Components Of Soluble Microbial Products Research Articles

Reaction sites of pyrimidine bases and nucleosides during chlorination: A computational study

As important components of soluble microbial products in water, nucleobases have attracted much attention due to the high toxicity of their direct aromatic halogenated disinfection by-products (AH-DBPs) during chlorination. However, multiple halogenation sites of AH-DBPs pose challenges to identify them. In this study, reaction sites of pyrimidine bases and nucleosides during chlorination were investigated by quantum chemical computational method. The results indicate that the anion salt forms play key roles in chlorination of uracil, thymine, and their nucleosides, while neutral forms make predominant contributions to cytosine and cytidine. In view of both kinetics and thermodynamics, C5 is the most reactive site for uracil and thymine, N3/C5 and N3 for respective uridine and thymidine, N1/C5/N4 and N4 for respective cytosine and cytidine, whose estimated apparent rate constants kobs-est of ∼103, 103/102, 106/102/104, and 103 M−1 s−1, respectively, in consistent with the known experimental results. C6 in all pyrimidine compounds is hardly attacked by Cl+ in HOCl ascribed to its positive charge, but readily attacked by OH‾ in hydrolysis and the N1=C6 bond was found to possess the highest reactivity in hydrolysis among all double bonds. In addition, the structure-kinetic reactivity relationship study reveals a relatively strong correlation between lgkobs-est and APT charge in all pyrimidine compounds rather than FED2 (HOMO). The results are helpful to further understand the reactivity of various reaction sites in aromatic compounds during chlorination.

Nitrogen removal performance and influencing factors of in situ utilization of soluble microbial products (SMPs) by an anammox and denitrification immobilized filler coupling system

An anaerobic ammonia oxidation (anammox) and denitrifying immobilized filler coupling reactor (RAD) was established to systematically evaluate its performance for enhancing nitrogen removal using endogenous soluble microbial products (SMPs) in the absence of exogenous COD, and was compared with the coupling mode with exogenous COD addition. The results showed that compared with independent anammox reactor (RA), the RAD can effectively use SMPs to reduce the NO3−–N yield and improve the total nitrogen removal efficiency. The NO3−–N yield of the RAD decreased over time during the cycle, decreasing by up to 70 % compared to the RA. 3D-excitation emission matrix showed that from the beginning to the end of the cycle, the SMP components changed from available tryptophan to difficult-to-use humic acids. In addition, the temperature and reaction cycle affected NOx−–N transformation, while low temperature and a long cycle were not conducive to the complete reduction of NO3−–N, leading to the accumulation of NO2−–N. In contrast, adding exogenous COD accelerated NO3−–N removal by the enhancing denitrification activity, but posed a potential threat to anammox activity. High-throughput sequencing analysis showed that Candidatus Kuenenia and Halomonas were the dominant species of the anammox and denitrifying immobilized fillers, respectively, which supported good coupling effect. These results provide valuable information for the optimization of anammox systems and the reduction of organic carbon consumption.

Formation mechanism and metabolic pathways of photogranule in batch and continuous-flow mode under high salinity stress

Photogranules have considerable advantages for treating high saline wastewater economically and efficiently. However, photogranulation mechanism needs to be further investigated. In this study, a continuous-flow photogranular bioreactor (R1) and sequencing batch photogranular bioreactor (R2) were setup for exploring the formation mechanism of photogranules. Results showed that R1 achieved satisfying pollutant removal efficiencies with TOC of 85.36 ± 2.84 %, NH4+ of 93.30 ± 2.07 % and PO43- of 77.68 ± 5.81 %. Microscopy and 16S/18S rRNA sequencing indicated that the dominate bacteria showed discrepancy with Phormidium sp. in R1 and Leptolyngbya sp. in R2, and a specific network structure was formed on photogranules in R1. Additionally, more abundant polysaccharides in soluble microbial products (SMP) were observed in R1, which facilitated cyanobacteria gliding motility, thereby accelerating the photogranulation. Meanwhile, three dimensional excitation-emission matrix (3D-EEM) analysis implied that the pivotal SMP components driving photogranulation were different, with aromatic protein-like substances accumulating in R1 and humic acid-like substances and soluble microbial by-product-like substances in R2. In contrast, R1 exhibited lower abundance of extracellular polymeric substances (EPS) but higher proteins to polysaccharides ratio (PN/PS) than those in R2. High PN/PS showed advantages for accelerating photogranule formation with a compact structure. Furthermore, more enriched aromatic protein-like and humic acid-like EPS were identified in R2 compared with R1, suggesting they were more significant contributors to granulation in R2. Finally, the Kyoto Encyclopedia of Genes and Genomes (KEGG) results revealed that metabolism and genetic information processing were the most abundant metabolic pathways, which were responsible for excellent pollutants removal and stable granulation. Therefore, this study demonstrates the impacts of SMP and EPS on photogranulation and reveals the biological mechanism that drives granular structure and function.

