The Effect of Nitro‐compounds and Some Other Substances on Production of Hydrogen Sulphide by Sulphate‐reducing Bacteria in Sewage

Summary. Development of hydrogen sulphidc in sewage, due to growth of sulphate‐reducing bacteria, is favoured by neutral or alkaline conditions and retarded by acidic conditions. Strains able to use lactate, formate, stearate, and cellulose as sources of carbon were detected by the use of appropriate media; no sulphate‐reducing bacteria capable of using tributyrin appeared to be present in the sample of sewage tested. Doses of chlorine much smaller than the chlorine demand delayed the formation of sulphide, sometimes for several days, but eventually the quantity formed was of the same order as that in untreated sewage. Addition to sewage of nitrobenzene, dinitrobenzene, picric acid, or T.N.T., in amounts ranging from 2 to 20 p.p.m. in different tests, delayed development of sulphide during subsequent incubation; sufficiently high concentrations prevented its formation for prolonged periods. Fumarate and nitrate also tended to inhibit formation of sulphide, but the concentrations required (100‐1,000 p.p.m. for nitrate and 1,000–10,000 p.p.m. for fumarate) were much higher than for the above nitro‐compounds. Neither T.N.T. nor picric acid had any marked bactericidal action. It is suggested that these nitro‐compounds retard the lowering of the oxidation‐reduction potential uf the sewage to the region favourable for development of the sulphate‐reducing anaerobes.