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.     

Impact of septic compounds and operational conditions on the microbiology of an activated sludge system.

In activated sludge (AS) biotreatment, septic compounds such as volatile organic acids and reduced sulphur compounds have been frequently cited as a major cause of Thiothrix and Type 021N filamentous bulking. These filaments are common in Canadian pulp and paper biotreatment systems, where they cause settling problems in secondary clarifiers. We conducted a 14-week study of a TMP/newsprint mill effluent to characterize the septic compounds entering the biotreatment, and to determine correlations with AS biomass characteristics and biotreatment operating parameters. A significant correlation was found between the sludge volume index, the abundance of Type 021N, and the propionic acid (PA) concentration in the primary clarified effluent. PA also induced a significant change in the flocculating bacteria size distribution determined by digital imaging. Consequently, the correlation observed between PA and Type 021N bulking is an indirect effect of inhibition of floc-forming microorganisms, giving a competitive advantage to filaments.     

基于LabVIEW的推流式活性污泥法动态仿真研究

介绍了利用LabVIEW6.1及其数学子模板中一阶微分方程组的龙格库塔算法函数,根据活性污泥法1号数学模型一阶微分方程组的特征,开发出适用于推流式活性污泥法仿真系统的方法。应用该仿真系统模拟了重庆某污水处理厂的实际运行记录,结果表明仿真效果良好。该方法降低了软件的编程难度。     

A comparison of conventional activated sludge and low sludge production strategies for advanced treatment of kraft pulp mill effluent.

Parallel laboratory investigations were conducted to examine aspects of two distinct but related bioprocess strategies for low sludge production in the treatment of the same TCF kraft pulp mill effluent. The purpose of this article has been to compare the performance results from these two bench-scale trials with respect to nutrient demands, nutrient discharge, COD removal, and waste sludge characteristics. The LSP (Low Sludge Production) process can be used to significantly reduce sludge yield with excellent sludge characteristics. These sludge characteristics seemed to be related to elevated protozoan grazing pressures. The BAS (Biofilm-Activated Sludge) process achieves similar reduced sludge yields and sludge characteristics while at the same time significantly reducing the nutrient demands and discharge levels. For both LSP and BAS process optimization, the selector nutrient loading is critical to the overall process performance. Selector nutrient requirements are distinct from the overall process nutrient requirements.     

Automatic monitoring of denitrification rates and capacities in activated sludge processes using fluorescence or redox potential

A novel method is described to automatically estimate several key parameters affecting denitrification in activated sludge processes: the nitrate concentration, the denitrification capacity, and the maximum (substrate unlimited) and actual denitrification rates. From these, the concentration of active denitrifying microorganisms and the quality of available organic substrate pool can be estimated. Additionally, a modification of the method allows the determination of the efficacy of various carbon substrates to enhance denitrification, and this can be used to determine optimal dosing rates of an external carbon source. The method is based on measurements of either fluorescence or redox potential (ORP) in an isolated mini-reactor, the Biological Activity Meter (BAM), situated in the anoxic zone of the wastewater treatment plant. Advantages of the method are that it is in situ, operating at the same temperature as in the measured anoxic zone, requires no pumps or pipes for mixed liquor sampling, consumes little or no reagents, and uses measurement signals which are instantaneous and low maintenance, one of which provides a direct measure of biological activity.     

基于扩展微分进化算法的渠道断面优化设计

传统的渠道断面设计方法需要进行反复试算,且精度不理想。1995年Rainer Storn等提出了微分进化算法,该算法是一种简单、有效的智能优化方法,在1996年首届IEEE进化算法大赛中被证明为所有参赛算法中最快的。将扩展微分进化算法应用于解决渠道断面设计中的非线性优化问题,并以实例进行了计算。算例表明扩展微分进化算法能有效解决渠道断面的优化设计问题,且具有全局寻优能力强、解的精度高等优点。     

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.     

Potential of OUR and OTR measurements for identification of activated sludge removal processes in aerated basins.

