Enhanced Sb(V) removal of sulfate-rich wastewater by anaerobic granular sludge assisted with Fe/C amendment.

Antimony (Sb) and sulfate are two common pollutants in Sb mine drainage and Sb-containing textile wastewater. In this paper, it was found that iron­carbon (Fe/C) enhanced Sb(V) removal from sulfate-rich wastewater by anaerobic granular sludge (AnGS). Sulfate inhibited Sb(V) removal (S + Sb, k = 0.101), while Fe/C alleviated the inhibition and increased Sb(V) removal rate by 2.3 times (Fe/C + S + Sb, k = 0.236). Fe/C could promote the removal of Sb(III), and Sb(III) content decreased significantly after 8 h. Meanwhile, Fe/C enhanced the removal of sulfate. The 3D-EEM spectrum of supernatant in Fe/C + S + Sb group (at 24 h) showed that Fe/C stimulated the production of soluble microbial products (SMP) in wastewater. SMP alleviated the inhibition of sulfate, promoting AnGS to reduce Sb(V). Sb(V) could be reduced to Sb(III) both by AnGS and sulfides produced from sulfate reduction. Further analysis of extracellular polymeric substances (EPS) and AnGS showed that Fe/C increased the adsorbed Sb(V) in EPS and the c-type cytochrome content in AnGS, which may be beneficial for Sb(V) removal. Sb(V) reduction in Fe/C + S + Sb group may be related to the genus Acinetobacter, while in Sb group, several bacteria may be involved in Sb(V) reduction, such as Acinetobacter, Pseudomonas and Corynebacterium. This study provided insights into Fe/C-enhanced Sb(V) removal from sulfate-rich wastewater.

Insight into the interaction between trimethoprim and soluble microbial products produced from biological wastewater treatment processes.

Soluble microbial products (SMPs), dissolved organic matter excreted by activated sludge, can interact with antibiotics in wastewater and natural water bodies. Interactions between SMPs and antibiotics can influence antibiotic migration, transformation, and toxicity but the mechanisms involved in such interactions are not fully understood. In this study, integrated spectroscopy approaches were used to investigate the mechanisms involved in interactions between SMPs and a representative antibiotic, trimethoprim (TMP), which has a low biodegradation rate and has been detected in wastewater. The results of liquid chromatography-organic carbon detection-organic nitrogen detection indicated that the SMPs used in the study contained 15% biopolymers and 28% humic-like substances (based on the total dissolved organic carbon concentration) so would have contained sites that could interact with TMP. A linear relationship of fluorescent intensities of tryptophan protein-like substances in SMP was observed (R2>0.99), indicating that the fluorescence enhancement between SMP and TMP occurred. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that carboxyl, carbonyl, and hydroxyl groups were the main functional groups involved in the interactions. The electrostatic and π-π interactions were discovered by the UV-vis spectra and 1H nuclear magnetic resonance spectra. Structural representations of the interactions between representative SMP subcomponents and TMP were calculated using density functional theory, and the results confirmed the conclusions drawn from the 1H nuclear magnetic resonance spectra. The results help characterize SMP-TMP complexes and will help understand antibiotic transformations in wastewater treatment plants and aquatic environments.

Membrane Fouling Mitigation in MBR via the Feast-Famine Strategy to Enhance PHA Production by Activated Sludge.

