Analytical methods for soluble microbial products (SMP) and extracellular polymers (ECP) in wastewater treatment systems: a review

Denitrification strategies of strain YSF15 in response to carbon scarcity: Based on organic nitrogen, soluble microbial products and extracellular polymeric substances

This paper aims to determine the denitrification strategies of strain YSF15 in carbon scarcity condition from novel view of organic nitrogen, soluble microbial products (SMP) and extracellular polymeric substances (EPS). The batch tests demonstrated that strain YSF15 could achieve complete denitrification at C/N of 3.0. The conversion ratio of nitrogen gas accounted for 89.03%, 85.29% and 82.95% among total nitrogen in C/N systems from 3.0 to 5.0, respectively, indicating denitrification instead of assimilation was the major contribution to nitrogen removal. C/N could affect composition and content of organic nitrogen, SMP and EPS. The biodegradability of EPS was better than SMP, whereas polysaccharide (PS) likely correlated with nitrogen removal, predating the protein (PN). These results implied high biodegradability of EPS and more electron donors for denitrification both improved denitrification capacity of strain YSF15, which revealed the potential contribution of bacterium with production of biodegradable SMP or EPS in biological treatment process.

Impacts of bio-carriers on the characteristics of soluble microbial products in a hybrid membrane bioreactor for treating mariculture wastewater

To gain greater insights into impacts of bio-carriers on the fate and characteristics of soluble microbial products (SMPs) for mariculture wastewater treatment, the hybrid membrane bioreactor (HMBR) and conventional membrane bioreactor (CMBR) were investigated. Both protein and polysaccharide exhibited lower level in HMBR (8.95 ± 0.28 mg/L and 20.49 ± 1.3 mg/L for anoxic stage, 5.16 ± 0.22 mg/L and 17.85 ± 0.92 mg/L for aerobic stage) than CMBR (14.6 ± 0.68 mg/L and 28.3 ± 2.99 mg/L for anoxic stage, 10.53 ± 0.68 and 26.04 ± 3.15 mg/L for aerobic stage). Three-dimensional fluorescence excitation emission matrix (EEM) revealed bio-carriers reduced the production of aromatic protein-like components in anoxic and aerobic supernatant and caused a blue-shift of soluble microbial product in aerobic stage. Molecular weight (Mw) distribution indicated that bio-carriers ameliorated the excretion of biopolymer (Mw > 500 kDa) in anoxic supernatant and intermediate Mw fractions (20-500 kDa) in aerobic supernatant. Moreover, little changes were observed in SMPs with Mw < 3 kDa down the whole treatment process of both systems. Gas chromatography-mass spectrometry (GC-MS) demonstrated that the major SMPs were long-chain alkanes and aromatics in all units of both systems and fewer aromatics were detected in HMBR. For anoxic stage, more peaks were identified in the HMBR (138) than CMBR (115), while for aerobic stage, more compounds were observed in the CMBR (94) than HMBR (70). Over 50% of the compounds in the anoxic supernatant for the HMBR were the same as in the CMBR. And 27 compounds were the same in aerobic supernatant for the HMBR and CMBR. Fewer compounds in the HMBR effluent (52) was observed, compared to CMBR effluent (80). Approximately 25.7% of compounds in the aerobic stage of the HMBR were rejected by membrane, while this value decreased to 14.9% in the CMBR.

Mechanistic insights into a novel nitrilotriacetic acid-Fe0 and CaO2 process for efficient anaerobic digestion sludge dewatering at near-neutral pH

Traditional Fenton or Fenton-like oxidation has been widely studied for waste activated sludge dewaterability. However, the narrow pH range (2.0-4.0) and the instabilities of Fe²⁺ and H₂O₂ have hindered its commercial application. Owing to the high alkalinity of anaerobic digestion (AD) sludge, traditional Fenton or Fenton-like oxidation is economically unfeasible for its dewatering. In this study, we successfully demonstrated a novel and feasible method that used nitrilotriacetic acid (NTA)-Fe⁰ combined with CaO₂ (NTA-Fe⁰/CaO₂) at near-neutral pH (∼6.0) (a slight pH adjustment) in which capillary suction time ratio (CST₀/CST) and centrifuged weight reduction (CWR) improved by 6 folds and 42.98 ± 0.37%, respectively, under the optimal conditions. The presence of NTA accelerated the Fe⁰ corrosion, Fe²⁺ stability and turnover between Fe²⁺ and Fe³⁺. As such, Fe⁰ could effectively catalyze CaO₂ to produce hydroxyl radicals (•OH) under near-neutral conditions. Accordingly, various molecular weight hydrophilic compounds in different extracellular polymeric substances fractions were significantly reduced after treatment. The hydrophilic functional groups especially protein molecules were largely reduced. Consequently, the viscosity of sludge and particle size effectively decreased, while the release of bound water, surface charge, flocculation, and flowability of sludge were improved. The cost-benefit analysis further demonstrated the NTA-Fe⁰/CaO₂ treatment has high reusability and stability and is also more economical over the FeCl₃/CaO and Fenton's reagent/CaO treatments. In summary, the NTA-Fe⁰/CaO₂ process is a cost-effective and practically feasible technology for improving AD sludge dewaterability.

Composition and biotransformational changes in soluble microbial products (SMPs) along an anaerobic baffled reactor (ABR)

This work examined the production and catabolism/biotransformation dynamics of SMPs down the length of an eight-compartment-anaerobic baffled reactor (ABR) which physically separates the biological processes, in contrast to completely mixed reactors which do not enable these dynamics to measured, and this is totally novel. SMPs were extracted and characterised by gas and liquid chromatography coupled mass spectrometry to determine their composition and production/catabolism. 60%-70% of the feed compounds decreased from the first to fourth compartment; the increase in SMPs after the fourth compartment suggested a mixture of degraded and biotransformed compounds, and microbial products. High concentrations of low MW alkanes and alkenes, and higher MW (up to 2000 Da) lipids and amino acid derivatives accumulate in the last compartment at pseudo-steady state, and past work identifying polysaccharides/peptides as major membrane biofoulants have excluded these lipids. In addition, lipids and changes detected during feed transients have not been noted before in previous work. Finally, feed step-increases also increased some amino acid derivatives used in cell-signalling. Interestingly, some natural products from plant and fungal extracts were also found in the fourth compartment, where methanogenesis was the dominant process.