Active assimilators of soluble microbial products produced by wastewater anammox bacteria and their roles revealed by DNA-SIP coupled to metagenomics

Heterotrophic bacteria grow on influent organics or soluble microbial products (SMP) in wastewater anammox processes, playing key roles in facilitating microbial aggregation and reducing excess nitrate. The overgrowth of heterotrophs represents one of the major causes of anammox process failure, while the metabolic functions of coexisting heterotrophs and their roles in anammox process remain vague. This study aimed at revealing metabolic interactions between AnAOB and active SMP assimilators by integrating 13C DNA-stable isotope probing, metabolomic and metagenomic approaches. Glycine, aspartate, and glutamate with low biosynthetic energy cost were the major SMP components produced by AnAOB (net yield: 44.8, 10.4, 8.1mg·g NH4+-N-1). Glycine was likely synthesized by AnAOB via the reductive glycine pathway which is oxygen-tolerant, supporting heterotrophic growth. Fermentative Chloroflexi bacterium OLB13, denitrifying Gemmatimonadaceae and Burkholderiaceae bacterium JOSHI-001 were active SMP assimilators, which were prevalent in globally distributed wastewater anammox reactors as core taxa. They likely formed a mutualistic relationship with auxotrophic Ca. Kuenenia by providing necessities such as methionine, folate, 4'-phosphopantetheine, and molybdopterin cofactor, and receiving vitamin B12 for methionine synthesis. For the first time, the identify and metabolic features of SMP assimilators in wastewater anammox communities were revealed. Supplying necessities secreted by heterotrophs could be helpful to the endeavor of AnAOB enrichment. Practically, maintaining active but not overgrown SMP assimilators is critical to efficient and stable operation of wastewater anammox processes.

Effect of liquid carbon sources on nitrate removal, characteristics of soluble microbial products and microbial community in denitrification biofilters

This study investigated the effects of different carbon sources on the denitrification performance, soluble microbial products (SMPs), and microbial community in lab-scale denitrification biofilters (DNBFs) treating simulated secondary effluent. Three biofilters, named D1, D2, and D3, were fed with sufficient supplies of sodium acetate, methanol, and glucose, respectively. The denitrification efficiencies and denitrification rates of the three DNBFs followed the order D2 > D1 > D3. The final effluent SMP concentrations were 26.24 ± 3.55 mg/L, 24.95 ± 2.67 mg/L, and 28.00 ± 2.44 mg/L in D1, D2, and D3, respectively. The results also showed that the proteins were the main components of SMPs. External carbon sources were also involved in the initial denitrification in D1 and D2, while denitrifying bacteria were induced to utilize SMPs in D3. The total relative abundance of these denitrifying bacteria followed the order D1 > D2 > D3. Moreover, fluorescent soluble microbial byproduct-like substances inhibited the growth of functional bacteria, resulting in a decrease in denitrification efficiency. Therefore, because the SMPs also significantly affected nitrate removal in the DNBFs, their different components exhibited differing effects on denitrification.

