HYDROGEN-SULFIDE CONVERSION TO ELEMENTAL SULFUR IN A SUSPENDED-GROWTHCONTINUOUS STIRRED-TANK REACTOR USING CHLOROBIUM-LIMICOLA

A biological process employing green sulphur bacteria to remove sulphi de (S2-) from industrial wastewaters and convert it to elemental sulph ur was investigated. This research was unique in that dissolved sulphi de was present in the liquid influent fed into a continuous-flow photo synthetic bioreactor. A suspended-growth once-through continuous-flow stirred-tank bioreactor was successfully operated under five different experimental conditions. For the first three experiments, concentrate d nutrient solution and sulphide stock solution were pumped separately into a 13.7 litre reactor at a hydraulic retention time of 45 h and S 2- loading rates of 2.1, 4.4, and 5.6 mg/h.l. At the lowest loading ra te, nearly all influent S2- was oxidized to sulphate. The middle loadi ng rate resulted in complete conversion of S2- to elemental sulphur. S teady stare conditions were not achieved at the highest loading rate,a nd S2- accumulated in the bioreactor. In two more experiments, nutrien t medium and S2- stock solution were separately fed into a 12.0 litre bioreactor at S2- loading rates of 3.2 and 2.7 mg/h.l and hydraulic re tention times of 173 and 99 h respectively. In these trials, the loadi ng rates were adjusted:to maintain a residual of 20 to 30 mg S2-/h.l i n the bioreactor, and consequently, there was nearly complete conversi on of the consumed S2- to elemental sulphur. A parameter was developed to relate the results from these experiments to those reported in the literature, where smaller reactors and higher bacterial concentration s were used in batch reactors fed with H2S(g). This parameter describe d the capacity of the bioreactor to consume S2- and was calculated as the product of the radiant flux per unit reactor volume and the bacter iochlorophyll concentration. (C) 1998 Elsevier Science Ltd. All rights reserved.