| With economy and urbanization level developing, in China, the air pollution has become more serious and in recent years most air pollution was caused by haze, especially in Jing-Jin-Ji region, Yangtze River-delta region and pearl-delta region, where the haze weather happened badly. To solve this problem, the Chinese government introduced several stricter emissions standards than ever, such as "fossil-fuel power plant atmospheric pollutant emission standard"(GB13223-2011), which limited emission of coal-fired boiler SO2and NOx to50mg/m3and100mg/m3. To meet the requirement of new standard, it is necessary to improve the current process of removal of SO2and NOx simultaneously from flue gas.At present, biological pollution control technology intensified by means of chemical is a hot research topic in the field of environmental protection.This test study aimed intensifying the purification efficiency of the biofilm-packing tower by means of adding chemicals. And in this way, the growth of microorganisms in the tower could be promoted and purification efficiency of the biofilm-packing tower could be also improved. By the orthogonal experiment design, the optimum concentration of the chemicals was0.25mg/L lanthanum nitrate,0.25mg/L cerium nitrate,0.5g/L magnesium sulfate and0.3g/L sodium acetate. And adding chemicals with this concentration, the biofilm-packing tower’s purification efficiency of SO2and NOx could reach100%and61.78%respectively. And through a long-time continuous running test, the results indicated that the NOx purification efficiency of biofilm-packing tower with chemicals added was much better than that of the blank test, the mean value of NOx purification efficiency was increased by14.78%, and the SO2purification efficiency was still100%.Because rare earth element had the greater impact than other two components of chemical enhancer on intensifying the purification efficiency of the biofilm-packing tower, this project made some further analysis on rare earth element. The results of analysis and experiment indicated that adding rare earth element had greater influence than magnesium salt and carbon source on NOx purification efficiency of biofilm-packing tower not only at initial phase but also over the whole process. And adding rare earth element could improve the growth of denitrification bacteria over the entire process of the biological removal of SO2and NOx Through the existing research results, this project made analysis about mechanism of rare earth element intensifying the purification efficiency of the biofilm-packing tower. The results showed that there might be some chemical reaction caused by rare earth element with cytomembrane, protein, enzyme in organism, and rare earth element could also make some difference on free radical produced in the metabolic process. And this reaction led to Hormesis effect of rare earth elements on organisms. This test study used the Hormesis effect of rare earth elements, that rare earth elements at low level could promote microorganisms, to strengthen the biofilm-packing tower purification efficiency.This test study has provided the foundation for the new chemical enhancement technology on promoting the performance of biofilm-packing tower to removal of SO2and NOx simultaneously from flue gas, especially for promoting the removal of NOx. |
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