Production of soluble microbial products in aerobic granular sludge system under the stress of toxic 4-chlorophenol

ABSTRACTThe purpose of this study was to evaluate the effect of toxic 4-chlorophenol (4-CP) on the production of soluble microbial products (SMP) in an aerobic granular sludge system. Compared with the control experiment, removal efficiency generally reduced by 37.90% after the exposure of 4-CP of 10 mg L−1, indicating that 4-CP had a toxic effect on the performance of biological nitrification. Meanwhile, the contents of polysaccharides and proteins (PN) of SMP increased from 31.0 ± 0.32 and 0.8 ± 0.12 mg L−1 to 39.0 ± 0.56 and 61.70 ± 0.78 mg L−1, respectively. Specific oxygen uptake rate (SOUR) showed that the values of (SOUR)H, and reduced by 27%, 48% and 41% in the presence of 4-CP. The characteristic and chemical components of SMP were assessed by using three-dimensional excitation-emission matrix (3D-EEM), synchronous fluorescence spectra, two-dimensional correlation spectroscopy (2D-COS), scanning electron microscope and Fourier transform infrared spectroscopy . 3D-EEM implied that SMP were mainly composed of tryptophan PN-like, aromatic PN-like and humic acid-like substances after 4-CP exposure. Synchronous fluorescence spectra coupled with 2D-COS suggested that SMP samples changed in the following sequences: PN-like substances > humic acid-like substances in the absence of 4-CP, and shorter wavelength > longer wavelength in PN-like substances in the presence of 4-CP.

Responses of soluble microbial products and extracellular polymeric substances to the presence of toxic 2,6-dichlorophenol in aerobic granular sludge system

The objective of this study was to evaluate the responses of soluble microbial products (SMP) and extracellular polymeric substances (EPS) to the presence of toxic 2,6-dichlorophenol (2,6-DCP) in aerobic granular sludge (AGS) system. Batch experiment showed that NH4+-N removal efficiency significantly decreased from 99.6% to 47.2% in the toxic 2,6-DCP of 20 mg/L. Moreover, the inhibition degrees of 2,6-DCP on (SOUR)H, (SOUR)NH4 and (SOUR)NO2 were 7.8%, 32.1% and 9.5%, respectively. The main components of SMP, including protein (PN) and polysaccharide (PS) increased from 2.3 ± 0.74 and 16.8 ± 0.12 mg/L to 66.4 ± 0.56 and 18.0 ± 0.19 mg/L in the presence of 2,6-DCP. Three-dimensional excitation-emission matrix (3D-EEM) spectroscopy identified tryptophan PN-like, humic acid-like and fulvic acid-like substances in the control SMP, and their fluorescence intensities increased after exposure to 2,6-DCP. Synchronous fluorescence spectra suggested that the fluorescence quenching between EPS and 2,6-DCP was a static quenching process. The obtained results could provide insightful information on the responses of microbial products to AGS in the presence of toxic chlorophenols.

Characterization of biofoulants illustrates different membrane fouling mechanisms for aerobic and anaerobic membrane bioreactors

Abstract This study compares the membrane fouling mechanisms of aerobic (AeMBR) and anaerobic membrane bioreactors (AnMBR) of the same reactor configuration at similar operating conditions. Although both the AeMBR and AnMBR achieved more than 90% COD removal efficiency, the fouling mechanisms were different. Molecular weight (MW) fingerprint profiles showed that a majority of fragments in anaerobic soluble microbial products (SMP) were retained by the membrane and some fragments were present in both SMP and in soluble extracellular polymeric substances (EPS), suggesting that the physical retention of SMP components contributed to the AnMBR membrane fouling. One of the dominant fragments was comprised of glycolipoprotein (size 630–640 kDa) and correlated in abundance in AnMBR–EPS with the extent of anaerobic membrane fouling. In contrast, all detected AeMBR–SMP fragments permeated through the membrane. Aerobic SMP and soluble EPS also showed very different fingerprinting profiles. A large amount of adenosine triphosphate was present in the AeMBR–EPS, suggesting that microbial activity arising from certain bacterial populations, such as unclassified Comamonadaceae and unclassified Chitinophagaceae, may play a role in aerobic membrane fouling. This study underlines the differences in fouling mechanisms between AeMBR and AnMBR systems and can be applied to facilitate the development of appropriate fouling control strategies.

