好氧颗粒污泥与絮体活性污泥的竞争试验研究

采用在序批式反应器中培养50 d的好氧颗粒污泥与同期反应器排出的絮体污泥,在高有机负荷下曝气4 h,颗粒污泥和絮体污泥MLSS较初始时分别增加了67.8%和58.5%,单位体积混合液中颗粒污泥和絮体污泥的个数分别增加了15.4%和4.8%。颗粒污泥和絮体污泥的粒径分布在4 h试验过程中处于动态稳定状态,基本保持不变。曝气4 h后颗粒污泥和絮体污泥平均粒重分别增加45.4%和51.4%,可以看出在对有机底物的竞争中,与絮体污泥相比较,颗粒污泥由于具有较高的活性而占有优势,颗粒污泥的增长速率大于絮体污泥,絮体污泥和颗粒污泥的密度均有明显增长,但颗粒污泥平均粒重增加比例小于絮体污泥。     

Reynolds number-dependent permeability of wastewater sludge flocs

Most theoretical models assume constant permeability of wastewater sludge floc. This work shows that, at creeping flow limit with small intrafloc Reynolds number, the permeability of floc can not only be affected by floc structure, but also by the external flow condition. The three-dimensional structure of flocs using the fluorescence in situ hybridization (FISH) and the confocal laser scanning microscope (CLSM) was firstly probed. Then, the volumetric grid models for sludge flocs were constructed. We noted that the floc permeability could keep unchanged, increased, or decreased at increased Reynolds number (Re). Flow redistribution among channels of various sizes contributes to the noted Re-dependent permeability of flocs.     

Population balance modelling of activated sludge flocculation: Investigating the size dependence of aggregation, breakage and collision efficiency

This paper describes the application of population balance models to activated sludge flocculation. It presents the development and selection of appropriate expressions for aggregation and breakage mechanisms within the population balance framework to describe the evolution of mean size and mass distribution of flocs under shear-induced conditions. To describe the flocculation process, 16 models with different size dependent aggregation and breakage expressions were compared and the kinetic parameters of aggregation rate constant and selection rate constant were extracted by fitting each model to the experimental data. Of the 16 models, the shear-induced aggregation and size-dependent selection model was found to best describe the experimental data, however there were some discrepancies between the model and experimental results at long experimental times. A size dependent collision efficiency was introduced into the aggregation expression and this improved the fitting of the model with the experimental data. However, the relationship between the kinetic parameters and shear rate did not follow expected physical relationships. Further improvements to the model were made by setting the aggregation rate constant proportional to shear rate and the selection rate size independent whilst still including the size-dependent collision efficiency. The aggregation rate constant, selection rate constant and critical size were extracted by fitting the model to the experimental data. This model was able to follow the change in mean size and evolution of mass and was used to predict other experimental data successfully. The modelling results indicated that the population balance model is a useful tool to describe the dynamics of activated sludge flocculation.     

Characterization of synthetic and activated sludge and conditioning with cationic polyelectrolytes

This study investigates the effect of cationic polyelectrolytes on the final properties of synthetic and activated sludge. Synthetic sludge was prepared according to established procedures. Activated sludge was produced in a labscale, continuous-flow reactor which was fed with live activated sludge from a waste-water treatment plant. Capillary suction time (CST) was used to evaluate the sludge dewatering behaviour. The results from experiments indicated that the cationic polyelectrolytes had a critical effect on sludge dewatering, and made an improvement in the final properties of sludge. The two types of sludge have very similar dewatering characteristics after cationic polymer conditioning. The development of synthetic sludge is suggested also to be a possible surrogate for studying the final properties of activated sludge.     

