Activated Sludge Filtration Research Articles

Activated sludge filterability improvement by nitrifying bacteria abundance regulation in an adsorption membrane bioreactor (Ad-MBR)

Autotrophic nitrifying bacteria have its intrinsic properties including low EPS production, dense colonial structure and slow-growth rate, favoring the sludge filterability improvement. An adsorption-MBR (Ad-MBR) was developed to enrich nitrifier abundance in the MBR chamber by inlet C/N regulation, and its possible positive effect on sludge filterability and underlying mechanisms were investigated. By DNA extraction, PCR amplification and Illumina high-throughput pyrosequencing, the abundance of nitrifying bacteria was accurately quantified. More than 8.29% nitrifier abundance was achieved in Ad-MBR sludge, which was above three times of that in conventional MBR. Regulated C/N ratio and thereafter nitrifier abundance enrichment improved sludge filterability by altering sludge mixture and its supernatant properties, reflected by a good sludge settleability, a low supernatant viscosity and turbidity, a low supernatant organic substances concentration, and a small amount of strong hydrophobic fractional components, thus to profoundly improve sludge filterability and decelerate membrane fouling.

Impact of inflow conditions on activated sludge filterability and membrane bioreactor (MBR) operational performance

Operation and performance of membrane bioreactors (MBRs) for wastewater treatment is influenced by changes in activated sludge properties. Therefore, understanding of the factors influencing sludge filterability is of major importance for efficient operation of MBR installations. This paper assesses the impact of the influent characteristics on activated sludge filterability and treatment performance of full-scale MBRs. The full-scale MBRs were closely monitored both in summer and winter. The measurement campaign, consisting of activated sludge filterability tests and physicochemical analyses, is supplemented with operational performance data evaluation of the various full-scale plants. Based on these data, it is shown that an undesired and refractory composition of incoming wastewater, hydraulic and/or organic load shocks, as well as abrupt temperature changes of the influent, lead to operational problems and affect sludge filterability.

Quantitative evaluation of fouling resistance of PVDF/PMMA-g-PEO polymer blend membranes for membrane bioreactor

Fouling resistance of various kinds of membrane materials including blends of poly(vinylidene difluoride) (PVDF) and copolymer of methyl methacrylate (MMA) and poly(ethylene glycol) methyl ether methacrylate (PVDF/PMMA-g-PEO) was quantitatively evaluated by measuring the amount of model fouling compounds adsorbed on the surface of membrane materials using a surface plasmon resonance (SPR) sensor. The order of the amount of adsorption in the adsorption tests negatively correlated with hydrophilicities of membrane materials. PVDF/PMMA-g-PEO demonstrated superior fouling resistance comparing to pure PVDF and other materials. Pure PVDF and PVDF/PMMA-g-PEO membranes with different length of PEO side chains were fabricated in non-solvent induced phase separation (NIPS) method. Membrane structure and surface composition were analyzed with scanning electron microscopy (SEM) and X-ray photoelectoron spectroscopy (XPS) respectively. Moreover, short-term and long-term activated sludge filtration experiments were conducted. The rate of increase of differential pressure during filtration process correlated with the amount of adsorbed BSA in the adsorption tests.

Filtration characterization method as tool to assess membrane bioreactor sludge filterability-the delft experience.

Prevention and removal of fouling is often the most energy intensive process in Membrane Bioreactors (MBRs), responsible for 40% to 50% of the total specific energy consumed in submerged MBRs. In the past decade, methods were developed to quantify and qualify fouling, aiming to support optimization in MBR operation. Therefore, there is a need for an evaluation of the lessons learned and how to proceed. In this article, five different methods for measuring MBR activated sludge filterability and critical flux are described, commented and evaluated. Both parameters characterize the fouling potential in full-scale MBRs. The article focuses on the Delft Filtration Characterization method (DFCm) as a convenient tool to characterize sludge properties, namely on data processing, accuracy, reproducibility, reliability, and applicability, defining the boundaries of the DFCm. Significant progress was made concerning fouling measurements in particular by using straight forward approaches focusing on the applicability of the obtained results. Nevertheless, a fouling measurement method is still to be defined which is capable of being unequivocal, concerning the fouling parameters definitions; practical and simple, in terms of set-up and operation; broad and useful, in terms of obtained results. A step forward would be the standardization of the aforementioned method to assess the sludge filtration quality.