Tracking variation of fluorescent dissolved organic matter during full-scale printing and dyeing wastewater treatment

In this study, fluorescent dissolved organic matter (FDOM) in real printing and dyeing wastewater (PDW) during full-scale two-stage treatment was characterized using excitation-emission matrix (EEM), apparent molecular weight (AMW) cutoff by centrifugal ultrafiltration and high-performance liquid chromatography with fluorescence detector (HPLC-FLD). EEMs of PDW during treatment were relatively invariable with two typical and dominant peaks (P1, 275/320 nm and P2, 230/340 nm). The removal rates of P1 intensity and P2 intensity were both lower than those of DOC or UVA₂₅₄ during the 1st stage and 2nd stage treatment. The <3 kDa fraction made major contribution to DOC, UVA₂₅₄, P1 and P2 intensity. The DOM fractions with different AMW exhibited different removal behaviors during the 1st stage and 2nd stage treatment. The <3 kDa fraction of FDOM was poorly removed by biological treatment alone. The HPLC-FLD multi-emission scan results indicated that the major part of FDOM clusters were hydrophilic and they were more difficult to remove than the transphilic and hydrophobic FDOM clusters. According to the physicochemical properties of FDOM in PDW, selective adsorption and advanced oxidation process could be prior options for PDW advanced treatment.

Wastewater treatment plant upgrade induces the receiving river retaining bioavailable nitrogen sources

Currently, wastewater treatment plant (WWTP) upgrades have been implemented in various countries to improve the water quality of the receiving ecosystems and protect aquatic species from potential deleterious effects. The impact of WWTP upgrades on biological communities and functions in receiving waters is a fundamental issue that remains largely unaddressed, especially for microbial communities. Here, we selected two wastewater-dominant rivers in Beijing (China) as study sites, i.e., one river receiving water from an upgraded WWTP to explore the impacts of upgrade on aquatic ecosystems and another river receiving water from a previously upgraded WWTP as a reference. After a five-year investigation, we found that WWTP upgrade significantly decreased total organic nitrogen (N) in the receiving river. As a biological response, N-metabolism-related bacterioplankton are accordingly altered in composition and tend to intensively interact according to the network analysis. Metagenomic analysis based on the N-cycling genes and metagenomic-assembled genomes revealed that WWTP upgrade decreased the abundance of nitrifying bacteria but increased that of denitrifying and dissimilatory nitrate reduction to ammonium (DNRA) bacteria in the receiving river, according to their marker gene abundances. After calculation of the ratios between DNRA and denitrifying bacteria and quantification of genes/bacteria related to ammonium cycling, we deduced the changes in N-metabolism-related bacteria are likely an attempt to provide enough bioavailable N for plankton growth as conservation of ammonium was enhanced in receiving river after WWTP upgrade.

High-level waste activated sludge dewaterability using Fenton-like process based on pretreated zero valent scrap iron as an in-situ cycle iron donator

A novel, recyclable, and rapid pre-ultrasound-thermal-acid-washed zero valent scrap iron/hydrogen peroxide (UTA-ZVSI/H2O2) method has been developed to effectively enhance waste activated sludge (WAS) dewaterability. The effects of UTA ultrasound densities, UTA temperature, newly generated iron solution, H2O2 concentrations, and WAS conditioning time on the WAS dewaterability were investigated using a bench-scale system. Results indicated that the UTA-ZVSI/H2O2 treatment significantly improved the WAS dewaterability. The water content of the dewatered cake decreased to 44.15 ± 0.98 wt% during optimal operational conditions, which was significantly lower than that achieved using Fenton-based processes. Based on this outcome, a three-step treatment mechanism involving UTA-ZVSI/H2O2 has been developed, including iron flocculation, hydroxyl radical oxidation, and skeleton building. The dewatering efficiencies of three types of representative WAS were consistently effective in the UTA-ZVSI/H2O2 reactor for up to 15 cycles. Efficiencies levels were significantly higher than those achieved with Fenton-based processes. Economic analysis illustrated that the developed UTA-ZVSI/H2O2 system was the most cost-effective among other WAS dewatering treatments. In addition, the treatment system significantly alleviated toxicity of heavy metals and phytotoxicity in the dewatered sludge. This supported subsequent agricultural use. In summary, this study provided a comprehensive and useful basis for improving WAS dewatering and subsequent disposal.

Persistence of native and bio-derived molecules of dissolved organic matters during simultaneous denitrification and methanogenesis for fresh waste leachate

Biological treatment of wastewater always leaves plenty of refractory dissolved organic matters (DOM) in effluents, specifically for fresh waste leachate. Aiming at comprehending the production and removal of these compounds, this study investigated DOM transformation in a simultaneous denitrification and methanogenesis with activated sludge (SDM-AS) system with NO₃^-/NO₂^- backflow for raw fresh leachate. Chemical oxygen demand (COD) was reduced to 854 ± 120 mg/L from 63000 ± 470 mg/L, and total nitrogen (TN) decreased from 2500 ± 647 mg/L to 404 ± 75 mg/L, during an operation of 440 days. The SDM reactor was fed at organic loading rate of 6.70 kgCOD/(m³·d) to generate 2.52 L CH₄/(L·d). Molecular information of leachate DOM was acquired by using ultra-performance liquid chromatography coupled with Orbitrap mass spectrometry. A DOM classification based on Venn diagram was proposed to divide leachate DOM into seven categories. It revealed that 76-84% of final effluent DOM stemmed from biological derivation. Posteriori non-target screening showed anthropogenic micropollutants, e.g. phosphate flame retardants and industrial agents, probably contributed to the remnant native inert DOM in the effluent at the levels of 5-200 μg/L. DOM Classification also showed a portion of bio-derived DOM can be completely removed by SDM-AS processes, while the rest bio-derived DOM can be partially removed depending on DOM nature and the recirculation ratio. The removal and production rate of a specific bio-derived molecule in respective SDM and AS units theoretically satisfied a hyperbolical and dual relationship in terms of mass balance. The persistence of each DOM category was sorted. These results showed anaerobic degradation could be a promising approach to reduce aerobic bio-derived DOM.

