Utilization-associated Products Research Articles

Impact of invertebrates on water quality safety and their sheltering effect on bacteria in water supply systems

Invertebrates in drinking water not only affect human health, but also provide migration and shelter for pathogenic microorganisms. Their residues and metabolites also produce DBPs (disinfection by-products), which have adverse effects on the health of residents. In this study, the contributions of the rotifers and nematodes to the BDOC (biodegradable dissolved organic carbon), BRP (bacterial regrowth potential) and DBPs in drinking water were explored, and the sheltering effects of chlorine-resistant invertebrates on indigenous bacteria and pathogenic bacteria were studied, and the health and safety risk of invertebrates in drinking water was also assessed. The contributions of rotifer BAPs (biomass-associated products), UAPs (utilization-associated products) of rotifer, and nematode BAPs to the BRP were 46, 1240, and 24 CFU/mL. Nematodes were found to have a sheltering effect on indigenous bacteria and pathogenic bacteria, allowing them to resist chlorine disinfection and UV (ultraviolet) disinfection. When subjected to a UV dose of 40 mJ/cm2, the inactivation rates of indigenous bacteria and three pathogenic bacteria decreased by 85% and 39–50% when bacteria were sheltered by the living nematodes; while decreased by 66% and 15–41% when they were sheltered by nematode residue. The safety risk posed by invertebrates in the drinking water was mainly due to their ability to promote bacterial regeneration and carry bacteria. This study aims to provide a theoretical basis and technical support for the risk control of invertebrates' pollution, and provides references for ensuring the safety of drinking water and formulating standards for the levels of invertebrates in drinking water.

Characterization and modelling of soluble microbial products in activated sludge systems treating municipal wastewater with special emphasis on temperature effect.

Soluble microbial products (SMP) classified as utilization-associated products (UAP) and biomass-associated products (BAP) are the predominant foulants determining fouling in tertiary filtration. However, the exact mechanisms of BAP and UAP generation when treating real wastewaters under cold temperatures remain unrevealed. This paper presents the first study linking biological processes and SMP formation when treating real wastewaters through a combination of bioprocess modelling and advanced SMP characterization. Further, the impact of low operating temperatures on SMP production which has received relatively little attention was studied in detail. The use of liquid chromatography-organic carbon detection (LC-OCD) revealed a significant increase in protein and polysaccharide concentrations in the treated effluents as temperature decreased with a more sensitive impact on polysaccharides. The generation of SMP from biomass decay (BAP) and substrate utilization (UAP) was derived from the LC-OCD data on the basis of protein and polysaccharide mass balances. UAP and BAP yields were estimated as the ratios of the observed generation rates to the rates of substrate utilization and endogenous decay respectively, which both declined as temperature increased. A strong correlation was observed between temperature and BAP/UAP yields whereas the generation of BAP was more temperature sensitive than UAP. Such process modelling can be employed to assist with the optimization of the design and operation of membrane processes when treating wastewaters under challenging conditions like low temperature.

Biochemical characteristics and membrane fouling behaviors of soluble microbial products during the lifecycle of Escherichia coli

The complexity of production process and chemical compositions of soluble microbial products (SMPs) largely limits the understanding of membrane fouling in membrane bioreactors (MBRs). Herein, we used a model single-strain Escherichia coli to better understand the chemical natures of SMPs and their roles in membrane fouling. The effects of carbon source and growth phase on the chemical compositions of SMPs were identified at both the compound and molecular levels by using advanced techniques including excitation emission matrix and parallel factor analysis (EEM-PARAFAC), size exclusion chromatography coupled with organic carbon detection (LC-OCD), and untargeted ultra-performance liquid chromatography - Q-Exactive - mass spectrometry (UPLC-Q-Exactive-MS). Subsequently, the roles of SMPs in the propensity of membrane fouling during ultrafiltration (UF) were studied. The results showed that the chemical compositions and fouling potentials of SMPs were carbon source- and growth phase-dependent. In the exponential phase, SMPs mainly consisted of utilization-associated products (UAPs) and remaining substrates. As the microorganism progressed into the stationary and senescent phases, UAPs and biomass-associated products (BAPs) were the main components, respectively. The SMP contents generated in glucose medium were higher than those generated in acetate medium, and higher abundances of humic fluorescent components were observed in glucose-fed SMPs. Van Krevelen diagrams of the UPLC-MS results revealed that acetate-fed SMPs contained more carboxylic-rich alicyclic molecules, peptides-like, aromatic, and carbohydrates-like components than glucose-fed SMPs in the stationary and senescent phases. These components played a significant role in irreversible membrane fouling, as evidenced in UF experiments. Standard blocking and cake filtration were the main fouling mechanisms for the filtration of SMPs collected in the exponential and stationary/senescent phases, respectively. Our findings highlight linkages between SMP compositions and membrane fouling at both the compound and molecular levels and suggest that both the carbon source and growth phase strongly determine the production potential, chemical nature, and fouling behavior of SMPs.