Membrane fouling mitigation by activated carbon addition in activated sludge filtration

Activated carbon (AC) was added into the activated sludge to alleviate membrane fouling during sludge microfiltration. The fouling mitigation profiles were evaluated at different AC sizes and doses by a single-fibre microfiltration system. It was found that the granular AC added in the sludge suspension can absorb the organic substances in the sludge in a certain level, including biopolymer clusters (BPC). There are three impacts from AC addition, including the positive effect by mechanically scouring the membrane surface, the positive effect by adsorb organic substances, and the negative impact of breaking up sludge flocs to release the organic matter. The whole effect of AC addition on membrane fouling has to depend on the relative intensity of these three effects. The suitable AC should have a smaller mean size below 200 μm, by which the membrane fouling mitigation efficiency was positively correlated with AC doses.

Impact of temperature on raw wastewater composition and activated sludge filterability in full-scale MBR systems for municipal sewage treatment

The main objective of this study was to investigate the influence of seasonal temperature fluctuations on raw domestic wastewater composition and MBR sludge filterability. The influent and sludge samples were collected from a full-scale MBR in Heenvliet. All samples were analyzed in terms of filterability, particle size distribution, respirometry, fractionation and were further characterized by an extensive set of physicochemical measurements. Typical seasonal fluctuations and deterioration of activated sludge filterability during low temperature periods were observed. Filterability deterioration at low temperatures was linked to the incoming organic load, reduced MBR biomass concentrations, increased VSS/TSS ratio and reduced biodegradation of wastewater in the mixed liquor. Biological activity of the biomass was concomitantly decreased with temperature to reach a minimum during the winter period. Results show that the colloidal and soluble fraction (<1μm) represents the majority of the constituents, contains most of the COD, and plays an important role in the membrane resistance increase.

Activated sludge characteristics affecting sludge filterability in municipal and industrial MBRs: Unraveling correlations using multi-component regression analysis

In the field of membrane bioreactors (MBRs) many membrane fouling related questions still remain unanswered. The goal of this research is to unveil some of the black-box features of activated sludge filterability by correlating the results from activated sludge filterability measurements following the Delft Filtration Characterization method (DFCm) with a large set of activated sludge characteristics. Ten different MBRs in Belgium and the Netherlands were sampled in both winter and summer. All samples were subjected to the DFCm, automated image analysis and an extensive set of standardized measurements. No clear correlation could be found between a single sludge parameter and activated sludge filterability. However, a combination of sludge morphology and relative hydrophobicity (RH) allows for a clear classification of activated sludge into two classes, i.e., bad and poor to good, implying that deflocculation and a low RH have a negative impact on activated sludge filterability. Furthermore, for sludge samples having poor to good filterability, accurate estimations of sludge filterability can be made when including more parameters. The main conclusion is that filterability can be predicted by analyzing the bioflocculation state of the activated sludge.

Performance of a novel ZrO 2/PES membrane for wastewater filtration

The membrane bioreactor (MBR) process has now become an attractive option for the treatment and reuse of industrial and municipal wastewaters. However, the MBR filtration performance inevitably decreases with filtration time due to membrane fouling. Over the past two decades, increased interests in improving the performance of filtration membranes (i.e., reducing membrane fouling) have encouraged the development of new classes of chemically modified membranes. In this study polyethersulfone (PES) membranes and membranes with five different weight ratios of ZrO 2 to PES of 0.01, 0.03, 0.05, 0.07 and 0.1, were prepared by the phase inversion method and applied to activated sludge filtration in order to evaluate their fouling characteristics. The membranes were characterized using field-emission scanning electron microscope (FESEM). The ZrO 2/PES membrane strengths were higher than those of the neat membrane. The membrane molecular weight cut-off (MWCO) and membrane thickness were slightly affected by the ZrO 2 addition. ZrO 2 entrapped membranes showed lower flux decline compared to the neat PES membrane, with fouling mitigation increasing with ZrO 2 particles content. The optimum load of ZrO 2 immobilized membranes for membrane bioreactor (MBR) application in terms of highest membrane permeability and lowest fouling rate was the 5% weight fraction of ZrO 2 with PES.

Full-Scale MBR Monitoring – Activated Sludge Filterability vs. Plant Performance

Full-Scale MBR Monitoring – Activated Sludge Filterability vs. Plant Performance

Activated sludge dewatering in a filtration compression cell: deviations in comparison to the classical theory

AbstractWastewater treatment plants produce a residue that must be usually dewatered to reduce volume before handling and disposal, but operating parameters may impact activated sludge dewatering. On the one hand, the results obtained from tests conducted in the filtration–compression cell (FCC) show an impact of the initial slurry concentration and its amount on filtration kinetic. However, a scaling with respect to the initial amount enables an interesting representation of these data. On the other hand, the working pressure does not modify filtration kinetics, but it has a significant effect on the expression stage. Larger amount of filtrate is extracted when a higher pressure is applied for the expression stage. Moreover, the squeezing ability of the filter cake greatly depends on the time when the pressure step is applied. All these results are not fully modelled by the current theories, and Ruth's equation, which is commonly used, has its limitations in being able to properly describe activated sludge filtration. Because the visco‐elastic behaviour of filter cake is generally not considered by classical dewatering models, further work is needed to take into account this phenomenon. Copyright © 2009 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Indirect effects of membrane configuration on MBR sludge filterability

