Effect of sludge properties on the filtration characteristics of self-forming dynamic membranes (SFDMs) in aerobic bioreactors: Formation time, filtration resistance, and fouling propensity

Anaerobic dynamic membrane bioreactor for the co-digestion of toilet blackwater and kitchen waste

Anaerobic co-digestion using an anaerobic dynamic membrane bioreactor (AnDMBR) can separate the sludge retention time and hydraulic retention time, retaining the biomass for efficient degradation and the use of less expensive large pore-size membrane materials and more sustainable dynamic membranes (DMs). Therefore, anaerobic co-digestion of toilet blackwater (BW) and kitchen waste (KW) using an AnDMBR was hypothesized to increase the potential for co-digestion. Here, the efficiency and stability of AnDMBR in anaerobic co-digestion of toilet BW and KW were investigated. DM morphology and structural characteristics, filtration properties, and composition, as well as membrane contamination and membrane regeneration mechanisms, were investigated. Average daily biogas yields of the reactor in two membrane cycles before and after cleaning were 788.67 and 746.09 ml/g volatile solids, with average methane content of 66.64% and 67.27% and average COD removal efficiencies of 82.03% and 80.96%, respectively. The results showed that the bioreactor obtained good performance and stability. During the stabilization phase of the DM operation, the flux was maintained between 43.65 and 65.15 L/m2/h. DM was mainly composed of organic and inorganic elements. Off-line cleaning facilitated DM regulation and regeneration, restoring new Anaerobic morphology and structure. PRACTITIONER POINTS: High efficiency co-digestion of BW and KW was realized in the DMBR system. Average daily biogas yields before and after membrane cleaning were 788.67 and 746.09 ml/g volatile solids. Off-line cleaning facilitated DM regulation and regeneration as well as system stability. The flux was maintained between 43.65 and 65.15 L/m2/h during operation.

Electro living membrane bioreactor for highly efficient wastewater treatment and fouling mitigation: Influence of current density on process performances

The next generation of the self-forming dynamic membrane, referred to in this study as the "Living Membrane (LM)", is a new patented technology based on an encapsulated biological layer that self-forms on a designed coarse-pore size support material during wastewater treatment and acts as a natural membrane filter. Integrating electrochemical processes with wastewater treatment using the LM approach has also been recently studied (the reactor is referred to as the Electro-Living Membrane Bioreactor or e-LMBR). This study investigated the effects of varying current densities, i.e., 0.3, 0.5, and 0.9 mA/cm2, on the performance of an e-LMBR. The results were also compared with those of the Living Membrane Bioreactor or LMBR (without applied current density). Higher pollutant removals were observed in the presence of the electric field. However, the effect of varying applied current densities on the COD (98-99 %), NH3-N (97-99 %), and PO43-P (100 %) removals was not statistically significant. The more prominent differences (p < 0.05) were observed in the decrease of NO3--N concentrations from mixed liquor to effluent, with increasing current density resulting in lower mean NO3--N effluent concentrations (0.3 mA/cm2: 6.13 mg/L; 0.5 mA/cm2: 4.38 mg/L; 0.9 mA/cm2: 3.70 mg/L). The reduction of NO3--N concentrations as wastewater permeated through the LM layer also confirmed its role in removing nitrogen-containing compounds. Higher current densities resulted in lower concentrations of fouling substances, particularly those of microbial extracellular polymeric substances (EPS) and transparent exopolymer particles (TEPs). The average values of the temporal variation of transmembrane pressure (d(TMP)/d(t)) in the e-LMBR were extremely low, in the range of 0.013-0.041 kPa/day, throughout the operation period. The highest (d(TMP)/d(t)) was observed for the highest current density. However, the TMP values remained below 2 kPa in all the e-LMBR runs even after the initial LM formation stage.

