Acute impact of salinity and C/N ratio on the formation and properties of soluble microbial products from activated sludge.

The present study investigated the shock of NaCl and C/N ratio on properties of soluble microbial products (SMPs), focusing on their sized fractions. The results indicated that the NaCl stress increased the content of biopolymers, humic substances, building blocks, and LMW substances in SMPs, while the addition of 40 g NaCl L-1 significantly changed their relative abundance in SMPs. The acute impact of both N-rich and N-deficient conditions accelerated the secretion of SMPs, but the characteristics of LMW substances differed. Meanwhile, the bio-utilization of SMPs has been enhanced with the increase of NaCl dosage but decreased with the increase of the C/N ratio. The mass balance of sized fractions in SMPs + EPS could be set up when NaCl dosage <10 g/L and C/N ratio >5, which indicates the hydrolysis of sized fractions in EPS mainly compensated for their increase/reduction in SMPs. Besides, the results of the toxic assessment indicated that the oxidative damage caused by the NaCl shock was an important factor affecting the property of SMPs, and the abnormal expression of DNA transcription cannot be neglected for bacteria metabolisms with the change of C/N ratio.

A new process to further remove dissolved organic matter and disinfection by-product formation potential during drinking water treatment.

Biological activated carbon (BAC) will produce soluble microbial products (SMPs), which affect effluent quality. To clarify the mechanism by which BAC affects effluent water quality, the processes of a drinking water plant in Jiangsu Province were investigated. It was found that during the O3-BAC process, although ozonation could remove dissolved organic matter (DOC) to a certain extent, the DOC increased from 4.44 to 4.47 mg/L after BAC. Dissolved organic matter (DOM) in effluent from different processes was divided into five fractions based on hydrophilicity and hydrophobicity by resin fractionation. Through fluorescence excitation-emission matrix (EEM) spectroscopy combined with DOC analysis, it was found that SMPs are mainly included in transitional hydrophilic neutral (TPIN) fraction, which was the main cause of the DOC increase. Therefore, a new combined process was designed to remove TPIN effectively by coagulation after biological treatment, and found that coagulation had a good removal rate (13.2%) on TPIN. The trihalomethane formation potential (THMFP) of TPIN could be reduced effectively by 44.9% after coagulation. Compared with the old process, the new combined process had a higher removal rate (14.2-30.0%) of DOC, as well as a greater reduction of THMFP (29.0-78.6%) and haloacetic acid formation potential (HAAFP) (46.4-75.3%). This study aims to reveal the mechanism by which SMPs affect effluent water quality and exacerbate health risks, and to propose a solution to provide theoretical support for the design and optimization of drinking water treatment processes.

Partnering of anammox and denitrifying bacteria benefits anammox's recovery from starvation and complete nitrogen removal.

The cooperative metabolic activity of anammox and denitrifying bacteria could speed up anammox's recovery and reduce nitrate generated from the anammox reaction. In this study, a laboratory-scale model system containing a defined anammox culture AMX and a simultaneous nitrification and denitrification (SND) bacterium - Thauera sp. strain SND5 was established and investigated. Several lines of evidence revealed that strain SND5 consumed soluble microbial products (SMPs) generated by culture AMX (as high as 1.5 mg/L), stimulating anammox activity after long-term starvation. At low C/N ratios with an optimal C/N of 1, SND5 completely consumed organic carbon first at anoxic condition, storing carbon intracellularly as poly-ß-hydroxybutyrate (PHB) (as high as 0.6 mg/L biomass), thereby creating a favorable environment for the growth of anammox bacteria. The anammox reaction and nitrate reduction supported by PHB catabolism could then proceed simultaneously, resulting in enhanced nitrogen removal. Cooperative interactions between anammox and denitrifying bacteria involving SMPs consumption and PHB synthesis may play a significant role in nitrogen cycling at nitrite- and carbon-limited environments.

SMP Production in an Anaerobic Submerged Membrane Bioreactor (AnMBR) at Different Organic Loading Rates.