Fouling is considered one of the main drawbacks of membrane bioreactor (MBR) technology. Among the main fouling agents, extracellular polymeric substances (EPS) are considered one of the most impactful since they cause the decrease of sludge filterability and decline of membrane flux in the long term. The present study investigated a biological strategy to reduce the membrane-fouling tendency in MBR systems. This consisted of seeding the reactor with activated sludge enriched in microorganisms with polyhydroxyalkanoate (PHA) storage ability and by imposing proper operating conditions to drive the carbon toward intracellular (PHA) rather than extracellular (EPS) accumulation. For that purpose, an MBR lab-scale plant was operated for 175 days, divided into four periods (1-4) according to different food to microorganisms' ratios (F/M) (0.80 kg COD kg TSS-1 d-1 (Period 1), 0.13 kg COD kg TSS-1 d-1 (Period 2), 0.28 kg COD kg TSS-1 d-1 (Period 3), and 0.38 kg COD kg TSS-1 d-1 (Period 4)). The application of the feast/famine strategy favored the accumulation of intracellular polymers by bacteria. The increase of the PHA accumulation inside the cells corresponded to the decrease of EPS and an F/M of 0.40-0.50 kg COD kg TSS-1 d-1 was found as optimum to maximize the PHA production, while minimizing EPS. The lowest EPS content in the sludge (18% of total suspended solids) that corresponded to the maximum content of PHA (9.3%) was found in Period 4 and determined significant mitigation of the fouling rate, whose value was close to 0.10 × 1011 m-1 h-1. Thus, by imposing proper operating conditions, it was possible to drive the organic matter toward PHA accumulation. Moreover, a lower EPS content corresponded to a decrease in the irreversible fouling mechanism, which would imply a lower frequency of the extraordinary cleaning operations. This study highlighted the possibility of obtaining a double benefit by applying an MBR system in the frame of wastewater valorization: minimizing the fouling tendency of the membrane and recovery precursors of bioplastics from wastewater in line with the circular economy model.

Effects of pure oxygen aeration on organic pollutants removal performance and soluble microbial products characteristics of salt-tolerant activated sludge.

The effects of pure oxygen aeration on organic pollutants removal performance and effluent soluble microbial products (SMP) characteristics of salt-tolerant sludge for the treatment of wastewater with the salinity from 1.0% to 3.5% were investigated. The results showed that the oxygen transfer efficiency of the pure oxygen aeration was higher than that of the air aeration. At the low salinities (0.5%, 1.0%, 1.5%), the total organic carbon (TOC) removal rates were 71.42%, 72.88% and 76.30%, respectively, much higher than those with air aeration. However, there were no significant differences of TOC removal efficiency between the air aeration and the pure oxygen aeration at high salinities (2.5% and 3.5%). The SMP contents showed a trend of first decline and then increase generally. The content of SMP with pure oxygen aeration was lower than that with air aeration at low salinity, whereas an opposite result was obtained for salinity above 2.5%. Five excitation-emission matrix (EEM) fluorescence peaks detected in the SMP with pure oxygen aeration and air aeration were assigned to tryptophan protein-like, tyrosine protein-like and humic acid-like substances. Humic acid-like fluorescence mainly appeared in the SMP with air aeration, which may be due to respiratory failure under air aeration conditions.

Application of hydrophilic modified nylon fabric membrane in an anammox-membrane bioreactor: performance and fouling characteristics.

The membrane fouling is the main bottleneck hindering the wide applications of anammox-membrane bioreactor (MBR). In this study, surface-coating hydrophilic modification of the membrane using polyvinyl alcohol was applied in a granular anammox-MBR. Stable anammox performance of >77% total nitrogen removal efficiency was achieved in both original and modified MBRs, along with decreasing anammox granule size. The modified membrane exhibited superior flux performance, and the membrane foulants were reduced in the MBR operation. Specifically, the foulant formation rate (f) was 0.46 g·m-2·d-1 for the modified membrane with 100-µm coating thickness (M100) compared with 0.75 g·m-2·d-1 for the original membrane (M0). However, the fouling cycle of the modified membrane with 250-µm coating thickness (M250) was greatly shortened (5 days compared with 19 days for M0) and f increased to 1.25 g·m-2·d-1. Specially, the excess adhesion of exopolysaccharides and humic substances to the hydrophilic modified membrane changed the fouling layer structure and filtration resistance distribution, ultimately causing higher filtration resistance when coating thickness increased. Notably, the flux decline contribution of the concentration polarization was only 33.3% for M0, while it was 71.3% for M250. Finally, it was revealed that using a modified membrane increased the biological secretion rate of polysaccharide but decreased the protein bio-production rate, leading to a high PS (polysaccharide)/PN (protein) ratio in the MBR. The fouling mechanism of the hydrophilic modified membrane applied in anammox-MBR was proposed, and we highlight that the degree of hydrophilic modification is crucial to mitigating membrane fouling.

Diversified metabolism makes novel Thauera strain highly competitive in low carbon wastewater treatment.