Cultivation substrata differentiate the properties of river biofilm EPS and their binding of heavy metals: A spectroscopic insight

River biofilms inevitably serve as recipients of heavy metals including copper (Cu) and cadmium (Cd) following their introduction in fluvial systems. Nevertheless, the effects of cultivation substrata on the characteristics of river biofilm extracellular polymeric substances (EPS) and the binding behaviors of heavy metals on biofilms remain unclear. Integrating spectroscopic methods with chemometric analyses, we explored the binding behaviors of Cu(II) and Cd(II) onto biofilm EPS cultivated from two representative substrata at the molecular level. Chemical analysis revealed that biofilm cultivated on polyethylene (PE) pieces contained more non-fluorescent protein fractions, whereas EPS from periphyton grown on mineral, i.e., cobblestones was richer in aromatic fractions and polysaccharides. Excitation-emmision matrix combined with parallel factor analysis suggested a stronger interaction between fluorophores in periphytic EPS with Cu(II) compared to fluorophores in plastic biofilm EPS. Integrated use of infrared spectroscopy and two-dimensional correlation analyses revealed that, during the heavy metal binding processes, the amines and phenolics in plastic biofilm EPS gave the fastest responses to metal binding. While the amides and the aliphatic fractions in periphytic EPS showed a preferential binding to heavy metals. This study differentiates the effects of cultivation substrata on structuring the biofilm EPS characteristics and offers new insights into the environmental behaviors of heavy metal discharge into fluvial systems in river biofilm matrix.

Considering a membrane bioreactor for the treatment of vegetable oil refinery wastewaters at industrially relevant organic loading rates

The present study aims to shed more light on the use of membrane bioreactors (MBRs) for the treatment of vegetable oil refinery wastewaters (VORWs). A MBR was operated for 157 days in which it was fed with real VORW of varying composition at a range of organic loading rates (0.20 ± 0.05-3.79 ± 0.29 kg COD m^-3 day^-1). The hitherto unconsidered fate of VORW constituents through the biological process was followed using gas chromatography/mass spectrometry analysis. This analysis revealed that only 19% of the identified feed constituents remained in the MBR effluent whereas ten new compounds were formed. Linear correlation analysis attributed the effluent residual COD to soluble microbial products (SMP) and non-readily biodegradable recalcitrant oily compounds. Trend of change of MLSS, mixed liquor viscosity and SMP with increasing OLR suggested that when MBR is operated under industrial conditions for the VORW treatment, the mixed liquor fouling propensity potentially increases with increasing OLR in the range studied.

Enhancement of the denitrification in low C/N condition and its mechanism by a novel isolated Comamonas sp. YSF15

A novel denitrifying bacterium YSF15 was isolated from the Lijiahe Reservoir in Xi'an and identified as Comamonas sp. It exhibited excellent nitrogen removal ability under low C/N conditions (C/N = 2.5) and 94.01% of nitrate was removed in 18 h, with no accumulation of nitrite. PCR amplification and nitrogen balance experiments were carried out, showing that 68.92% of initial nitrogen was removed as gas products and the nitrogen removal path was determined to be NO₃^--N→NO₂^--N→NO→N₂O→N₂. Scanning electron microscopy and three-dimensional fluorescence spectroscopy were used to track extracellular polymeric substances (EPS). The results show that complete-denitrification under low C/N conditions is associated with EPS, which may provide a reserve carbon source in extreme environments. These findings reveal that Comamonas sp. YSF15 can provide novel basic materials and a theoretical basis for wastewater bioremediation under low C/N conditions.

Impact of isolated dissolved organic fractions from seawater on biofouling in reverse osmosis (RO) desalination process

The biofouling potential of three isolated dissolved organic fractions from seawater according to their molecular weights (MWs), namely, fractions of biopolymers (F.BP, MW > 1000 Da), humic substances and building blocks (F.HS&BB, MW 350-1000 Da), and low molecular weight compounds (F.LMW, MW < 350 Da) were characterized by assimilable organic carbon (AOC) content. The AOC/DOC ratio was in the order of F.LMW (∼35%) > F.BP (∼19%) > F.HS&BB (∼8%); AOC/DOC of seawater was ∼20%; organic compositions of seawater were BP ∼6%, HS&BB ∼52% and LMW ∼42%; LMW accounted for >70% of AOC in seawater. Their impact on SWRO biofouling in term of flux decline rate was in the order of F. LMW (∼30%) > F.BP (∼20%) > F.HS&BB (<10%). Despite being the major organic compound in seawater, HS&BB showed marginal effect on biofouling. The role of indigenous BP was less critical owing to its relatively low concentration. LMW, which was the major AOC contributor, played a significant role in biofouling by promoting microbial growth that contributed to the build-up of soluble microbial products and exopolymeric substances (i.e., in particular BP). Therefore, seawater pretreatment shall focus on the removal of AOC (i.e., LMW) rather than the removal of biopolymer.

Microbial community evolution and fate of antibiotic resistance genes in anammox process under oxytetracycline and sulfamethoxazole stresses

The microbial community characteristics, functional and antibiotic resistance genes (ARGs), anammox performance under individual and combined oxytetracycline (OTC) and sulfamethoxazole (SMX) were tested under environmentally relevant levels. The results showed that anammox performance was inhibited when the OTC or SMX concentration increased from 0.5 to 1.0 mg L^-1. The absolute abundance of tetX in OTC (3.03 × 10⁶ copies mg^-1), SMX (2.80 × 10⁶ copies mg^-1) and OTC + SMX (2.03 × 10⁶ copies mg^-1) was the highest and one more order of magnitude higher than that of tetG, tetM, intI1, or sul2. The anammox performance in the presence of OTC or SMX was lower than that sum of their independent effects. The enrichment of sludge resistomes with prolonged exposure time and increasing OTC and SMX doses might be due to succession of bacterial hosts and potential elevation of ARGs by horizontal transfer.

