Microbial viability measurements and activated sludge kinetics

A laboratory study was performed to evaluate the influence of microbial viability information on a widely used steady-state kinetic model of slurry-type biological wastewater treatment processes. Adenosine triphosphate (ATP), determined by the luciferin-luciferase firefly lantern extract method using a liquid scintillation spectrometer to measure light emission, was used as the indicator of microbial viability. It was found that the microbial viability of activated sludge mixed liquor volatile suspended solids (MLVSS) exhibits a functional relationship with biological solids retention time (θ_c), i.e., being essentially 100% at low values of 0_c and decreasing to a nearly constant value at the higher values of 0_c, typical of activated sludge process operation. Values of the model coefficients were also affected by the microbial viability of the MLVSS.Based on mass balance considerations and ATP measurements, it is proposed that the MLVSS of an activated sludge system treating a soluble organic waste can be divided into the following three fractions: (I) active or viable microbial solids, (2) inert microbial debris solids, and (3) nonviable biodegradable microbial solids. Implications of viability information in design and operation are discussed.     

Evaluation on the impacts of predators on biomass components and oxygen uptake in sequencing batch reactor and continuous systems

An expanded unified model for the biomass fractions, soluble-organic fractions, and oxygen-uptake rates considering extracellular polymeric substances (EPS), intracellular storage products (X_STO), and predators for activated sludge is used to study the impacts of predators on biomass components and oxygen uptake. The new model is applied to evaluate how predation affects the oxygen-uptake rate (OUR) and the different forms of biomass: active bacteria (X_H), X_EPS, and X_STO, under dynamic feast-and-famine and continuous conditions. For the dynamic conditions of a sequencing batch reactor (SBR), eliminating predators from the model increases X_H and X_EPS fractions significantly, and this causes the substantial increases in OUR and MLVSS once the famine period begins. An analysis of how the OUR is distributed among the several respiration processes shows that the predation of X_H is the most significant oxygen utilization rate process in the system under famine conditions of an SBR. Application of the model to simulate the long-term operation of an SBR indicates that predators reach their maximum fraction in the MLVSS (∼4% of MLVSS) at a solids retention time of about 13 days, but they are washed out at a solids retention time less than ∼3 days. Simulation for a continuous system indicates that predators take more time (about 800 h) to reach steady state and reach their maximum fraction (∼5.5%) at an SRT of ∼14 days. Comparison of SBR and continuous systems reveals that the predators have greater impact in the continuous system because the permanent near-famine condition accentuates predation processes.     

Estimation of viable biomass in wastewater and activated sludge by determination of ATP, oxygen utilization rate and FDA hydrolysis

ATP content, oxygen utilization rate (OUR) and fluorescein diacetate (FDA) hydrolysis were tested for the ability to express the amount of viable biomass in wastewater and activated sludge.The relationship between biomass and these activity parameters was established in growth cultures made by inoculating a nutrient medium with either wastewater or activated sludge. Biomass was then determined directly by measurement of dry weight of growth culture (dw), and compared to data obtained by using the previously mentioned methods. In the exponential growth phase, ATP content showed the best correlation with biomass, while FDA hydrolysis in the sludge failed to show any such correlation. Conversion factors of 3 mg ATP/g dw, 300 mg O₂/h g dw and 0.4 A/h (mg dw/ml) for ATP, OUR and FDA methods, respectively, were calculated.When the methods were applied for in situ determinations in four different wastewater plants, it was found that ATP content and respiration rate estimated viable biomass to range from 81 to 293 mg dw/g SS for raw wastewater and from 67 to 187 mg dw/g SS for activated sludge with a rather weak correlation between ATP and respiration measurements. The FDA hydrolysis estimated viable biomass to be higher than suspended solids, for which reason this parameter could not be recommended for determination of viable biomass in wastewater and activated sludge.     

污泥接种量对剩余污泥水解酸化的影响研究

研究了厌氧条件下水解酸化污泥接种量及污泥浓度对剩余污泥水解产酸、污泥减量的影响.在各反应瓶污泥浓度不同的情况下接种等体积的水解酸化污泥,当污泥停留时间为7 d时,剩余污泥具有较高的产酸量,超过7 d则反应进入厌氧消化的产甲烷阶段,表明接种污泥在反应的前7 d对剩余污泥产酸具有促进作用;水解酸化污泥接种量最多(35%)时其产酸量最高,7 d后作用逐渐减弱,污泥浓度成为影响产酸的主要因素.剩余污泥的水解过程与产酸过程具有相似的规律,MLVSS浓度随着时间的增加而逐渐下降,7 d后降幅趋缓,经过7 d的反应,污泥接种量最多(35%)的MLVSS浓度较开始时下降了27%,MLSS浓度下降了25.5%.     