Thauera, as one of the core members of wastewater biological treatment systems, plays an important role in the process of nitrogen and phosphorus removal from low-carbon source sewage. However, there is a lack of systematic understanding of Thauera's metabolic pathway and genomics. Here we report on the newly isolated Thauera sp. RT1901, which is capable of denitrification using variety carbon sources including aromatic compounds. By comparing the denitrification processes under the conditions of insufficient, adequate and surplus carbon sources, it was found that strain RT1901 could simultaneously use soluble microbial products (SMP) and extracellular polymeric substances (EPS) as electron donors for denitrification. Strain RT1901 was also found to be a denitrifying phosphate accumulating bacterium, able to use nitrate, nitrite, or oxygen as electron acceptors during poly-ß-hydroxybutyrate (PHB) catabolism. The annotated genome was used to reconstruct the complete nitrogen and phosphorus metabolism pathways of RT1901. In the process of denitrifying phosphorus accumulation, glycolysis was the only pathway for glycogen metabolism, and the glyoxylic acid cycle replaced the tricarboxylic acid cycle (TCA) to supplement the reduced energy. In addition, the abundance of conventional phosphorus accumulating bacteria decreased significantly and the removal rates of total nitrogen (TN) and chemical oxygen demand (COD) increased after the addition of RT1901 in the low carbon/nitrogen (C/N) ratio of anaerobic aerobic anoxic-sequencing batch reactor (AOA-SBR). This research indicated that the diverse metabolic capabilities of Thauera made it more competitive than other bacteria in the wastewater treatment system.

Fate and role of fluorescence moieties in extracellular polymeric substances during biological wastewater treatment: A review.

In biological wastewater treatment systems, extracellular polymeric substances (EPS) are continuously excreted as a response to environmental changes and substrate conditions. It could severely affect the treatment efficacy such as membrane fouling, dewaterability and the formation of carcinogenic disinfection by-products (DBPs). The heterogeneous dissolved organic matter (DOM) with varying size and chemical nature constitute a primary proportion of EPS. In the last few decades, fluorescence spectroscopy has received increasing attention for characterizing these organic substances due to the attractive features of this low-cost spectroscopic approach, including easy sample handling, rapid, non-destructive and highly sensitive nature. In this review, we summarize the application of fluorescence spectroscopy for characterizing EPS and provide the potential implications for online monitoring of water quality along with its limitations. We also link the dynamics of fluorescent dissolved organic matter (FDOM) in EPS with operational and environmental changes in wastewater treatment systems as well as their associations with metal binding, membrane fouling, adsorption, toxicity, and dewaterability. The multiple modes of exploration of fluorescence spectra, such as synchronous spectra with or without coupling with two-dimensional correlation spectroscopy (2D-COS), excitation-emission matrix (EEM) deconvoluted fluorescence regional integration (FRI), and parallel factor analysis (PARAFAC) are also discussed. The potential fluorescence indicators to depict the composition and bulk characteristics of EPS are also of interest. Further studies are highly recommended to expand the application of fluorescence spectroscopy paired with appropriate supplementary techniques to fully unravel the underlying mechanisms associated with EPS.

Characteristics of extracellular polymeric substances and soluble microbial products of activated sludge in a pulse aerated reactor.

This study aimed to investigate the stratification characteristics of extracellular polymeric substances (EPS) and the properties of soluble microbial products (SMP) of the activated sludge with pulse aeration. The activated sludge was acclimated with aeration on/off time of 5 min/10 min for 60 days. The results showed that both polysaccharides (PS) and proteins (PN) increased in the loosely bound EPS (LB-EPS) and the tightly bound EPS (TB-EPS) with the increase of operational time. Both the PN/PS ratio and the total LB-EPS increased in the later period of the pulse aerated acclimation process. There was an obvious positive correlation between sludge volume index (SVI) and LB-EPS (R 2 = 0.871), mainly due to the PS in LB-EPS which was also significantly correlated with SVI (R 2 = 0.954). A downward trend of SMP concentrations occurred at the end of acclimation which was opposite to the upward change of EPS contents. Two obvious fluorescence peaks were detected respectively in EPS and SMP by 3D-EEM fluorescence spectroscopy. Peak A was detected in both LB-EPS and TB-EPS, which was associated with tryptophan protein-like substances. Peak B representing humus carbon and carboxylic acids was mainly detected in SMP. The release of humus-like components in SMP from activated sludge was mainly in accordance with the dissolution and hydrolysis of PN in TB-EPS.