Importance of nutrient availability for soluble microbial products formation during a famine period of activated sludge: Evidence from multiple analyses

Much remains unknown about compositional variations in soluble microbial products (SMP) with the shift of the substrate condition from a feast to a famine phase in biological treatment systems. This study demonstrated that the formation of SMP could be suppressed by up to 75% during the famine phase with the addition of essential nutrients. In contrast, presence of electron acceptor did not play any significant role during the stress condition, showing the similar amounts of SMP (r = 0.98, p < 0.05) formation between the bioreactors supplied with air and N₂. The SMP formed in the famine phase was more bio-refractory in the famine versus the feast phase with a linear correlation shown between the production and their aromatic structures in the composition (R² > 0.95). The fluorescence excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) revealed the presence of four different fluorescent components, including two protein-like (C1 and C4), fulvic-like (C2), and humic-like (C3) components, in the SMP and bEPS formed at different conditions. Both C1 and C4 showed increasing trends (R² > 0.95) with the length of starvation in the bioreactors without essential nutrients. Nutrient availability was found to be a key factor to quench the production of large-sized biopolymers. This study provides a wealth of information on operation conditions of activated sludge treatment systems to minimize large sized SMP molecules (particularly proteins), which typically exert many environmental concerns to effluent organic matter quality.

Effect of temperature on the characterization of soluble microbial products in activated sludge system with special emphasis on dissolved organic nitrogen

Previous research has focused on dissolved organic carbon (DOC) as a surrogate for soluble microbial products (SMPs) and found that temperature has a significant influence on the production of SMP-based DOC (SDOC) during biological processes. Little is known about the SMP-based dissolved organic nitrogen (SDON), although some nitrogenous organic matter has been identified as an important part of SMPs. This study investigated the effect of temperature (8 °C, 15 °C and 25 °C) on the characterization of SMPs in an activated sludge system with special emphasis on SDON. Results showed the positive effect of reduced temperature on SDON production. Fluorescence spectroscopy and ultrahigh-resolution mass spectrometry showed the produced SDON at 8 °C and 15 °C exhibits more lability than at 25 °C. This was also supported by the algal bioassay, indicating the SDON produced at low temperature is highly bioavailable and prone to stimulate algae and microorganisms. In addition, principal component analysis demonstrated that the effect of temperature on the chemical characterization of SDON is different from that of SDOC. Overall, this study highlights the importance of SDON control during biological processes at a low temperature to reduce the potential impact of effluent SMPs on receiving waters or wastewater reuse.

Different removal efficiency of disinfection-byproduct precursors between dichloroacetonitrile (DCAN) and dichloroacetamide (DCAcAm) by up-flow biological activated carbon (UBAC) process

Up-flow biological activated carbon (UBAC) filter has been widely used in waterworks due to its less hydraulic loss, stronger biodegradation ability, and the prevention of excessive biomass growth relative to down-flow BAC treatment. In this study, the different removal efficiency (DRE) of disinfection byproduct precursors between dichloroacetonitrile (DCAN) and dichloroacetamide (DCAcAm) was evaluated when UBAC filter was used as advanced treatment process. Results showed that the UBAC filter with approximately 36 months of usage time had a poor performance in the removal of DCAcAm formation potential (FP) (i.e. 9.3-19.1%) compared to DCAN FP (i.e., 22.5-34.1%). After chlorination of UBAC effluent, the hydrolysis of DCAN to form DCAcAm only partly contributed to the DRE variations of both DCAN FP and DCAcAm FP. Using the high-throughput sequencing technology and the redundancy analysis (RDA), the second dominant genus Bacillus in UBAC filter, which may transform precursors of DCAN into inorganic matters, could be another reason that led to the DRE in DCAN and DCAcAm FP. The formation and leakage of soluble microbial products (SMPs) was identified by excitation-emission matrix (EEM) peak intensities as well as variation of biological index (BIX). The SMPs released into UBAC effluent, favoring the formation of DCAcAm, also contributed to the precursors of both DCAN and DCAcAm, causing a poor removal performance in DCAcAm FP by UBAC filter.

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.

Characteristics and influencing factors of organic fouling in forward osmosis operation for wastewater applications: A comprehensive review

Wastewater reuse is considered one of the most promising practices for the achievement of sustainable water management on a global scale. In the context of the safe reuse of water, membrane filtration is a competitive technique due to its superior efficiency in several processes. However, membrane fouling by organics is an inevitable challenge that is encountered during the practical application of membrane processes. The resolution of the membrane fouling challenge requires an in-depth understanding of many complex interactions between organic foulants and the membrane. In the last few decades, the forward osmosis (FO) membrane process, which exploits osmosis as a driving force, has emerged as an effective technology for water production with low energy consumption, thus leveraging the water-energy nexus. However, their successful application is severely hampered by membrane fouling, which is caused by such complex fouling mechanisms as cake enhanced osmotic pressure (CEOP), reverse salt diffusion (RSD), internal, and external concentration polarization as well as by the traditional fouling processes encompassing colloids, microbial (biofouling), inorganic, and organic fouling. Of these fouling types, the fouling potential of organic matter in FO has not been given sufficient attention, in particular, when FO is applied to wastewater treatment. This paper aims to provide a comprehensive overview of FO membrane fouling for wastewater applications with a special focus on the identification of the major factors that lead to the unique properties of organic fouling in this filtration process. Based on the critical assessment of organic fouling formation and the governing mechanisms, proposals were advanced for future research aimed at the mitigation of FO membrane fouling to enhance process efficiency in wastewater applications.

Effect of microbial activity and microbial community structure on the formation of dissolved organic nitrogen (DON) and bioavailable DON driven by low temperatures

Dissolved organic nitrogen (DON) formed by microbial metabolism in wastewater treatment processes adversely impacts wastewater reuse and receiving waters quality, and microbial metabolism is greatly influenced by temperatures. However, little is known about the effect of microorganisms on DON and bioavailable DON (ABDON) formation under low temperatures. In this study, six reactors were operated at low (8 °C and 15 °C) and room (25 °C) temperatures to evaluate the relationship between microbial activity, microbial communities, and DON and ABDON. Results showed that DON and ABDON concentrations significantly increased at low temperatures (p < 0.05, t-test). DON formation was significantly correlated to microbial activity only, with adenosine triphosphate (negative, r = -0.64) and polysaccharide (positive, r = 0.61) as key indicators; however, ABDON formation was influenced by both microbial activity (polysaccharide > triphenyltetrazolium chloride-dehydrogenases > adenosine triphosphate) and microbial community structure. Short-term tests using the biomass from six reactors were performed at room temperature to further validate the relationship. The distinct differences between these results provide a basis for different strategies on reducing effluent DON and ABDON under low temperatures.

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.

