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.