| With the development of industry, the problem of heavy metal pollution in water body becomes worse and worse. Traditional physical and chemical methods such as chemical neutralization, electrolytic method, adsorption and so on can achieve a better removal effect treating relatively high concentration of heavy metal wastewater. However, when the concentration of heavy metal ions to is varying a few milligrams to dozens of milligrams, these methods would have disadvantages including large investment, high energy consumption, operation difficulty and great amount of sediments. These make it necessary to seek a high-efficiency, economic and feasible method without secondary pollution. Heavy metal wastewater treatment by sulfate-reducing bacteria (SRB) has many advantages, becoming one of the hot spot of current research.Carbon source is an important factor of SRB growth, choosing an effective and cheap one is of great significance for long-term operation without artificial maintenance. At present, the study of carbon source is mainly focused on 1) separate organic waste as carbon source; 2) organic waste and cellulose waste mixed in proportion. However, little research effort has apparently been undertaken to remove heavy metals soon and effectively by SRB bioremediation system only using cellulose as carbon source. Therefore, the objective of this study is aimed to study the influence law of SRB growth factor, investigate the feasibility of Cu2+removal on the anaerobic reduction of sulfate using sugarcane bagasse as carbon source, discuss the long-term removal of copper ions and analyse removal mechanism by the modern analytical methods such as SEM, EDS and XRD. The results show that:(1) SRB could grow in the pH range of 5-9, especially when pH value was 5,6 and 7; The difference of SO42- concentration had dissimilar effects on the sulphate removal rate, the highest removal rate can reach 85%; When Fe2+ concentration was in the range of 0～450 mg/L, SO42-removal rate would increases along with the rise of concentration of Fe2+. SO42- removal rate gradually decreased when the concentration of Fe2+ increased to more than 650 mg/L; When COD/SO42->2, the removal rate of SO42- was 94.92%. While COD/SO42-≤2, SO42- reduction rate could only reach to 46.73%. Sulfate reduction result was great using sodium lactate as carbon source, ethanol can be used as the electron donor while glucose and glycerol didn’t performance well. and sulfate reduction rate was only 23.2% with sodium acetate as carbon source. The utilization order of five kinds of organic carbon source by SRB was bagasse> peanut shell> straw> sunflower seed shell> soybean dregs.(2) Low concentration of Cu2+ in synthetic leaching wastewater was treated by SRB using sugarcane bagasse as carbon source and carrier. The impact of pH, ORP, concentration of SO42-and COD was analyzed and the form of the precipitate was also investigated. The results showed that the pH values increased slowly, the values of ORP all decreased to below-100 mV and the reduction percent of SO42- could reach to 92.4% during the period. Besides, the COD was maintained in the range of 200～300 mg/L. The microflora in the system had a tolerance to the inhibition of the high concentration of Cu2+, and the SRB could reduce sulfate by small molecules which produced by the biological degradation of bagasse. At the end of experiment, the concentration of Cu2+ would be removed from 20 mg/L to below 0.5 mg/L, while the high concentration of Cu2+ could be removed by several multi-stage reactors in series. Moreover, the reaction rate of SO42- and that of Cu2+ indicated 1 mg Cu2+ could be removed when SRB reduced 15 mg SO42-(3) COD removed steadily gradually, confirming that the long-term effectiveness of bagasse as a sustained-release carbon source. The continuous decline of sulfate indicated that the SRB in the reactor had become superiority strains, or they had adapted to the anaerobic environment with heavy metal ions; After long-term running, Cu2+ concentration dropped to below 0.5 mg/L, meeting emission standard of pollutants for copper, nickel, cobalt industry (GB 25467-2010). Until the end of reaction period, Cu2+concentration could be kept in 0.1-0.2 mg/L; SRB biofilm formed on the bagasse surface through optical microscope, and SEM images showed that both surface and internal structure of the bagasse had been destroyed by microorganism and most of the organic matter had been decomposed; The results of EDS, sequential extraction procedure by Tessier and XRD proved the main components of the sediment was copper sulfide, and it was a nanoscale aggregates that the EPS functioned as a skeleton which could be adsorbed by the metal sulfide bound and the carbonate bound combined with the copper ions. |
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