Characterization, DBPs formation, and mutagenicity of soluble microbial products (SMPs) in wastewater under simulated stressful conditions

Soluble microbial products (SMPs) are an important group of components in activated sludge-treated wastewater effluents. Chlorination is the most widely used method for disinfecting wastewater effluents. During chlorination of wastewater effluents, SMPs may act as precursors to form disinfection by-products (DBPs), which may pose adverse impacts on the organisms in the receiving water body. In this study, SMPs were prepared by simulating activated sludge under different stressful conditions, including high ammonia content (HA), high salinity (HS), high levels of heavy metals (HM) and high temperature (HT), as well as a normal state (NS). The molecular weight (MW) distribution of SMPs was characterized using gel permeation chromatography (GPC). Chlorination of SMPs was conducted with sodium hypochlorite. Several species of DBPs were detected using gas chromatography–mass spectrometry (GC–MS). The mutagenicity of SMPs solutions and SMPs solutions treated with chlorination was also evaluated using the umu test. Compared with NS, stressful conditions were induced to produce more low MW components of SMPs. Stressful conditions, had no significant effect on the species of DBPs, but played a crucial role in the levels of DBPs produced in SMPs solutions during chlorination. Among the stressful conditions tested, HT and HS resulted in higher levels of both carbon-containing DBPs (C-DBPs) and nitrogen-containing DBPs (N-DBPs). Levels of C-DBPs and N-DBPs were lower under HM condition. HA stimulated the production of N-DBPs, but had no impact on the levels of C-DBPs. The mutagenicity of SMPs solutions was higher under the stressful conditions than that under NS condition in both before and after chlorination. For each SMPs solution, the mutagenicity of SMPs increased after the chlorination, except for SMPs solution under HM and NS conditions.

A Mini Review of Soluble Microbial Products in the Membrane Bioreactor Systems

The membrane bioreactor (MBR) systems have been increasingly used in water treatment in recent years. However, fouling by soluble microbial products (SMP) remains one of the key performance limitations for more widespread applications. A brief review concerning the characterization, production, affecting factors, components of SMP in MBR systems is presented.

Formation of soluble microbial products (SMP) by activated sludge at various salinities

Soluble microbial products (SMP) present a significant component of effluent organic matter from biological wastewater treatment reactors, and can affect the membrane fouling and formation of disinfection by-products. Thus, SMP have attracted increasing concerns in wastewater treatment and reclamation. In this work, the formation of SMP by activated sludge at various NaCl concentrations is investigated by using fluorescence excitation-emission matrix (EEM) spectroscopy with parallel factor analysis (PARAFAC) and fluorescence regional integration (FRI). The results show that a high level of salinity decreases substrate removal efficiency and leads to an accumulation of SMP, especially proteins. Three components of SMP, one protein-like and two humic-acid-like components, are identified by PARAFAC, which exhibit different trends with the variation of NaCl concentration. FRI analysis reveals that the majority of protein fluorescence is attributed to tryptophan and tryptophan-like proteins, rather than tyrosine and tyrosine-like proteins. With an increase in NaCl concentration, the normalized volume percentages of tyrosine and tryptophan region increase, while those of humic- and fulvic-acid-like region decrease significantly. This work demonstrates that salinity affects the formation of SMP, and that EEM with PARAFAC in combination with FRI analysis is a useful tool to get insight into the formation of SMP by activated sludge.

Soluble microbial products and their implications in mixed culture biotechnology

Soluble microbial products (SMP) are soluble organic compounds released during normal biomass metabolism in mixed culture biotechnology. In this review, we give the up-to-date status on several essential SMP issues: mechanisms of SMP formation, differentiation between utilization-associated products (UAP) and biomass-associated products (BAP), biodegradability of the SMP components, how formation of SMP by autotrophs controls effluent quality and supports a substantial population of heterotrophs, mathematical modeling that includes SMP, and improving effluent quality by controlling SMP. We also present two timely examples that highlight our current understanding and give an indication of how SMP affects the performance of modern mixed culture biotechnology: membrane fouling of membrane bioreactors (MBRs) and the dynamics of SMP in anaerobic systems.

