复合混凝剂对MBR工艺中污泥性能的影响研究

为了缓解MBR工艺的膜污染,向MBR工艺中投加复合混凝剂,考察了复合混凝剂对污泥性能的影响.结果表明,投加复合混凝剂可降低污泥比阻,明显增大污泥絮体的平均粒径、降低其分形维数,且污泥的可溶性微生物产物(SMP)含量也明显下降,这样有利于增强污泥的沉降性能、降低膜滤饼层的污染、增强膜表面的透水性.     

Effect of PAC addition on sludge properties in an MBR treating high strength wastewater

This paper examines the sludge characteristics in a submerged membrane bioreactor (MBR) operated on a high strength wastewater from an alcohol distillery. Two membrane bioreactors, each with a 30 μm mesh filter, were investigated with and without addition of powdered activated carbon (PAC). Experiments were conducted with varying organic loading rates ranging from 3.4 to 6.9 kgCOD m⁻³ day⁻¹ and the specific oxygen uptake rate (SOUR), sludge volume index (SVI), mixed liquor suspended solids (MLSS), particle size and extracellular polymeric substances (EPS) were monitored over a 180 day period. Respirometric experiments did not show enhancement in microbial activity with PAC supplementation. Addition of PAC decreased the SVI thereby perceptibly improving sludge dewaterability. The sludge particle size, which increased with time, appeared to be independent of PAC addition but was influenced by the aeration intensity. PAC also did not affect the sludge EPS concentration; however, the EPS composition, in terms of protein/carbohydrate (polysaccharide) ratio was altered resulting in a high P/C ratio. FTIR analysis of the sludge samples indicated that the functional groups associated with the sludge polysaccharides appear to be involved in its interaction with PAC.     

一种基于流固耦合理论处理污泥池的工程方案研究

传统的污泥掩埋方式需要对原态污泥脱水,将其变为塑态或半塑态后,方可满足掩埋的施工要求,这种处理方案复杂、费用高,本文另辟蹊径,基于流固耦合理论,创造性地提出无需脱水、直接掩埋的方案—高强度薄膜和污泥体流固耦合承载的方案,具有造价低、施工快、安全可靠的优点。基于流固耦合数值计算模型,划分3种加载工况,进行数值仿真验证,计算表明:膜体和污泥池组成的流固耦合结构可以承受较大均布载荷,且膜体结构最大轴力主要出现在加载的过程中,均布加载完毕后,膜体结构受力趋于很小;膜体和污泥池组成的流固耦合结构最大变位出现在加载过程中,局部加载完毕后,结构变位趋于平衡;加载过程中,膜体结构最大受力出现在边界锚固点,且受力较大,最大可达350kN/m,膜体结构本身的强度以及边界牢固可靠的锚固至关重要。最后,通过理论和实践相结合,给出了工程案例。     

SMSBR中PAC对膜污染的防治作用

在SMSBR处理焦化废水的过程中，通过向反应器中投加粉末活性炭（PAC）进而形成生物活性炭（BAC）来实现对膜污染的防治，并通过对BAC污泥的终端过滤来反映其对膜污染的改善作用。试验结果表明，BAC污泥在终端过滤过程中，其相对通量的变化规律与普通活性污泥相同，但投加PAC后的膜通量明显提高。另外，在相同压力下普通活性污泥的通量衰减指数要远高于BAC污泥，而在相同PAC浓度下BAC污泥的通量衰减指数随压力的变化与普通活性污泥一样，未表现出一定的规律性。BAC污泥的阻力分布表明，沉积层阻力仍占有绝对优势（大于80％），并随压力的升高而增大，但与普通活性污泥相比该比例有明显下降，膜的固有阻力所占比例明显提高，体现了PAC对膜污染的防治作用。     

A comparative study of fouling-related properties of sludge from conventional and membrane enhanced biological phosphorus removal processes

