Achieving nitrification in pure oxygen activated sludge by seeding

An innovative “seeding” approach was used to increase the nitrification capacity of a pure oxygen activated sludge plant. In this approach, waste activated sludge from a parallel air activated sludge system was used to seed nitrifiers to the pure oxygen plant to increase the apparent sludge age and achieve nitrification under the high loading in the pure oxygen system. Calculations indicate that nitrification can be achieved at a traditional sludge age of 3 days with a seeding rate of 20 percent. Full-scale tests showed that nitrification can be achieved at a seed rate of 35 percent and a traditional sludge age of 4.6 days, producing effluent ammonia below 5 mg/l. Secondary clarification remained good during the operation of the system even at the higher solids loading rates, with effluent TSS concentrations at 6 mg/l.     

Comparison of nitrification performance and microbial community between submerged membrane bioreactor and conventional activated sludge system.

A submerged membrane bioreactor (SMBR) and a conventional activated sludge system (CAS) were compared in parallel over a period of more than 260 days on treating synthetic ammonia-bearing inorganic wastewater without sludge purge under decreased hydraulic retention times (HRTs). Conversion of NH4(+)-N to NO3(-)-N was achieved with an efficiency of over 98% at an HRT > or = 10 h in the SMBR, while similar performance was obtained at an HRT > or = 20 h in the CAS. Denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR) amplified 16S rDNA was used to monitor variations of community structures in the two systems. With the prolongation of operation, the number of DGGE bands in the SMBR gradually increased from the initial 11 bands to the final 22 bands, whereas that in the CAS varied in a range between 13 and 183 Sequence analysis indicates that Nitrosomonas sp. and Nitrospira sp. were the dominating nitrification species responsible for ammonia and nitrite oxidation, respectively. Heterotrophic bacteria like Pseudomonas sp. and Flavobacteria sp. existed in both of the systems although only inorganic wastewater was fed. Substantive accumulation of extracellular polymeric substances (EPS) in the SMBR was confirmed by scanning electron microscopy and EPS analysis.     

循环式活性污泥法工程设计方法探讨

分析了CASS与CAST工艺的异同点,指出SBR工艺可以模拟多种不同的连续处理工艺,而CAST可以根据连续流A2/O工艺的设计方法进行设计.通过定义(进水 反应)阶段占每个运行周期的比例(§),引入有效污泥龄与有效水力停留时间的概念,分析了CAST同步硝化反硝化功能对主反应区DO的控制要求及对好氧SRT的影响,推荐采用CAST处理城市污水时使用经验值θc厌∶θc缺∶θc好=1∶2∶17;强调系统生物量的衰减由系统总SRT决定,调整(§)即可调整总污泥龄,并影响总产率系数.最后,给出了设计步骤和计算实例.当采用平均日流量设计时,建议采用较长的运行周期(6 h),便于在峰值流量时增加周期数,以保持CAST运行的灵活性.     

Molecular microbial ecology of nitrification in an activated sludge process treating refinery wastewater

The diversity of autotrophic ammonia-oxidizing bacteria (AOB) of the b-subdivision of the class Proteobacteria was investigated in a laboratory-scale denitrification-nitrification bioreactor (DNB) treating a synthetic waste stream. 16S ribosomal RNA (rRNA) gene sequences were amplified from DNA extracted from the oxic DNB sludge. Comparative analysis of the rRNA sequences revealed considerable diversity among the AOB-like sequences. The majority of sequences recovered were related to Nitrosomonas spp. but a smaller number of Nitrosospira-like sequences were obtained. Since different AOB may have different kinetic properties the high diversity of AOB, even in a simple laboratory biotreater treating a simple waste stream, has important implications for the operation of nitrifying wastewater treatment processes.     

Theoretical and practical identifiability of a reduced order model in an activated sludge process doing nitrification and denitrification

This paper deals with the structural identifiability and the identification of the parameters of a reduced order model used for control of a single reactor activated sludge process doing nitrification and denitrification. This reduced order model is splitted into two submodels, one 3-dimensional state submodel in aerobic conditions and one 2-dimensional state submodel in anoxic conditions. The identifiability analysis is based on on-line oxygen and nitrate concentrations data. It has been shown that the reduced order model is structurally identifiable. The parameter identification has been carried out by using the simplex method of Neider and Mead. Simulation results performed over a range of six hours (two aerobic/anoxic cycles), show that there exists a good fit between the simulated solution and the actual behavior of a lab scale pilot plant.     

Nitrogen removal and sludge reduction in a symbiotic activated sludge system between anaerobic archaea and bacteria.