Size-dependent microbial diversity of sub-visible particles in a submerged anaerobic membrane bioreactor (SAnMBR): Implications for membrane fouling

Sub-visible particles, an often-overlooked fine particle (0.45-10 μm) with a size between sludge solids and soluble microbial products (SMP), have recently been identified as a critical foulant in anaerobic membrane bioreactors (AnMBRs), and our recent new insights into the size-fractionation and composition of sub-visible particles in AnMBRs have enabled fouling to be understood in more depth. Here, we investigated the microbial diversity of the sub-visible particles in three size fractions (i.e., 5-10, 1-5, and 0.45-1 μm) from bulk and cake solutions in a lab-scale AnMBR, and their fouling potential was further explored based on their filtration behavior and biofilm formation. Results show that with decreasing particle size, a significant shift in microbial communities was observed for the sub-visible particles in both bulk and cake solutions; (a) with notable decreases in filamentous microbes in the order SJA-15, GCA004, and Anaerolineales of phylum Chloroflexi, and, (b) with substantial increases in sulfate-reducing bacteria (i.e., the family Syntrophobacteraceae, genus DCE29 of family Thermodesulfovibrionaceae, Desulfovibrio, and Geobacter). More importantly, the filamentous microbes associated with micro-particles (5-10 μm) led to higher cake fouling resistances while free living cells in the form of colloidal particles (0.45-1 μm) induced severer pore blocking. Moreover, the micro-particles had an enhanced capacity to favor biofilm formation (OD595 = 1.0-2.5, categorized as highly positive), thus potentially aggravating biofouling. This work advances our knowledge on the effect of particle size on communities and underlying fouling behavior of microbes associated with fine particles in AnMBRs.

Control of indigenous quorum quenching bacteria on membrane biofouling in a short-period MBR

In this paper, the immobilized quorum quenching (QQ) bacteria - microbial bag was added to a short-period membrane bioreactor (MBR) and its antifouling ability and mechanism were studied by monitoring the changes in transmembrane pressure (TMP), along with the production of N-acyl-homoserine lactones (AHLs), extracellular polymeric substance (EPS) and soluble microbial products (SMP). The QQ bacteria showed efficient mitigation of TMP increase in different membrane fouling stages. In the control MBR group, the TMP reached 43 kPa on the 4th day, while in the experimental group, TMP of QQ-MBR was only 18 kPa at the same time. The detection result of EPS and SMP content of protein and polysaccharide in MBRs showed that QQ bacteria had significant inhibitory effects on EPS and SMP. Also, the QQ bacterial exhibited excellent AHLs degradation rate in MBR reaction tank.

Analysis of the relationship of extracellular polymeric substances to the dewaterability and rheological properties of sludge treated by acidification and anaerobic mesophilic digestion

The initial pH value of sludge affects sludge anaerobic digestion and dewatering performance. In order to determine the suitable pH value and decrease the sludge digestion time, in this study, the effect and the mechanism of combined acidification and anaerobic mesophilic digestion (acid-AMD) on sludge dewaterability were investigated. The changes and relationships among the extracellular polymeric substances (EPS), physicochemical properties, and rheological behavior of the treated sludge were analyzed. The results indicated that the combined acid-AMD treatment improved sludge dewaterability approximately 36.08% and 30.28% compared to the acid conditioning and AMD treatment, respectively. The factors improving sludge dewaterability include a lower sludge pH value and appropriate duration of AMD, changes in particle size, surface properties and distribution of the EPS fractions. The acid-AMD treatment hydrolyzed the EPS, loosening the sludge structure. These changes reflected in the rheological properties of the sludge. After the treatment, the network strength and colloid force of the sludge weakened. The linear viscoelastic region contracted, and the sludge system became sensitive to shear. These results demonstrated that rheological analysis can help explain the sludge dewatering mechanism. The acid-AMD treatment effectively changed the distribution of EPS that play a vital role in sludge dewaterability.

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%.

Deciphering the evolution characteristics of extracellular microbial products from autotrophic and mixotrophic anammox consortia in response to nitrogen loading variations

Extracellular microbial products (EMP) in biological wastewater treatment systems vary with operational conditions and in turn indicate the metabolic status of functional bacteria. In this study, the response of EMP from autotrophic and mixotrophic anammox consortia (AAC and MAC) to the variation of total nitrogen loading rates (TNLR) were investigated as well as their correlations with the community evolution. The variation of TNLR showed a significantly negative correlation with the production of bound microbial products (BMP) but a significantly positive correlation with the production of soluble microbial products (SMP). The presence of organic matters with COD/TN ratio of 0.15 limited the abundance of anammox bacteria in MAC at the full-load phase and suppressed their proliferation at the restart phase. Due to the improved abundance of carbohydrate metabolism genes, MAC with lower abundance of anammox bacteria produced lower soluble polysaccharides than AMC at the full-load phase. Furthermore, four components (C1-4) were identified on the excitation-emission matrix fluorescence spectra of SMP using parallel factor analysis. C1 exhibited a relative higher proportion at the full-load phase, whereas C4 was generated only at the light-load phase or empty-load phase. At the restart phase, C2 and C3 appeared simultaneously and accounted for a high proportion. The information of four components also suggested the metabolic status of AC as revealed by the specific anammox activity, which therefore provided a novel complementary but direct approach for monitoring the operation status of anammox bioreactors.

Prevention of UF membrane fouling in drinking water treatment by addition of H2O2 during membrane backwashing

Although conventional coagulation pre-treatment can mitigate the fouling of ultrafiltration (UF) membrane when treating raw waters, it is insufficient to restrict the development of irreversible fouling and reversible fouling to a low level. In this paper we demonstrate that the intermittent addition of H₂O₂ into the membrane tank during backwash events (after coagulation pre-treatment) successfully prevented the development of any significant membrane fouling. Laboratory-scale tests were undertaken using two membrane systems operated in parallel over 60 days, one serving as a reference coagulation-ultrafiltration (CUF) process, and the other receiving the H₂O₂ (CUF-H₂O₂), with a decreasing dose in three successive phases: 10, 5 and 2 mg/L. The results showed that the addition of H₂O₂ (via a separate dosing tube) during a 1 min backwash process (at 30 min intervals) reduced the growth of bacteria in the membrane tank, and the associated concentrations of soluble microbial products (SMP, including protein and polysaccharide). This resulted in a much reduced cake layer, which contained significantly less high MW organic matter (>50%), such as EPS, thereby improving the interaction between particles in the cake layer and/or particles and the membrane surface. There was also less organic matter, of all MW fractions, adsorbed in the membrane pores of the CUF-H₂O₂ system. The addition of H₂O₂ in the membrane tank appeared to alter the nature of the organic matter with a conversion of hydrophobic to hydrophilic fractions, which induced less organics adsorption within the hydrophobic PVDF membrane pores, and a reduced bonding ability for particles. There was no physico-chemical evidence of any deterioration of the membrane from exposure to H₂O₂, which indicates the feasibility of applying this novel method of fouling control for full-scale UF based water treatment processes.