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.

In-situ utilization of soluble microbial product (SMP) cooperated with enhancing SMP-dependent denitrification in aerobic-anoxic sequencing batch reactor

Soluble microbial products (SMPs), as secondary pollutants, comprise a dominant percentage of residual COD in effluents from biological wastewater treatment processes. They can also be regarded as substitute electron sources if the in-situ utilization of SMPs could be achieved. In this study, the fate of SMPs in a sequencing batch reactor (SBR) treating artificial municipal sewage was investigated. Based on the regular SBR operation mode, a 3 h extension of anoxic phase was provided to promote SMP degradation. Meanwhile, the denitrification efficiencies achieved by adopting SMPs and influent organic substrates (IOSs) were compared to reveal the significant contribution of the in-situ utilization of SMP for nitrogen removal. Approximately 21.1 mg N/L of total nitrogen (TN) was removed over a single cyclic reaction, in which only 13.2 mg N/L was removed via IOS-dependent denitrification. The remaining 7.9 mg N/L of TN was realized via SMP-dependent denitrification, including 3.9 mg N/L by utilization-associated products and 4.0 mg N/L by biomass-associated products, which significantly contributed 37.4% of TN removal. The aromatic proteins, tryptophan-like proteins, polysaccharides and fulvic acids contained in SMP were the potential precursors of electron donors to support SMP-dependent denitrification process.

Activity enhancement of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria in activated sludge process: metabolite reduction and CO2 mitigation intensification process

The interaction of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) is of considerable importance in nitrification process. Ecophysiological interactions between the communities of AOB and NOB were investigated by monitoring NO2− as the intermediate compound in an organic carbon-depleted nitrifying activated sludge fed only NH4+ as a nitrogen source (40 mg/L). The presence of boom and bust (feast and famine) cycle successfully indicates the activity cycles of AOB and NOB through cultivation-dependent method. The maximum growth rate and yield for AOB in nitritation-dominant period were (0.67 day−1, 0.17 gVSS gN−1) and for NOB in nitratation-dominant period were (0.71 day−1, 0.072 gVSS gN−1). Soluble microbial products (SMP) and extracellular polymeric substances (EPS) generated by AOB were 1.2 and 1.8 mg/L, respectively, while NOB produced 0.6 mg/L of SMP and 1 mg/L of EPS. While NOB were low in utilization-associated products (UAP) (0.07 mg/L) and biomass-associated products (BAP) (0.12 mg/L), AOB were higher in UAP (0.15 mg/L) and BAP (0.3 mg/L). The continuation presence of zero C/N ratio, in either inlet ratio or net available ratio for the microbial community, can prolong and enhance nitratation process. NOB enrichment and nitratation intensification strategy through zero C/N ratio are able to reduce remarkably microbial metabolites 50% lower than conventional process and enhance nitrification efficiency in activated sludge-involved processes.

