Examination of the Fouling and Treatment Performance of a Hybrid Membrane Bioreactor for Decentralized Greywater Reclamation

Abstract

An examination of the fouling behaviour and treatment performance of a hybrid membrane bioreactor (HMBR) was made to assess its viability for decentralized greywater reclamation. In comparison to a conventional membrane bioreactor (MBR), the HMBR was able to operate 1{11 days (4{42%) longer between cleaning cycles. These reductions in the rate of membrane fouling could not be attributed to any scouring e ects caused by the biocarriers, since they were prevented from contacting the membranes throughout operation. An examination of the biofoulants within each bioreactor indicated that the ratio of proteins to polysaccharides was signi cantly lower in the extracellular polymeric substances extracted from the HMBR than the MBR. However, these di erences showed no signi cant correlation to the improvements in operating time. The most signi cant di erence between the two bioreactors was in the settleability of their sludge. The di erences in the sludge volume indices of each bioreactor were strongly correlated to the lling ratio and moderately correlated to the improvements in operating time. An analysis of the permeate indicated that the HMBR was able to achieve greater reductions in nitrogen than the MBR. The average removal e ciencies for the chemical oxygen demand, biochemical oxygen demand, total nitrogen, total Kjeldahl nitrogen, ammonia, and total phosphorus were 92%, 97%, 66%, 74%, 93%, and 90% for the HMBR, and 91%, 97%, 58%, 71%, 88%, and 90% for the MBR, respectively. These improvements were attributed to the attached biomass within the biocarriers of the HMBR. The e ects of an eight week starvation period resulted in a six-fold increase in soluble microbial products within both bioreactors, and a rapid increase in the rate of membrane fouling. Both bioreactors fouled within four days of reactivation. During this time, the concentrations of ammonia and total phosphorus were observed to be greater in the permeate than in the in uent greywater, and hence exhibited negative removal e ciencies. Nevertheless, both bioreactors recovered relatively quickly, and exhibited normal fouling behaviour and treatment performance after only one week of the recovery period. This level of resiliency suggests that both bioreactors may be feasibly implemented for certain decentralized applications, such as schools, where periodic shutdowns are common.