The relationship between cation ions and polysaccharide on the floc formation of synthetic and activated sludge

This study has investigated in a comparative fashion the effect of cation ions and polysaccharide on the floc formation of both synthetic and activated sludge. Synthetic sludge was prepared according to established procedures; activated sludge was produced in a lab-scale, continuous-flow reactor which was fed with live activated sludge from a wastewater treatment plant. The results from experiments indicate that cation ions and polysaccharide could influence sludge floc formation. The relationship between polysaccharide concentration and cation ions concentration was examined at laboratory scale during flocculation with both synthetic and activated sludge; an increase in feed cation ions concentration led to a decrease in final polysaccharide concentration in the supernatant. An increase in cation ions concentration in the feed to the reactors was also associated with an increase in the bound biopolymer concentration. The changes in the bound biopolymer were explained according to the cation bridging model. Synthetic and activated sludge behave very similarly in terms of their characteristics and synthetic sludge can be used as a surrogate in activated sludge studies. The results of this work also indicate that the formation of cation-polymer complexes and polymer gelation are amongst the most important mechanisms for sludge coagulation-flocculation, and offer a means for optimisation of the activated sludge process.     

Modelling the electro-osmotically enhanced pressure dewatering of activated sludge

The mechanical dewatering of biological materials, such as activated sludge, is troublesome due to their high compressibility. The dewatering can be improved drastically by the use of electro-osmosis, a technique in which a direct current electric field is applied to the filter cake, inducing an electro-kinetic displacement of the liquid phase. In this article, a model is presented which describes this process for a one-dimensional, one-sided filter press. The model starts from two existing models, each describing a part of the process [Iwata, M., Igami, H., Murase, T., 1991. Analysis of electroosmotic dewatering. Journal of Chemical Engineering of Japan 24(1), 45-50; Sørensen, P.B., Moldrup, P., Hansem, J.A., 1996. Filtration and expression of compressible cakes. Chemical Engineering Science 51(6), 967-979]. A robust solution scheme for the basic flux and continuity equations is used to describe filtration and expression. Regarding the electro-osmosis, an adapted form of the Darcy equation, expressing electro-osmotic induced flow as well as pressure induced flow, is integrated into the former solution scheme. This permits the simulation of the overall process using a single model. Validation of the model revealed that the experimental piston height during dewatering can be described accurately provided that temperature effects are taken into account.     

Flotation efficiency of activated sludge flocs using population balance model in dissolved air flotation

The activated sludge process is one of the most frequently used processes for biological wastewater treatment. Conventional gravity sedimentation (CGS), which is widely used as a secondary clarifier in activated sludge processes, has a routine problem due to floating tendency, called bulking, caused by filamentous microorganisms. Dissolved air flotation (DAF) has been applied as potential alternative to CGS as a secondary clarifier. A series of experiments were performed to measure physico-chemical characteristics and removal efficiency of activated sludge flocs. The removal efficiency of flocs corresponding in lag and exponential growth phases was lower, while that of flocs both in stationary and endogenous phases considerably increased. The rise velocity of floc/bubble agglomerates was calculated by using a population balance (PB) model explaining the distribution of floc/bubble agglomerates. The experimental results of flotation efficiency showed a similar tendency with the results predicted by PB model for the rise velocity and distribution of floc/bubble agglomerates. It was found from our study that the DAF process was very effective as a secondary clarifier in the activated sludge process.     

Comparison of the filtration characteristics between biological powdered activated carbon sludge and activated sludge in submerged membrane bioreactors

The filtration performances of submerged membrane bioreactors (SMBR) with and without the addition of powdered activated carbon (PAC) were investigated respectively under the same feed and operation conditions. A series of experiments were conducted to analyze near-critical flux, effect of air-scouring rate and time of stable filtration operation of both systems. The experimental results demonstrated that pronounced flux enhancement was achieved by adding 1.2 g/L PAC. The near-critical flux for the biological powdered activated carbon (BPAC) system was about 32% higher than that for the activated sludge (AS) system. Increasing the air-scouring rate led to a more significant flux improvement for the BPAC system compared to the AS system. Long-term operation indicated that, at constant flux, the TMP increasing rate of the BPAC system could be lagged and thus cause the extension of operating intervals about 1.8 times compared to the AS system. Quantitative calculations showed the total hydraulic resistance of the BPAC system was about 44% lower than that of the AS system, and this decrease was mainly caused by the reduction in cake resistance. Analyses were then made from various aspects such as floc size distribution and apparent viscosity of the mixed liquor to elucidate the major factors giving rise to different filtration characteristics.     