Characterizations of dissolved organic matter and bacterial community structures in rice washing drainage (RWD)-based synthetic groundwater denitrification

In this study, characteristics of dissolved organic matter (DOM) and bacterial community structure in rice washing drainage (RWD)-based groundwater denitrification systems inoculated with and without seeding sludge were investigated. Complete nitrate removal was achieved with a maximum denitrification rate of 64.1 mg NO₃^--N·(gVSS·h)^-1. Analysis of three-dimension fluorescence excitation-emission matrix (FEEM) identified three main compositions of DOM associated with tryptophan protein-like, aromatic protein-like, and polycarboxylate humic acid-like substances in the inoculated system, while one composition associated with tryptophan protein-like substance in the un-inoculated system. Illumina sequencing analysis revealed a distinguished bacterial community structure in two systems over time. Notably, the microbial diversity was significant lower in the un-inoculated system than that in the system inoculated with seeding sludge. The predominant phyla shifted from Proteobacteria (49.2%), Bacteroidetes (20.5%) and Chloroflexi (14.8%) in the seeding sludge to Bacteroidetes (56.3%) and Proteobacteria (37.7%) after the RWD addition in the inoculated system. With RWD as sole microbe source, temporal changes in the bacterial structure from Proteobacteria (99.4%) and Bacteroidetes (5.3%) to Proteobacteria (88.8%) and Bacteroidetes (10.3%) were observed in the un-inoculated system. Specific comparison down to the genus level showed the dominant denitrifying bacteria of Thiobacillus, Anaerolineaceae and Methylophilaceae in the seeding sludge. Ideonella, Cloacibacterium and Enterobacter were dominant after the RWD addition in the inoculated system, while Stenotrophomonas and Enterobacter were dominant genera when RWD as sole bacteria source in the un-inoculated system. This finding indicates that both RWD addition and inoculation had strong impacts on bacterial community structure.

Evaluation of a novel quorum quenching strain for MBR biofouling mitigation

Membrane biofouling, due to Soluble Microbial Products (SMP) and Extracellular Polymeric Substances (EPS) deposition, results in reduction of the performance of Membrane Bioreactors (MBRs). However, recently, a new method of biofouling control has been developed, utilizing the interference of the bacterial inter- and intra-species' communication. Bacteria use Quorum Sensing (QS) to regulate the production of SMP and EPS. Therefore, disruption of Quorum Sensing (Quorum Quenching: QQ), by enzymes or microorganisms, may be a simple mean to control membrane biofouling. In the present study, a novel QQ-bacterium, namely Lactobacillus sp. SBR04MA, was isolated from municipal wastewater sludge and its ability to mitigate biofouling was evaluated by monitoring the changes in critical flux and transmembrane pressure, along with the production of EPS and SMP, in a lab-scale MBR system treating synthetic wastewater. Lactobacillus sp. SBR04MA showed great potential for biofouling control, which was evidenced by the ∼3-fold increase in critical flux (8.3 → 24.25 L/m²/h), as well as by reduction of the SMP and EPS production, which was lower during the QQ-period when compared against the control period. Furthermore, the addition of the QQ-strain did not affect the COD removal rate. Results suggested that Lactobacillus sp. SBR04MA represents a novel and promising strain for biofouling mitigation and enhancement of MBRs performance.

Removal of precursors of typical nitrogenous disinfection byproducts in ozonation integrated with biological activated carbon (O3/BAC)

The O₃/BAC process has been widely used in drinking water treatment to improve the removal of dissolved organic matters (DOMs), including the precursors of nitrogenous disinfection byproducts (N-DBPs). In this study, the removal of N-DBP precursors by biological activated carbon (BAC) filters with different usage time of granular activated carbon (GAC) was investigated. Results showed that the BAC filter with 6 years of usage time of GAC (old BAC filter) had a poor performance in the removal of precursors of N-DBPs such as dichloroacetonitrile (DCAN; an average of only 4.7%), dichloroacetamide (DCAcAm), and trichloronitromethane (TCNM) when compared with the BAC filter with 1 year of usage time of GAC (new BAC filter). Particularly, the organic fraction >10 kDa and the percentage of autochthonous substances were increased in the effluent of the old BAC filter. The red shift of the fluorescence peaks was evident in the excitation-emission matrix spectrum of the effluent from the old BAC filter. The abiotic adsorption of precursors by the old BAC filter was less. In addition, less amino acids and polysaccharides were removed, but more amino sugars and proteins were produced because of microbial metabolism. The metabolism strength of the attached biofilm decreased with increased operation time of the BAC filter. The relative abundance of Sphingomonas significantly decreased in the biofilm of the old BAC filter. The diversity of microbial community in the old BAC filter was higher, but the equitability was lower than those of the new BAC filter. The less removal of N-DBP precursors by the old BAC filter was attributed to the changes in abiotic adsorption capacity and microbial metabolism properties, in which soluble microbial products played an important role.

Multivariate Chemometric Analysis of Membrane Fouling Patterns in Biofilm Ceramic Membrane Bioreactor

Membrane fouling highly limits the development of Membrane bioreactor technology (MBR), which is among the key solutions to water scarcity. The current study deals with the determination of the fouling propensity of filtered biomass in a pilot-scale biofilm membrane bioreactor to enable the prediction of fouling intensity. The system was designed to treat domestic wastewater with the application of ceramic microfiltration membranes. Partial least squares regression analysis of the data obtained during the long-term operation of the biofilm-MBR (BF-MBR) system demonstrated that Mixed liquor suspended solids (MLSS), diluted sludge volume index (DSVI), chemical oxygen demand (COD), and their slopes are the most significant for the estimation and prediction of fouling intensity, while normalized permeability and its slope were found to be the most reliable fouling indicators. Three models were derived depending on the applied operating conditions, which enabled an accurate prediction of the fouling intensities in the system. The results will help to prevent severe membrane fouling via the change of operating conditions to prolong the effective lifetime of the membrane modules and to save energy and resources for the maintenance of the system.