A comparative study on membrane fouling alleviation mechanisms by using nanoscale Fe3O4 and poly dimethyldiallylammonium chloride.

Membrane bioreactor (MBR) has become a promising technology for wastewater treatment. However, membrane fouling frequently occurred which greatly increased operational expense. Two different membrane fouling alleviation mechanisms were explored in this study. Addition of poly dimethyldiallylammonium chloride (PDMDAAC) facilitated formation of flocs-flocs aggregates, which were more adaptable to the changing environment, resulting in less soluble microbial products (SMP) secretion. However, PDMDAAC lose activity gradually, and had a less sustainable effect on membrane fouling alleviation. Nanoscale Fe3O4 was applied to alleviate membrane fouling, and membrane sustainable filtration cycle extended 2-fold compared to the control group. Results showed that dehydrogenase activity in the reactor with optimal addition of nanoscale Fe3O4 increased 2.86 ± 0.11 times compared to control group. SMP (especially tryptophan protein-like substances) decreased to 9.79 ± 1.34 mg L-1 with the addition of nanoscale Fe3O4, which was lower than that in the control group (15.31 ± 0.53 mg L-1). It's speculated that nanoscale Fe3O4 performed as conductive material, which intensified interspecies electron transfer. The sludge dehydrogenase activity was then enhanced, which facilitated the utilization and microbial degradation of SMP, suppressing membrane fouling consequently.

Identification of soluble microbial products (SMPs) from the fermentation and methanogenic phases of anaerobic digestion.

The production and transformation of Soluble Microbial Products (SMPs) in biological treatment systems is complex, and their genesis and reasons for production are still unclear. SMPs are important since they constitute the main fraction of effluent COD (both aerobic and anaerobic), and hence are the main precursors for disinfection by-products (DBPs). In addition, they are a key component of fouling in membrane bioreactors. Hence, it is important to identify the chemical composition of SMPs, determine their origin, and understand what system parameters influence their production so we can possibly develop strategies to control their production. This study focuses on the production and identification of SMPs in an anaerobic batch process being fed a synthetic feed. To further understand the origins of SMPs, and how they are produced, we analysed the processes of fermentation and methanogenesis independently which has never been done in detail before. SMP concentration, molecular weight distribution and carbohydrate analyses were used to estimate the amount of SMPs in the supernatants. Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-Time-of-Flight mass spectrometry (LC-ESI-Q-ToF) were used to identify many of the SMPs which have relative masses up to 2 kDa. Our results showed that fermentation released much higher SMP concentrations compared to methanogenesis, especially in the range of 70 k-1000 k Da and 106-1500 Da. Alkanes, alkenes, alcohols, acids, and nitrogen-compounds were the major group of compounds identified in the supernatant of both fermentation and methanogenesis, and 71% of the compounds identified were found in both phases of digestion. Results from LC-ESI-Q-ToF analysis identified components of the cell membrane, such as phosphatidylglycerol, phosphatidylethanolamine and phosphatidylserine, as well as other compounds such as flavonoids, acylglycerol, terpene and terpenoids, benzenoid, glyceride, steroid and steroid derivatives.

Organic carbon source-dependent properties of soluble microbial products in sequencing batch reactors and its effects on membrane fouling.