In order to develop a process control scheme to reduce energy costs for aeration in activated sludge systems with biological P removal, pre-denitrification and nitrification stages, the spatial distribution of carbon oxidation and nitrification was evaluated over a long full-scale plug flow aeration basin using an externally measured specific oxygen uptake rate (sOUR) and in basin measurement of the actual specific oxygen transfer rate (sOTR) with off-gas testing as well as with the calculated oxygen demand from NH4-N concentrations (sOTR(N)). Using a simple static model, a gas phase balance on oxygen and carbon dioxide, sOTR(N) values were also calculated from off-gas testing. Comparison of sOTR(N) to sOTR and sOUR for carbon oxidation (sOUR(C)) to nitrification (sOUR(N)) at different loading conditions allowed the oxidation processes to be followed over the three zones of the aeration basin. As expected, the distribution depended on the dissolved oxygen concentration (DO) in the basin. However, the major change was in the C-oxidation rate and not the nitrification rate. At a low DO, and when NH4-N was present in the zone, the amount of oxygen transferred for nitrification was nearly the same, but the overall sOTR was lower. The externally measured sOUR was only useful when it was differentiated into sOUR(N) and sOUR(C). sOUR(N) could be used to predict the nitrification rate in the basin. With further refinement, the gas phase balance model has potential to be used to monitor the degree of nitrification over the basin length. This can be integrated into a control scheme to reduce aeration costs by adjusting the DO setpoint according to loading conditions in the     

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。     

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.     

The assessment of different operating strategies for minimising activated sludge deflocculation under temperature transient conditions.

Three operating strategies were tested for decreasing activated sludge deflocculation due to temperature shifts from 30 degrees to 45 degrees C: magnesium sludge enrichment, increased sludge retention time (33 d), and spikes of an easily degradable substrate (methanol). The temperature shifts were conducted sequentially in 4 parallel lab-scale sequencing batch reactors (SBRs) treating kraft pulp mill effluent. Three SBRs operated at an SRT = 20 days, and in one of them the sludge was not manipulated, thus, serving as a reference SBR. The temperature shift was associated with decreased soluble chemical oxygen demand (SCOD) removals, decreased sludge settleability and substrate removal capacity, and increased effluent suspended solids (ESS) and turbidity levels. The shift also increased the sludge specific respiration rates and reduced the sludge substrate removal capacity. Sludge deflocculation was assessed as floc solubilisation (increased effluent SCOD levels) and floc fragmentation (increase in effluent solids smaller than 50 microm). Mg enrichment of the sludge and methanol spikes reduced the ESS levels (in 9 and 25%), and the three operating strategies decreased effluent turbidity (in 22-35%) compared to the maximum levels from the non-manipulated reactor (44 mg ESS/L). The stronger sludge floc structure achieved by magnesium enrichment and a high sludge age of 33 days was unsuccessful in significantly decreasing deflocculation. The mechanisms involved in sludge deflocculation require further fundamental research.     

Towards mechanistic models for activated sludge flocculation under different conditions based on inverse problems

Experimental data of Ca-induced activated sludge flocculation under different conditions of temperature and dissolved oxygen are investigated in order to model the influence of changing physical and chemical factors. However, current kernel structures for collision frequency and efficiency are unable to describe activated sludge flocculation data. Therefore, an earlier developed methodology based on an inverse problem is applied, yielding empirical models, to find out how flocculation is affected by these different environmental conditions. This contribution shows the useful application of inverse problems to improve the understanding of complex aggregation mechanisms.     

活性污泥胞外聚合物EPS的影响因素研究

胞外聚合物EPS对活性污泥的表面特性、生物絮凝、沉降及脱水性能等具有重要的影响,主要对污泥负荷Ns,DO,温度,Ca2+,pH及废水水质等因素对EPS的影响进行了研究。试验结果表明:Ns,pH及废水水质对EPS的含量、成分有显著的影响;DO,温度对EPS的影响较小;同时随着进水Ca2+浓度的增加,污泥的EPS,脱氢酶及OUR增加。     

Potential of activated sludge ozonation.

The disposal of sewage sludge and the agricultural use of stabilised sludge are decreasing due to more stringent regulations in Europe. An increasing fraction of sewage sludge must therefore be dewatered, dried, incinerated and the ashes disposed of in landfills. These processes are cost-intensive and also lead to the loss of the valuable phosphate resources incorporated in the sludge ash. The implementation of processes that could reduce excess sludge production and recycle phosphate is therefore recommended. Partial ozonation of the return sludge of an activated sludge system significantly reduces excess sludge production, improves the settling properties of the sludge and reduces bulking and scumming. The solubilised COD will also improve denitrification if the treated sludge is recycled to the anoxic zone. However, ozonation partly kills nitrifiers and could therefore lead to a decrease of the effective solid retention time of the nitrifier, thus reducing the safety of the nitrification. This paper discusses the effect of ozonation on sludge reduction, the operating stability of nitrification, the improvement of denitrification and also presents an energy and cost evaluation.     

Potential of activated sludge disintegration.