An ATP luminescence method for direct toxicity assessment of pollutants impacting on the activated sewage sludge process

An ATP luminescence method was used to determine the toxicity of three reference toxicants to two sources of domestic activated sludge, and an activated sludge from a laboratory model plant. Repeatability in the ATP test was demonstrated for Cr (as K2Cr2O7), Zn (as ZnSO4 x 7H2O), and 3,5-dichlorophenol (3,5-DCP) using each source of activated sludge. The three sources of sludge showed sensitivity to Cr and 3,5-DCP, and insensitivity to Zn using the ATP luminescence method. Sludge source did not appear to effect test response. The toxic response to 3,5-DCP in model and domestic activated sludge was shown to be dependent on sludge solid concentration (measured as total suspended solids, gTSS(-1). It is recommended that a standard solids concentration is used during toxicity evaluation.     

Aerobic batch degradation of 17-beta estradiol (E2) by activated sludge: effects of spiking E2 concentrations, MLVSS and temperatures

Aerobic batch degradation of 17beta estradiol (E2) spiked into the activated sludge liquor from a sewage treatment plant was studied; and the likely impacts of E2's initial concentrations (C0), microbial population densities (MLVSS) and temperatures (TEMPT) were examined for a variety of combinations of these three factors: C0 = 10, 30 and 50 microgl(-1); MLVSS = 1750, 875 and 435 mgl(-1); and TEMPT = 5, 20 and 35 degrees C. The results, together with those obtained through two control runs performed using a killed sludge sample, demonstrated clearly that E2 was eliminated from the aqueous phase readily under appropriate MLVSS and temperature levels, with the role of sorption by biomass being less significant. By fitting observed concentration data with a first-order rate expression, the degradation rate constants (k) under all experimental conditions were estimated. The magnitude of k changed markedly in the range of 0.23-4.79 h(-1), following a general order that the higher the MLVSS was, the higher the rate constant, and that the higher the temperature, the higher the rate constant. An obvious increasing trend of the biomass-modified average rate constant (k') with increases in the temperature was also presented: the k' values at 5, 20 and 35 degrees C were 0.79, 1.77 and 3.29l MLVSS g(-1)h(-1), respectively. Furthermore, based upon the estimated k values, the temperature coefficients (theta) over the ranges of 5-20 and 20-35 degrees C were determined. In similarity with the magnitude of theta reported for ordinary BOD-based organic matrices in domestic wastewater, the theta values of E2 varied in the range of 1.026-1.09, suggesting that the temperature impacts on the degradation rates of E2 and BOD constituents are probably similar.     

Monitoring off-gas O2/CO2 to predict nitrification performance in activated sludge processes

Nitrification/denitrification (NDN) processes are the most widely used technique to remove nitrogenous pollutants from municipal wastewater. The performance of nitrogen removal in the NDN process depends on the metabolism of nitrifying bacteria, and is dependent on adequate oxygen supply. Off-gas testing is a convenient and popular method for measuring oxygen transfer efficiency (OTE) under process conditions and can be performed in real-time. Since carbon dioxide is produced by carbonaceous oxidizing organism and not by nitrifiers, it should be possible to use the off-gas carbon dioxide mole fraction to estimate nitrification performance independently of the oxygen uptake rate (OUR) or OTE. This paper used off-gas data with a dynamic model to estimate nitrifying efficiency for various activated sludge process conditions. The relationship among nitrification, oxygen transfer, carbon dioxide production, and pH change was investigated. Experimental results of an online off-gas monitoring for a full-scale treatment plant were used to validate the model. The results showed measurable differences in OUR and carbon dioxide transfer rate (CTR) and the simulations successfully predicted the effluent ammonia by using the measured CO₂ and O₂ contents in off-gas as input signal. Carbon dioxide in the off-gas could be a useful technique to control aeration and to monitor nitrification rate.     