This study investigated the influence of three different organic carbon sources including sodium acetate (SOD), glucose (GLU), and starch (STAR), on soluble microbial products (SMP), which presumably have dissimilar uptake rates and metabolic pathways, in sequencing batch reactors (SBR) and their subsequent effects on membrane fouling of ultrafiltration (UF). SMP were mainly characterized by fluorescence excitation emission matrix coupled with parallel factor analysis (EEM-PARAFAC) and size exclusion chromatography (SEC). SMP produced in SOD-fed SBR showed higher abundances of protein-like fluorescent component and large sized aliphatic biopolymer (BP) than GLU- or STAR-fed counterpart did, while the STAR-based operation resulted in more SMP enriched with humic-like fluorescence. The differences in SMP exerted marked effects on UF membrane fouling as indicated by the highest fouling potential with reversibility shown for the SMP from the SOD-fed reactor. Regardless of the carbon source, BP fraction and protein-like component exhibited the greatest extent of reversible fouling, suggesting that size exclusion plays a critical role. However, notable differences in the reversible fouling propensity of relatively smaller size fractions among the three SBRs signified the possible involvement of chemical interactions as a secondary fouling mechanism and its dependency on different carbon sources. Our results provide a new insight into the roles of carbon sources in the characteristics of SMP in biological treatment systems and their effects on the post-treatment using membrane filtration, which is ultimately beneficial to the optimization of biological treatment design and membrane filtration operation.

Biological denitrification in an anoxic sequencing batch biofilm reactor: Performance evaluation, nitrous oxide emission and microbial community.

The present study evaluated the performance of biological denitrification in an anoxic sequencing batch biofilm reactor (ASBBR) and its nitrous oxide (N2O) emission. After 90 days operation, the effluent chemical oxygen demand and total nitrogen removal efficiencies high of 94.8% and 95.0%, respectively. Both polysaccharides and protein contents were reduced in bound EPS (TB-EPS) and loosely bound EPS (LB-EPS) after biofilm formation. According to typical cycle, N2O release rate was related to the free nitrous acid (FNA) concentration with the maximum value of 3.88 µg/min and total conversion rate of 1.27%. Two components were identified from EEM-PARAFAC model in soluble microbial products (SMP). Protein-like substances for component 1 changed significantly in denitrification process, whereas humic-like and fulvic acid-like substances for component 2 remained relatively stable. High-throughput sequencing results showed that Lysobacter, Tolumonas and Thauera were the dominant genera, indicating the co-existence of autotrophic and heterotrophic denitrifiers in ASBBR.

Organic degradation and extracellular products of pure oxygen aerated activated sludge under different F/M conditions.

This study aimed to investigate the effect of food to microorganisms rate (F/M) on organic removal, extracellular polymeric substances (EPS) and soluble microbial products (SMP) of the pure oxygen aerated activated sludge running in batch mode. The F/M rates were controlled by adjusting the MLSS concentrations (2000, 5000, 8000 mg/L) and/or the initial TOC concentrations (100, 500 mg/L). Results showed that at high F/M rate (0.25 kg TOC/kg MLSS), the substrate degradation rate in the oxygen aerated reactor could reach 1.347 mg TOC/(L·min)), much higher than that in the air aerated reactor (0.640 mg TOC/(L·min)). The SMP concentrations with oxygen aeration were also higher than those with air aeration under high F/M conditions. The total EPS contents in the pure oxygen aerated sludge were significantly lower regardless of the different F/M rates. High F/M condition would lead to more amount of polysaccharides synthesis rather than proteins synthesis in EPS.

Tracing membrane biofouling to the microbial community structure and its metabolic products: An investigation on the three-stage MBR combined with worm reactor process.

The biofouling characteristics of an MBR (S-MBR) combined with the worm reactor and a conventional MBR (C-MBR) were analyzed, respectively, over the three-stage (fast-slow-fast) process. Whether it was in the C-MBR or the S-MBR, the species of the active sludge (AS) were similar to that of the cake sludge (CS) in stage 1 (before day 1), the bacterial adsorption and the metabolites attachment contributed to this transmembrane pressure (TMP) rise. In the stage 2, the TMP increasing rate of the C-MBR was eight times more than that of the S-MBR. During this period, a characteristic community colonized the AS and CS of the S-MBR with the microbes, ie Flavobacteria, Firmicutes and Chloroflexi which were responsible for the degradation of extracellular polymeric substances (EPS) and soluble microbial products (SMP). These dominant species caused the slower accumulation of biofouling metabolites in the CS, resulting in the slow rise-related in TMP. Meanwhile, the enrichment of ß-proteobacterium and the absence of Mycobacterium and Propionibacterium in AS and CS of the C-MBR were deemed as the main biological factors bringing about the rise-associated in TMP. In the stage 3, the biofilm was matured, and the cake layer was more compacted, which resulted in an abrupt rise in TMP and severe membrane fouling. Additionally, the statistical analysis revealed that a highly correlation between the TMP increasing rate and the content of carbonhydrates in SMP (SMPc). When the SMPc content increased slowly, there was a relatively slow biofouling. But, when the SMPc increasing rate was greater, it led to a more serious membrane fouling with the sudden TMP jump. Additionally, there was also a highly significant correlation coefficient for the TMP rise and the content of carbonhydrates in EPS (EPSc) and the protein in SMP (SMPp), rather than the protein in EPS (EPSp). The cluster analysis showed that the microbes contributing to membrane fouling were more abundant in the C-MBR, while the microbes related to organic compounds degradation were more abundant in the S-MBR. There was significant correlation between the microbes and their metabolites. The SMPc in conjunction with EPSc and SMPp were the main factors accelerating the membrane fouling. It was concluded that a quick rise in SMPc triggered an abrupt increase in TMP, while the EPSc and SMPp caused the sustained increase in TMP.