High-rate anaerobic digestion of sewage sludge using anaerobic dynamic membrane bioreactor under various sludge composition and organic loading rates

This study investigates the effects of sludge compositions and organic loading rates (OLRs) on stable biomethane production during sludge digestion. Batch digestion experiments evaluate the effects of alkaline-thermal pretreatment and waste activated sludge (WAS) fractions on the biochemical methane potential (BMP) of sludge. A lab-scale anaerobic dynamic membrane bioreactor (AnDMBR) is fed with a mixture of primary sludge and pretreated WAS. Monitoring of volatile fatty acid to total alkalinity (FOS/TAC) helps maintain operational stability. The highest average biomethane production rate of 0.7 L/L·d is achieved when the OLR, hydraulic retention time, WAS volume fraction, and FOS/TAC ratio are 5.0 g COD/L·d, 12 days, 0.75, and 0.32, respectively. This study finds functional redundancy in two pathways: hydrogenotrophic and acetolactic. An increase in OLR promotes bacterial and archaeal abundance and specific methanogenic activity. These results can be applied to the design and operation of sludge digestion for stable, high-rate biomethane recovery.

Towards a Better Understanding of Long-Term Self-Forming Dynamic Membrane Bioreactor (SFDMBR) Performance: Effect of Aeration Intensity

This study aims to provide valuable new insights regarding the effect of aeration intensity on long-term self-forming dynamic membrane bioreactor (SFDMBR) performance and the associated mechanisms. Three identical SFDMBRs, with different aeration intensities (i.e., 200, 500 and 800 L/h), were operated in constant transmembrane (TMP) mode for 60 days. The best chemical oxygen demand (COD) removal performance was achieved at medium aeration intensity, owing to the enhanced COD removal contribution by the self-forming dynamic membrane (SFDM). As expected, the SFDM formation time was extended with increasing aeration intensity. Different from the initial short-term stage results, it was interestingly found that the SFDMBR operated at medium aeration intensity exhibited the best long-term filtration performance, followed in order by the SFDMBRs with low and high aeration intensity, respectively. Further analysis revealed that the governing fouling mechanism transited from biomass accumulation to the increase of specific resistance, as aeration intensity increased. The variation of SFDM-specific resistance was verified with particle size distribution (PSD) data and scanning electron microscopy (SEM) images. The long-term increasing rate of SFDM filtration resistance was consistent with both extracellular polymeric substances (EPS) content and the proteins/polysaccharides (PN/PS) ratio of SFDMs. Internal EPS production was enhanced in the thicker SFDM formed at a lower aeration intensity.

Effects of inorganic particles and their interactions with biofilms on dynamic membrane structure and long-term filtration performance

In present study, the effects of inorganic particles and their interaction with biofilms on the filtration behavior of dynamic membrane bioreactor (DMBR) were investigated. When no inorganic particles were included in the simulated domestic wastewater, a porous biofilm DM was formed on support materials. As a result, the transmembrane pressure (TMP) did not increase (< 10 Pa) during the 97 days' experiment and the effluent turbidity was consistently lower than 1.0 NTU. When sands (1.3-69.2 μm; 50 mg/L) were the only inorganic particles contained in wastewater, the effluent turbidity became instable and ranged from 0.31 to 3.88 NTU, probably because the DM structures were disturbed by sand scouring. The natural clays (0.5-2.7 μm) in wastewater were very liable to deposit on the support materials of DMBRs to form thick and compact DMs with greater contents of biomass and EPS, especially co-existing with sands. Due to the existence of natural clays, the DM porosity decreased significantly and rapid rising in TMP occurred frequently. This study demonstrated that pure biofilms without containing inorganic particles were ideal materials for DMs, which could achieve long-term stable operation with low effluent turbidity (< 1 NTU) and low TMP (< 10 Pa), while inorganic particles with any size could deteriorate the filtration performance. Therefore, removing the inorganic particles in wastewater as many as possible prior DMBR is critically important for achieving long-term stable operation.