Anaerobic membrane bioreactors (AnMBRs) have demonstrated an excellent capability to treat domestic wastewater. However, biofouling reduces membrane permeability, increasing operational costs and overall energy demand. Soluble microbial products (SMPs) that build up on the membrane surface play a significant role in the biofouling. In this study, the production of SMPs in a 32 L submerged AnMBR operated at three different organic loads (3.0, 4.1 and 1.2 kg chemical oxygen demand (COD)/m3d for phases 1, 2 and 3, respectively) during long-term operation of the reactor (144, 83 and 94 days) were evaluated. The samples were taken from both the permeate and the sludge at three different heights (0.14, 0.44 and 0.75 m). Higher production of SMPs was obtained in phase 2, which was proportional to the membrane fouling. There were no statistically significant differences (p > 0.05) in the SMPs extracted from sludge at different heights among the three phases. In the permeate of phases 1, 2 and 3, the membrane allowed the removal of 56%, 70% and 64% of the SMP concentration in the sludge. SMPs were characterized by molecular weight (MW). A bimodal behavior was obtained, where fractions prevailed with an MW < 1 kDa, associated with SMPs as utilization-associated products (UAPs) caused fouling by the pore-blocking mechanism. The chemical analysis found that, in the SMPs, the unknown COD predominated over the known COD, such as carbohydrates and proteins. These results suggest that further studies in SMP characterization should focus on the unknown COD fraction to understand the membrane fouling in AnMBR systems better.

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.

Photodegradation of soluble microbial products (SMPs) from membrane bioreactor by GO-COOH/TiO2/Ag.

This study aimed to explore a new degradation method - photocatalysis technology to polish membrane bioreactor (MBR) effluent, using 2,6-di-tert-butylphenol (2,6-DTBP) as a model soluble microbial product (SMP). 2,6-DTBP is one of the predominant SMPs in MBR effluent, which is refractory and difficult to biodegrade. This study developed a novel carboxylated graphene oxide/titanium dioxide/silver (GO-COOH/TiO2/Ag) nanocomposite to photodegrade 2,6-DTBP. GO-COOH/TiO2/Ag was successfully synthesized, using l-cysteine as the linker bonding TiO2/Ag to GO-COOH. The structural, morphological and optical properties of the GO-COOH/TiO2/Ag nanocomposite were characterized using various techniques. Owing to synergistic effects, the GO-COOH/TiO2/Ag nanocomposite exhibited enhanced photocatalytic degradation performance under solar light irradiation when compared to TiO2, Ag and GO-COOH. To remove 25 mg/L 2,6-DTBP, the reaction time for GO-COOH/TiO2/Ag was only 30 min, faster than the 90 min required for pure TiO2 or Ag. In addition, the 200 mg/L GO-COOH/TiO2/Ag nanocomposite aqueous solution showed the best performance under solar light, with 99% removal of 2,6-DTBP. This enhanced capability is likely due to the surface plasmon resonance (SPR) effect contributed by Ag nanoparticles (NPs) doped onto the TiO2. In addition, GO-COOH had a high effective surface area, which assisted in degrading the 2,6-DTBP through improved adsorption. The stability study showed that the photocatalytic activity of the GO-COOH/TiO2/Ag was stable enough for recycling multiple times. The effective degradation performance and excellent stability demonstrates that the GO-COOH/TiO2/Ag nanocomposite can be a promising photocatalyst in the field of effluent SMP photodegradation, which solves the problem of the difficult biodegradation of highly toxic 2,6-DTBP.

UASB-modified Bardenpho process for enhancing bio-treatment efficiency of leachate from a municipal solid waste incineration plant.

Generally, the bio-treatment effluent of municipal solid waste incineration (MSWI) leachate was difficult to meet the local leachate discharge standards for chemical oxygen demand (COD) (100 mg/L), ammonia nitrogen (NH4+-N) (25 mg/L), and total nitrogen (TN) (40 mg/L), and advanced treatment (such as coagulation, membrane filtration, advanced oxidation) is required. However, the cost of advanced treatments is proportional to the concentration of the pollutant. Therefore, improved bio-treatment efficiency is the key to reduce the treatment cost of MSWI leachate. In this study, the up-flow anaerobic sludge blanket (UASB) -modified Bardenpho process was used for the treatment of MSWI leachate. The results showed that it was feasible to dilute the leachate by recirculation of the settling tank effluent, which has great significance in the bio-treatment efficiency. The treatment process achieved removal efficiencies of COD and NH4+-N of 97.5-99.5% and 99.3-99.7%, respectively. Adjustments to the operational conditions of the primary anoxic tank, such as adding an organic carbon source and increasing the hydraulic retention time and the nitrification reflux ratio resulted in a TN removal efficiency of 97.7-98.7%. Controlling the generation of dissolved organic nitrogen (DON) and increasing its removal efficiency significantly improved the TN removal efficiency. The concentrations of NH4+-N and TN in the settling tank effluent complied with the local leachate discharge standard, which minimized the cost of advanced treatment. The results provide new ideas for enhancing the bio-treatment efficiency of leachate and theoretical and technical support for reducing the cost of treatment.

