Study On The Removal Of Typical Malodorous Gas Components In Livestock By Biotrickling Filter

In the process of livestock breeding,a large number of typical odor gases such as ammonia and hydrogen sulfide will be produced,which will cause air pollution and affect the normal life of surrounding residents.Therefore,in order to reduce the environmental pollution and disturbance to the people,and to realize the large-scale breeding of livestock and poultry with green environmental protection and sustainable development,it is necessary to deal with the odor of livestock and poultry farm.Biological methods are suitable for the treatment of livestock waste gas,which is of low concentration,large flow and complex composition.Among them,the biotrickling filter is very suitable for the removal of livestock waste gas because of its ability to bear large pollution load,controllable p H and good stability.However,the existing research shows that the removal effect of biotrickling filter is often not ideal for the odor substances with poor water solubility and low odor threshold such as hydrogen sulfide,so it is necessary to explore the removal process of hydrogen sulfide to improve its removal rate.In addition,the co-removal of hydrogen sulfide and ammonia in the biotrickling filter and the interaction between them are currently poorly studied,and ammonia degradation may be partially converted into nitrous oxide,while volatile organic compounds in odor may provide a carbon source for them,and the mechanism is not yet clear.Therefore,this study explored the removal process of low-concentration hydrogen sulfide,the co-removal of hydrogen sulfide and ammonia,and the interaction between them.Taking p-cresol as the representative of volatile organic compounds,the impact of p-cresol on the formation of nitrous oxide in the process of ammonia removal was compared.In addition,in view of the low removal rate of hydrogen sulfide,low-concentration ozone was introduced into the biotrickling filter to investigate its effect.The results are as follows:(1)For the two-stage biotrickling filter with ceramsite and porcelain Rasching ring as fillers,the activated sludge of sewage treatment plant can be inoculated to accelerate the start-up when hydrogen sulfide is removed.The addition of sodium thiosulfate in the nutrient solution at the start-up stage was conducive to the rapid propagation of sulfur-oxidizing bacteria.After the start-up,the removal rate of hydrogen sulfide by the biotrickling filter was more than 99.2%(the empty bed residence time was 10.2 s,and the maximum loading rate was 2332.0 mg/(m~3·h)).The results of high-throughput sequencing showed that the sulfur-oxidizing bacteria in the biotrickling filter were mainly Acidithiobacilli,accounting for 2.3%on average,which may be caused by the degradation of hydrogen sulfide,resulting in the decrease of p H value of the circulating liquid and the acidity of the solution.(2)Compared with hydrogen sulfide,the start-up speed of biotrickling filter for ammonia was obviously slower.After the introduction of ammonia,the removal rate of hydrogen sulfide did not change obviously with the increase of the removal rate of ammonia.When the empty bed residence time was 10.2 s,the inlet concentration of hydrogen sulfide and ammonia was 1.8 ppmv and 35.3 ppmv respectively,the outlet concentration of hydrogen sulfide was lower than the detection limit(3.6 ppbv),and the outlet concentration of ammonia was lower than 0.5 ppmv.The study found that when the inlet concentration of ammonia increased,the outlet concentration of hydrogen sulfide decreased accordingly.The reason may be that the dissolution of ammonia affected the p H value of the circulating liquid and improved the solubility of hydrogen sulfide.The conversion rate of ammonia to nitrous oxide was lower than 2%,which was at a low level.At this time,the main ammonia-oxidizing bacteria were Nitrosomonas(0.8%)and Thiobacillus(10.0%).(3)For the polyurethane foam biotrickling filter,the effect of p-cresol on the treatment of hydrogen sulfide and ammonia in the biotrickling filter at low concentration was investigated.The results showed that the overall removal rate of hydrogen sulfide in the No.2 biotrickling filter(with p-cresol)was higher than that in the No.1 biotrickling filter(without p-cresol)(P<0.01).The two biotrickling filters had high ammonia removal rates during normal operation,both of which were above 95%.The removal rate of p-cresol in No.2 biotrickling filter was more than 99%.The average conversion rate of nitrous oxide in No.1 biotrickling filter was 1.3%,and that in No.2biotrickling filter was 1.9%.The conversion rate of No.2 biotrickling filter was significantly higher in some periods,which indicated that p-cresol as an organic carbon source would increase the generation of nitrous oxide.The removal rate of hydrogen sulfide did not change obviously after the biotrickling filter was introduced with low concentration ozone,but the removal of hydrogen sulfide by ozone did exist.Perhaps it would be more appropriate to use ozone for the treatment of the outlet gas of biotrickling filter.Thermomonas,Comamonas,Rhodanobacter and other denitrification related bacteria were detected in both biotrickling filters,and the proportions of No.2 were more than those of No.1(0.3%and 7.4%,0.2%and 5.8%,1.6%and 3.9%,respectively),indicating that more denitrification occurred in No.2biotrickling filter.