Congruence in the performance of model nitrifying activated sludge plants located in Germany,Scotland and Spain

A laboratory model nitrifying activated sludge plant treating OECD synthetic sewage was designed and constructed by each of three laboratories in Germany, Scotland and Spain in order to produce a sludge inoculum for 5 rapid toxicity bioassays. The plants were run for 3 years and produced sludge for the microbially based bioassays Vibrio fischeri bioluminescence, ATP luminescence and respiration, and, nitrification and enzyme inhibition. Although the initial sludge inoculum for the plants differed, as did some of the running conditions such as temperature regime, the sludge produced within the different countries had similar characteristics with respect to sludge age, total suspended solids and volatile suspended solids. Nitrification was generally maintained over the 3-year period although there were occasions when the process was inconsistent. Nitrification recovery was afforded by reseeding with a nitrifying sludge from a local wastewater treatment works (WWTW) or imposition of starvation conditions for a period of time. The sludge produced was used to carry out toxicity testing and results compared well with those using sludge from a WWTW. Overall, the use of sludge generated in the laboratory could be used for toxicity testing negating the need to resort to the use of natural WWTW sludge, which may contain a range of toxic substances due to uncontrolled industrial and domestic inputs and an unbalanced microbial consortium.     

Performance evaluation of an oily industrial wastewater treatment system using the application of activated sludge model No. 3

The purpose of the present study was to adapt the activated sludge model No. 3 (ASM3) to the characteristics of oily industrial wastewater, determining the utmost significant and appropriate kinetic as well as stoichiometric parameters. An oily industrial wastewater treatment system was simulated to assess ASM3 validation and perform sensitivity analysis using the STOAT program. The obtained results revealed that the ASM3 model, which was calibrated after adding the Arrhenius equation into consideration, provided strong correlations with the analytical results of chemical oxygen demand (COD), total suspended solids (TSS), mixed liquor volatile suspended solids (MLVSS) and total suspended solids in the return activated sludge flow (TSS in RAS) concentrations. The values of modelled effluent COD and TSS are very close to those corresponding real values of the treated wastewater by a difference of between 0.5% and 1.5%. Thus, this model becomes successful in representing oily industrial wastewater treatment as a new trend added to the traditional modelling of sewage treatment.     

低能量超声波辐射提高好氧污泥活性研究

以功率密度为50W／L的低能量超声波对活性污泥进行不同时间的辐射，在辐射停止时及停止后的一段时间内分别测定了污泥的OUR、蛋白酶活性和脱氢酶活性。结果表明，适当的低能量超声波辐射可显著提高污泥活性，其中辐射10min后的污泥OUR值较作用前提高了129％，蛋白酶活性提高了23．7％，脱氢酶活性提高了24．6％。若超声波辐射时间过短，则辐射停止后对污泥生物代谢和酶活性的强化效应会很快消失；当辐射时间适当时，在辐射停止后污泥活性仍处在较高水平且持续时间较长；当超声波辐射时间超过一定限度后会导致污泥活性下降。     

Assessment of activated sludge viability with flow cytometry

The aim of the study was to evaluate the applicability of fluorescent dyes and multiparameter flow cytometry for the rapid and direct viability/activity assessment of activated sludge samples taken from wastewater treatment plants. Viability and activity of the biomass were estimated respectively through cellular membrane integrity, staining with SYBR Green I and Propidium Iodide, and through fluorogenic dyes capable of detecting enzymatic activity, as FDA and BCECF-AM. A procedure has been developed to disaggregate sludge flocs before dyes staining and cytometric analysis. The developed procedure allows a high recovery of bacteria with good accuracy and repeatability, and minimize the damage of the cells suspension obtained from the disaggregation of the flocs. These measurements were applied to estimate the two main parameters required to define the biological activated sludge process: the endogenous decay rate and the specific growth rate in exponential phase with high F/M ratio. Oxygen utilization rate measurements (OUR) were conducted to conventionally monitor the activity of the biomass. The preliminary data are encouraging and support the possibility to investigate bacteria dynamics on wastewater treatment plants.     

