Novel application of sulphur metabolism in domestic wastewater treatment

Abstract

The feasibility of utilizing the symbiotic relationship of bacteria related to sulphur metabolism was investigated for organic matter removal in a sludge blanket type reactor. The microaerophilic upflow sludge bed reactor (MUSB) relies on the interaction between sulphate reducing bacteria (SRB) and microaerophilic sulphide oxidizing bacteria (SOB), Beggiatoa, for organic matter removal. A five-stage MUSB reactor with a volume of 173 L was operated for 120 days at three hydraulic loadings. The efficiency of the process to remove total-COD (T-COD), filtered-COD (F-COD), and suspended solids (SS) depended on the hydraulic loading. Maximum removals of T-COD, F-COD, and SS were 92%, 94%, and 87% respectively at hydraulic retention time (HRT) of 4.5 h. At a low HRT of 2.5 h, a F-COD removal efficiency of 89% could still be achieved. Although no granulation was observed, a dense flocculated biomass developed which exhibited very good settleability (SVI = 16 mL/g). While the effluent SS increased at the lower HRTs of 3.5 and 2.5 h, the system still operated effectively without a secondary sedimentation tank. Sulphate balance, batch studies, and microscopic examinations indicated the proliferation of SRB and SOB, Beggiatoa, in the biological vessels. Although some COD removal took place by aerobic metabolism in the aeration vessels, sulphur metabolism appears to be the principal mechanism responsible for organic matter removal in the MUSB process. Key words: bacterial symbiosis, sulphur metabolism, microaerophilic upflow sludge bed reactor, sulphate reducing bacteria, sulphide oxidizing bacteria, Beggiatoa.