Insights into fouling behavior in a novel anammox self-forming dynamic membrane bioreactor by the fluorescence EEM-PARAFAC analysis

Fouling behavior of the novel anaerobic ammonium oxidation (anammox) self-forming dynamic membrane bioreactor (SFDMBR) was elucidated, which is using nylon mesh as the filter with controlled fouling and successful anammox process. Properties of anammox sludge and foulants in the anammox SFDMBR and MBR (using PVDF microfiltration membrane) were compared to analyze the alleviated fouling in the SFDMBR, of which transmembrane pressure could be kept below 10 kPa for 50 days in one filtration cycle of 82 days with flux of 12 L m^-2 h^-1. Colorimetrical determination and excitation emission matrices-parallel factor (EEM-PARAFAC) analysis of the foulants showed that humic acid content in foulants on nylon mesh was obviously lower than that on PVDF membrane. Considering that the small-sized and flexible humic acids prefer to plug into membrane pores, the alleviated irreversible fouling in the SFDMBR could be attributed to the less microbial humic acid content of foulants (8.8 ± 1.0%) compared with the MBR (20.7 ± 2.9%). The adequate efflux of humic-like substances in the operation with nylon mesh was speculated to be the main mechanism of fouling control in the SFDMBR. These findings highlighted the potential of anammox SFDMBR in practical applications, because of the high humic acid contents in real ammonium-laden wastewater. Our study highlights the important role of humic acids in fouling behavior of the novel anammox SFDMBR to provide guidance for fouling control strategies. Graphical abstract.

Studies on a new stainless steel mesh dynamic membrane for wastewater treatment

In this study an innovative dynamic membrane bioreactor (DMBR) was implemented from a stainless-steel mesh filter, which was used as a support material, and activated sludge used as an adsorption and filtration interface containing particulate organics. This work indicated that DMBR can achieve rapid solid-liquid pollutants separation. The activated sludge in the aeration tank quickly formed a thin dynamic membrane layer on the filter. The layer was automatically regenerated as the sludge traveled through the reactor. The experimental results for the new DMBR showed good biodegradability in sewage treatment when the activated sludge concentrations ranged between 3000 and 7000 mg/L. Excellent adsorption and filtration performance were also achieved. This dynamic membrane layer significantly improved the effluent quality. The average removal rates were 92.2% and 91.5% for Chemical Oxygen Demand (COD) and Total Phosphorus (TP), respectively. The sewage treatment index was better than the current standard activated sludge process.

Exploring dynamic membrane as an alternative for conventional membrane for the treatment of old landfill leachate

This study compares the performance of a lab-scale pre-anoxic and post-aerobic submerged dynamic membrane bioreactor (DMBR) with similar studies on conventional membrane bioreactors (MBRs) for the treatment of old landfill leachate (LFL) while presenting a strategy to achieve stable DMBR operation. The results suggested that DMBR performed similar, or in some cases, better than MBRs. Like conventional MBRs treating LFL, DMBR can also accommodate large variations in operating parameters including influent feed composition and loading rates and thus, it can guarantee long term stable bioreactor operation (total nitrogen removal up to 98%) with acceptable effluent quality (Turbidity < 10 NTU). The results also demonstrated that gradual increment in influent LFL concentration was found to be effective for a stable DMBR operation however, it significantly deteriorated dynamic membrane (DM) filtration performance (p < 10E-7), resulting in higher fouling rate and deteriorated effluent quality. Nonetheless, poor DM performance and higher fouling rate were effectively controlled by using lower mesh porosity (52 μm instead of 200 μm) and increase in DM effective filtration area.

Thermodynamic prediction and experimental investigation of short-term dynamic membrane formation in dynamic membrane bioreactors: Effects of sludge properties

In dynamic membrane bioreactors (DMBRs), a dynamic membrane (DM) forms on a support material to act as the separation membrane for solids and liquids. In this study, batch filtration tests were carried out in a DMBR using nylon mesh (25 μm) as support material to filtrate sludge suspensions of variable properties from three different sources to evaluate the effects on the short-term DM formation process (within 240 min). Furthermore, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory was applied to analyze the sludge adhesion and cohesion behaviors on the mesh surface to predict quantitative parameters of the short-term DM formation process (including initial formation and maturation stage). The filtration results showed that the order of the initial DM formation time (permeate turbidity <1 NTU as an indicator) was as follows: sludge with poor settleability and dewaterability < normal sludge < sludge with poor flocculability. Moreover, normal sludge (regarding settleability, dewaterability, flocculability, and extracellular polymeric substance) showed a more acceptable DM formation performance (short DM formation time, low permeate turbidity, and high permeate flux) than sludge with poor settleability, dewaterability and flocculability. The influence of sludge properties on the initial DM formation time corroborates the prediction of sludge adhesion behaviors by XDLVO theory. Additionally, the XDLVO calculation results showed that acid-based interaction, energy barrier, and secondary energy minimum were important determinants of the sludge adhesion and cohesion behaviors. Therefore, short-term DM formation process may be enhanced to achieve stable long-term DMBR operation through positive modification of the sludge properties.