Bioactivities and formation/utilization of soluble microbial products (SMP) in the biological sulfate reduction under different conditions.

The biological sulfate reduction (BSR) plays a critical role in the organic compound removal in the sulfur bioconversion-associated sewage treatment process. The soluble microbial products (SMP) are the major components of residual organic compounds in the secondary treatment effluent and its presence directly affects treatment capacity. In addition, the SMP could be one of the available organic substrates and be utilized as an electron donor in the bioreactions. However, the SMP formation and utilization in the BSR are poorly understood. Herein, the BSR activities and SMP generation/utilization were simultaneously investigated under different conditions, i.e. pH, temperature and ratio of organic carbon (C) to sulfur (S). The role of SMP as the electron donor for BSR was also identified. The higher BSR activities and rapid SMP synthesis were found under neutral and alkaline conditions, but the SMP utilization as the electron donor is not favorable at pH 7.0. The BSR activity became higher and more SMP was synthesized by raising the temperature. The ratio of C to S rarely affected the sulfidogenic activity but has an effect on the net SMP generation (total SMP generation - SMP consumption by SBR as the electron donor). The lower ratio of C/S could result in the low residual SMP level in the reactor. And the SMP-induced BSR activity was higher under the acid and alkaline conditions compared with the neutral condition.

Impact of poly dimethyldiallylammonium chloride on membrane fouling mitigation in a membrane bioreactor.

Poly dimethyldiallylammonium chloride (PDMDAAC) was applied in a membrane bioreactor (MBR) to study its effects on mitigation of MBR membrane fouling. Floc size, zeta potential, soluble microbial substances (SMP) and extracellular polymeric substances (EPS) secretion were studied with respect to PDMMAAC-dosing operations. Results demonstrated that a sustainable filtration cycle extended 3.3 times with the optimal PDMDAAC dosage of 90 mg L-1. The addition of PDMDAAC could increase zeta potential of sludge floc, which led to the decrease in repulsive electrostatic interactions between flocs, as well as the facilitation of flocs-to-flocs aggregation. With the optimal dosage of PDMDAAC, the mean size of sludge was 3.23 ± 0.55 times higher than the control group, resulting in higher impact resistance and better adaptive capacity to the changing environment, which led to less SMP secretion. Moreover, a high contaminants removal rate was achieved in the reactor that was dosed with PDMDAAC. The average effluent concentrations of chemical oxygen demand and total nitrogen were less than 45.6 ± 2.85 and 5.23 ± 0.61 mg L-1, respectively, and the corresponding removal rates were 93.1 ± 5.81% and 89.1 ± 9.61%.

Salinity stresses make a difference in the start-up of membrane bioreactor: performance, microbial community and membrane fouling.