Study of saline wastewater influence on activated sludge flocs through automated image analysis

BACKGROUND: In activated sludge systems, sludge settling ability is considered a critical step in effluent quality and determinant of solid–liquid separation processes. However, few studies have reported the influence of saline wastewater on activated sludge. This work aims the evaluation of settling ability properties of microbial aggregates in a sequencing batch reactor treating saline wastewaters of up to 60 g L^?1 NaCl, by image analysis procedures. RESULTS: It was found that the sludge volume index (SVI) decreased with salt content up to 20 g L^?1, remaining somewhat stable above this value. Furthermore, it was found that between the first salt concentration (5 g L^?1) and 20 g L^?1 aggregates suffered a strong deflocculation phenomenon, leading to a heavy loss of aggregated biomass. Regarding SVI prediction ability, a good correlation coefficient of 0.991 between observed and predicted SVI values was attained. CONCLUSION: From this work the deflocculation of aggregated biomass with salt addition due to pinpoint floc formation, dispersed bacteria growth and protozoa absence could be established. With respect to SVI estimation, and despite the good correlation obtained, caution is advisable given the low number of SVI data points. Copyright © 2008 Society of Chemical Industry     

Membrane filtration characteristics in membrane-coupled activated sludge system - the effect of physiological states of activated sludge on membrane fouling

The effect of sludge physiology on membrane fouling was investigated in a membrane-coupled activated sludge (MCAS) system. A series of ultrafiltrations were performed to assess the flux behaviors according to foaming potential, solids retention time (SRT), growth phase and nutrient condition of the activated sludge. The foaming sludge showed greater flux decline than the non-foaming sludge. The extraordinary increase, that is, more than 100 times in membrane fouling for the foaming sludge, was attributed to the hydrophobic and waxy nature of the foaming sludge surface, which was confirmed by a comparison with relative hydrophobicity. Membrane fouling tendency was increased as SRT decreased. A greater flux decline was observed at the endogenous phase than at the log growth phase. The activated sludge acclimated to the nitrogen deficient substrates produced less extracellular polymeric substances (EPS) and exhibited higher flux than the control activated sludge. The quantitative measurements of EPS content in order to estimate the extent of membrane fouling in various activated sludges showed that, in any physiological states of activated sludge, the higher the content of EPS the activated sludge had, the greater the membrane fouling proceeded. The EPS content of activated sludge is suggested as a probable index for the membrane fouling in a MCAS system.     

Filterability of activated sludge in membrane bioreactors

The filterability of activated sludge is an important factor for the economical operation of membrane bioreactors (MBR). In the literature mainly investigations on sludge dewaterability in respect to further disposal are published. In this study, a procedure for determining filterability in a crossflow test cell is introduced. Its features are: no increase in sludge concentration during batch trials, crossflow conditions, and little impact on the sludge structure. The activated sludge filterability is given as the ratio of permeate flux after 40 min of operation to clear water flux. Sludge samples of eight different MBR and one conventional wastewater treatment plant (wwtp) have been examined and compared. Contrary to the literature, no impact of suspended solids (SS) concentration, sludge viscosity, or extractable extracellular polymer substances (EPS) concentration on the filterability was found. Instead, the composition of the liquid phase was found to effect most the filterability of activated sludge, a major influence being the concentration of suspended EPS: the higher the suspended EPS concentration, the lower the filtration index. Suspended EPS concentration increases with high mechanical stress in the MBR and high F/M ratios, if the treated wastewater contains considerable amounts of proteins or polysaccharides.     