OUR和INT-ETS表征污泥活性的比较

为探寻能快速评价重金属对污泥活性影响的方法,开展了抑制污泥OUR和INT-ETS活性的试验研究.结果表明,OUR反映重金属毒性作用的灵敏性高于INT-ETS;当活性污泥受到重金属污染后,其OUR降低情况与COD的相似,而INT-ETS活性受到的抑制作用相对较小;各重金属离子表现出了不同的毒性作用,以OUR为评价参数时毒性顺序为:Hg2 ＞Cu2 ＞Ag ＞Cd2 ＞Zn2 ＞Ni2 ＞Pb2 ,以INT-ETS活性为评价参数时则为:Hg2 ＞Ag ＞Cu2 ＞Cd2 ＞Zn2 ＞Ni2 ＞Pb2 .OUR是表征污泥活性受重金属影响的较佳参数.     

Bacterial growth kinetics in the completely mixed activated sludge treatment of fellmongery effluent

Fellmongery effluent was successfully treated (± 85% OA reduction) in a laboratory scale completely mixed activated sludge (CMAS) reactor with sludge recycle and controlled wasting. Varying the sludge age was found to have a significant effect on effluent quality. A mathematical model useful in the design and operation of effluent treatment plants was used to describe microbial growth in the treatment process. In the development of the model it is shown how a clear distinction must be made between the volatile suspended solids and the active volatile suspended solids for the model to accurately describe microbial growth kinetics.     

Active biomass in activated sludge: Comparison of respirometry with catalase activity measured using an on-line monitor

On-line measurements of the activity of activated sludge biomass may allow more efficient operation of treatment plants. A novel monitor for activity which can be used on-line follows oxygen evolution from hydrogen peroxide by catalase activity in activated sludge. Results from this monitor were compared with assays of oxygen uptake rate (OUR) by respirometry. Samples from the five activated sludge plants were assayed and showed, as expected, that the mixed liquor suspended solids (MLSS) and volatile suspended solids (VSS) levels were a poor measure of the activity of the sample determined by OUR. However, the activity of the biomass determined by the catalase activity biomass monitor correlated well with the respiration rate. This monitor should provide a simple and robust alternative to OUR measurements in activated sludge plants.     

Decay processes of nitrifying bacteria in biological wastewater treatment systems

A knowledge of the decay rates of autotrophic bacteria is important for reliably modeling nitrification in activated sludge plants. The introduction of nitrite to activated sludge models also requires the separate determination of the kinetics of ammonia- and nitrite-oxidizing bacteria. Batch experiments were carried out in order to study the effects of different oxidiation-reduction potential conditions and membrane separation on the separate decay of these bacteria. It was found that decay is negligible in both cases under anoxic conditions. No significant differences were detected between the membrane and conventional activated sludge. The aerobic decay of these two types of bacteria did not diverge significantly either. However, the measured loss of autotrophic activity was only partly explained by the endogenous respiration concept as incorporated in activated sludge model no. 3 (ASM3). In contrast to nitrite-oxidizing bacteria, ammonia-oxidizing bacteria needed 1-2 h after substrate addition to reach their maximum growth rate measured as a maximum OUR. This pattern could be successfully modeled using the ASM3 extended by enzyme kinetics. The significance of these findings on wastewater treatment is discussed on the basis of the extended ASM3.     

基于常规运行数据的污水处理厂污泥量核算方法

为了满足第一次全国污染源普查和日常环境管理中污泥量申报数据审核的技术需求,在分析污泥产生机理与来源构成的基础上,以SS去除量、COD去除量、絮凝剂使用量以及混合液f值等为自变量,建立了基于常规运行数据的污水处理厂污泥量核算方法。通过模拟试验、典型实测和理论推算等方法,分别测算了相应的化学污泥产率系数、挥发性污泥产率系数和污泥消化减量系数。典型污水处理厂验证结果表明,该方法的核算误差基本在±30%以内,具有较好的准确性。     

A new interpretation of endogenous respiration profiles for the evaluation of the endogenous decay rate of heterotrophic biomass in activated sludge

In current activated sludge models aerobic degradation, resulting in loss of activity and mass of activated sludge is expressed with only one process called decay. The kinetics of this process is regarded to be first order and constant with respect to the loading conditions. In this work twelve aerobic digestion batch experiments were conducted for the activated sludge of seven different water resource recovery facilities (WRRFs). An analysis of the obtained respirograms shows three clearly distinguishable phases. The first phase is assumed to be due to the degradation of stored material (X_STOR) and active biomass simultaneously. The second phase is exclusively due to the degradation of active biomass that is regarded to consist mainly of ordinary heterotrophic biomass (X_OHO). The first order decay rate is slower than the degradation rate in phase 1 and varies between samples. The decay rate correlates with the activity of the activated sludge expressed as the ratio of initial heterotrophic OUR and the initial organic fraction X_ORG of the activated sludge. This second phase was detectable until day 5 of most of the experiments. After that time within phase 3 the OUR decrease slows down and the OUR even increased for short intervals. This behaviour is thought to be due to the activity of higher organisms and the adaptation of microorganisms to starvation.     