The physical and biochemical properties of activated sludge mixed liquor, including floc size distribution, zeta potential, relative hydrophobicity, and bound and unbound (soluble) extracellular polymeric substances (EPS), were examined in this study to evaluate their relationship to membrane fouling. Mixed liquors from a membrane enhanced biological phosphorus removal (MEBPR) process and a conventional enhanced biological phosphorus removal (CEBPR) process were compared. It was found that the floc size distribution and the amount of soluble EPS in the mixed liquor were the most important properties that significantly influenced the fouling propensity of sludge. Contrary to the literature, the content of EPS bound in activated sludge flocs was not found to be directly associated with membrane fouling, and sludge surface properties such as zeta potential and relative hydrophobicity were not closely related to the observed differences in the fouling tendencies of the two types of sludge.     

A/O-MBR处理低浓度生活污水的试验研究

针对传统活性污泥法处理低浓度生活污水难度大的问题,采用缺氧-好氧膜生物反应器(A/O-MBR)处理该类污水,并考察了其处理效果.结果表明,在污泥浓度为4 000～6 000mg/L、HRT为19.2 h、好氧段溶解氧浓度为1.5～2.5 mg/L、污泥回流比为200%～300%的条件下,A/O-MBR对COD和氨氮的去除效果良好,平均去除率分别为92.2%和95.9%.在无排泥的情况下,系统连续运行近100d,出水水质稳定.     

Effect of temperature shocks on membrane fouling in membrane bioreactors

Temperature is known to influence the biological performance of conventional activated sludge systems. In membrane bioreactors (MBRs), temperature not only affects the bioconversion process but is also shown to have an effect on the membrane performance. Four phenomena are generally reported to explain the higher resistance for membrane filtration found at lower temperatures: (1) increased mixed liquor viscosity, reducing the shear stress generated by coarse bubbles, (2) intensified deflocculation, reducing biomass floc size and releasing EPS into the mixed liquor, (3) lower backtransport velocity and (4) reduced biodegradation of COD. Although the higher resistance at low temperatures has been reported in several papers, the relation with supernatant composition has not been investigated before. In this paper, the composition of the soluble fraction of the mixed liquor is related to membrane performance after exposing the sludge to temperature shocks. Flux step experiments were performed in an experimental system at 7, 15, and 25° Celsius with sludge that was continuously recirculated from a pilot-scale MBR. After correcting the permeate viscosity for temperature, higher membrane fouling rates were obtained for the lower temperature in combination with low fouling reversibility. The soluble fraction of the MBR mixed liquor was analysed for polysaccharides, proteins and submicron particle size distribution. At low temperature, a high polysaccharide concentration was found in the experimental system as compared to the MBR pilot. Upon decreasing the temperature of the mixed liquor, a shift was found in particle size towards smaller particles. These results show that the release of polysaccharides and/or submicron particles from sludge flocs could explain the increased membrane fouling at low temperatures.     

Effect of low ORP in anoxic sludge zone on excess sludge production in oxic-settling-anoxic activated sludge process

This paper studied the effect of oxidation-reduction potential (ORP) in the anoxic sludge zone on the excess sludge production in the oxic-settling-anoxic process (OSA process), a modified activated sludge process. Two pilot-scale activated sludge systems were employed in this study: (1) an OSA process that was modified from a conventional activated sludge process by inserting a sludge holding tank or namely the "anoxic" tank in the sludge return line; and (2) a conventional process used as the reference system. Each was composed of a membrane bioreactor to serve the aeration tank and solid/liquid separator. Both systems were operated with synthetic wastewater for 9 months. During the operation, the OSA system was operated with different ORP levels (+100 to -250 mV) in its anoxic tank. It has been confirmed that the OSA system produced much less excess sludge than the reference system. A lower ORP level than +100 mV in the anoxic tank is in favor of the excess sludge reduction. When the ORP level decreased from +100 to -250 mV the sludge reduction efficiency was increased from 23% to 58%. It has also been found that the OSA system performed better than the reference system with respect to the chemical oxygen demand removal efficiency and sludge settleability. The OSA process may present a potential low-cost solution to the excess sludge problem in an activated sludge process because addition of a sludge holding tank is only needed.     