An approach for modeling two-step denitrification in activated sludge systems

In the widely used Activated Sludge Models (ASMs) for biological wastewater treatment, denitrification is assumed as a single-step process, which is not true for some cases where a considerable amount of nitrite is build-up in system. This causes limitation to the application of ASMs. In this work, with a consideration of denitrification on both nitrite and nitrate, and an introduction of the simultaneous storage and growth concept, a two-step ASM3-based denitrification model is established. The sensitivity of the effluent chemical oxygen demand, and concentrations toward the stoichiometric and kinetic coefficients is analyzed. Model calibration is performed by comparing the measured and predicted values for model components. Thereafter, this model is evaluated with the experimental results of four different case studies on denitrification and compared with the original ASM3. The evaluation and comparison results demonstrate that the developed model is able to better and more mechanistically describe the denitrification process in the activated sludge systems.     

Kinetic modeling microbial storage process in activated sludge under anoxic conditions

A new kinetic model is developed to describe the microbial storage process under anoxic conditions in activated sludge. The accumulation of nitrite in denitrification is taken into account in this model. The formation of storage polymers under anoxic conditions is coupled with energy generation and anoxic respiration, and their formation rate is found to be proportional to the substrate utilization rate. The sensitivity of the nitrogen uptake rate toward the stoichiometric and kinetic coefficients of the established model is analyzed by using an “absolute-relative” sensitivity function implemented in software AQUASIM. Batch denitrifying experiments were conducted to calibrate and validate the established model. The model is compared with ASM1 and ASM3, the two commonly used activated sludge models. Results show that the kinetic model established in this work is able to better describe the microbial storage processes under anoxic conditions.     

Fouling control in activated sludge submerged hollow fiber membrane bioreactors

The goal of this study is to determine the impact of various operating factors on membrane fouling in activated sludge membrane bioreactor (MBR) process, typically used for water reclamation. In this process, ultrafiltration (UF) and microfiltration (MF) hollow fiber membranes, submerged in the bioreactor, provided a solid—liquid separation by replacing gravity settling. Activated sludge from a food wastewater treatment plant was inoculated to purify synthetic wastewater consisting of glucose and (NH₄)₂SO₄ as a source of carbon and nitrogen, respectively. The results clearly showed that membrane fouling, defined as permeate flux decline due to accumulation of substances within membrane pores and/or onto membrane surface, was greatly influenced by membrane type and module configuration. It was also found that the rate and extent of permeate flux decline increased with increasing suction pressure (or initial operating flux) and with decreasing air-scouring rate. The mixed liquor suspended solids (MLSS) concentrations, however, exhibited very little influence on permeate flux for the range of 3600-8400 mg/L. Another important finding of this investigation was that non-continuous membrane operation significantly improved membrane productivity. This observation can be explained by the enhanced back transport of foulants under pressure relaxation. During non-suction periods, the foulants not irreversibly attached to the membrane surface, diffused away from the membrane surface because of concentration gradient. Furthermore, the effectiveness of air scouring was greatly enhanced in the absence of transmembrane suction pressure, resulting in higher removal of foulants accumulated on the membrane surface. The use of intermittent suction operation may not be economically feasible at large-scale, but it may offer an effective fouling control means for small-scale MBR processes treating wastewaters with high fouling potential.     

Role of intermittent aeration in domestic wastewater treatment by submerged membrane activated sludge system

In this study, the treatment of domestic wastewater in a lab-scale submerged membrane activated sludge system (sMBR) was investigated under different aeration intervals. The COD concentration of the system effluent varied generally between 5 and 25 mg/l and the COD removal at the organic loads of 0.6-0.8 kg COD/m³.d was observed to be above 98%. The total phosphorus content of the filtrate was decreased to a level that was less than 1 mg/l under the aerobic conditions in which the aeration was continuously made. A dramatic increase in the total phosphorus content of filtrate was observed under the aerobic + anoxic conditions in which the aeration was made at differential intervals. The filtrate was free of suspended solid (SS) and total coliform bacteria and a percent removal of 100 was achieved in terms of these parameters. The influent turbidity removal was 97-99.8%. Generally, the removal of total Kjeldahl nitrogen (TKN) and ammonium nitrogen varied in the ranges of 87.8-99.1% and in the ranges of 89.4-99.8%, respectively. While the nitrate concentrations in the filtrate increased to 26.8 mg/l under the aerobic conditions, it was determined that this value was decreased to 2.4 mg/l under the aerobic + anoxic conditions.     