The possible symbiosis between bacteria and anaerobic archaea was investigated in intermittent aeration (I/A) systems. Archaea solution added to I/A reactor might play an important role in biological activities as well as in improvement of mineralization of organic matter. I/A reactor with archaea solution (I/A-arch) could increase both nitrification and denitrification rate and also reduce the sludge yield remarkably. These results indicate the possibility of the symbiotic activated sludge system with anaerobic archaea by controlling the DO level in the aeration tank. In this study, DO was controlled by intermittent aeration schemes and a successful symbiotic activated sludge system was achieved to reach the following conclusions. 1) SOUR of I/A-arch system was 2.9 mg-O2/g-VSS x min. SOUR and nitrification rate of the sludge from I/A-arch was higher than those from the I/A and A/S reactors. 2) Removal efficiencies of organic matter (TCOD(Cr)) in I/A-arch, I/A and conventional activated sludge (A/S) reactors were 93, 90 and 87%, respectively. 3) Nitrification occurred successfully in each reactor, while denitrification rate was much higher in the I/A-arch reactor. Efficiencies of TN removal in A/I-arch, I/A and A/S reactors were 75, 63 and 33%, respectively. 4) Observed yield coefficients of I/A-arch, I/A and A/S reactors were 0.28, 0.41 and 0.37 g-VSS/g-COD.     

Behaviour of activated sludge from a system with anoxic phosphate uptake

Activated sludge from a new activated sludge modification for biological phosphorus and nitrogen removal was studied. Population dynamics and the phenomenon of anoxic phosphate uptake with simultaneous denitrification were investigated.The ability of the process to remove nutrients and to suppress filamentous bulking was studied. The course of phosphate concentrations along the tested system showed an anoxic phosphate uptake with simultaneous denitrification. The mechanism of anoxic phosphate uptake was confirmed using kinetic batch tests. © 1998 IAWQ. Published by Elsevier Science Ltd     

Fe3+对活性污泥系统的影响

通过小试研究了微量Fe3+对活性污泥系统的影响.将浓度为3 mg/L,5 mg/L,10 mg/L,20 mg/L,30 mg/L,50 mg/L和80 mg/L的Fe3+分别投加到活性污泥系统中,反应4 h后测定系统出水COD、活性污泥的SVI、脱氢酶活性及其EPS组分.结果表明,Fe3+浓度小于50 mg/L时对活性污泥的脱氢酶活性具有促进作用,浓度为10 mg/L时促进作用最强;Fe3+浓度在80 mg/L以下均具有良好的絮凝作用,浓度在30 mg/L以下时絮凝作用最强.两种作用的共同结果影响系统对COD的去除效果.对活性污泥EPS组分的测定表明,Fe3+的絮凝作用对SVI的影响是主要的.     

非线性规划在活性污泥法系统方案优化设计中的应用

将常规的活性污泥法工艺系统方案设计过程整合为一个最优化的非线性规划问题 ,提出了一种活性污泥法工艺方案的最优化设计方法。对优化原理、寻优求解的序列二次规划方法 (SQP)以及其Matlab的实现方法进行了介绍。设计算例表明 ,经优化后的设计方案较之传统的设计方案 ,在满足出水水质标准的基础上 ,可极大提高设计方案的经济可行性。     

生物捕食污泥减量化系统的污泥特性

通过中试分析了以减量化为目的的微型动物捕食系统中活性污泥的特性.结果表明,细菌分散培养段的悬浮污泥浓度比原生动物捕食段约高15%,比大型微型动物捕食段约高40%;微型动物的捕食作用在减少剩余污泥产率的同时,可以提高悬浮污泥的沉降性能约36%,轮虫可作为该系统污泥沉降性能的指示生物;低底物浓度下,大型微型动物的捕食活动可以增强污泥的活性.     

SBBR自养型短程硝化的实现及其影响因素研究

采用序批式生物膜反应器(SBBR)以及模拟无碳源的理想生活污水,对系统内各参数进行反复调试,在一个月内实现了自养型短程硝化系统的启动,氨氮去除率为98%,亚硝态氮积累率为95.29%。当温度控制在20～35℃时都会实现短程硝化,而30℃时短程硝化的效果最佳;系统其他条件不变的情况下DO为1.5 mg/L时,短程硝化的效果最好;系统具有一定的承受有机负荷的能力,在进水中外加COD_(Cr)浓度不超过75 mg/L时,不会对系统产生影响且COD_(Cr)的去除率为50%。     

A pilot study on a step-feeding anoxic/oxic activated sludge system.

A four stage pilot plant of step-feed biological nutrient removal (BNR) was employed to investigate reactor performance and process stability. The results obtained showed that step-feed BNR is efficient and cost-effective for nitrogen and carbonaceous removal from municipal wastewater. The total average removal efficiencies of COD, NH3-N, TN and TP could reach as high as 89.5, 97.8, 73 and 75%, respectively, with 50% of return activated sludge (RAS), 9 h of hydraulic retention time (HRT) and 20 d of sludge retention time (SRT). Step-feed BNR is an alternative and effective technology of nutrient removal for municipal wastewater treatment.     

