Biological Treatment Of Sulfate-Rich Wastewater Produced By Flue Gas Desulfurization With Landfill Leachate

It is urgent to control the pollution of flue gas that caused acid rain and resulted in large economy loss every year.At the same time, huge amount of household garbage has to be treated by filling into the grouand, which consequently produces substantive poisonous and harmful organic waste water (landfill leachate). Therefore, how to handle, convert or even make use of the landfill leachate becomes a new task in the field of environmental protection.In order to treat both of the landfill leachate and flue gas mentioned above, an integrated system of flue gas wet desulfurization with landfill leachate and microbial transformation of sulfur was proposed and investigated in this paper.The landfill leachate turned into high-sulfate organic wastewater after absorbed sulfur dioxide in flue gas. The biological removal of sulfur from these wastewaters could happen in two steps as follows.Firstly, sulfate or sulfite was anaerobically reduced to sulfide,which was subsequently partially reoxidized to elemental sulfur, a recoverable product. In order to obtain superiority bacteria that can convert sulfate or sulfide effectively, an important task in this research was to separate and purify the two strains of bacteria of SRB and sulfur-oxidizing photo synthetic bacteria (SPSB). SRB convert sulfate to sulfide, and SPSB convert sulfide to elementary sulfur. Furthermore their biological characters were studied as well as their microbial transformation for sulfate or sulfide in waste water by flue gas desulfurization with landfill leachate, and the productivity of elementary sulfur were investigated systematically. Several conclusions could be made as follows.A strain of sulfate-reducing bacteria was isolated from the sullage of SichuanSulfate Factory. This sulfate-reducing bacteria belongs to Desulfovibrio.The bacteria cells are vibrioid-shaped or of thin rod shape with the size of 0.4~0.6X3.0~5.0 u m. They are motile with single polar flagella and non-spore-forming. The cells strain is Gram-negative. The optimum temperature in the growth process of the strain(SRB) is 35 , the optimum pH range was 6.0~6.5, and it was not strictly anaerobic.A strain of sulfur-oxidizing photo synthetic bacteria was isolated from city back-water. The cells are thin rod shape with the size of 1.0~ 1.0X2.0 micro meters. They are flagella and non-spore-forming. The cells strain is Gram-negative. The isolated SPSB bacteria belongs to the middle temperate bacteria. It is strictly anaerobic. The optimum growth temperature of the strain(SPSB) was 30 ,the pH range was 6.0-9.0, with an optimum pH value being 8.0. The optimum lightflux was 15001ux , and chlorophyll a was the main photosynthesis pigment contained in SPSB cells. The SPSB strain was considered to be Chromatium minus.During the process of sulfate being transformed, the strain (SRB) could digest organics, such as methyl alcohol, ether, lactic acid, glucose,...,etc,and thus COD could also be reduced at the same time. The experiments results showed that the efficiency of sulfate dissimilation process improved with the ratio of COD/ SO42-below 2.5, while decreased slowly as the ration exceed 2.5. When the ratio of COD/ SO42-was kept between 2.0~2.5, COD reduction efficiency was 55% and that of SO42- was 70%.Without special request at nutrition need, the strain could grow well in the landfill leachate treated by SRB, if only sunlight provided.During the process of oxidizing sulfide, the strain(SPSB) could use lactic acid , citric acid and sodium bicarbonate, but it could not utilize acetic acid, ethanol, methanoic acid and glucose. For the utilization of nitrogen , the separated bacteria (SPSB) could fully utilize NH4+ ,but it could not utilize NO2- NO3- and carbamide .The orthogonal experimental results indicated that KH2PO4 and NaCl played an important role during the growth of the strain (SRB). The metabolism of SRB cellswas very active when concertration of the Fe 2+ was below to 3-4g/l, and the need of cells to Fe2+ would attain to saturation as the Fe2+concertration exceeded 3~4g/l.The strain...