A unified thermodynamic mechanism underlying fouling behaviors of soluble microbial products (SMPs) in a membrane bioreactor

Soluble microbial products (SMPs) are the predominate foulants determining fouling extent in membrane bioreactors (MBRs). However, exact mechanism underlying their typical fouling behaviors remains unrevealed. In this study, the typical fouling behaviors of SMPs during initial operational period of a MBR were characterized. It was found that, although being low content, SMPs rather than sludge particulates preferentially adhered to membrane surface to accumulate a gel layer, and moreover, specific filtration resistance (SFR) of SMPs was approximately 700 times larger than that of the sludge particulates at operational day 3. According to energy balance principle, a unified thermodynamic mechanism underlying these fouling behaviors of SMPs was proposed. Thermodynamic analyses demonstrated that, the attractive interaction energy strength in contact between SMPs and membrane was larger by around 3700 times than that between sludge particulates and membrane, well explaining the extremely high adhesive ability of SMPs over sludge particlulates. Meanwhile, filtration through a SMPs layer was modelled and simulated as a thermodynamic process. Simulation on an agar gel showed that, about 92.6% of SFR was originated from mixing free energy change during filtration. Such a result satisfactorily interpreted the extremely high SFR of SMPs layer over sludge cake layer. The revealed thermodynamic mechanism underlying SMPs fouling behaviors significantly deepened understanding of fouling, and facilitated to development of effective fouling control strategies.

Dynamic membrane bioreactor performance enhancement by powdered activated carbon addition: Evaluation of sludge morphological, aggregative and microbial properties

The effects of powdered activated carbon (PAC) addition on sludge morphological, aggregative and microbial properties in a dynamic membrane bioreactor (DMBR) were investigated to explore the enhancement mechanism of pollutants removal and filtration performance. Sludge properties were analyzed through various analytical measurements. The results showed that the improved sludge aggregation ability and the evolution of microbial communities affected sludge morphology in PAC-DMBR, as evidenced by the formation of large, regularly shaped and strengthened sludge flocs. The modifications of sludge characteristics promoted the formation process and filtration flux of the dynamic membrane (DM) layer. Additionally, PAC addition did not exert very significant influence on the propagation of eukaryotes (protists and metazoans) and microbial metabolic activity. High-throughput pyrosequencing results indicated that adding PAC improved the bacterial diversity in activated sludge, as PAC addition brought about additional microenvironment in the form of biological PAC (BPAC), which promoted the enrichment of Acinetobacter (13.9%), Comamonas (2.9%), Flavobacterium (0.31%) and Pseudomonas (0.62%), all contributing to sludge flocs formation and several (such as Acinetobacter) capable of biodegrading relatively complex organics. Therefore, PAC addition could favorably modify sludge properties from various aspects and thus enhance the DMBR performance.

Dynamic analysis of self-forming dynamic membrane (SFDM) filtration in submerged anaerobic bioreactor: Performance, characteristic, and mechanism

This study attempts to provide an improved fundamental understanding of the self-forming dynamic membrane (SFDM) filtration process in submerged anaerobic bioreactors. Excellent system performances were achieved in terms of high COD removal efficiency (∼ 90%), fast formation/reformation of SFDM (<1 h), and sustainable low-resistance (3.92 × 10¹⁰ m^-1) high-flux (10-30 L/m²·h) filtration. A typical flux-variation profile consisted of an initial abruptly fast decrease followed by a gradually slow reduction, corresponding to the formation and sustainable operation period, respectively. The increase of SFDM resistance in formation period was attributable to the fast deposition of large particles on coarse-pore support materials. After SFDM formation, the subsequent increase of SFDM resistance was controlled more by the increase of specific resistance, which was firstly mainly resulted from the increasing accumulation of small particles with higher hydrophobicity and the external deposition of eEPS but later most attributable to the increase of internal release of eEPS.

