Study On Rice Straw And Sewage Sludge As Nutrition Sources For Sulfate-reducing Bacteria Biological Treatment Of Acid Mine Drainage

In this thesis, a series of experiments were conducted to offer a low cost and effective way for in situ acid mine drainage (AMD) treatment. Sewage sludge was used as sulfate-reducing bacteria (SRB) seed and the tolerance degree of inoculation bacteria to initial pH of acid waste water was tested. Five organic materials (rice straw, rape straw, ethanol, acetate and glucose) were selected to investigate how well these promote sulfate reduction by SRB. A further research was carried out to study the process of SRB biological treatment of synthetic acid mine drainage (pH=2.5) by using rice straw and sewage sludge as nutrition sources, and to analyze the effect function of dosage of these two organic substrates.Batch experiment results showed that when sewage sludge was used as SRB seed, SRB acclimation was achieved and sulfate reduction was detected in reactors containing waste water with initial pH 3～7 after a short-term incubation, but three weeks later in the reactor containing waste water with initial pH 2, no sulfate reduction was observed because the activity of SRB was inhibited. A small quantity (~ 50 mg/L) sulfate was reduced in the control reactor containing only sewage sludge. When the five organic materials were added, ethanol was most effective in promoting sulfate reduction (94.5 %), followed by rice straw (54.2 %), the other three materials generally showed low reactivity. This suggests that SRB acclimation and sulfate reduction can be enhanced by additional organic carbon source.A further research indicated that certain amount of alkaline substance present in sewage sludge could neutralize acidity of synthetic acid mine drainage on the first day of experiment, elevating pH value from the initial 2.5 to around 5.4~6.3 and achieving suitable pH condition for SRB growth. Sewage sludge contained fewer biodegradable organic substances, reactive mixture with single sewage sludge showed the lowest sulfate reduction (65.9 %). When the single sewage sludge was supplemented with rice straw, SRB reducing sulfate was enhanced (79.2 %), because the degradation rate of rice straw was accelerated by the specific bacteria in sewage sludge, providing relatively abundant carbon source for SRB. Metal removal efficiency in all reactors was as high as 99 % for copper, early copper removal was mainly attributed to the adsorption capacity of sewage sludge prior to SRB acclimation. The proportion of sewage sludge and rice straw could have effect on both pH value and the three nutritious elements (carbon, nitrate and phosphate) present in reaction system, because the acid neutralization capacity of sludge depended on its dosage or concentration, and the available level of C, N and P was determined by the proportion of sewage sludge and rice straw. When the dosing ratio of sewage sludge and rice straw was up to 0.077, sulfate reduction rate reached 79.8 %, this indicated that C:N:P with a ratio of 92:3.2:1 was most suitable for SRB growth and promoting sulfate reduction as the activity of SRB was not inhibited by pH .It is feasible for using rice straw and sewage sludge as nutrition sources for SRB treating acid mine drainage at a low cost, this may have significant implication for in situ bioremediation of mine environment.