复合膜生物反应器处理生活污水的特性

通过对投加填料的膜生物反应器处理生活污水的特性进行了系统的研究 ,研究结果表明投加填料的膜生物反应器的上清液及系统出水COD浓度低于不加填料的 ;反应器稳定运行后膜的通透性随运行时间的延长而缓慢下降 ,且较投加填料前明显增大 ;反应器中 ,附着相和悬浮相污泥共存 ,并以附着生长的微生物为主 ,悬浮污泥浓度低可以有效的减缓膜过滤阻力的上升和膜的堵塞 .维持反应器内总污泥浓度较高的条件下 ,使随混合液进入膜分离的悬浮污泥量保持很低 ,减少了其对膜的通透能力的影响 .     

Hydraulic effects on sludge accumulation on membrane surface in crossflow filtration

Membrane filtration technology for application of wastewater treatment has been developing recently. In the application to wastewater treatment, it is major concern to remove cake layer on membrane surface effectively with crossflow shear stress. Hydraulic effect of sludge accumulation process on membrane surface in bubble and non-bubble driven crossflow filtration was studied. Maximum sludge accumulation. sludge accumulation rate, and lag phase were introduced to describe sludge accumulation process, and the effects of hydraulic conditions were clarified experimentally. Maximum sludge accumulation and sludge accumulation rate were dependent on aeration intensity, and were less depend on flow channel width and MLSS concentration. Their tendencies were explained by shear stress. Shear stress was thought to be the major hydraulic factor that influences them. Lag phase was dependent on aeration intensity, flow channel width, and MLSS concentration. A non-dimensional equation was proposed to explain dependencies of flow channel width based on consideration of hydraulic behavior of MLSS particles and shear stress.     

Physical characteristics of the sludge in a complete retention membrane bioreactor

Sludge physical characteristics play an important role in the operation of membrane bioreactors (MBR) due to their influence on filtration and their effects on handling of excess sludge. These systems are designed to maintain high solid concentrations, thus limiting sludge production and the related operational costs of the process. In this study, the sludge from a bench scale MBR operated for about 1 year with complete solid retention was investigated to assess its physical and rheological properties. Concentrations of mixed liquor suspended solids (MLSS) up to 24 gTSSL(-1) affected the diluted sludge volume index (DSVI), the capillary suction time (CST), the specific resistance to filtration (SRF) and the compressibility (s). The MBR sludge displayed similar dewatering properties of conventional waste activated sludge, suggesting that the upgrade of wastewater treatment plants with the MBR technology would not affect the behaviour of the dewatering equipment. The apparent viscosity was expressed as a function of the MLSS and the experimental data were interpreted by comparing different models. Ostwald model was chosen, and two equations for viscosity were proposed. The thixotropy of MBR sludge was also evaluated by measuring the reduced hysteresis area (rHa) and relating this parameter to the characteristics of the sludge. The evaluation of energy consumption for mixing evidenced that, under the tested conditions, the increase of solid concentration from 3 to 30 gTSSL(-1) resulted in a limited increase of energy requirements (25-30%).     

Influence of operational conditions on the performance of a mesh filter activated sludge process

Recently, a new type of wastewater treatment system became the focus of scientific research, the mesh filter activated sludge system. It is a modification of the membrane bioreactor where a membrane filtration process serves to separate the sludge from the purified effluent. The difference is that a mesh filter is used instead of the membrane. Due to the much larger pore size of the mesh, the effluent is not of the same excellent quality as with membrane bioreactors. Nevertheless, it still resembles the quality of the now most widely used standard treatment system, where settling tanks are used to retain the activated sludge. At the same time, the new system features all the other advantages of membrane bioreactors including elevated sludge concentrations resulting in decreased volumina of basins and complete substitution of the settling tank. Therefore, this process presents a potential future alternative where a small footprint of the plant is required. However, so far only a few preliminary studies on this innovative process type have been done. In this paper, the effects of suspended solids concentration, flux rate as well as aeration rate on the effluent quality are discussed. Furthermore, the characteristic of the sludge floc was identified as a factor of vital importance. Therefore, another influencing parameter, the food to microorganism (F/M) ratio, which is known to have a significant effect on floc characteristics, was studied. The main result demonstrated that the process was very effective under most of the operation conditions. The suspended solids concentration in the effluent was below 12 mg l(-1), the average COD in the effluent was between 24 and 45 mg l(-1) and the BOD(5) was lower than 5 mg l(-1). High flux rates of up to 150 l m(-2)h(-1) were also achieved.     