Characterization of Soluble Microbial Products and Their Fouling Impacts in Membrane Bioreactors

Membrane bioreactor (MBR) fouling is not only influenced by the soluble microbial products (SMP) concentration but by their characteristics. Experiments of separate producing biomass associated products (BAP) and utilization associated products (UAP) allowed the separation of BAP and UAP effects from sludge water (SW). Thus, filtration of individual SMP components and further characterization becomes possible. Unstirred cell filtration was used to study fouling mechanisms and liquid chromatography--organic carbon detection (LC-OCD) and fluorescence excitation--emission matrix (EEM) were used to characterize the foulant. Generally, the SMP exhibiting characteristics of higher molecular weight, greater hydrophilicity and a more reduced state showed a higher retention percentage. However, the higher retention does not always yield higher fouling effects. The UAP filtration showed the highest specific cake resistance and pore blocking resistance attributed to their higher percentage of low molecular weight molecules, although their retention percentage was lower than the SW and BAP filtration. The UAP produced in the cell proliferation phase appeared to have the highest fouling potential.

Characteristics of soluble microbial products in membrane bioreactor and its effect on membrane fouling

In this study, the accumulation and characteristics of soluble microbial products (SMP) in the mixed liquor and the effluent of the membrane bioreactor (MBR) were measured and compared. It was found that the concentration of SMP decreased when the SRT was increased from 10 days to 30 days, and then stabilized as SRT was increased to 60 days. The molecular weight (MW) distributions of SMP indicated that the SMP of larger MW (> 30 kDa) was the most abundant fraction in the MBR. The similar MW distributions of SMP in the mixed liquor and effluent implied that membrane fouling due to SMP in the initial slow fouling stage was not due to size sieving. After the MBR was operated for a period of time, only the SMP of relatively large MW (> 30 kDa) was detected in the mixed liquor. The result indicated that size sieving of SMP occurred only after a cake layer was formed on the membrane surface although the effect was not significant and only worked on larger molecules. The accumulation of hydrophilic components of SMP in the mixed liquor of the bioreactor suggested that the hydrophilic fraction (in carbohydrates) could be the major cause for membrane fouling.

Retention of soluble microbial products in submerged membrane bioreactors

The retention of soluble microbial products (SMP) is significant for the operation of membrane bioreactors (MBRs) from the aspect of both effluent quality and membrane fouling. Constant flux stirred dead-end filtration of a MBR sludge supernatant was conducted. The SMP retention by the membrane is dynamic rather than consistent during filtration. Polysaccharides and proteins are the major components of SMP that are most easily retained by the membrane. The framework of the gel layer is mainly formed from polysaccharides, which controls its permeability. The SMP proteins appear to be trapped in the gel layer by steric and/or adsorptive effects but play little structural role. The underlying mechanism for adsorptive retention may arise from intermolecular electrostatic attraction or chemical complexation involving metal ions.

Evaluation of rapid methods for in-situ characterization of organic contaminant load and biodegradation rates in winery wastewater

Rapid methods for the in-situ evaluation of the organic load have recently been developed and successfully implemented in municipal wastewater treatment systems. Their direct application to winery wastewater treatment is questionable due to substantial differences between municipal and winery wastewater. We critically evaluate the use of UV-VIS spectrometry, buffer capacity testing (BCT), and respirometry as rapid methods to determine organic load and biodegradation rates of winery wastewater. We tested three types of samples: actual and treated winery wastewater, synthetic winery wastewater, and samples from a biological batch reactor. Not surprisingly, respirometry gave a good estimation of biodegradation rates for substrate of different complexities, whereas UV-VIS and BCT did not provide a quantitative measure of the easily degradable sugars and ethanol, typically the main components of the COD in the influent. However, our results strongly suggest that UV-VIS and BCT can be used to identify and estimate the concentration of complex substrates in the influent and soluble microbial products (SMP) in biological reactors and their effluent. Furthermore, the integration of UV-VIS spectrometry, BCT, and mathematical modeling was able to differentiate between the two components of SMPs: substrate utilization associated products (UAP) and biomass associated products (BAP). Since the effluent COD in biologically treated wastewaters is composed primarily by SMPs, the quantitative information given by these techniques may be used for plant control and optimization.