A titrimetric respirometer measuring the nitrifiable nitrogen in wastewater using insensor-experiment

Measurement of nitrifiable nitrogen contained in wastewater by combining the existing respirometric and titrimetric principles is reported. During an in-sensor-experiment using nitrifying activated sludge, both the dissolved oxygen (DO) and pH in the mixed liquor were measured, and the pH was controlled at a set-point through titration of base or acid. A combination of the oxygen uptake rate (OUR), which was obtained from the measured DO signal, and the titration data allowed calculation of the nitrifiable nitrogen and the short-term biological oxygen demand (BOD) of the wastewater sample that was initially added to the sludge. The calculation was based solely on stoichiometric relationships. The approach was preliminarily tested with two types of wastewaters using a prototype sensor. Good correlation was obtained.     

Effect of chlorine on filamentous microorganisms present in activated sludge as evaluated by respirometry and INT-dehydrogenase activity

Activated sludge technology is more used than any other for biological treatment of wastewater. However, filamentous bulking is a very common problem in activated sludge plants, chlorine being the chemical agent normally used to control it. In this work the effect of chlorine on microorganisms present in activated sludge flocs was assessed by a respirometric technique (oxygen uptake rate, OUR) and by the INT-dehydrogenase activity test (DHA) measured by two techniques: spectrophotometry (DHA(a)) and image analysis (DHA(i)). Both DHA tests were optimized and correlated with the respirometric technique (OUR) using pure cultures of a filamentous microorganism (Sphaerotilus natans) under chlorine inhibition. Using these correlations the tested methods were applied to determine the action of chlorine on respiratory activity in activated sludge. The OUR and the DHA(a) quantifies the action of chlorine on the total respiratory activity (RA) of flocs (filamentous and floc-forming bacteria); in contrast, the DHA(i) test evaluates specific action of chlorine on the RA of filamentous microorganisms. In activated sludge flocs containing filamentous microorganisms, a chlorine dose of 4.75 mgCl(2) (gVSS)(-1) with a contact time of 20 min reduced about 80% of the RA of filamentous bacteria while affecting only 50-60% of the total RA of flocs. Besides, a chlorine dose of 7.9 mgCl(2) (gVSS)(-1) produced the total respiratory inactivation of filamentous microorganisms after 10 min contact, however, with this dose the total RA of activated sludge flocs was reduced only about 45-65%; controlling filamentous bulking without affecting too much floc-forming bacteria. At the tested chlorine concentrations the inhibition of filamentous microorganisms was higher than in the whole activated sludge. Although floc-forming microorganisms were demonstrated to be more susceptible to chlorine than filamentous in pure cultures, results obtained in the present work confirmed that it is the location of the filamentous microorganisms in the flocs and the presence of extracellular polymer substances which largely determines their higher susceptibility to chlorine; consequently this feature plays a critical role in bulking control.     

超声强化污泥释磷及MAP法磷回收优化研究

为提高剩余污泥的磷释放与回收效果,采用超声强化EDTA-厌氧处理后的剩余污泥释磷,并以鸟粪石(MAP)结晶法回收上清液中的磷,探究超声对磷释放的影响,同时确定了最佳超声工作参数,采用响应曲面法构建MAP法磷回收的二次多项式模型并验证了模型的适用性。结果表明,超声可以强化污泥中磷的释放,最佳超声工作参数如下:声能密度为1.0 W/m L、超声时间为40 min,在最佳工作参数下可向液相释放60%的TP,TP、PO34--P浓度分别达到未超声处理的1.6倍和1.4倍;经超声后污泥上清液中TP增加量与MLSS、MLVSS减少量呈正相关关系,每溶解1 mg的MLSS向上清液中释放0.010 1 mg的TP;磷回收的最优工艺条件:nMg/nP=2、pH值=9、搅拌时间为21 min,此时磷回收率为89.29%,回收的晶体产物主要成分是磷酸铵镁,其纯度为77.56%,且相比未超声,该条件下的回收量提高了30%。