Comparison of sludge characteristics and performance of a submerged membrane bioreactor and an activated sludge process at high solids retention time

This work aims to compare biomass structure and performance of a submerged membrane bioreactor (SMBR) and an activated sludge process (ASP) treating the same domestic wastewater. The influence of the separation technique (membrane filtration or settling) and operation at high sludge-retention time (SRT) were investigated. Over the entire range of SRT (10-110 days), the SMBR achieved very good organic removal efficiencies, ranging from 90.8+/-0.2% to 94.2+/-1.6% based on total COD (TCOD), whereas those of ASP were between 87.4+/-1.8% and 90.3+/-0.8%. The contribution of the membrane in the increase in performance was due to total suspended solid retention and also partly due to retention of proteins and polysaccharides of the sludge supernatant. No significant difference in excess sludge production was observed between the two processes operated at the same SRT, but sludge production in SMBR decreased from 0.31 to 0.13 g(VSS)g(COD)(-1) as SRT increased from 9 to 110 days. The difference in sludge characteristics and performance was especially pronounced as SRT increased, resulting in deterioration of sludge settleability and effluent quality of the ASP (filamentous bacteria, increase of protein and polysaccharide release). Membrane filtration induced accumulation of soluble and colloidal proteins and polysaccharides which were progressively degraded in the supernatant as the SRT increased. At similar SRT, no significant difference was observed in the amount of extractable exocellular polymeric substances (bound EPS) from ASP and SMBR sludge. However as the SRT increased, the total specific amount of bound EPS in flocs decreased and the ratio proteins/polysaccharides also decreased. Concomitantly, laser diffraction analysis, microscopic observations, turbidity and DSVI measurement showed that the SRT increase induced significant modifications in sludge morphology in SMBR: decrease in floc size, densification of aggregates, and development of non-flocculating organisms.     

Effects of chemical sludge disintegration on the performances of wastewater treatment by membrane bioreactor

A new wastewater treatment process combining a membrane bioreactor (MBR) with chemical sludge disintegration was tested in bench scale experiments. In particular, the effects of the disintegration treatment on the excess sludge production in MBR were investigated. Two MBRs were operated. In one reactor, a part of the mixed liquor was treated with NaOH and ozone gas consecutively and was returned to the bioreactor. The flow rate of the sludge disintegration stream was 1.5% of the influent flow rate. During the 200 days of operation, the MLSS level in the bioreactor with the disintegration treatment was maintained relatively constant at the range of 10,000-11,000 mg/L while it increased steadily up to 25,000 mg/L in the absence of the treatment. In the MBR with the sludge disintegration, relatively constant transmembrane pressures (TMPs) could be maintained for more than 6 months while the MBR without disintegration showed an abrupt increase of TMP in the later phase of the operation. In conclusion, a complete control of excess sludge production in the membrane-coupled bioreactor was possible without significant deterioration of the treated water quality and membrane performances.     