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.

Effects of feed water NOM variation on chloramine demand from chloramine-decaying soluble microbial products during rechloramination.

Earlier, we reported on soluble microbial products-mediated chloramine decay in nitrifying waters. However, we neither separated the agent(s) nor identified the factors that enhanced the production of chloramine-decaying soluble microbial products (cSMPs). Experiments were conducted by feeding reactor sets (each consisting of five reactors connected in series) with treated water (3-8 mg-DOC.L-1) obtained from a water treatment plant. The reactors simulated various nitrifying conditions that are experienced in a chloraminated system. In unfiltered samples obtained from nitrified reactors, about 89-93% of the dosed chloramine decayed within 40 h. The cSMP-mediated decay accounted for 21-39% of all chloramine decay in the samples from 0 to 5 mg-C.L-1 fed reactors and 15% in the samples from 7 to 8 mg-C.L-1 fed reactors. Microbial processes (mediated by nitrifiers and/or heterotrophs) and biomass-associated microbial products (BMPs) in insoluble form accounted for 13-21% for the reactors fed with 0-5 mg-C.L-1 and 34% for those fed with 7-8 mg-C.L-1. The cSMPs were separable with a 30 kDa cut-off membrane but not with 50 or 100 kDa membranes, i.e., they were above 30 kDa but below 50 kDa in size, and were confirmed to be a protein(s). The protein(s) accelerated chloramine decay by accelerating chloramine auto-decomposition and nitrite oxidation. As opposed to the traditional belief, unknown factors accounted for approximately 34-53% in commonly encountered re-chloraminated nitrifying waters (2-5 mg-DOC.L-1). Understanding the identity and role of these factors - such as cSMPs, BMPs, heterotrophs - will lead to a better control of chloramine.

Post-treatment of anaerobic membrane bioreactor (AnMBR) effluent using activated carbon.

Anaerobic membrane bioreactors (AnMBR) are very effective for wastewater treatment, however, with the antibiotic ciprofloxacin (CIP) (0-4.7 mg CIP/L) in the feed their performance decreases, the characteristics of the effluent changes, and further treatment is needed to recycle or discharge the treated effluent. Batch experiments using six activated carbons to treat AnMBR effluents resulting from the treatment of a synthetic wastewater containing ciprofloxacin were carried out at 35 °C. 22-82% COD was removed at a dose of 1 g activated carbon/L, while size characterization showed the 13.4 kDa and <1 kDa fractions were the most difficult to adsorb, while CIP was often removed with high efficiencies of mainly 100%. Significant removal of VFAs also occurred, up to 100%, and this contributed greatly to COD removal. Nitrogen containing compounds and phenols showed the highest removal (∼100%), whereas other groups such as esters, alkanes, and alkenes showed lower removal efficiency.

Assessment of microbial products in the biosorption process of Cu(II) onto aerobic granular sludge: Extracellular polymeric substances contribution and soluble microbial products release.

In the present study, the responses of microbial products in the biosorption process of Cu(II) onto aerobic granular sludge were evaluated by using batch and spectroscopic approaches. Batch experimental data showed that extracellular polymeric substances (EPSs) contributed to Cu(II) removal from an aqueous solution, especially when treating low metal concentrations, whereas soluble microbial products (SMPs) were released under the metal stress during biosorption process. A three-dimensional excitation-emission matrix (3D-EEM) identified four main fluorescence peaks in the EPS, i.e., tryptophan protein-like, aromatic protein-like, humic-like and fulvic acid-like substances, and their fluorescence intensities decreased gradually in the presence of Cu(II) during the sorption process. Particularly, tryptophan protein-like substances quenched the Cu(II) binding to a much higher extent through a static quenching process with less than one class of binding sites. According to the synchronous fluorescence spectra, the whole fluorescence intensity of released SMP samples expressed an increased trend with different degrees along with contact time. Two-dimensional correlation spectroscopy (2D-COS) suggested that the fulvic-like fluorescence fraction might be more susceptible to metal exposure than other fractions. The result of molecular weight distribution demonstrated that the SMPs released from the biosorption process differed significantly according to contact time. The result obtained could provide new insights into the responses of microbial products from aerobic granular sludge with heavy metal treatment.