Model-evaluation of the erosion behavior of activated sludge under shear conditions using a chemical-equilibrium-based model

The primary particles would erode from the sludge surface under shear conditions. As the primary particles have significant effects on the solid–liquid separation process, the erosion behaviors of activated sludge in biological wastewater treatment processes under shear conditions were investigated using a chemical-equilibrium-based model. The equilibrium dispersed mass concentration of the primary particles in the sludge solution was found to nonlinearly increase with the solid content and shear intensity, and could be well described by the model. Compared with other sludge reported in literatures, the activated sludge used in this study was found to be more stable during the shear test, with a high equilibrium constant K⁰ of 30.2 and a low Gibbs’ free energy of adhesion (ΔG⁰) of −3.41 at a shear intensity of 800 s⁻¹. The two parameters could be used to evaluate the strength of the sludge. The negative value of ΔH indicates the energy demand for the erosion process. The low value of ΔH for the activated sludge used in this study indicates that the erosion process was more energy demanding and the erosion process was less shear dependent for the activated sludge used in this study.     

Characterizing activated sludge process effluent by particle size distribution, respirometry and modelling

The particle size distribution (PSD) of the effluent from a typical activated sludge process was measured. The relation between the particle size distribution (PSD), residual biomass and conventional suspended solids (SS) and turbidity of a typical activated sludge process effluent was established with the help of laser scattering, oxygen uptake rate (OUR) measurement and the IWA model analysis. The laser scattering technique is capable of measuring particles between 20 nm and 2000 µm. The final effluent also consists of residual biomass which is unsettled in the secondary settling tank (SST) and the amount of this residual biomass was estimated using OUR measurement and IWA model. The final effluent was found to be dominated by the particles of size 1-10 µm, the size range for most of the bacterial cells (Ekama et al. 1997). The results showed that the total number of particles was correlated to the amount of residual biomass. Correlation determining the relation between laser particle size monitoring results and SS/turbidity measurements was also found. The results showed that the particle monitoring was more sensitive than the SS/turbidity measurement and with further development and improved control, it can used for more complex and sensitive data.     

活性污泥与灭活污泥的吸附性能比较

用活性污泥制备灭活干污泥来与原活性污泥进行针对生活污水的吸附试验,比较两种污泥吸附能力的差别,分析生物作用对吸附的影响。发现温度对活性污泥的影响比对灭活污泥的影响大;两种污泥的吸附结果都能用伪一级和伪二级方程进行拟合;活性污泥比灭活污泥的吸附容量大,活性污泥和灭活污泥的最大吸附容量分别为101.01和35.46 mg/g。     

Model-based characterization of endogenous maintenance, cell death and predation processes of activated sludge in sequencing batch reactors

Maintenance, cell death and predation are endogenous processes of microorganisms and play an important role in governing the overall performance of biological wastewater treatment systems. However, in the previous studies on the activated sludge system, a widely used biological wastewater treatment process, the endogenous processes are summarized as a single process and the kinetics of all related processes are lumped into a single parameter set. In order to better understand the endogenous processes, efforts are made to quantify the maintenance, cell death and predation processes separately with both experimental and mathematical approaches in this work. A model-based analysis on endogenous processes of activated sludge is performed. Both oxygen uptake and biomass concentration gradually decrease with the increasing length of aerobic starvation. Model predictions are in accordance with experimental data. The active bacteria content is reduced to about 23% of the initial value after 10-day starvation, and the maintenance energy consumption rate under non-growth conditions is found to be about four times of that when the microbial growth is of its maximum level. The active microorganisms form the prey for the predator growth. The oxygen consumption related to the predation of active bacteria significantly contributes to the total oxygen consumption.