Effect Of Soluble Microbial Products Research Articles

Review of Nitrification Monitoring and Control Strategies in Drinking Water System.

Nitrification is a major challenge in chloraminated drinking water systems, resulting in undesirable loss of disinfectant residual. Consequently, heterotrophic bacteria growth is increased, which adversely affects the water quality, causing taste, odour, and health issues. Regular monitoring of various water quality parameters at susceptible areas of the water distribution system (WDS) helps to detect nitrification at an earlier stage and allows sufficient time to take corrective actions to control it. Strategies to monitor nitrification in a WDS require conducting various microbiological tests or assessing surrogate parameters that are affected by microbiological activities. Additionally, microbial decay factor () is used by water utilities to monitor the status of nitrification. In contrast, approaches to manage nitrification in a WDS include controlling various factors that affect monochloramine decay rate and ammonium substrate availability, and that can inhibit nitrification. However, some of these control strategies may increase the regulated disinfection-by-products level, which may be a potential health concern. In this paper, various strategies to monitor and control nitrification in a WDS are critically examined. The key findings are: (i) the applicability of some methods require further validation using real WDS, as the original studies were conducted on laboratory or pilot systems; (ii) there is no linkage/formula found to relate the surrogate parameters to the concentration of nitrifying bacteria, which possibly improve nitrification monitoring performance; (iii) improved methods/monitoring tools are required to detect nitrification at an earlier stage; (iv) further studies are required to understand the effect of soluble microbial products on the change of surrogate parameters. Based on the current review, we recommend that the successful outcome using many of these methods is often site-specific, hence, water utilities should decide based on their regular experiences when considering economic and sustainability aspects.

Integrated mathematical model to simulate the performance of a membrane bioreactor

Membrane bioreactor technology includes the integration of biological wastewater treatment and physical separation by membrane filtration. When analyzing the system performance, efficiency of biological processes, physical separation and membrane fouling must be taken into consideration. Over the years, mathematical modelling of wastewater treatment has evolved and is being used extensively to optimize the performance of treatment systems. A Number of attempts have been made towards the development of mathematical models for membrane bioreactors and most of these models have not considered the effect of soluble microbial products on membrane fouling. Also the effect of periodic membrane cleaning was neglected. In this study, an integrated mathematical model was developed for the membrane bioreactor. A biological model based on activated sludge processes (extended with biopolymer kinetics) and a physical model with cake layer kinetics and membrane fouling have been combined. In order to overcome the drawbacks of previous attempts of modelling, the influence of soluble microbial products and extracellular polymeric substances are considered in the model integration. Further, the physical processes of the sludge removal and membrane cleaning which have strong influence on membrane fouling are considered in the model. “AQUASIM”, a computer program for the identification and simulation of aquatic systems, was used for solving the processes. Calibrated and validated model enables the prediction of the system performance and membrane fouling under different operating conditions.

Polytetrafluoroethylene (PTFE) hollow fiber AnMBR performance in the treatment of organic wastewater with varying salinity and membrane cleaning behavior

PTFE hollow fiber anaerobic membrane bio-reactor (AnMBR) performance was investigated in the treatment of organic wastewater, with varying salinity and PTFE membrane cleaning behavior. The AnMBR was operated for 226 days, with a total and biological COD removal efficiency of 97.2% and 89.9% respectively, at a NaCl concentration of 35 g L−1. A high number of Proteobacteria (38.2%) and Bacteroidetes (25.9%) were present in the system, with an increase in membrane fouling rate from 1.88 × 1011 to 2.63 × 1011 m−1 d−1 with higher salinity. The effects of soluble microbial products (SMP), extracellular polymeric substances (EPS), low molecular-weight (LMW) carbohydrates, sludge particle size and inorganic element accumulation, were evaluated on membrane fouling. Flux recovery of fouled PTFE membranes reached 91.6% with offline cleaning. Overall, results indicate that PTFE hollow fiber AnMBR provides a promising method for the treatment of saline organic wastewater.

Effects of soluble microbial products (SMP) on the performance of an anammox attached film expanded bed (AAFEB) reactor: Synergistic interaction and toxic shock

The accumulation of soluble microbial production (SMP) in an anammox attached film expanded bed (AAFEB) and its effect on the reactor performance were investigated in this study. During the long-term experiment, an extended HRT resulted in the accumulation of SMP and the change of treatment performance. When the SMP increased from 10.5±1.5mgL−1 to 31.7±6.4mgL−1 with the increase of influent TN concentration from 313mgL−1 to 2500mgL−1, the TN removal efficiency was stable. However, when the influent TN concentration was 3500mgL−1, the SMP concentration increased higher than 100mgL−1, the reactor soon became inhibited. Bath tests indicated that both the specific anammox activity (SAA) and the substrate tolerance ability decreased during the stable operation phases, whereas the specific denitrification activity (SDA) was significantly enhanced. In addition, N2O emissions in the anammox-denitrifier symbiotic system were greater than in the conventional nitrogen removal process.