Enhanced anoxic biodegradation of pyridine coupled to nitrification in an inner loop anoxic/oxic-dynamic membrane bioreactor (A/O-DMBR)

Enhanced biodegradation of high-strength pyridine was successfully achieved in the inner loop anoxic/oxic-dynamic membrane bioreactor (A/O-DMBR) in this study. Due to the key role of dynamic membrane in biomass retention, NH₄⁺ released from pyridine biodegradation could be effectively nitrified to NO₃^- in oxic zone, which was then recirculated into the anoxic zone to serve as electron acceptor for pyridine biodegradation. Acetate dosage adversely affected pyridine biodegradation, due to the competitive effect of acetate towards NO₃^-. Increase of recirculation ratio positively affected pyridine biodegradation, due to high availability of NO₃^- at high recirculation ratio. At influent pyridine concentration as high as 1500 mg L^-1, effluent turbidity was well maintained below 10 NTU, indicating excellent biomass retention performance of the dynamic membrane. Microbial community analysis confirmed the enrichment of specific functional species in both anoxic and oxic zones. Stable performance during 260 days' operation confirmed the potential of A/O-DMBR for full-scale application.

Sludge cake and biofilm formation as valuable tools in wastewater treatment by coupling Integrated Fixed-film Activated Sludge (IFAS) with Self Forming Dynamic Membrane BioReactors (SFD-MBR)

Two lab-scale Self Forming Dynamic Membrane BioReactors (SFD-MBR), equipped with 50 µm nylon meshes were set up and operated for the treatment of real municipal wastewater. Plastic carriers were added in one of the two bioreactors to generate a combination of the Integrated Fixed-film Activated Sludge (IFAS) and the SFD-MBR technologies. Overall, the two systems performed very well, achieving excellent effluent quality under steady state conditions and showing good resilience to extreme organic loading conditions. Continuous air scouring and periodical mesh cleaning by jet rinsing with tap water were effective in maintaining stable and high productivity (membrane flux around 67 L m² h^-1) over a period of 140 days. The application of the IFAS process resulted in lower production of excess sludge and improved denitrification. On the other hand, under the tested conditions the combined IFAS-SFD-MBR showed a higher tendency to mesh clogging with respect to the SFD-MBR.

Changes in the physical properties of the dynamic layer and its correlation with permeate quality in a self-forming dynamic membrane bioreactor

The self-forming dynamic membrane bioreactor (SFDMBR) is a biological wastewater treatment technology based on the conventional membrane bioreactor (MBR) with membrane material modification to a large pore size (30-100 μm). This modification requires a dynamic layer formed by activated sludge to provide effective filtration function for high-quality permeate production. The properties of the dynamic layer are therefore important for permeate quality in SFDMBRs. The interaction between the structure of the dynamic layer and the performance of SFDMBRs is little known but understandably complex. To elucidate the interaction, a lab-scale SFDMBR system coupled with a nylon woven mesh as the supporting material was operated. After development of a mature dynamic layer, excellent solid-liquid separation was achieved, as evidenced by a low permeate turbidity of less than 2 NTU. The permeate turbidity stayed below this level for nearly 80 days. In the fouling phase, the dynamic layer was compressed with an increase in the trans-membrane pressure and the quality of the permeate kept deteriorating until the turbidity exceeded 10 NTU. The investigation revealed that the majority of permeate particles were dissociated from the dynamic layer on the back surface of the supporting material, which is caused by the compression, breakdown, and dissociation of the dynamic layer. This phenomenon was observed directly in experiment instead of model prediction or conjecture for the first time.

