Biodegradation Of The Sulfate In Karst Water By Photosynthetic Bacteria

Underground karst water is a kind of special water, characterized by having of high salinity, high hardness and high sulphate content. It mainly contains large amounts ions such as Ca2+、Mg2+、Na+、K+、and SO42-. The total content of soluble solids can reach1g/L. And most of them are neutral or meta-acid, with a bitter taste. Nevertheless the karst water would bring some harm to the ecological environment if it is not treated, and the industrial production of districts where this water in distribution will be affected simultaneously.XiaoDian District is located in the south Taiyuan, Shanxi Province. It is arid or semi-arid areas where water shortage is severe. The underground water is the karst water and could not be used directly in living and production because the degree of mineralization, the total hardness and sulphate content are all higher than the standards of drinking water. In recent year, with the rapid development of industrialization and urbanization, there are a lot of sewage and waste water discharge. The surface and groundwater resources are polluted seriously. So severe water shortages of XiaoDian District have seriously affected people and livestock drinking and economic development. In this paper, the authors devised some treatment to in order to reduce the sulphate content in the Karst water in Xiao dian, Taiyuan, Shanxi Province, and to meet the drinking water standards. Thus we can get abundant water for production and life, avoid the waste of groundwater resources, and improve XiaoDian district ecological environment.The conventional water treatment methods mainly use physical and chemical methods. Currently, the methods of reducing the salt content in karst water include chemical dosing, ion exchange, electrodialysis and reverse osmosis. But no matter what method of desalination, the cost of investment operation is larger, which is also the biggest problem in the treatment of karst water with high salinity, high hardness and high sulphate. However, the biological method is highly efficienct, low cost, fast effects and has no secondary pollution, which can degradate the salinity, hardness and SO42-of karst water, and also accord with the requirements of environment protection.The project is mainly about degrading the salinity, hardness and sulphate of underground karst water in xiaodian district, Taiyuan city, in order to make the content of salinity, hardness and sulphate reach the standard of drinking water. That is to say, salinity degradation below1000mg/L, total hardness degradation below450mg/L, sulfate degradation below250～900mg/L. However, this thesis is mainly to degradae sulfate in the karst water, make its content lower and up to the standard of drinking water.The traditional sulfate reducing bacteria (SRB) will reduct the sulfur into H2S in the processing of treatment with high concentrations sulfate. H2S will produce certain inhibitory action on the microbes in the reaction system. And the H2S is malodorous and toxic. Without proper treatment, it will pollute the air and cause the second pollution. Yet the Photosynthetic bacteria (PSB) can take many kind of organic matters as the carbon sources and act high yield of energy metabolism with the help of light energy. PSB is one of the common microbes used to treat the organic wastewater, and the application of PSB will be very wide. The suitable environment temperature range for PSB is wide (10-40℃). PSB is avirulent and harmless, and can deal with high concentration organic wastewater without dilution. This method is suited for the water-deficient area and elicits no toxic action. PSB method will become one of the most promising microbe treatment method for its dazzling characteristics such as fast effects, less investment, strong maneuverability and no secondary pollution. It can also be used for agriculture, aquatic products industry, animal husbandry, food industry and development of new energy fields etc.In this degree paper, we chose PSB (Rhodopseudanonas palustris, Rhodopseudomonas sphaeroides, and the mixture of R. palustris and R. sphaeroides) to treat the karst water with three kinds of methods in order to reduce the sulphate content in Xiao dian, Taiyuan, Shanxi Province and to meet drinking water standards. One way uses only R. palustris. The second way is adding growth nutrients that R. palustris required. And the last way is polymerization aluminium chlorination (PAC) flocculation R. palustris. This paper mainly include three parts:the cultivating of R. palustris and treatment of karst water, the cultivating of R. sphaeroides and treatment of karst water, the cultivating of the mixture of R. palustris and R. sphaeroides and treatment of karst water.The results showed that treating karst water with R. palustris can cause sulfate to be degraded. Moreover, after flocculated R. palustris by PAC and kept under anaerobic light conditions, the sulfate concentration dropped from1999.6mg/L to720.24mg/L. While processing karst water via R. palustris only, and when the volume ratio of bacterial solution and karst water was1:3, after4days of treatment, the sulfate concentration was lowest and the density of bacterial community tends to decrease. After adding necessary nutrients for bacterial growth, the density of community increase with treatment time, sulfate concentration in water was decreased; while using flocculated R. palustris by PAC, which concentration is0.010mol/L, after60minutes, the bacterial gained best effect of flocculation, and it has the best effect to degrade sulfate solution.Treating karst water with spherical R. sphaeroides and after cultivattion for96h,the bacterial entered logarithmic phase, after6days of culture, the bacterial was available. Under anaerobic and aerobic condition, using spherical R. sphaeroides to treat the karst water, there is little difference of sulfate concentration between the two conditions. Compared with the control group, the density of R. sphaeroides in the karst water increased with increasing processing time.Treating the karst water with a mixture of R. palustris and R. sphaeroides can decrease the sulfate contect in anaerobic light condition. This can reduce the sulphate content from2021.64mg/L to1211.75mg/L But it cannot meet the drinking water standard. The sulfate content in the krast water was reduced to a minimum value at4days when added the nutrients and flocculation of mixed bacterium needed.In conclusion, using R. palustris to treat the karst water, the effect is better. And the contect of sulfate can meet the standards for drinking water after treatment.