Leakage of soluble microbial products from biological activated carbon filtration in drinking water treatment plants and its influence on health risks.

The application of ozone-biological activated carbon (O3-BAC) as an advanced treatment method in drinking water treatment plants (DWTPs) can help to remove organic micropollutants and further decrease the dissolved organic carbon (DOC) level in finished water. With the increase attention to microbial safety of drinking water, a pre-positioned O3-BAC followed by a sand filter has been implanted into DWTP located in Shanghai, China to increase the biostability of effluents. The results showed that BAC had high removal efficiencies of UV254, DOC and disinfection by-product formation potential (DBPFP). The removal efficiencies between pre- and post-positioned BAC filtrations were similar. Based on the analyses of fluorescence excitation-emission matrix spectrophotometry (FEEM), the generation and leakage of soluble microbial products (SMPs) were found in both two BAC filtrations on account of the increased fluorescence intensities and fluorescence regional integration (FRI) distribution of protein-like organics, as well as the enhanced biological index (BIX). The leakage of SMPs produced by metabolism of microbes during BAC process resulted in increased DBPFP yield and carcinogenic factor per unit of DOC (CF/DOC). Although BAC filtration reduced the DBPFP and CF, there still was high health risk of effluents for the production of SMPs. Therefore, the health risks for SMPs generated by BAC filtration in drinking water advanced treatment process should be addressed, especially with that at high temperature.

Impact of feed carbohydrates and nitrogen source on the production of soluble microbial products (SMPs) in anaerobic digestion.

Six stirred fill-and-draw batch reactors with a range of carbohydrate feeds (glucose, fructose and sucrose), and nitrogen sources (NH4Cl, urea) at various concentrations were used to investigate the effect of feed composition on the production of soluble microbial products (SMPs) during anaerobic digestion (AD). To gain greater insights into the SMPs produced, the composition of various fractions was analyzed, while the low molecular weight (MW) SMPs generated with different feeds and nutrients were collected and chemically analyzed using GC-MS. Other organic solutes such as free amino acids were determined using HPLC, and this level of chemical analysis has never been carried out in past work because of analytical limitations. It was found that the presence of ammonium salts rather than urea at 200 mg/L stimulated the production of not only volatile fatty acids, but also SMPs of different MW fractions, and reduced the production of biogas significantly. The study also revealed that the type of SMP that dominates in a particular system depends on the chemical characteristics of the feed, and this insight has implications on the composition of the effluent from anaerobic digesters (and their potential chlorination by-products), and membrane fouling in membrane bioreactors.

Generation of soluble microbial products by bio-activated carbon filter during drinking water advanced treatment and its influence on spectral characteristics.

In order to improve our understanding of bio-activated carbon (BAC) filter, the water quality of influent and effluent treated with BAC in a drinking water treatment plant (DWTP) of Shanghai during 2015 was valued. Combining the results from UV254, SUVA254, dissolved organic carbon (DOC) and scanning electron microscopic (SEM), it is found that performance of BAC treatment will be affected by characteristics of activated carbon (AC), which is relevant to the type of activated carbon (including shape and operating time) in this study. Fluorescence excitation-emission matrix (FEEM) shows that the humification index (HIX) and index of recent autochthonous contribution (BIX) is a reliable indicator to descript the variation of dissolved organic matter (DOM) during BAC process. The pattern of variation in BIX and HIX implies that soluble microbial products (SMPs) are formed and humic-like substances are removed during BAC treatment, which is also confirmed by the change of peaks of FEEM in BAC effluent. Large, positive correlations between SUVA254 and disinfection by-products formation potential yield (DBPFP yield) demonstrate that UV-absorbing DOM is directly related to the generation of DBPs. Poor correlations of HIX with DBPFP suggest that non-humic substances with UV-absorbing properties play an important role in the generation of DBPs in water with low SUVA254. Finally, strong but negative correlations between BIX and DBPFP suggest that vigorous microbial metabolism of BAC results in a decrease in DBPFP. However, the DBPFP yield will be enhanced for the generation of SMPs by BAC, especially in summer.

Membrane Bioreactor (MBR) Technology for Wastewater Treatment and Reclamation: Membrane Fouling.