Evaluation of disinfection by-products (DBPs) formation potential in ANAMMOX effluents

Disinfection by-products (DBPs), major health concerns in the potable reuse of municipal wastewater effluent, are process-related in wastewater treatment systems. Anammox is a promising and increasingly-applied technology for nitrogen removal in wastewater. In this study, the relationship between DBP formation potential and the anammox process has been investigated based on a lab-scale sequencing batch reactor (SBR). Excitation and emission matrix (EEM) fluorescence spectroscopy was employed to identify the compositions of the DBP precursors. The results showed that the effluents from the anammox SBR could yield both carbonaceous and nitrogenous DBPs after chlorination. Trichloromethane (TCM) was the dominant product among all DBPs detected. The anammox effluent has a low specific TCM formation potential of 0.778 μmol/mmol C and a trichloronitromethane (TCNM) formation potential of 0.0725 μmol/mmol C, leading to a TCM and TCNM formation potential ratio of 10.7. We found that substrate utilization of anammox did not enhance DBP yields, and the DBP formation potential decreased after 10 hour starvation. High pH conditions stimulated the production of TCM precursors in the anammox reactor. Humic acid-like and protein-like substances were identified in the EEM spectra of anammox effluents.

Understanding the Role of Extracellular Polymeric Substances on Ciprofloxacin Adsorption in Aerobic Sludge, Anaerobic Sludge, and Sulfate-Reducing Bacteria Sludge Systems

Extracellular polymeric substances (EPS) of microbial sludge play a crucial role in removal of organic micropollutants during biological wastewater treatment. In this study, we examined ciprofloxacin (CIP) removal in three parallel bench-scale reactors using aerobic sludge (AS), anaerobic sludge (AnS), and sulfate-reducing bacteria (SRB) sludge. The results showed that the SRB sludge had the highest specific CIP removal rate via adsorption and biodegradation. CIP removal by EPS accounted up to 35. 6 ± 1.4%, 23.7 ± 0.6%, and 25.5 ± 0.4% of total removal in AS, AnS, and SRB sludge systems, respectively, at influent CIP concentration of 1000 μg/L, which implied that EPS played a critical role in CIP removal. The binding mechanism of EPS on CIP adsorption in three sludge systems were further investigated using a series of batch tests. The results suggested that EPS of SRB sludge possessed stronger hydrophobicity (proteins/polysaccharides (PN/PS) ratio), higher availability of adsorption sites (binding sites ( n)), and higher binding strength (binding constant ( K_b)) between EPS and CIP compared to those of AS and AnS. The findings of this study provide an insight into the role of EPS in biological process for treating CIP-laden wastewaters.

Characterization of soluble microbial products in a partial nitrification sequencing batch biofilm reactor treating high ammonia nitrogen wastewater

In present study, the characterization of soluble microbial products (SMP) was evaluated in a partial nitrification sequencing batch biofilm reactor (SBBR). During the stable operation of SBBR, the NH₄⁺-N removal efficiency and nitrite accumulation ratio were 96.70±0.41% and 93.77±1.04%, respectively. According to excitation-emission matrix (EEM), the intensities of protein-like substances were reduced under anoxic and aerobic phases, whereas humic-like substances had little change during the whole cycle. Parallel factor analysis (PARAFAC) further indentified two components and their fluorescence intensity scores were both reduced. Synchronous fluorescence spectra revealed that the fluorescence intensity of protein-like fraction decreased with reaction time. Two-dimensional correlation spectroscopy (2D-COS) further demonstrated that protein-like fraction might decrease earlier than the other fractions. The information obtained in present study is of fundamental significance for understanding the key components in SMP and their changes in partial nitrification system by using a spectral approach.

Novel anaerobic membrane bioreactor (AnMBR) design for wastewater treatment at long HRT and high solid concentration

Performance of two novel designed anaerobic membrane bioreactor (AnMBRs) for wastewater treatment at long hydraulic retention time (HRT, 47 days) and high sludge concentration (22 g·L^-1) was investigated. Results showed steady chemical oxygen demand (COD) removal (>98%) and mean biogas generation of 0.29 LCH₄·g^-1COD. Average permeates flux of 58.70 L·m^-2·h^-1 and 54.00 L·m^-2·h^-1 were achieved for reactors A and B, respectively. On top of reactor configuration, long HRT caused biofilm reduction by heterotrophic bacteria Chloroflexi resulting in high membrane flux. Mean total membrane resistances (2.23 × 10⁹ m^-1) and fouling rates (4.00 × 10⁸ m^-1·day^-1) of both reactors were low suggesting better membrane fouling control ability of both AnMBRs. Effluent quality analysis showed the effluent soluble microbial products (SMP) were dominated by proteins compared to carbohydrates, and specific ultraviolet absorbance (SUVA) analysis revealed effluent from both reactors had low aromaticity with SUVA < 1 (L·mg^-1·m^-1) except for the first ten days.

Fate and behavior of dissolved organic matter in a submerged anoxic-aerobic membrane bioreactor (MBR)

In this study, the production, composition, and characteristics of dissolved organic matter (DOM) in an anoxic-aerobic submerged membrane bioreactor (MBR) were investigated. The average concentrations of proteins and carbohydrates in the MBR aerobic stage were 3.96 ± 0.28 and 8.36 ± 0.89 mg/L, respectively. After membrane filtration, these values decreased to 2.9 ± 0.2 and 2.8 ± 0.2 mg/L, respectively. High performance size exclusion chromatograph (HP-SEC) analysis indicated a bimodal molecular weight (MW) distribution of DOMs, and that the intensities of all the peaks were reduced in the MBR effluent compared to the influent. Three-dimensional fluorescence excitation emission matrix (FEEM) indicated that fulvic and humic acid-like substances were the predominant DOMs in biological treatment processes. Precise identification and characterization of low-MW DOMs was carried out using gas chromatography-mass spectrometry (GC-MS). The GC-MS analysis indicated that the highest peak numbers (170) were found in the anoxic stage, and 54 (32%) compounds were identified with a similarity greater than 80%. Alkanes (28), esters (11), and aromatics (7) were the main compounds detected. DOMs exhibited both biodegradable and recalcitrant characteristics. There were noticeable differences in the low-MW DOMs present down the treatment process train in terms of numbers, concentrations, molecular weight, biodegradability, and recalcitrance.

