、车辆冲洗的要求。一体式A^(2)O-MBR在一定程度上可以降低膜组件的污染程度,从而降低系统的维护运行成本,可为高速公路服务区污水处理实际工程改造提供参考。

A^(2)O-SBR工艺在城镇污水处理厂中的应用

A^(2)O-SBR工艺为A2O工艺与SBR工艺串联组合,为了探究A^(2)O-SBR工艺在城镇污水处理厂的应用效果,分析广西壮族自治区东兴市城东污水处理厂2021年运行情况,结果表明:厂区出水稳定达标排放,A^(2)O-SBR工艺脱氮除磷效果好;COD、NH_(4)^(+)-N、TP平均去除率为87.05%、97.23%、80.86%,最高去除率为97.55%、98.36%、91.21%;出水浓度相对稳定,A^(2)O-SBR工艺对上述三种污染物的去除率也相对稳定,对NH_(4)^(+)-N效果最好,全年去除率稳定达到95%以上;该污水处理厂平均处理成本0.53元/m^(3)。

A-O模式MBBR工艺对村镇社区污水的脱氮效果

采用快速排泥法对硝化型和反硝化型MBBR反应器进行启动,并形成A-O模式工艺处理村镇生活污水。结果显示,通过快速排泥法,可以分别在20 d和10 d内完成硝化生物膜和反硝化生物膜的培养;在填充率为40%时,(20.0±0.5)℃水温条件下填料的平均硝化速率和反硝化速率分别为0.48 kgN/(m^(3)·d)和0.55 kgN/(m^(3)·d);当水温为(16.2±2.4)℃时,不投加外碳源,A-O模式的MBBR工艺出水氨氮和总氮可达到一级A标准;反硝化作用主要发生在缺氧池前端,硝化作用主要发生在好氧池后端。高通量测序结果显示,缺氧池前端反硝化菌主要为异养反硝化菌(相对丰度为19.14%),好氧池从前端到后端,硝化细菌菌属逐渐增加(相对丰度从3.09%增加到11.88%),好氧区填料存在一定比例的反硝化菌属(相对丰度为1.35%~4.11%)。A-O模式纯膜MBBR工艺启动迅速,脱氮效率高,系统简单、易于维护,适用于村镇污水处理。

磁环境下AAO工艺中的微生物群落演替规律

将AAO反应器置于5 mT大小的平均磁场环境,文中研究了磁场对AAO工艺效能的影响,并从分子生物学的角度对其影响机理进行了初步探究。结果表明,在5 mT磁场环境下,AAO工艺启动阶段的平均总氮去除率有较明显提升,比对照组上升6%;AAO反应器启动时间较对照组缩短了5 d;AAO中以固氮螺旋菌(Azospira)为代表的反硝化菌群的相对丰度占比明显提升,丝硫菌属(Thiothrix)的相对丰度占比大幅降低,对污泥膨胀的抑制作用较明显;通过基因功能预测发现磁环境下细胞运动类基因相对丰度相对无磁场条件提升75%,膜运输类基因大幅下降,从而提高了AAO的启动速度,提升了脱氮效能。

微塑料对序批式生物膜反应器除碳脱氮及N_(2)O释放特征的影响

微塑料是污水中常被检测到的新型污染物,然而微塑料对序批式生物膜反应器同步脱氮及N_(2)O释放特征的探究较少。本工作以实际市政废水为探究对象,建立中试规模的SBBR,考察了不同微塑料浓度(0、0.2、2.0和10.0mg/L)对SBBR长期运行除碳脱氮效率及N_(2)O释放规律的影响,并揭示了相关影响机制。结果表明,低浓度微塑料对SBBR除碳脱氮效率及N_(2)O释放规律影响不明显,但当进水微塑料浓度超过2.0 mg/L,碳脱氮效率呈现下降趋势,N_(2)O产率增加。当微塑料浓度为10.0 mg/L时,稳定时期出水COD维持在35.3~37.9 mg/L,COD和NH_(4)^(+)-N去除效率分别下降至82.4%~83.5%和80.2%~82.3%,低于工况I,此外,N_(2)O产率高达10.2%~10.8%。内聚物分析表明高浓度微塑料降低了PHA和糖原质的净合成,进而导致内碳源消耗脱氮动力不足。比耗氧速率(SOUR)分析表明高浓度微塑料降低了全部微生物代谢活性。

