Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/17862
Title: Study of submerged anaerobic membrane bioreactor for low-strength wastewater treatment
Authors: HUANG ZHI
Keywords: Anaerobic membrane bioreactor, biogas production, low-strength wastewater, SMP, EPS, membrane fou
Issue Date: 19-Jan-2010
Source: HUANG ZHI (2010-01-19). Study of submerged anaerobic membrane bioreactor for low-strength wastewater treatment. ScholarBank@NUS Repository.
Abstract: Hydraulic retention time (HRT) and sludge retention time (SRT), as controllable operation parameters, are two major factors that contribute to treatment performance and determine biomass characteristics, which inevitably affect membrane fouling development in a SAnMBR. This study was organized into two phases to illustrate the influence of HRT and SRT on treatment performance and membrane fouling in SAnMBR for treatment of low-strength wastewater. In Phase 1, synthetic wastewater was used to examine the feasibility of SAnMBR for treating low-strength wastewater under different operating conditions. To investigate membrane fouling mechanism, soluble microbial products (SMP) and extracellular polymeric substances (EPS), which have been identified as two key fouling factors, were further studied in SAnMBR systems. The optimized HRT obtained was then applied in Phase 2 to treat domestic wastewater and to investigate the impact of SRT. The study of microorganism community by both conventional and molecular biological technologies (i.e. T-RFLP and FISH) identified the main groups of microorganisms and suggested the optimal operation conditions. In Phase 1, three 6-L SAnMBRs with SRT of 30, 60 and infinite days (denoted as R30, R60 and R8) were set up to treat synthetic low-strength wastewater at HRT of 12, 10 and 8 h. Total COD removal efficiencies higher than 97% were achieved for all operating conditions studied. The maximum biogas production rate was 0.056 L CH4/g MLVSS·d at an infinite SRT. A shorter HRT or longer SRT increased biogas production due to increased organic loading rate or enhanced dominancy of methanogenics. A decrease in HRT enhanced growth of biomass and accumulation of SMP which in turn accelerated membrane fouling. A decrease in carbohydrate to protein ratio also inversely affected fouling. At 12-h HRT, the effect of SRT on biomass concentration in SAnMBRs was negligible and membrane fouling was controlled by variant surface modification due to different SMP compositions. That is, higher carbohydrate and protein concentrations present in SMP observed at longer SRT led to a higher membrane fouling rate. At 8 and 10-h HRTs, infinite SRT in SAnMBR caused highest MLSS and SMP concentrations, which sped up particle deposition and biocake/biofilm development. At longer SRT, lower EPS reduced flocculation of particulates and particle sizes, further aggravated membrane fouling. For domestic wastewater treatment conducted in Phase 2, a similar phenomenon about the treatment performance was observed. Total COD removal efficiencies were around 84% for three reactors (R30, R60 and R90). The maximum biogas production rate was as low as 0.01 L CH4/g MLVSS·d at 90-d SRT. A longer SRT benefited the multiplication of microorganisms, organics degradation and biogas generation. Nevertheless, due to the inert fraction or difficult-to-be-biodegraded fraction of domestic wastewater as well as incomplete hydrolysis, poorer gas production was obtained, compared to that obtained from synthetic wastewater treatment. The investigation of membrane fouling demonstrated that SMP concentration and compositions were dominant factors compared with sludge concentration and EPS for domestic wastewater treatment. Similar results in terms of the effects of SRT on sludge concentration, SMP and EPS were found in R60 and R90. However, a large amount of un-decomposed compounds present in bulk solution led to a high SMP and specific SMP concentration that in turn accelerated fouling of membrane unit installed in R30. Both bacteria and archaea, two important domains of microorganisms, were found by the analysis of TRFLP and FISH. The community structure was affected by HRT and SRT and the relationship between dominance and the operating conditions was consistent with that found by physicochemical methods.
URI: http://scholarbank.nus.edu.sg/handle/10635/17862
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