The disposal of sewage sludge and the agricultural use of stabilised sludge are decreasing due to more stringent regulations in Europe. An increasing fraction of sewage sludge must therefore be dewatered, dried, incinerated and the ashes disposed of in landfills. These processes are cost-intensive and also lead to the loss of valuable phosphate resources incorporated in the sludge ash. The implementation of processes that could reduce excess sludge production and recycle phosphate is therefore recommended. Disintegration of biological sludge by mechanical, thermal and physical methods could significantly reduce excess sludge production, improve the settling properties of the sludge and reduce bulking and scumming. The solubilised COD could also improve denitrification if the treated sludge is recycled to the anoxic zone. However, disintegration partly inhibits and kills nitrifiers and could therefore shorten their effective solid retention time, thus reducing the safety of the nitrification. This paper discusses the potential of disintegration on sludge reduction, the operating stability of nitrification, the improvement of denitrification and also presents an energy and cost evaluation.     

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.     

活性污泥工艺中污泥减量化技术研究进展

污泥减量化技术是在剩余污泥资源化基础上进一步提出的剩余污泥处置新概念;根据生物处理工艺中影响剩余污泥产生的可能途径,将污泥减量技术归纳为降低细菌合成量的解偶联技术、增强微生物进行内源呼吸代谢的溶胞技术、利用食物链作用强化微型动物对细菌捕食的技术;并对当前污泥减量化技术进行了理论分析和应用上的概述。     

A nitrate biosensor based methodology for monitoring anoxic activated sludge activity.

An improved methodology based on a nitrate biosensor is developed and applied successfully for in-depth monitoring and study of anoxic activated sludge activities. The major advantages of the methodology are its simplicity, reliability and high data quality. The resulting data allowed for the first time to monitor anoxic respiration rate of activated sludge (nitrate uptake rate (NUR)) at a high time resolution making it clearly comparable with high frequency oxygen uptake rate (OUR) measurements obtained under aerobic conditions. Further, the anoxic respiration data resulting from a pulse addition of carbon source to endogenously respiring anoxic activated sludge shows a clear start-up phenomenon and storage tail that is usually also observed in high-frequency OUR measurements. Finally, the improved methodology can be expected to serve as an anoxic respirometer for activated sludge treatment plants where denitrification process occurs in single-step. Further, it can be used for a variety of purposes e.g. for toxicity and activity monitoring, process control and parameter estimation of the activated sludge process, similar to the aerobic respirometers.     

Distribution of ammonia-oxidizing bacteria in sewage activated sludge: analysis based on 16S rDNA sequence.

This study carried out analysis of ammonia-oxidizing bacteria (AOB) communities in 12 sewage activated sludge systems standing in eight sewage treatment plants located in Tokyo. The systems were different in the treatment process configuration: anaerobic/anoxic/aerobic (A20), anaerobic/aerobic (AO), and conventional activated sludge (AS) processes. AOB communities were analyzed by sequences of 16S rDNA amplicons, which were separated by denaturing gradient gel eletrophoresis (DGGE) after specific polymerase chain reaction (PCR) amplification. The results demonstrated that low ammonium concentrations in the influents of the 12 sewage activated sludge systems resulted in the dominance of Nitrosomonas oligotropha-like sequences. Further, Nitrosomonas europaea- and Nitrosomonas cryotolerans-like sequences were recovered from only one A20 system of which the influent contained higher ammonium and chloride concentrations than those of other systems. Nitrosomonas communis-like sequences were found in every A20 and AO system, but mostly not found in every AS system. In summary, influent characteristics and treatment process configuration affected the AOB communities in the 12 sewage activated sludge systems.     

Towards exposure of elusive metabolic mixed-culture processes: the application of metaproteomic analyses to activated sludge.

Protein expression is a direct reflection of specific microbial activities in any ecosystem. In order to assess protein expression in mixed microbial communities, the feasibility of applying proteomic techniques to activated sludge samples has recently been demonstrated. We report the application of metaproteomics to two activated sludges from a laboratory-scale sequencing batch reactor with dissimilar phosphorus removal performances. Fluorescence in situ hybridization (FISH) revealed that the sludge with good enhanced biological phosphorus removal performance (EBPR) was dominated by Betaproteobacteria (65% of EUBMIX binding cells) and gave positive signals for the Rhodocyclus-type PAO specific probe (59%). The non-EBPR sludge was dominated by tetrad-forming Alphaproteobacteria (75%). With regard to the proteomic investigation, 630 individual protein spots were matched across the replicate groups of the anaerobic and aerobic phases of the EBPR sludge with 9.4% of all spots being statistically different between the two phases. The non-EBPR metaproteomic maps exhibited 590 matched spots with 14.7% statistical differences between the two phases. Overall, the non-EBPR sludge expressed around 30% more significant differences than the EBPR sludge. The comparison of protein expression in the two sludges showed that their metaproteomes were substantially different and this was reflected in their microbial community structures and metabolic transformations.