Heterotrophic denitrifiers growing on soluble microbial products contribute to nitrous oxide production in anammox biofilm: Model evaluation

In this work, a model framework was constructed to assess and predict nitrous oxide (N2O) production, substrate and microbe interactions in an anammox biofilm bioreactor. The anammox kinetics were extended by including kinetics of autotrophic soluble microbial products (SMP) formation, which consisted of utilization-associated products (UAP) and biomass-associated products (BAP). Heterotrophic bacteria growing on UAP, BAP and decay released substance (SS) were modelled to perform four-step sequential reductions from nitrate to dinitrogen gas. N2O was modelled as an intermidiate of heterotrophic denitrification via three pathways with UAP, BAP and SS as the electron donors. The developed model framework was evaluated using long-term operational data from an anammox biofilm reactor and satisfactorily reproduced effluent nitrogen and SMP as well as N2O emission factors under different operational conditions. The modeling results revealed that N2O was mainly produced with UAP as the electron donor while BAP and SS play minor roles. Heterotrophic denitrifiers growing on UAP would significantly contribute to N2O emission from anammox biofilm reactor even though heterotrophs only account for a relatively small fraction of active biomass in the anammox biofilm. Comprehensive simulations were conducted to investigate the effects of N loading rate and biofilm thickness, which indicated that maintaining a low N loading rate and a thick biofilm thickness were essential for high total nitrogen removal efficiency and low N2O emission.

The effect of toxic carbon source on the reaction of activated sludge in the batch reactor

The toxic carbon source can cause higher residual effluent dissolved organic carbon than easily biodegraded carbon source in activated sludge process. In this study, an integrated activated sludge model is developed as the tool to understand the mechanism of toxic carbon source (phenol) on the reaction, regarding the carbon flows during the aeration period in the batch reactor. To estimate the toxic function of phenol, the microbial cells death rate (kdeath) is introduced into the model. The integrated model was calibrated and validated by the experimental data and it was found the model simulations matched the all experimental measurements. In the steady state, the toxicity of phenol can result in higher microbial cells death rate (0.1637 h−1 vs 0.0028 h−1) and decay rate coefficient of biomass (0.0115 h−1 vs 0.0107 h−1) than acetate. In addition, the utilization-associated products (UAP) and extracellular polymeric substances (EPS) formation coefficients of phenol are higher than that of acetate, indicating that more carbon flows into the extracellular components, such as soluble microbial products (SMP), when degrading toxic organics. In the non-steady state of feeding phenol, the yield coefficient for growth and maximum specific growth rate are very low in the first few days (1–10 d), while the decay rate coefficient of biomass and microbial cells death rate are relatively high. The model provides insights into the difference of the dynamic reaction with different carbon sources in the batch reactor.

Production of biogenic manganese oxides coupled with methane oxidation in a bioreactor for removing metals from wastewater

Biogenic manganese oxide (BioMnOx) can efficiently adsorb various minor metals. The production of BioMnOx in reactors to remove metals during wastewater treatment processes is a promising biotechnological method. However, it is difficult to preferentially enrich manganese-oxidizing bacteria (MnOB) to produce BioMnOx during wastewater treatment processes. A unique method of cultivating MnOB using methane-oxidizing bacteria (MOB) to produce soluble microbial products is proposed here. MnOB were successfully enriched in a methane-fed reactor containing MOB. BioMnOx production during the wastewater treatment process was confirmed. Long-term continual operation of the reactor allowed simultaneous removal of Mn(II), Co(II), and Ni(II). The Co(II)/Mn(II) and Ni(II)/Mn(II) removal ratios were 53% and 19%, respectively. The degree to which Mn(II) was removed indicated that the enriched MnOB used utilization-associated products and/or biomass-associated products. Microbial community analysis revealed that methanol-oxidizing bacteria belonging to the Hyphomicrobiaceae family played important roles in the oxidation of Mn(II) by using utilization-associated products. Methane-oxidizing bacteria were found to be inhibited by MnO2, but the maximum Mn(II) removal rate was 0.49 kg m−3 d−1.