Carbonate Mineral Formation under the Influence of Limestone-Colonizing Actinobacteria: Morphology and Polymorphism.

Microorganisms and their biomineralization processes are widespread in almost every environment on earth. In this work, Streptomyces luteogriseus DHS C014, a dominant lithophilous actinobacteria isolated from microbial mats on limestone rocks, was used to investigate its potential biomineralization to allow a better understanding of bacterial contributions to carbonate mineralization in nature. The ammonium carbonate free-drift method was used with mycelium pellets, culture supernatant, and spent culture of the strain. Mineralogical analyses showed that hexagonal prism calcite was only observed in the sub-surfaces of the mycelium pellets, which is a novel morphology mediated by microbes. Hemispheroidal vaterite appeared in the presence of spent culture, mainly because of the effects of soluble microbial products (SMP) during mineralization. When using the culture supernatant, doughnut-like vaterite was favored by actinobacterial mycelia, which has not yet been captured in previous studies. Our analyses suggested that the effects of mycelium pellets as a molecular template almost gained an advantage over SMP both in crystal nucleation and growth, having nothing to do with biological activity. It is thereby convinced that lithophilous actinobacteria, S. luteogriseus DHS C014, owing to its advantageous genetic metabolism and filamentous structure, showed good biomineralization abilities, maybe it would have geoactive potential for biogenic carbonate in local microenvironments.

The effect of soluble microbial products on membrane fouling in a fixed carrier biological system

The fixed carrier biological system (FCBS) has been developed for treatment of wastewater with an intent to achieve high simultaneous removal of carbon and nitrogen in a single through-put process. It is believed that a longer sludge retention time (SRT), high dissolved oxygen (DO), low suspended solids and good contact with the bio-balls in an FCBS possibly enable less production of extracellular polymeric substances (EPS) and soluble microbial products (SMP). The present study relates the role of SMP in membrane fouling and the characteristics of SMP in two different biological processes, a fixed carrier biological system (FCBS) with 300 d SRT and an activated sludge process (ASP) with 15 d SRT. Unfiltered effluent was directly taken from both reactors and filtered effluent was also produced to eliminate the role of suspended solids, and both were subjected to the membrane module for fouling studies. Results of this study indicated that suspended solids and bound EPS unexpectedly played a negligible role in membrane fouling and the fouling was actually controlled by SMP. The results also showed that the FCBS achieved an approximately 25–30% higher permeate flux than that of the ASP because of the presence of higher SMP (71%), total carbohydrate (60%) and total protein (77.5%) in the ASP as compared to the FCBS. Studies on gel filtration chromatography (GFC) revealed that smaller molecular weight fractions (<1 kDa and 1–10 kDa) from both the FCBS and the ASP might be responsible for most of the membrane fouling. Further, the findings with l -tyrosine and glucose as the model foulants for protein and carbohydrate respectively showed that protein ( l -tyrosine) caused more severe permeate flux decline than carbohydrate (glucose). The conclusions suggest that the use of an FCBS could hamper membrane fouling by producing less SMP.

Comparison of the Modeling Approach between Membrane Bioreactor and Conventional Activated Sludge Processes

Activated sludge models (ASM) have been developed and largely applied in conventional activated sludge (CAS) systems. The applicability of ASM to model membrane bioreactors (MBR) and the differences in modeling approaches have not been studied in detail. A laboratory-scale MBR was modeled using ASM2d. It was found that the ASM2d model structure can still be used for MBR modeling. There are significant differences related to ASM modeling. First, a lower maximum specific growth rate for MBR nitrifiers was estimated. Independent experiments demonstrated that this might be attributed to the inhibition effect of soluble microbial products (SMP) at elevated concentration. Second, a greater biomass affinity to oxygen and ammonium was found, which was probably related to smaller MBR sludge flocs. Finally, the membrane throughput during membrane backwashing/relaxation can be normalized and the membrane can be modeled as a continuous flow-through point separator. This simplicity has only a minor effect on ASM simulation results; however, it significantly improved simulation speed.