Start-up of membrane bioreactor under different NaCl stress was investigated in this study. Results showed that nearly 90% chemical oxygen demands and ammonia nitrogen ([Formula: see text]-N) was oxidized in none and 0.5% NaCl condition during the start-up stage. While 1% NaCl dramatically depressed the utilization of [Formula: see text]-N and about 4 weeks were required for adaption of sludge biomass to saline condition. In addition, the accumulation of nitrite high to 11.84 mg/L was observed in 1% NaCl stress, indicating the more inhibition on the activity of nitrite oxidizing bacteria. Microbial community responded to the different salinity levels. The phylum Proteobacteria and Bacteroidetes occupied over 60% in all the three MBRs. Salinity enriched the relative abundance of Maribacter, Methyloversatilis, Aeromonas and Curvibacter, while reducing the proportion of Nitrospira and Haliscomenobacter. Nitrospirae decreased sharply at 1% NaCl accounting for the accumulation of nitrite. Higher content of soluble microbial products (SMP) under saliferous MBR were released, which deteriorated the permeability of membrane module. Protein-like substances and humic substances were the main ingredients of SMP, of which the former contributed more to membrane flux decline. This study provided better understanding on the impact of salinity on the start-up of MBR.

[Characterization Composition of Soluble Microbial Products in an Aerobic Granular Sludge System].

Using flocculent activated sludge as seed sludge to cultivate aerobic granular sludge in a SBR, the main objective of this study was focused on the accumulation, relative molecular mass distribution, and composition of soluble microbial products (SMP) in an aerobic granular sludge (AGS) system. SMP were predominant (71-85 mg·L-1) in the effluent of the AGS system. The formation of SMP was related to substrate utilization, biomass decay, and EPS hydrolysis. A relative molecular mass distribution analysis indicated that the majority of SMP, accounting for about 54.8%-71.7%, had Mr<3×103; whereas, the Mr>100×103 formed a small fraction, constituting only 9.3%-14.5%. Three-dimensional excitation emission matrix fluorescence spectra (3D-EEM) identified four peaks in SMP, belonging to aromatic protein-like, tryptophan protein-like, humic acid-like, and fulvic acid-like substances. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that esters (39.0%), short chain alkanes (14.9%), alkenes (11.7%), and alcohols (7.6%) were the main compounds in SMP. Most notably, bis(2-ethylhexyl) phthalate, as one kind of ester, accounted for 32% of the identified SMP.

Qualitative and quantitative spectrometric evaluation of soluble microbial products formation in aerobic granular sludge system treating nitrate wastewater.

In present study, the characteristics of soluble microbial products (SMP) were evaluated in aerobic granular sludge system during denitrification process under different chemical oxygen demand/nitrogen (C/N) ratios. Batch experiment showed that the effluent nitrate (NO3--N) concentration were 15.24 ± 1.83 and 1.72 ± 1.53 mg/L at C/N ratio of 1 and 6, respectively. For the release of SMP, the protein (PN) and polysaccharide contents increased from 1.23 ± 0.38 and 7.46 ± 1.13 mg/L to 1.80 ± 0.76 and 10.53 ± 1.24 mg/L with increasing C/N ratios, respectively. Excitation-emission matrix identified four peaks in SMP, including aromatic PN-like, tryptophan PN-like, fulvic acid-like and humic acid-like substances. Fluorescence regional integration suggested that biodegradable PN-like substances occupied the percentage between 53.0 and 61.7% in SMP. Synchronous fluorescence spectra coupled with two-dimensional correlation spectroscopy indicated that the release of SMP fractions in the early stage (0-150 min) changed in the following sequences: PN-like fraction > fulvic acid-like fraction.

Purification and molecular weight distribution of a key exopolysaccharide component of Bacillus megaterium TF10.

Extracellular polymeric substances (EPS) are organic metabolic compounds excreted by microorganisms. They largely impact microbial aggregate structures and functions. Extracellular polysaccharides (EP) in EPS are responsible for the formation of microbial aggregates. In this work, we successfully separated and characterized EP from EPS of the bacterium Bacillus megaterium TF10. Extraction of EP from EPS was optimized using Sevag's reagent. Chemical characteristics, functional groups, and molecular weight (MW) distribution of EP were compared with the harvested EPS and soluble microbial products (SMP). We found that the polymers of lower MW and free proteins were successfully removed by Sevag's reagent. The higher MW components of EPS were predominantly polysaccharides, while the polymers of lower MW tended to secrete to the supernatant and were described as SMP. A part of the proteins in the EP was polysaccharide-bonded. Our results can be further used in elucidating the complex flocculation mechanisms in which EP play a major role.