Novel membrane bioreactor (MBR) coupled with a nonwoven fabric filter for household wastewater treatment

Conventional and modified membrane bioreactors (MBRs) are increasingly used in small-scale wastewater treatment. However, their widespread applications are hindered by their relatively high cost and operational complexity. In this study, we investigate a new concept of wastewater treatment using a nonwoven fabric filter bag (NFFB) as the membrane bioreactor. Activated sludge is charged in the nonwoven fabric filter bag and membrane filtration via the fabric is achieved under gravity flow without a suction pump. This study found that the biofilm layer formed inside the NFFB achieved 10 mg/L of suspended solids in the permeate within 20 min of initial operation. The dynamic biofilter layer showed good filterability and the specific membrane resistance consisted of 0.3-1.9 × 10¹² m/kg. Due to the low F/M ratio (0.04-0.10 kg BOD₅/m³/d) and the resultant low sludge yield, the reactor was operated without forming excess sludge. Although the reactor provided aerobic conditions, denitrification occurred in the biofilm layer to recover the alkalinity, thereby eliminating the need to supplement the alkalinity. This study indicates that the NFFB system provides a high potential of effective wastewater treatment with simple operation at reduced cost, and hence offer an attractive solution for widespread use in rural and sparsely populated areas.     

Correlation of EPS content in activated sludge at different sludge retention times with membrane fouling phenomena

In this study, activated sludge characteristics were studied with regard to membrane fouling in membrane bioreactors (MBRs) for two pilot plants and one full-scale plant treating municipal wastewater. For the full-scale MBR, concentrations of extracellular polymeric substances (EPS) bound to sludge flocs were shown to have seasonal variations from as low as 17mgg(-1) dry matter (DM) in summer up to 51mg(gDM)(-1) in winter, which correlated with an increased occurrence of filamentous bacteria in the colder season. Therefore, it was investigated at pilot-scale MBRs with different sludge retention times (SRTs) whether different EPS contents and corresponding sludge properties influence membrane fouling. Activated sludge from the pilot MBR with low SRT (23d) was found to have worse filterability, settleability and dewaterability. Photometric analysis of EPS extracts as well as LC-OCD measurements showed that it contained significantly higher concentrations of floc-bound EPS than sludge at higher SRT (40d) The formation of fouling layers on the membranes, characterised by SEM-EDX as well as photometric analysis of EPS extracts, was more distinct at lower SRT where concentrations of deposited EPS were 40-fold higher for proteins and 5-fold higher for carbohydrates compared with the membrane at higher SRT. Floc-bound EPS and metals were suggested to play a role in the fouling process at the full-scale MBR and this was confirmed by the pilot-scale study. However, despite the different sludge properties, the permeability of membranes was found to be similar.     

粉末活性炭/污泥回流工艺强化膜前预处理的研究

采用粉末活性炭(PAC)吸附/混凝沉淀/浸没式超滤膜组合工艺处理苏州市某河水,考察了PAC/污泥回流工艺对膜前预处理的强化效果及对膜污染的影响,并与常规混凝沉淀、污泥回流强化混凝沉淀、PAC吸附/混凝沉淀等3种预处理工艺进行了对比。结果表明,PAC/污泥回流强化预处理工艺对浊度、DOC、UV254和THMFP的去除率分别为80.2%、47.5%、42.3%和52.3%,均比其他预处理工艺的高,对MW30 ku和MW1 ku有机物的去除效果明显。PAC/污泥回流强化预处理和超滤膜组合工艺对浊度、DOC、UV254和THMFP的去除率分别可达到99.2%、54.1%、47.2%和60.2%;经过15 d的运行,超滤膜的跨膜压差基本保持稳定,而其他预处理工艺虽能在一定程度上减轻膜污染,但无法避免不可逆膜污染的发生。     

Influence of residual organic macromolecules produced in biological wastewater treatment processes on removal of pharmaceuticals by NF/RO membranes