New insights into the treatment of realN,N-dimethylacetamide contaminated wastewater using a membrane bioreactor and its membrane fouling implications

Treatment of N,N-dimethylacetamide (DMAC) wastewater is an important step in achieving the sustainable industrial application of DMAC as an organic solvent. This is the first time that treatment of a high concentration of DMAC in real wastewater has been assessed using membrane bioreactor technology. In this study, an anoxic–oxic membrane bioreactor (MBR) was operated over a month to mineralize concentrated DMAC wastewater. Severe membrane fouling occurred during the short-term operation of the MBR as the membrane flux decreased from 11.52 to 5.28 L (m² h)⁻¹. The membrane fouling was aggravated by the increased amount of protein fractions present in the MBR mixed liquor. Moreover, results from the excitation–emission matrix analysis identified tryptophan and other protein-like related substances as the major membrane-fouling components. Furthermore, analysis of the DMAC degradation mechanism via high performance liquid chromatography (HPLC) and ion chromatography (IC) revealed that the major degradation products were ammonium and dimethylamine (DMA). Although the MBR system achieved the steady removal of DMAC and chemical oxygen demand (COD) by up to 98% and 80%, respectively at DMAC₀ ≤ 7548 mg L⁻¹, DMA was found to have accumulated in the treated effluent. Our investigation provides insight into the prospect and challenges of using MBR systems for DMAC wastewater degradation.

Treatment of N,N-dimethylacetamide (DMAC) wastewater is an important step in achieving the sustainable industrial application of DMAC as an organic solvent.

Behaviour of biopolymeric substances in the activated sludge of an MBR system working with high hydraulic retention time

This study was undertaken to analyse the activated sludge of a membrane bioreactor (MBR), the behaviour of extracellular polymeric substances (EPS) and soluble microbial products (SMP) as well as their biopolymers composition, in the activated sludge of a membrane bioreactor (MBR) and their influence on membrane fouling were analysed. For the experiment an experimental fullscale MBR working with real urban wastewater at high hydraulic retention time with a variable sludge-retention time (SRT) was used. The MBR system worked in denitrification/nitrification conformation at a constant flow rate (Q = 0.45 m³/h) with a recirculation flow rate of 4Q. The concentrations of SMP in the activated sludge were lower than the concentrations of EPS over the entire study, with humic substances being the main components of the two biopolymers. SMP and, more specifically, SMP carbohydrates, were the most influential biopolymers in membrane fouling, while for EPS and their components, no relation was found with fouling. The SRT and temperature were the operational variables that most influenced the SMP and EPS concentration, causing the increase of SRT and temperature a lower concentration in both biopolymers, although the effect was not the same for all the components, particularly for the EPS carbohydrates, which increased with longer SRTs. Both operational variables were also the ones most influential on the concentration of organic matter of the effluent, due to their effect on the SMP. The volatile suspended solid/total suspended solid (VSS/TSS) ratio in the activated sludge can be applied as a good indicator of the risk of membrane fouling by biopolymers in MBR systems.

Spectroscopic descriptors for dynamic changes of soluble microbial products from activated sludge at different biomass growth phases under prolonged starvation

In this study, the spectroscopic indices of soluble microbial products (SMP) were explored using absorption and fluorescence spectroscopy to identify different distinctive biomass growth phases (i.e., exponential phase, pseudo-endogenous phase, and endogenous phase) and to describe the microbial activity of activated sludge in a batch type bioreactor under prolonged starvation. The optical descriptors, including UV absorption at 254 nm (UVA254), spectral slope, absorbance slope index (ASI), biological index (BIX), humification index (HIX), and the ratio of tryptophan-like to humic-like components (C1/C2), were examined to describe the dynamic changes in SMP. These indices were mostly associated with dissolved organic carbon (DOC) of SMPs and specific oxygen uptake rate (SOUR). Among those, ASI was the most strongly correlated with the SOUR data for the pseudo-endogenous and the endogenous periods. Although the three microbial phases were well discriminated using the spectral slope, BIX, and the C1/C2 ratio, the C1/C2 ratio can be suggested as the most preferable indicator as it can also trace the changes of the relative abundance of proteins to humic-like substances in SMPs. The suggested spectroscopic descriptors were reasonably explained by the general trends of decreased large-sized biopolymer fractions (e.g., proteins) and increased humic substrates (HS) with starvation time, which were detected by size exclusion chromatography. This study provides a novel insight into the strong potential of using optical descriptors to easily probe microbial status in biological treatment systems.

Conformations and molecular interactions of poly-γ-glutamic acid as a soluble microbial product in aqueous solutions

Soluble microbial products (SMPs) are of significant concern in the natural environment and in engineered systems. In this work, poly-γ-glutamic acid (γ-PGA), which is predominantly produced by Bacillus sp., was investigated in terms of pH-induced conformational changes and molecular interactions in aqueous solutions; accordingly, its sedimentation coefficient distribution and viscosity were also elucidated. Experimental results indicate that pH has a significant impact on the structure and molecular interactions of γ-PGA. The conformation of the γ-PGA acid form (γ-PGA-H) is rod-like while that of the γ-PGA sodium form (γ-PGA-Na) is sphere-like. The transformation from α-helix to random coil in the γ-PGA secondary structure is primarily responsible for this shape variation. The intramolecular hydrogen bonds in the γ-PGA-H structure decrease and intramolecular electrostatic repulsion increases as pH increases; however, the sedimentation coefficient distributions of γ-PGA are dependent on intermolecular interactions rather than intramolecular interactions. Concentration has a more substantial effect on intermolecular electrostatic repulsion and chain entanglement at higher pH values. Consequently, the sedimentation coefficient distributions of γ-PGA shift significantly at pH 8.9 from 0.1 to 1.0 g/L, and the viscosity of γ-PGA (5% w/v) significantly increases as pH increases from 2.3 to 6.0.