Progress of studies on soluble microbial products in a membrane bioreactor
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A review concerning the production of soluble microbial products (SMP) and their impact in a membrane bioreactor is presented in this paper. The high performance of membrane separation in the membrane bioreactor not only results in an increased organic loading rate and an improved effluent quality, but also builds the bioreactor as a relatively closed system. SMP, most of which have been identified as humic acid, polysaccharide and protein released from substrate metabolism and microbial endogenous growth, are found to comprise the majority of soluble TOC or COD in the biologically treated effluent. SMP accumulation was always observed in a membrane bioreactor due to its considerable macromolecular content and its slow biodegradable nature. Too much accumulated SMP may decrease the stability of the effluent quality, repress microbial viability, as well as result in serious membrane fouling. SMP formation is greatly influenced by influent concentration and sludge concentration. The knowledge about SMP in a membrane bioreactor is far from completion. Much work is still required to be done.Keywords:
Membrane bioreactor
Membrane Fouling
Membrane reactor
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Upflow anaerobic sludge bed reactors fed on glucose were used to investigate the effects of Ce(3+) on soluble microbial products (SMP) production, which is the majority of the residual chemical oxygen demand present in the effluent. It was found that Ce(3+) concentration of 0.05 mg/L had no significant effect on the amount of SMP production, whereas that of 1 mg/L led to the increase in SMP production. The molecular-weight distribution and carbohydrate analysis indicated that an increase in SMP production may be partly attributed to the release of extracellular polymeric substances (EPS) into the bulk solution resulted from cerium toxicity, and the nucleic acids analysis suggested that increased cell lysis also contributed to SMP accumulation in the presence of Ce(3+). The increase in SMP production in the presence of Ce(3+) is possibly a consequence of the release of EPS and increased cell lysis due to cerium toxicity.
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Using n-butanol as carbon source, the concentration of soluble microbial products (SMP) was assessed through determining the dissolved organic carbon (DOC) of mixed liquid in membrane bioreactor (MBR). Dead-end filtration test was used to determine the influence of the generation of SMP on membrane fouling. The concentration of large molecule organic matter in biomass associated products (BAP) was greater than that of substrate utilization associated products (UAP). Organic large molecule with molecule weight of more than 100 K in BAP was over 18%. BAP concentration was a key factor influencing membrane fouling. The resistance distribution test showed that the BAP was the main source of gelatinoids layer resistance. The BAP producing amount had very good correlativity with filtration total resistance, their relationship was R=1.76×1012 TOC0.191 4 .
Membrane bioreactor
Filtration (mathematics)
Membrane Fouling
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Methanosaeta
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Accumulation of SMP in the membrane bioreactor(MBR) and its influence to bioreactor operation were studied.The result showed that the predominant constituent of SMP was carbonhydrate in the bioreactor during steady state.Furthermore,compared to the conventional activated sludge process(CAS),concentrations of SMP were higher in the MBR due to efficient interception performance of the membrane.It was found that the accumulation of SMP in the MBR had adverse effect on sludge MLVSS/MLSS value and dehydrogenase activity,and microbial metabolism activity was restrained.During steady state,the concentration of protein and carbonhydrate in the effluent and mixture supernatant respectively contributed to 95% and 64% of the TOC.SMP were main pollutants of mixture supernatant and effluent in the MBR.
Membrane bioreactor
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