Impact of ambient conditions on SMP elimination and rejection in MBRs

The widespread application of the membrane-assisted activated sludge process is restricted by membrane fouling, which increases investment and operating costs. Soluble microbial products (SMPs) are currently considered as the major cause of membrane fouling in membrane bioreactors (MBRs). This study aims at elucidating and quantifying the effects of varying environmental conditions on SMP elimination and rejection based on findings in a pilot MBR and in well-defined lab trials. Several factors are thought to influence the concentration of SMP and their fouling propensity in one way or the other, but findings are often inconsistent or even contradictory. Here, SMP loading rate was found to have the greatest effect on SMP elimination and thus on concentration in the MBR. The degree of elimination decreased at very low DO and low nitrate concentrations. On average, 75% of influent SMP were eliminated in both pilot and lab trials, with the elimination of polysaccharides (PS) mostly above 80%. Rejection of SMP components by the used membrane (PAN, 37 nm) ranged mainly from 20% to 70% for proteins and from 75% to 100% for PS. Especially protein rejection decreased at higher temperatures and higher nitrification activity. The increased fouling rates at lower temperatures might therefore partly be explained by this increased rejection. Apparently, mainly the nitrite-oxidising community is responsible for the formation for smaller SMP molecules that can pass the membrane.

Role of Soluble Microbial Products (SMP) in Membrane Fouling and Flux Decline

Soluble microbial products (SMP), a significant component of effluent organic matter (EfOM), play an important role in membrane fouling and flux decline in wastewater reclamation/reuse applications. The SMP compounds of a microbial origin are derived during biological processes of wastewater treatment. They exhibit the characteristics of hydrophilic organic colloids and macromolecules. These high molecular weight compounds play an important role in creating high resistance of the membrane, leading to a reduction of permeate flux. The SMP fouling of RO, NF, and tight UF membranes is associated with formation of a cake/gel layer due to size (steric) exclusion. FTIR spectra of SMP- and EfOM-fouled membranes exhibited foulants' composition, consisting of polysaccharides, proteins, and/or aminosugar-like compounds. This finding reveals the important role of the SMP components as factors in membrane fouling and flux decline associated with EfOM source waters. Solids retention time (SRT) affects the characteristics and amounts of SMP, however, SRT did not affect flux decline trends of RO and NF membranes.

Adaptive response of microbial communities to soluble microbial products

We carried out two experiments to study the influence of soluble microbial products (SMP) on biomass concentration [defined as mixed liquor suspended solids (MLSS)] and removal of soluble biological and chemical oxygen demands (sBOD5 and sCOD): (1) SMP were allowed to accumulate, and (2) SMP content was artificially reduced by washing the biomass. The daily initial sCOD in both experiments was kept constant at 859+/-6 mg/l for 16 days. In experiment 1, the highest sCOD removal (80%) occurred during the first day. Thereafter, it decreased successively to 40% [sludge retention time (SRT), 12 days], after which it increased steadily to 50+/-4%. Variations in residual sCOD were accompanied by variations in sBOD5, showing that the biodegradability of the accumulated SMP components was changing. MLSS fluctuated within the range 1,200+/-25-1,993+/-58 mg/l. We attributed the irregular accumulation of the biomass to variations in the biodegradability of SMP components. The initial sBOD5/MLSS ratio varied according to variations in initial sBOD5 and MLSS, whereas the residual ratio was constant at 0.025+/-0.008. This indicated a direct relationship between the concentrations of biomass and SMP produced. In experiment 2, MLSS increased from 1,200+/-25 to a constant value (2,810+/-16 mg/l; SRT, 12 days). After this time, no decrease or increase in MLSS was observed. Correspondingly, sCOD and sBOD5 removal increased from 80-97 to 84-99%. A stable microbial community that could consume organic matter efficiently was developed under these conditions.