Anaerobic processes in activated sludge

We found anoxic zones in aerated activated sludge flocs, and demonstrated denitrification under normal operating conditions. Sulfate reduction was not found. Micro-environments and microbial conversions in flocs from bulking and non-bulking activated sludge were determined with microsensors for H₂S, O₂, NO₂₋ and NO₃₋. Denitriftcation and sulfate reduction rates were measured with ¹⁵N- and ³⁵S-tracer techniques. We showed that under normal reactor conditions (ca. 20% air saturation) anoxic zones develop within flocs allowing denitrification. The denitrtftcation rates amounted to 40% of the rates under anoxic conditions. At 100% air saturation no anoxic zones were found and no denitrification occurred. However, in flocs from bulking sludge (at 20% air saturation) anoxic zones were absent and denitrification did not occur. In bulking sludge only at total anoxia was denitrification found. Confocal microscopy showed that flocs from bulking sludge were much looser than those from non-bulking sludge. The absence of anoxic zones and of denitrification was attributed to the open floc structure, allowing advective oxygen transport.Sulfate reduction was not detected in any of the sludges tested by microsensors or by tracer techniques even under anoxic conditions. This indicates that the sulfur cycle (sulfate reduction and sulfide oxidation) does not play a role in mineralization processes and bulking in activated sludge. Preliminary molecular work (in situ hybridization with the 16S-rRNA probe SRB385) indicated the presence of small amounts of sulfate reducing bacteria in all sludges. Either the probe is not specific or the sulfate reducers present are not active under reactor conditions.     

Analysing sludge balance in activated sludge systems with a novel mass transport model

In activated sludge systems the mechanically treated wastewater is biologically cleaned by biomass (activated sludge). The basic requirement of an efficient biological wastewater treatment is to have as a high biomass concentration in the biological reactor (BR) as possible. The activated sludge balance in activated sludge systems is controlled by the settling, thickening, scraper mechanism in the secondary settling tank (SST) and sludge returning. These processes aim at keeping maximum sludge mass in the BR and minimum sludge mass in the SST even in peak flow events (storm water flow). It can be, however, only reached by a high SST performance. The main physical processes and boundary conditions such as inhomogeneous turbulent flow, geometrical features of the SST, wastewater treatment plant (WWTP) load, return sludge flow, sludge volume index etc. all influence settling thickening and sludge returning. In the paper a novel mass transport model of an activated sludge system is presented which involves a 2-dimensional SST model coupled with a mixed reactor model of the biological reactor. It makes possible to investigate different sludge returning strategies and their influence on the sludge balance of the investigated activated sludge system, furthermore, the processes determining the flow and concentration patterns in the SST. The paper gives an overview on the first promising model results of a prevailing peak flow event investigation at the WWTP of Graz.     

Short circuiting in a denitrifying activated sludge tank.

The presence of a short circuit flow in a denitrifying activated sludge tank was identified and modelled. Tracer tests with pulse addition of lithium salt were used to investigate the hydraulics of the tank. The lithium concentration in the effluent was detected and residence time distribution (RTD) curves were generated. Hydraulic models based on completely stirred tank reactors (CSTRs) in series were generated from the RTD curves and the models were compared. The short circuit problem was successfully described using the Martin model, where the inflow is divided into two strands. Each strand was modelled as a number of CSTRs in series. At a normal flow the results of the model show that the tank has 12.8% dead volume, 85.8% main volume and 1.3% short circuiting volume. The inflow was divided into 91.9% entering the main volume and 8.1% entering the short circuiting volume. The mean velocity of the short circuiting stream was estimated to 0.4 m/s. At maximum flow the short circuiting stream was even larger and handled 24.3% of the flow. The short circuiting stream was identified in the upper part of the tank due to the position of the inlet and the outlet. The configuration of a tank including the use of baffles, the geometry of the inlet and mixer configuration should be considered carefully if short circuiting is to be avoided.     

Co-conditioning and dewatering of alum sludge and waste activated sludge.

Co-conditioning and dewatering behaviors of alum sludge and waste activated sludge were investigated. Two different sludges were mixed at various ratios (2:1; 1:1; 1:2; 1:4) for study. Capillary suction time (CST) and specific resistance to filtration (SRF) were utilized to assess sludge dewaterability. Relatively speaking, waste activated sludge, though of higher solid content, was more difficult to be dewatered than alum sludge. It was found that sludge dewaterability and settlability became better with increasing fraction of alum sludge in the mixed sludge. Dosage required of the cationic polyelectrolyte (KP-201C) for dewatering was reduced as well. It is proposed that alum sludge acts as skeleton builder in the mixed sludge, and renders the mixed sludge more incompressible which is beneficial for sludge dewatering. Implications of the results of the study to the sludge management plan for Taipei City that generates both alum sludge and waste activated sludge at significant amount are also discussed. The current sludge treatment and disposal plan in Metropolitan Taipei could be made more cost-effective.     