During a combined pilot-scale study, operating conditions were fixed for three different membrane configurations a multi tube, a hollow fibre and a flat sheet membrane type. Changes in activated sludge filterability were quantified depending on the membrane chambers, the permeate flux of extraction and the membrane chamber aeration. The aim of this study was to provide a better understanding of the interactions between MBR activated sludges and hydraulic circumstances depending on membrane configurations. Two mechanisms can be distinguished from this study: Due to practical arrangements, hydraulic conditions in each membrane unit are different, leading to different total suspended solids concentrations (TSS). These margins in TSS contents cause differences in filtration behaviour. The multi tube configuration did not affect the activated sludge filterability. The activated sludge filterability remained the same in spite of flux and air-lift velocity changes. The fl at sheet and the hollow fibre configuration did affect the sludge filterability. The filterability improved significantly at high flux and at low air-lift velocity (from 20% to 90% of improvement). The TSS concentration phenomenon is likely to be responsible for the activated sludge filterability improvement. It might be due to floc structure modifications resulting in a better cake layer porosity. No correlations were found between SMP and filterability.

Preparation, characterization and performance of Al 2O 3/PES membrane for wastewater filtration

Membrane bioreactors (MBRs) have been widely used as advanced wastewater treatment processes in recent years. However, membrane fouling and its consequences in terms of plant maintenance and operating costs limit the widespread application of MBRs. Thus great efforts have focused on fouling mitigation. In this study, Al 2O 3 entrapped polyethersulfone (PES) ultrafiltration membranes were prepared and applied to activated sludge filtration in order to evaluate their fouling characteristics. The impact of solvent evaporation time and polymer concentrations on ultrafiltration (UF) membrane characteristics and performance was studied. PES was employed as a base polymer, while N-methyl pyrrolidone (NMP) was used as a solvent. The flat sheet membranes, prepared via phase inversion, were characterized using scanning electron microscope (SEM). Membrane performance was changed by the addition of Al 2O 3 nanoparticles to the casting solution. Al 2O 3 entrapped membrane showed lower flux decline compared to that of neat polymeric membrane. Fouling mitigation effect increased with nanoparticle content. No significant effect of the nanoparticles distribution pattern inside the membrane matrix was found on the membrane performance. This study highlights the potential of Al 2O 3 immobilized membranes in MBR application.

The (in)significance of apparent viscosity in full-scale municipal membrane bioreactors

Ten pilot and full-scale municipal membrane bioreactor (MBR) plants throughout Europe were investigated during the period 2007–2008 using the Delft Filtration Characterisation method. Next to information on filterability the data also contain the necessary information to determine the apparent viscosity of activated sludge. The aim of this study was to quantify variations in the apparent viscosity of activated sludge in pilot and full-scale municipal MBR plants and correlate them with membrane performance. A statistical analysis was carried out in order to quantify the significance of the correlations between apparent viscosity and activated sludge characteristics. The main factor influencing activated sludge's apparent viscosity was found to be total suspended solids. Temperature was found not to have a direct impact on apparent viscosity within the range of temperatures of the pilot and full-scale municipal MBR plants studied (9.7–27.4°C). In terms of the reversible fouling potential and membrane performance, activated sludge filterability and MBR plant membrane permeability were not statistically affected by activated sludge's apparent viscosity variations. Therefore, even if apparent viscosity plays a major role in terms of oxygen transfer efficiency, it is not relevant when optimising membrane fouling control and membrane performance of current, full-scale municipal MBR applications.

Antifouling characteristics of sugar immobilized polypropylene microporous membrane by activated sludge and bovine serum albumin

α-Allyl glucoside (AG) was immobilized on the polypropylene microporous membranes (PPMMs) surface by nitrogen plasma treatment. The change of surface wettability was monitored by water contact angle measurement. Water contact angle on the modified membrane showed a minimum value of 54°, approximately 74° lower than that on the unmodified membrane. With the increase of immobilization degree from 0 to 4.6 wt.%, the relative pure water flux increased first, then decreased. The maximum value of the relative pure water flux was 1.44, which occurred at the immobilization degree of 2.03 wt.%. The antifouling characteristics during the filtration of the activated sludge (AS) in a submerged membrane bioreactor (SMBR) and of bovine serum albumin (BSA) dispersion were investigated and compared. The results showed that membranes possessed the same antifouling characteristics during the filtration of AS and BSA, which demonstrated that proteins in the SMBR mixed liquor suspension played a more important role in membrane fouling.