Formation of soluble microbial products and their contribution as electron donors for denitrification

Soluble microbial products (SMP) cause major soluble chemical oxygen demands (sCOD) in secondary effluent and significantly affect effluent quality. However, SMP can be also treated as new organic carbon resource, which can provide electrons for denitrification under anoxic conditions. This work investigated contribution of SMP as electron donors during denitrification under different conditions (feast, feast–famine, and famine). Only fraction of utilization-associated products could be adopted as electron donors for denitrification in feast condition because of sufficient organic carbon supply. Most biomass-associated products remained in water. In feast-famine condition, the nitrogen (nitrate and nitrite) reduction using influent TOC and SMP as electron donors were 86.4 and 55.2mgN/L respectively. SMP accounted for 33.6% and 39.0% of total nitrogen (TN) removal and total nitrogen (nitrate and nitrite) reduction, respectively. Only SMP can be adopted as sole electron donors in famine condition. Approximately 128.7mgN/L of nitrogen (nitrate and nitrite) reduction was calculated. Nitrate and TN removal were 91.4% and 51.7%, respectively. As electron acceptors under anoxic conditions, nitrate or nitrite can stimulate SMP generation from hydrolysis of extracellular polymeric substances.

Assessment of Heterotrophic Growth Supported by Soluble Microbial Products in Anammox Biofilm using Multidimensional Modeling.

Anaerobic ammonium oxidation (anammox) is known to autotrophically convert ammonium to dinitrogen gas with nitrite as the electron acceptor, but little is known about their released microbial products and how these are relative to heterotrophic growth in anammox system. In this work, we applied a mathematical model to assess the heterotrophic growth supported by three key microbial products produced by bacteria in anammox biofilm (utilization associated products (UAP), biomass associated products (BAP), and decay released substrate). Both One-dimensional and two-dimensional numerical biofilm models were developed to describe the development of anammox biofilm as a function of the multiple bacteria–substrate interactions. Model simulations show that UAP of anammox is the main organic carbon source for heterotrophs. Heterotrophs are mainly dominant at the surface of the anammox biofilm with small fraction inside the biofilm. 1-D model is sufficient to describe the main substrate concentrations/fluxes within the anammox biofilm, while the 2-D model can give a more detailed biomass distribution. The heterotrophic growth on UAP is mainly present at the outside of anammox biofilm, their growth on BAP (HetB) are present throughout the biofilm, while the growth on decay released substrate (HetD) is mainly located in the inner layers of the biofilm.

Characterization of soluble microbial products in a drinking water biological aerated filter.

Utilization-associated products (UAPs) and biomass-associated products (BAPs) were quantified separately in this study to characterize soluble microbial products (SMPs) in a drinking water lab-scale biological aerated filter (BAF), and their basic characteristics were explored using gel filtration chromatography and three-dimensional excitation-emission matrix (3D-EEM) spectrophotometry with fluorescence regional integration analysis and parallel factor model. UAPs were observed increased with the increase of filter media depth and accumulated after BAF treatment, whereas BAPs were basically constant. 3D-EEM spectroscopy analysis result showed that tryptophan and protein-like compounds were the main components of UAPs and BAPs, and fulvic-acid-like substance was a major component of BAPs, rather than UAPs. In terms of molecular weight (MW) distribution, UAP MW presented a bimodal distribution in the range of 1-5 and >10kDa, while BAP MW exhibited unimodal distribution with MW >20kDa fraction accounting for more than 90%. The macromolecules of UAPs accumulated after BAF treatment. This study provides theoretical support for in-depth study of SMP characteristics.

Quantification and kinetic characterization of soluble microbial products from municipal wastewater treatment plants

Soluble microbial products (SMP) formed by microorganisms in wastewater treatment plants (WWTPs) adversely affect final effluent quality and treatment efficiency. It is difficult to distinguish SMP from residual proteins, lipids and carbohydrates present in the influent that may persist during treatment. No method is currently available to determine quantitatively the extent to which SMP contribute to organic discharges from municipal WWTPs. In this work a modeling approach is presented which allows the SMP fraction of the effluent of a municipal WWTP to be quantified and described. The model is validated, in terms of utilization-associated products, biomass-associated products and extracellular polymeric substances, using influent from a municipal WWTP. SMP was found to account for, on average, 27 mg/L of chemical oxygen demand (COD), or 61% of the total COD in the WWTP effluent. Over 90% of the SMP was comprised of biomass-associated products. Five main factors influencing SMP formation in WWTP were evaluated. Neither wastewater composition nor mixed liquor suspended solids concentration was found to affect SMP production. On the other hand, a positive correlation was observed for SMP formation with both solids retention time and influent COD concentration, and a negative correlation with hydraulic retention time. Thus, operating or designing WWTPs with short solids retention and long hydraulic retention times could be considered as solutions for minimizing SMP production.