Formation and performance of self-forming dynamic membrane (SFDM) in membrane bioreactor (MBR) for treating low-strength wastewater

This study introduces a self-forming dynamic membrane (SFDM) with large-pore mesh filter materials instead of conventional MF/UF membranes for wastewater treatment. Development of SFDM on the mesh filter surface plays a major role in reducing the wastewater turbidity and its performance in a self-formation dynamic membrane bioreactor (SFDMBR). To evaluate formation of the dynamic membrane, biological and hydrodynamic parameters, including mixed liquor suspended solids (MLSS) and aeration rate, were examined. The experimental results showed that with elevation of MLSS in the bioreactor (up to MLSS = 9,000 mg/L), the effluent turbidity diminishes with rapid formation of SFDM, with the shortest formation time (5 min) obtained in SFDM operations, though it results in increased membrane fouling. SFDM was well formed at low aeration rates of 2.5 L/min and 5 L/min, due to very low shear stress on the mesh filter surface, given the results of turbidity in comparison with aeration rates of 10 L/min and 15 L/min. The filtration performance of SFDM in treatment of synthetic wastewater was tested under a constant operational flux (58 L/m² h). Total chemical oxygen demand (COD) and NH₄-N removals were 88-93% and 96-98.8%, respectively. These results indicated that the treatment process can be performed effectively by SFDMBR.

Anaerobic dynamic membrane bioreactor (AnDMBR) for wastewater treatment: A review

Recently, an increasing level of attention has focused on the emerging technology of anaerobic dynamic membrane bioreactors (AnDMBRs), owing to its merits such as low membrane module cost, easy control of membrane fouling, low energy consumption and sludge production, as well as biogas production. As research on AnDMBRs is still in the nascent stage, an introduction of bioreactor configurations, dynamic membrane (DM) module, and DM layer formation and cleaning is firstly presented. The process performance of the AnDMBR for wastewater treatment is then reviewed with regard to pollutant removal, DM filterability, biogas production, and potential advantages over the conventional anaerobic membrane bioreactor (AnMBR). In addition, the important parameters affecting process performance are briefly discussed. Lastly, the challenges encountered and perspectives regarding the future development of the AnDMBR process to promote its practical applications are presented.

Soluble microbial products (SMPs) in a sequencing batch reactor with novel cake filtration system

The formation, composition and characteristics of soluble microbial products (SMPs) were investigated in a novel system which coupled a sequencing batch reactor with a cake filtration system. Both suspended solids (SS) and turbidity were significantly removed, resulting in effluent SS of 0.12 mg L^-1 and turbidity of 0.72 NTU after cake filtration. The average concentrations of proteins and carbohydrates decreased respectively from 4.0 ± 0.4 and 7.1 ± 0.6 mg/L in the sequencing batch reactor (SBR) mixed liquor, to 0.85 ± 0.21 and 1.39 ± 0.29 mg/L in the cake filtration effluent. Analysis of the molecular weight (MW) distribution of SMPs revealed a substantial reduction in the intensity of high-MW peaks (503 and 22.71 kDa) after cake filtration, which implied the sludge cake layer and the underlying gel layer may play a role in the effectiveness of cake filtration beyond the physical phenomenon. Three-dimensional excitation emission matrix fluorescence spectroscopy indicated that polycarboxylate- and polyaromatic humic acids were the dominant compounds and a noticeable decrease in the fraction of these compounds was observed in the cake filtration effluent. Analysis with GC-MS set for detecting low-MW SMPs identified aromatics, alcohols, alkanes and esters as the dominant compounds. SMPs exhibited both biodegradable and recalcitrant characteristics. More SMPs (total number of 91) were accumulated during the SBR start-up stage. A noticeable increase in the aromatic fractions was seen in the SBR effluent accoutring for 39% of total compounds, compared to the SBR mixed liquor (28%). Fewer compounds (total number of 66) were identified in cake filtration effluent compared to the SBR effluent (total number of 75).

Dynamic membrane-assisted fermentation of food wastes for enhancing lactic acid production

A dynamic membrane (DM) module was inserted into a fermentation reactor to separate soluble products from the fermented mixture to increase lactic acid (LA) production from food wastes under acidogenic conditions (uncontrolled pH, pH 4 and 5). With a high total suspended solid content (20-40g/L) in the fermenter, a stable DM could be maintained through regular backwashing. By effectively intercepting suspended solids and lactic acid bacteria (LAB), the fermenter was able to increase microbial activity and largely promote LA yield. Hydrolysis and acidogenesis rates increased with pH, and the highest LA yield (as high as 0.57g/g-TS) was obtained at pH 4. The microbial community analysis showed that the relative abundance of Lactobacillus increased to 96.4% at pH 4, but decreased to 43.3% at pH 5. In addition, the DM could be easily recovered by intercepting larger particles in less than 2h after each cycle of periodic backwashing.