Creep effects in activated sludge filter cakes

Constant-pressure and stepped-pressure filtrations have been used to study the creep behaviour of filter cakes formed of activated sludge, anatase, or poly(styrene- co-acrylic acid) particles, respectively. No creep is observed in the case of the anatase filter cake, whereas the poly(styrene- co-acrylic acid) and activated sludge filter cakes exhibit pronounced creep behaviour. The consolidation stage for the poly(styrene- co-acrylic acid) filter cake can be divided into a primary consolidation stage controlled by hydrodynamic effects and a secondary consolidation stage controlled by creep effects. Up to 70% of the consolidation stage was secondary consolidation. Furthermore, the retardation time due to creep deformation was found to be much longer than the filtration time, which suggests that creep does not influence the filtration stage. The creep behaviour observed in activated sludge is pronounced, however no clear transition between primary and secondary consolidation was found. The retardation time is of the same magnitude as the filtration time. This suggests that activated sludge filtration is strongly influenced by creep, and may explain the difficulties in modelling activated sludge filtration and dewatering.

Effect of activated carbon on fouling of activated sludge filtration

The effect of adding activated carbon on the fouling of activated sludge filtration was investigated using a complete-mix cell with a flat-sheet cellulosic membrane at a constant pressure gradient of 70 kN/m 2. Four sludge samples were tested in parallel: a sludge without additive served as control, plus three sludge samples dosed with individual additives, including inert diatomaceous earth, activated carbon pre-sorbed with 112 mg-C/g of EPS (extracellular polymeric substance), and virgin activated carbon. Results showed that the EPS of activated sludge was a major contributor of membrane fouling. Additives may reduce the filtration resistance of the film deposited on the membrane surface, depending upon their EPS-sorbing capacity. As compared with the control, virgin activated carbon reduced the film filtration resistance by 22%, from 6.4 ± 0.5×10 12 m –1 to 5.0 ± 0.1×10 12 m –1, whereas the reduction was only 14% by the activated carbon pre-sorbed with EPS and negligible by the inert diatomaceous earth. Of the three main constituents of EPS, polysaccharide and humic substance were of significance to the fouling; protein had little effect.

Effect of TiO 2 nanoparticles on fouling mitigation of ultrafiltration membranes for activated sludge filtration

Membrane bioreactors (MBRs) have been widely used as advanced wastewater treatment process in recent years. However, MBR system has a membrane fouling problem, which makes the system less competitive. Thus there have been great efforts for fouling mitigation. In this study, two types of TiO 2 immobilized ultrafiltration membranes (TiO 2 entrapped and deposited membranes) were prepared and applied to activated sludge filtration in order to evaluate their fouling mitigation effect. Membrane performances were changed by addition of TiO 2 nanoparticles to the casting solution. TiO 2 entrapped membrane showed lower flux decline compared to that of neat polymeric membrane. Fouling mitigation effect increased with nanoparticle content, but it reached limit content above which fouling mitigation did not increase. Regardless of polymeric materials, membrane fouling was mitigated by TiO 2 immobilization. TiO 2 deposited membrane showed greater fouling mitigation effect compared to that of TiO 2 entrapped membrane, since larger amount of nanoparticle was located on membrane surface. It can be concluded that TiO 2 immobilized membranes are simple and powerful alternative for fouling mitigation in MBR application.

Influence of pretreating activated sludge with acid and surfactant prior to conventional conditioning on filtration dewatering

Chemical conditioners have been employed widely to improve sludge mechanical dewaterability, but there is still a large quantity of water in the flocculating constituent of activated sludge, which leads to the difficulty in further reducing the water content of dewatered sludge. The presence of extracellular polymers (ECP) is believed to be one of the unfavorable elements in activated sludge dewatering. This paper investigated the effect of removal of ECP from the solid surface by the use of surfactant and acid before commonly used conditioners utilized on activated sludge filtration dewatering. The moisture content of dewatered sludge dropped by 3–5% if activated sludge was pretreated with acid or surfactant ahead of the conventional conditioners used, which decreased by 7–11% in the case of combining the utilization of acid and surfactant. It was found that the use of acid and surfactant pretreatments before conditioning with polyacrylamide or calcium oxide and ferric chloride reduced the sludge water content from around 82 and 80% to about 75 and 69% when sludge MLSS was 12.5 and 9.9 g/l, respectively, which resulted in an almost 28 and 35% reduction in dewatered sludge volume compared to that without surfactant and acid pretreatments.

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.

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.