Fractionation, characterization and C-, N-disinfection byproduct formation of soluble microbial products in MBR processes

Soluble microbial products are heterogeneous organic materials generated during microbial growth and decay, which are the major soluble organic matters in MBR effluents and are the primary precursors forming disinfection by-products (DBPs). In this study, biomass associated products (BAP) and utilization associated products (UAP) were separately produced to investigate their physical chemical characteristics and disinfection byproduct (DBP) formation during chlorination in the presence of ammonia. BAP had higher formation reactivity of halogenated carbonaceous and nitrogenous DBPs including trihalomethanes, haloketones, haloacetonitriles and trichloronitromethane due to their higher percentage of large molecular weight (MW) materials and humic substances compared with UAP. However, the nonhalogenated species N-nitrosodimethylamine (NDMA) yield of UAP was twice higher than that of BAP because UAP contained more nitrogenous organic matters with MW<500Da including aromatic polypeptide/amino acid-like materials and secondary amines, which have been proved to have high NDMA formation potential.

Relationship between soluble microbial products (SMP) and effluent organic matter (EfOM): Characterized by fluorescence excitation emission matrix coupled with parallel factor analysis

Effluent organic matter (EfOM) originating from wastewater treatment plant (WWTP) is of significant concern, as it not only influences the discharge quality of WWTP but also exerts a significant effect on the efficiency of the downstream advanced treatment facilities. Soluble microbial products (SMP) is a major part of EfOM. In order to further understand the relationship between soluble microbial products (SMP) and EfOM, and in turn, to propose measures for EfOM control, the formation of SMP and EfOM in identical activated sludge sequencing batch reactors (SBR) with different feed water was investigated using fluorescence excitation and emission spectroscopy matrix coupled with parallel factor analysis (EEM–PARAFAC) as well as other organic matter quantification tools. Results showed that EfOM contained not only SMP but also a considerable amount of allochthonous organic matter that derived not merely from natural organic matter (NOM). Four components in EfOM/SMP were identified by EEM–PARAFAC. Tyrosine-like substances in EfOM (Component 3, λex/em=270/316nm) were mainly originated from utilization associated products (UAP) of SMP. Tryptophan-like substances (Component 2, λex/em=280/336nm) as well as fulvic-like and humic-like substances in EfOM (Component 1, λex/em=240(290)/392nm and Component 4, λex/em=260(365)/444nm) were majorly derived from the refractory substances introduced along with the influent, among which Component 2 was stemmed from sources other than NOM. As solid retention time (SRT) increased, Component 2 and polysaccharides in SMP/EfOM decreased, while Component 4 in SMP increased.

Implication of endogenous decay current and quantification of soluble microbial products (SMP) in microbial electrolysis cells

We designed a dual-chamber microbial electrolysis cell (MEC) which provided a large anode surface area against membrane surface area, but kept a short distance between the anode and the cathode. Current density ranged from 8.3 to 11 A m−2 of membrane surface area for chemical oxygen demand (COD) loading rate 0.3–6.3 kg COD/m3 d. Hydrogen recovery (from coulombs to H2) was as high as 93 ± 25% in the MEC, and hydrogen production rate ranged from 66.4 ± 18.0 to 137.2 ± 14.4 L H2/m2 d at an applied voltage of ∼1.2 V. As a result, H2 production costs were computed at $0.17–0.25/m3 H2 ($1.7–2.6/kg H2 at 25 °C and 1 atm) in the MEC using stainless steel mesh as the cathode. The MEC designed for maintaining high concentration of anode-respiring bacteria per membrane surface area generated 8.3 A m−2 of membrane area of which 57% was produced by endogenous decay of ARB under substrate deficient conditions. Soluble microbial products (SMP) were quantified for acetate-utilizing ARB in the MEC, and SMP fraction of influent COD was 23%. We separately measured biomass-associated products and utilization-associated products of SMP experimentally, which were 286 ± 100 mg L−1 and 59 ± 30 mg COD L−1, respectively.