Effect of soluble microbial products on microbial metabolisms related to nutrient removal

In this study, the effect of soluble microbial products (SMP) on the metabolisms related to phosphate or nitrogen removal of activated sludge was investigated. Two anaerobic–aerobic activated sludge processes were operated, one with a hydraulic retention time (HRT) of 48 h (RunL) and the other 6.4 h (RunS). The longer HRT of RunL was intended to promote the accumulation of SMPs in the supernatant. With the sludge from RunS and the supernatant from both of the runs, supernatant exchange batch experiments (SEBEs) were conducted, in which the acetate uptake rate and phosphate release rates under anaerobic conditions and the phosphate uptake rate under aerobic conditions were measured as these metabolisms are related to enhanced biological phosphorus removal. The nitrification rate was also measured. The statistical analyses of the results from the SEBEs showed that the supernatant from RunL had an inhibitory effect on the anaerobic acetate uptake and nitrification of the sludge from RunS. The cause of which was attributed to SMPs in the supernatant from RunL. As a result, the inhibitory effect of SMPs on nitrification and anaerobic acetate uptake was confirmed.

Modification of ASM No.1 for a submerged membrane bioreactor system: including the effects of soluble microbial products on membrane fouling

In this study, a mathematical model for the submerged membrane bioreactor (SMBR) was developed by combining the activated sludge model (ASM) with a membrane resistance-in-series model. Some modifications were introduced to make ASM to be suitable for describing the characteristics of SMBR. A set of the 1st-order differential equations was established for 13 dependent variables relevant to particles and soluble matters. Performing model simulations for various conditions, the time when a membrane would be fouled could be predicted as well as the effluent quality. From simulation results, F/M ratio and SRT can be considered as major factors of the soluble microbial products (SMP) concentration in a reactor and it is clear that SMP can play an important role in membrane fouling and water quality simultaneously. The model would be very helpful in optimizing operation conditions as well as in designing an optimal SMBR system.

Ecotoxicological Assessment and Effects of Physicochemical Factors on Biofilm Development in Groundwater Conditions

A new concept in groundwater containment is the development of a biobarrier formed by the biostimulation of a microbial population and exopolysaccharides (EPS) production. Although the efficiency of biofilms to clog porous media and biotransform contaminants suggests their ap plication in aquifers, work on groundwater conditions has to be performed to confirm the potential of this technology. To determine the feasibility and the ecotoxic potential of biobarrier development, a groundwater indigenous population was inoculated in semicontinuous reactors. The effects of aeration, carbon source, feeding rate, C:N:P ratio, calcium ions, and pentachlorophenol (PCP) on biomass, EPS, and biofilm production was studied by a statistical design. The ecotoxic effect of soluble microbial products (SMPs) was assessed using two biotests: the Selenastrum capricornutum and Microtox (Vibrio fischeri) tests. Results showed that the carbon source type and its feeding rate had a significant impact on biofilm development leading to a maximum biofilm thickness of 250 μm after only 144 h. The ecotoxicological assessment revealed that S. capricornutum growth inhibition reached 80% while 90% of V. fischeri bioluminescence was affected by the presence of SMPs. Also, a toxic response was induced by the presence of PCP. These results showed the potential use of an indigenous microbial population and suggested that the ecotoxic potential has to be taken into account for in situ biobarrier development.

膜分離活性汚泥法における膜透過性能に対する生物代謝成分の影響

Effect of soluble microbial products (SMP) on permeate flux in a cross-flow type ultrafiltration was investigated.Synthetic wastewater (phenol) was continuously treated by an activated sludge process incorporating membrane solid-liquid separation. Hydraulic retention times and the sludge concentrations of the reactor were kept at 12 hours and 5,000 mg VSS·l-1, respectively. At certain intervals, batch filtration tests using mixed liquor of the reactor were conducted to investigate the mechanism of membrane fouling. The permeate flux dropped gradually, due to increase of SMP concentrations and of fouling mass adhered onto the membrane surface.Batch phenol-degradation reactor and aerobic sludge digestion reactor were operated, and batch filtration tests were conducted to examine which type of SMP has more important role in flux drop. Higher flux drop was observed when the mixed liquor of the sludge digestion reactor was tested at a same level TOC concentrations of SMP. It was found by gel-chromatogram that high-molecular-weight SMP was dominant in the sludge digestion reactor. The results suggest that SMPe (SMP resulted from endogenous cell decomposition) has more significant effect on flux drop.