Reduce Membrane Fouling in a Novel Bio-Entrapped Membrane Reactor: Impact of Soluble Microbial Products
Date Issued
2012
Date
2012
Author(s)
Ng, Kok-Kwang
Abstract
Membrane bioreactors (MBRs) have been widely adopted for secondary treatment of municipal wastewater in the past decade, especially in developed countries. However, a major issue of MBRs is the rapid decline of permeate flux due to a high level of biomass in the reactor that accelerates membrane fouling. High sludge concentration and extracellular polymeric substances (EPS) or soluble microbial products (SMP) have been determined to be the major factors affecting membrane bioreactor operation. Therefore, the development of a novel biological reactor that contains a lower concentration of biomass and SMP is warranted. The bio-entrapped reactor (BER) has been developed for treatment of various wastewaters to achieve high simultaneous removal of carbon and nitrogen, and that reduced suspended biomass and increased SRT in the reactor with the objectives to achieve high organics removal in a more facile operation with a short start-up period. Thus, the BER was coupled with membrane as bio-entrapped membrane reactor (BEMR) was investigated the SMP and their characteristics on membrane fouling in treating food processing wastewater, and also compared with conventional membrane bioreactor (CMBR) with the overall study goal is to reduce membrane fouling commonly encountered in MBRs.
The results show that BER with a longer sludge retention time (SRT) has demonstrated that membrane filtration performed well and achieved an approximately 25%-30% higher filtration flux and better flux recovery after backwashing than the activated sludge process (ASP) system. The BEMR could remove the carbon and ammonia nitrogen with more than 90% under different hydraulic retention time (HRT). The novel BEMR sustained operation at constant permeate flux (20 LMH) that required seven times less frequent chemical cleaning than did the conventional membrane bioreactor. Membrane fouling was improved in the new reactor, which led to a longer membrane service period with the new reactor. As in the CMBR, rapid membrane fouling was attributed to increased production of biomass and SMP, this is because the BEMR produced less SMP than did CMBR (34%-48% less protein and 16%-29% less carbohydrate) due to slow-growing microorganisms with longer SRT in the BEMR. Further, results of this thesis also indicated that suspended solids and bound EPS unexpectedly played a negligible role in membrane fouling and the fouling was actually controlled by SMP, which proved the SMP was the major contributor or foulant to the membrane fouling. Both MBRs (BEMR and CMBR) produced SMP of 10-100 kDa primarily of protein (59% in BEMR and 64% in CMBR), which likely caused membrane pores clogging because the 10-100 kDa of SMP could easily penetrate to the membrane pores by adsorption in a 100 kDa membrane used in this work. The impact of protein and carbohydrate to the membrane fouling was also been found because, 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 conclusion stated that the bio-entrapped membrane reactor could really improve the MBR performance by reducing the membrane fouling and producing less concentration of SMP with conventional membrane bioreactor. Therefore, the new BEMR offers effective organics removal while reducing membrane fouling with the potential for improving and encountering the current problems faced by conventional MBR.
Subjects
bio-entrapped membrane reactor
conventional membrane reactor
membrane fouling
soluble microbial products
sludge retention time
SDGs
Type
thesis
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