Increasing attention has been given to pollution of the water environment by pharmaceutical compounds discharged from wastewater treatment plants. High-pressure driven membranes such as a nanofiltration (NF) membrane and a reverse osmosis (RO) membrane are considered to be effective for control of pharmaceuticals in wastewater treatment. In practical applications of NF/RO membranes to municipal wastewater treatment, feed water for the membranes always contains organic macromolecules at concentrations of up to 10 mg-TOC/L, which are mainly composed of soluble microbial products (SMPs) produced during biological wastewater treatment such as an activated sludge process. In this study, influence of these organic macromolecules on removal of six pharmaceuticals by NF/RO membranes (UTC-60 and LF10) was investigated. Two types of biological treatment (conventional activated sludge process followed by media filtration (i.e., tertiary treatment) and treatment with a membrane bioreactor (MBR)) were examined as pretreatments for NF/RO membranes in this study. In the filtration tests with wastewater effluents, removal of the pharmaceuticals was higher than that seen with deionized pure water spiked with the pharmaceuticals. The increase was significant in the case of the NF membrane. Both alteration of membrane surface properties due to membrane fouling and association of the pharmaceuticals with organic macromolecules contributed to the increase in removal of pharmaceuticals by the membranes. Characteristics of the organic macromolecules contained in the wastewater effluents differed depending on the type of treatment, implying that removal of pharmaceuticals by NF/RO membranes is influenced by the type of pretreatment employed.     

The influence of sludge age on heavy metal removal in the activated sludge process

In a laboratory simulation of the activated sludge process ten heavy metals were added continuously to the system which was allowed to equilibrate at six sludge ages between 3 and 18d. Cobalt, manganese and molybdenum removals were poor and were unaffected by changes in the sludge age. The highest removal efficiencies for the other metals occurred at the 15d sludge age. Chromium (trivalent) and cadmium had the highest removal efficiencies, typically greater than 50%. The behaviour of the majority of the metals which were removed to a significant extent was related to one of the parameters influenced by sludge age, i.e. mixed liquor suspended solids, effluent suspended solids or effluent chemical oxygen demand. The metals which were poorly removed showed little affinity for the activated sludge, while most metals exhibited maximum specific uptake by the mixed liquor at a sludge age of 9–12d. However, the affinity of silver for the mixed liquor continued to increase as the sludge age increased to 18d. An affinity series, based on an arbitrary measure of the specific accumulation of metals by the mixed liquor, indicated that chromium, cadmium and silver were most readily adsorbed by the activated sludge.     

Effect of feeding pattern and storage on the sludge settleability under aerobic conditions

The selection of filamentous bacteria is often assumed to be associated with specific microbial properties such as growth rate, substrate uptake rate, substrate affinity and potential for substrate storage. In this study we aimed to verify some of these factors. Sequencing batch reactor (SBR) systems were used to scale-down aerobic activated sludge systems with an aerobic selector. Adding acetate in different aerobic feeding periods allowed us to simulate a variable relative size of aerobic selector with different bulk liquid substrate concentrations. The experiments showed that as expected, the aerobic fill time ratio (FTR(ox)) and the corresponding feast period, which can be assumed similar to contact time in an aerobic selector, had a strong effect on the sludge settleability. Promoting a strong substrate gradient in the SBR (FTR(ox)<5.4%) resulted in good sludge settleability (SVI<120mLg(-1)). Whenever acetate was added in a limiting rate (FTR(ox)>6.2%), a condition in which the acetate concentration in the reactor was always very low, the sludge settleability decreased (SVI>150mLg(-1)). Sludge settleability could be improved by changing the feeding strategy to a pulse feed. The maximum specific acetate uptake rate and poly beta-hydroxybutyrate (PHB) production rate of bad settling sludge, including bulking sludge, was similar to well-settling sludge, which is not in accordance with the general assumptions that well settling sludge have a higher maximal substrate uptake rate and better storage capacities. An alternative hypothesis for the development of filamentous structures in biological flocs has been formulated. It is hypothesized that bulking sludge originates from the presence of substrate gradients in sludge aggregates. Whereas at low bulk liquid substrate concentration filamentous bacteria give easier access to the substrate at the outside of the flocs and thereby proliferate, at high bulk liquid substrate concentration there is no substrate advantage for filamentous organisms and smooth bacterial structures predominate. In this hypothesis there is no need for an intrinsic difference in kinetic parameters between floc and filamentous bacteria. Where presence of filamentous bacteria is related to process conditions, the presence of a specific filament is likely due to presence of a specific limiting substrate.