Study On The Formation Process Of Black-odor Water And Producing Conditions Of Odorous Substances

Hydrogen sulfide（H₂S）is an important substance which turns the river into black and odorous water,and is a key factor in forming black-odor water.This paper was based on the main strains of black-odor water in the south.Under the conditions of artificially simulating black and odorous water bodies,the conditions of formation of odorous substances in black and odorous water were determined by adding different basic substances,including sulfur-containing substances,inorganic salts,metal ions and controlling environmental factors;also,and an initial analysis of the floar in black and odorous water was performed.By measuring and analyzing the generated black and odorous substances,the production mechanism and formation process of substances which cause the black and odorous were studied,the main conclusions as following:（Ⅰ）The formation conditions of black-odor water.Based on the diversity analysis,the bacterial flora of the black and odorous water in Tingzichong River,Nanning mainly includes Proteobacteria（67.26%-73.52%）,ε-Proteobacteria（10.1%-21.2%）,Bacteroidetes（10.53%-13.5%）.The cause of formation of black-odor water was studied by adding the bacterial flora into the simulated water.The critical dissolved oxygen（DO）for the formation of black and odorous water was 2mg/L,and it was an important sign of production for H₂S that the redox potential（ORP）was less than-250m V.The best condiction of H₂S production was 25℃.As the temperature increases,DO and ORP decreased as well as the released of black-causing substances.Cysteine and sulfate mainly produced H₂S under anaerobic conditions,and methionine mainly produced methyl mercaptan（MT）.The concentration of H₂S prodeced from high to low was cysteine>sulfate>methionine,the odor threshold value（TON）produced was methionine>cysteine>sulfate,and the chromaticity（CH）of water was cysteine>sulfate>methionine.（Ⅱ）The odor-causing factors for the formation of black-odor water mainly include light,metal ions and nitrogen-containing inorganic salts.（1）Light,metal ions and nitrogen-containing inorganic salts were important factors for black and odorous produced.It plays an important role in the formation of hydrogen sulfide in water.The strong light can promote the reduction and decomposition of organic sulfides to produce TON,and accelerate the procedure for turning into black-odor water.Under the condition of non-light and weak light,it speeds up the reduction of sulfur-containing inorganic salts into H₂S to produce TON.Combined with the analysis of DO,ORP,CH and TON,metal ions inhibit the degree of odor-causing in water was Cu²⁺>Fe²⁺>Mn²⁺.Nitrate nitrogen（NO₃-N）is converted into nitrite nitrogen（NO₂-N）under anaerobic conditions to inhibit the production of H₂S.When the concentration of NO₂-N is higher than 5 mg/L,it can inhibit the production of H₂S and TON.Conversely,the inhibition was released.（2）The orthogonal experiments of light and metal ions and nitrogen-containing inorganic salts showed that the primary and secondary sequence of parameters was NO₃^--N>Fe²⁺>light.The effect on oxidation of hydrogen sulfide into SO₄²was light>NO₃-N>Fe²⁺.（Ⅲ）Analysis of the formation mechanism of black-odor water.The highest values of cysteine intermediate product changes were pyruvic acid（481μg/L）andβ-mercaptopyruvate（135μg/L）.During the formation of black and odorous water bodies,the proportions of Proteobacteria in microorganisms were respectively 77.26%,83.07%,80.44%,and 79.55%.The proportion of Bacteroides were 5.32%,1.71%,10.53%,23.60%.Therefore,it can be speculated that desulphovibrio could make high-valence organic compounds containing sulfur become low-valence simple sulfides through reducing desulfurization.