Sulfide Production by Sulfate Reducing Bacteria with Lactate as Feed in an Upflow Anaerobic Fixed Film Reactor

The sulfate reducing bacteria (SRB) have the capability of reducing sulfate (SO4-2) under anaerobic conditions into sulfide (S-2) which can precipitate metals as metal sulfides. The optimum conditions for sulfide production by SRB utilizing lactate, in an upflow anaerobic fixed film reactor (UAFFR) were not previously established. The main objective of this research was to investigate these conditions for the growth of SRB to ensure the highest sulfide production under consistent behaviour of the system. Substrate containing lactate as the organic carbon source along with sulfate, nitrogen and phosphorus as the required nutrients was used as a feed to the UAFER which was seeded with SRB. It was found that an optimum sulfide production occurred with an organic loading rate (OLR) of 6 kg d-1 m-3, while the theoretical oxygen demand to sulfate ratio (ThOD/SO4) ranged from 1.5 to 2.25. Also, the optimum total nitrogen and phosphorus demands were determined to be about 250 and 50 mg L-1 respectively. A total nitrogen concentration above 600 mg L-1 started showing toxicity and lowered the sulfide production. The optimum ThOD:N:P for sulfide production and growth of SRB in the UAFFR was 100:5:1 under optimum conditions.