A/A/O微曝氧化沟工艺提标改造效果分析

采用固定式填料对A/A/O微曝氧化沟工艺进行提标改造,可提升系统的脱氮除磷性能。在生化池固定式填料填充体积比为10%的条件下,出水COD、NH_(4)^(+)-N、TN及TP平均质量浓度分别为28.7、2.42、6.86和0.32 mg/L,满足GB 18918—2002《城镇污水处理厂污染物排放标准》一级A排放标准,且处理水量提升了17.43%。高通量测序结果表明,提标改造后在门水平优势菌群主要为绿湾菌门(Chloroflexi)、放线菌门(Actinobacteriota)及拟杆菌门(Bacteroidota),三者相对丰度之和大于60%,且Chloroflexi相对丰度大于30%。在属水平优势菌群为硝化菌属(norank_f_Saprospiraceae、Nitrospira、Mycobacterium)、反硝化菌属(Rhodoplanes)及聚磷菌属(Acinetobacter及Tetrasphaera)。固定式填料-泥膜复合A/A/O微曝氧化沟中填料生物膜有利于菌群结构优化和功能微生物的富集。

不同运行条件下改进型A^(2)/O工艺脱氮除磷性能研究

为了提升传统A^(2)/O工艺的脱氮除磷效果,采用改进型A^(2)/O工艺,探究不同影响因素对其脱氮除磷效果的影响,并确定了改进型A^(2)/O工艺的最佳运行条件。通过调整消化液回流比、进水分配比、溶解氧(DO)浓度,确定改进型A^(2)/O工艺的最佳运行工况为消化液回流比200%、进水分配比6∶4、DO浓度1.9~2.0 mg/L,该运行条件下,脱氮除磷效果得到有效提升,出水水质能够稳定地达到一级A排放标准。

改良A^(2)O工艺与多级AO工艺在污水处理厂设计中的应用对比

东莞市某污水处理厂现状工程规模为20万m^(3)/d,文章以该工程中的新建三期工程为研究案例,工程规模为10万m^(3)/d。基于相关政策对污水处理厂总氮指标的逐步提升,通过对现状进水水质及其脱氮除氯工艺效率进行分析,对比同等进水水质情况下的改良A^(2)O工艺与多级AO工艺的设计,分析两者不同的设计参数、投资运维费用和生物脱氮除磷效率,总结两种工艺各自的优势及特点,为污水处理厂生化池工艺的选择提供参考。

基于嗜盐微生物的两级A/O工艺高效处理榨菜废水实践

榨菜废水呈高盐度、高有机物、高氮磷等特点,处理难度大、处理费用高。为了研究两级厌氧好氧(Anaerobic Oxic,A/O)工艺结合嗜盐微生物处理榨菜腌制废水的可行性及适宜条件,在充分调研分析榨菜腌制废水性质基础上,开展了为期近180 d的两级A/O中试试验,分析了不同盐度不同进水条件对出水水质的影响。在4~11 g/L进水盐度条件下,均可实现出水达到重庆市榨菜行业排放标准;进水盐度为11 g/L时,系统仍能稳定运行,一级A/O已完成大部分化学需氧量(chemical oxygen demand,COD)、总氮(total nitrogen,TN)、氨氮(ammonia nitrogen,NH3-N)等污染物的去除,两级A/O对COD、NH3-N、TN、总磷(total phosphorus,TP)污染物的处理能力平均分别约为1437 mg/L、158 mg/L、161 mg/L、23 mg/L,处理费用平均约为7.25元/t;系统对进水盐度及进水污染物浓度变化的抗冲击能力较强。研究结果表明,两级A/O工艺结合嗜盐微生物处理榨菜废水,技术经济可行。研究结果可为榨菜行业废水处理工艺、参数选择和优化提供参考。