Characterization of autotrophic and heterotrophic soluble microbial product (SMP) fractions from activated sludge

Soluble microbial products (SMP) generated by microbial populations can adversely affect the efficiency of biological wastewater treatment systems and secondary effluent quality. In this work, both experimental and modeling approaches were used to investigate the formation of SMP by both heterotrophic and autotrophic bacteria. Strategies to control and reduce SMP in activated sludge systems were thus evaluated. SMP produced by heterotrophs were found to account for more than 92% of total SMP. The SMP produced by autotrophs contributed to less than 8% of the total SMP, with 5% attributable to the ammonia-oxidizing bacteria (AOB) and 3% to the nitrite-oxidizing bacteria (NOB). When external organic substrate was present, the utilization-associated products (UAP) were the main component of SMP. When external organic substrate was completely consumed, biomass-associated products (BAP) from the hydrolysis of extracellular polymeric substances (EPS) dominated the SMP. The model developed in this study described the fractions and dynamics of UAP and BAP produced by heterotrophs, AOB and NOB. Solids retention time of the reactor had a significant effect on SMP production, while the effect of the hydraulic retention time was only minor. Decreasing the solids retention time from 15 to 0.5 d reduced SMP production in the reactor by 62%.

Formation of Distinct Soluble Microbial Products by Activated Sludge: Kinetic Analysis and Quantitative Determination

Soluble microbial products (SMP) released by microorganisms in bioreactors are classified into two distinct groups according to their different chemical and degradation kinetics: utilization-associated products (UAP) and biomass-associated products (BAP). SMP are responsible for effluent chemical oxygen demand or for membrane fouling of membrane bioreactor. Here an effective and convenient approach, other than the complicated chemical methods or complex models, is developed to quantify the formation of UAP and BAP together with their kinetics in activated sludge process. In this approach, an integrated substrate utilization equation is developed and used to determine UAP and their production kinetics. On the basis of total SMP measurements, BAP formation is determined with an integrated BAP formation equation. The fraction of substrate electrons diverted to UAP, and the content of BAP derived from biomass can then be calculated. Dynamic quantification data are obtained for UAP and BAP separately and conveniently. The obtained kinetic parameters are found to be reasonable as they are generally bounded and comparable to the literature values. The validity of this approach is confirmed by independent SMP production tests in six different activated sludge systems, which demonstrates its applicability in a wide range of engineered system regarding SMP production. This work provides a widely applied approach to determine the formation of UAP and BAP conveniently, which may offer engineers with basis to optimize bioreactor operation to avoid a high effluent soluble organics from SMP or SMP-based membrane fouling in membrane bioreactors.

Development of mechanistically based model for simulating soluble microbial products generation in an aerated/non-aerated SBR

Soluble microbial products (SMPs) are considered as the main organic components in wastewater treatment plant effluent from biological wastewater treatment systems. To investigate and explore SMP metabolism pathway for further treatment and control, two innovative mechanistically based activated sludge models were developed by extension of activated sludge model no.3 (ASM3). One was the model by combining SMP formation and degradation (ASM3-SMP model) processes with ASM3, and the other by combining both SMP and simultaneous substrate storage and growth (SSSG) mechanisms with ASM3 (SSSG-ASM3-SMP model). The detailed schematic modification and process supplements were introduced for comprehensively understanding all the mechanisms involved in the activated sludge process. The evaluations of these two models were demonstrated by a laboratory-scale sequencing batch reactor (SBR) operated under aerated/non-aerated conditions. The simulated and measured results indicated that SMP comprised about 83% of total soluble chemical oxygen demand (SCOD) in which biomass-associated products (BAPs) were predominant compared with utilization-associated products (UAPs). It also elucidated that there should be a minimum SMP value as the reactive time increases continuously and this conclusion could be used to optimize effluent SCOD in activated sludge processes. The comparative results among ASM3, ASM3-SMP and SSSG-ASM3-SMP models and the experimental measurements (SCOD, ammonia and nitrate nitrogen) showed clearly the best agreement with SSSG-ASM3-SMP simulation values (R=0.993), strongly suggesting that both SMP formation and degradation and SSSG mechanisms are necessary in biologically activated sludge modeling for municipal wastewater treatment.

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.