The membrane bioreactor (MBR) has emerged as an efficient compact technology for municipal and industrial wastewater treatment. The major drawback impeding wider application of MBRs is membrane fouling, which significantly reduces membrane performance and lifespan, resulting in a significant increase in maintenance and operating costs. Finding sustainable membrane fouling mitigation strategies in MBRs has been one of the main concerns over the last two decades. This paper provides an overview of membrane fouling and studies conducted to identify mitigating strategies for fouling in MBRs. Classes of foulants, including biofoulants, organic foulants and inorganic foulants, as well as factors influencing membrane fouling are outlined. Recent research attempts on fouling control, including addition of coagulants and adsorbents, combination of aerobic granulation with MBRs, introduction of granular materials with air scouring in the MBR tank, and quorum quenching are presented. The addition of coagulants and adsorbents shows a significant membrane fouling reduction, but further research is needed to establish optimum dosages of the various coagulants/adsorbents. Similarly, the integration of aerobic granulation with MBRs, which targets biofoulants and organic foulants, shows outstanding filtration performance and a significant reduction in fouling rate, as well as excellent nutrients removal. However, further research is needed on the enhancement of long-term granule integrity. Quorum quenching also offers a strong potential for fouling control, but pilot-scale testing is required to explore the feasibility of full-scale application.

Colorimetric measurement of carbohydrates in biological wastewater treatment systems: A critical evaluation.

Four laboratory preparations and three commercially available assay kits were tested on the same carbohydrate samples with the addition of 14 different interfering solutes typically found in wastewater treatment plants. This work shows that a wide variety of solutes can interfere with these assays. In addition, a comparative study on the use of these assays with different carbohydrate samples was also carried out, and the metachromatic response was clearly influenced by variation in sample composition. The carbohydrate content in the supernatant of a submerged anaerobic membrane bioreactor (SAMBR) was also measured using these assays, and the amount in the different supernatant samples, with and without a standard addition of glucose to the samples, showed substantial differences. We concluded that the carbohydrates present in wastewater measured using these colorimetric methods could be seriously under- or over-estimated. A new analytical method needs to be developed in order to better understand the biological transformations occurring in anaerobic digestion that leads to the production of soluble microbial products (SMPs) and extracellular polymeric substance (EPS).

Removal of soluble microbial products as the precursors of disinfection by-products in drinking water supplies.

Water pollution worsens the problem of disinfection by-products (DBPs) in drinking water supply. Biodegradation of wastewater organics produces soluble microbial products (SMPs), which can be important DBP precursors. In this laboratory study, a number of enhanced water treatment methods for DBP control, including enhanced coagulation, ozonation, and activated carbon adsorption, were evaluated for their effectiveness in treating SMP-containing water for the DBP reduction purpose. The results show that enhanced coagulation with alum could remove SMPs only marginally and decrease the DBP formation potential (DBPFP) of the water by less than 20%. Although ozone could cause destruction of SMPs in water, the overall DBPFP of the water did not decrease but increased after ozonation. In contrast, adsorption by granular activated carbon could remove the SMP organics from water by more than 60% and reduce the DBPFP by more than 70%. It is apparent that enhanced coagulation and ozonation are not suitable for the removal of SMPs as DBP precursors from polluted water, although enhanced coagulation has been commonly used to reduce the DBP formation caused by natural organic matter. In comparison, activated carbon adsorption is shown as a more effective means to remove the SMP content from water and hence to control the wastewater-derived DBP problem in water supply.

Characterization of soluble microbial products as precursors of disinfection byproducts in drinking water supply.

Water pollution by wastewater discharge can cause the problem of disinfection byproducts (DBPs) in drinking water supply. In this study, DBP formation characteristics of soluble microbial products (SMPs) as the main products of wastewater organic biodegradation were investigated. The results show that SMPs can act as DBP precursors in simulated wastewater biodegradation process. Under the experimental conditions, stabilized SMPs had DBPFP (DBP formation potential) yield of around 5.6 µmol mmol(-1)-DOC (dissolved organic carbon) and DBP speciation profile different from that of the conventional precursor, natural organic matter (NOM). SMPs contained polysaccharides, proteins, and humic-like substances, and the latter two groups can act as reactive DBP precursors. SMP fraction with molecular weight of <1 kDa accounted for 85% of the organic carbon and 65% of the DBP formation. As small SMP molecules are more difficult to remove by conventional water treatment processes, more efforts are needed to control wastewater-derived DBP problem in water resource management.