Evaluation of filamentous microorganism growth factors in an industrial wastewater activated sludge system

An investigation comprising four studies was undertaken to determine possible factors affecting the growth of several different types of filamentous microorganisms present in a bulking industrial wastewater activated sludge. Results from laboratory-scale continuous-flow and full-scale studies suggested that DO concentration and F:M ratio were the likely key factors affecting filamentous growth in the activated sludge. From the results of two laboratory studies isolating the effects of DO concentration and F:M ratio on filamentous growth, favorable growth ranges of DO concentration or F:M ratio were estimated for the following filaments: Microthrix parvicella, Nocardia spp., Nostocoida limicola II, and Types 0041, 1851, and 1863. Most of the bacteria causing filamentous bulking of the activated sludge were found to be filaments typically associated with low F:M, and increasing the F:M ratio appeared to cause N. limicola II to lose its competitive advantage in the activated sludge system. Type 1863, on the other hand, was found to be a low DO filament, as DO concentrations of 0.1 mg O₂/l or less appeared to be a necessary condition for its filamentous growth. Though Nocardia was found to be a low F:M filament, its growth also seemed to be affected by DO concentration, as its growth was stimulated by concentrations of 1.0 mg O₂/l or greater, with a near linear relationship up to at least 5 mg O₂/l.     

多级高浓度活性污泥法脱氮除磷中试研究

多级高浓度活性污泥法在不征地、不增加处理构筑物的情况下,以提高活性污泥浓度为指导思想,对现有城市污水处理厂进行升级改造,达到脱氮除磷的目的。中试研究表明,在试验条件下,出水CODCr为33～43mg/L,去除率92%左右;NH3-N为3～5mg/L,去除率90%左右;TP为1～1.7mg/L,去除率72%左右。系统保证了良好的脱氮除磷效果。     

Extracellular redox activity in activated sludge

The tetrazolium salts triphenyltetrazoltum chloride (TTC) and 2-(p-iodophenyl)-3-(p-nitrophenyl)-5phenylteirazolium chloride (INT) have been used extensively for the measurement of respiratory activity in natural waters, drinking water, sediments and activated sludge. Usually this is done spectrophotometrically after extracting the reduced formazan salt. Other tetrazolium salts like 5-cyano-2,3-di-4-tolyl-tetrazolium chloride (CTC) are reduced to formazan salts which are fluorescent. This property has been used to microscopically determine the proportion of metabolically active cells in a sample. The observation that CTC is also reduced extracellularly prompted an investigation of the role of this activity in activated sludge. In order to test the assumption that extracellular reduction is stimulated by recalcitrant molecules a bench-scale sequencing batch reactor (SBR) was fed with synthetic wastewater containing either lignin or amylose as well as hexanoic acid, glycerol and sucrose as organic constituents. About 4 times as much tetrazolium salt 3′-(I-|(phenylamino-)carbonyl]-3,4-tetrazolium)-bis (4-methoxy-6-nitro) benzene-sulfonic acid hydrate (XTP) was reduced by extracts containing extracellular polymeric substances (EPS) produced in the presence of lignin than by extracts derived from amylose-fed cells. These differences are statistically significant at P > 0.05. Extracellular redox activity m lignin-containing activated sludge accounted for approximately 2% of total redox activity. In addition to experiments involving reactors fed with different substrates, the extracellular redox activity was measured microscopically using a Zeiss confocal laser microscope. Planktonically grown cells of Escherichia coli or activated sludge flocs were treated with CTC and the nucleic acid stain PicoGreen which fluoresces in the red and green visible light regions, respectively. In Escherichia coli preparations, CTC-formazan crystals were found exclusively inside cells. By contrast, activated sludge flocs revealed crystals both inside and outside the cells. Formaldehyde-treated flocs did not show any reduction of CTC. The extracellular crystals accounted for up to 50% of the total CTC reduction. It follows that extracellular redox activity is associated with the production of EPS. Its role may be to help microbial systems to deal with organic materials which are difficult to utilize.     

用污泥沉降比指导活性污泥法运行的探讨

总结讨论了污泥沉降比在活性污泥法污水处理过程中与MLSS的关系和对活性污泥法处理效果的影响,分析其与季节变化的关系,指出污泥沉降比在预防污泥膨胀及维持曝气池稳定运行方面的作用,影响污水处理效果因素之间的关系,以及污泥沉降比在实际生产运行管理中的指导作用。