Characterization of a hybrid powdered activated carbon-dynamic membrane bioreactor (PAC-DMBR) process with high flux by gravity flow: Operational performance and sludge properties

Three PAC-DMBRs were developed for wastewater treatment under different PAC dosages with biomass concentrations averaged at 2.5, 3.5 and 5.0g/L. The DMBRs could be continuously operated at 40-100L/m²h, while higher fluxes were obtained within the PAC-DMBRs with hydraulic retention times varying in 4-10h. A dose of 1g/L PAC brought about obvious improvement in the sludge particle size distribution, settling, flocculating and dewatering properties due to the formation of biological PAC, and the sludge properties were further improved at a higher PAC dose (3g/L). The addition of PAC notably shortened the DM formation time after air backwashing and enhanced pollutant removal. Moreover, under a long solid retention time (approximately 150d), the concentrations of both soluble and bound extracellular polymeric substances (EPS) decreased substantially because of the adsorption and biodegradation effects of the biological PAC. No obvious impact on biomass activity was observed with PAC addition.

Significantly enhanced dewatering performance of drinking water sludge from a coagulation process using a novel chitosan–aluminum chloride composite coagulant in the treatment of cyanobacteria-laden source water

The enhanced dewatering performance and the fate of cyanobacterial cells in the filtration of cyanobacteria-laden sludge, generated by a coagulation process using a novel composite chitosan–aluminum chloride (CTSAC) coagulant, were studied.

Dynamic Membrane Formation in Anaerobic Dynamic Membrane Bioreactors: Role of Extracellular Polymeric Substances

Dynamic membrane (DM) formation in dynamic membrane bioreactors plays an important role in achieving efficient solid-liquid separation. In order to study the contribution of extracellular polymeric substances (EPS) to DM formation in anaerobic dynamic membrane bioreactor (AnDMBR) processes, EPS extraction from and re-addition to bulk sludge were carried out in short-term filtration tests. DM formation behaviors could be well simulated by cake filtration model, and sludge with EPS re-addition showed the highest resistance coefficient, followed by sludge after EPS extraction. The DM layers exhibited a higher resistance and a lower porosity for the sludge sample after EPS extraction and for the sludge with EPS re-addition. Particle size of sludge flocs decreased after EPS extraction, and changed little with EPS re-addition, which was confirmed by interaction energy analysis. Further investigations by confocal laser scanning microscopy (CLSM) analysis and batch tests suggested that the removal of in-situ EPS stimulated release of soluble EPS, and re-added EPS were present as soluble EPS rather than bound EPS, which thus improved the formation of DM. The present work revealed the role of EPS in anaerobic DM formation, and could facilitate the operation of AnDMBR processes.

Implications of changes in solids retention time on long term evolution of sludge filterability in anaerobic membrane bioreactors treating high strength industrial wastewater

Long-term experiments were conducted to assess the impact of changing the solids retention time (SRT) on sludge filterability in anaerobic membrane bioreactors (AnMBRs), treating corn-based bioethanol thin stillage. Well established parameters, such as capillary suction time (CST) and specific resistance to filtration (SRF), developed for sludge dewatering, were used to evaluate the SRT effect on sludge filterability. Our results clearly demonstrated that SRT is one of the most important factors influencing sludge filterability in AnMBRs. SRT effects the accumulation of fine particles and solutes, which were found to affect attainable flux and fouling, in reactor broth. A better filterability was observed at a SRT of 20 days compared to elevated SRTs, i.e. 50 days. A clear correlation between sludge filtration characteristics and membrane filtration resistance could not be established especially at short SRTs, whereas many parameters such as total suspended solids (TSS), CST, soluble microbial products (SMP) and supernatant filterability were found to be mutually correlated. Net membrane fluxes between 9 and 13 L m(-2) h(-1) were obtained at 0.5 m s(-1) cross-flow velocity and the long term fouling was controlled by using frequent filtration and backwash cycles.