Emission Characteristics And Purification Study Of Malodorous Gas In Sludge Treatment In Municipal Wastewater Treatment Plant

During the sewage treatment process in wastewater treatment plants?WWTSs?,a great deal of harmful sludge is produced,which is needed to be effectively treated.However,a great deal of odor is produced during the sludge treatment process,which causes a serious secondary pollution.In this paper,the on-site monitor and assessment were conducted in order to identify emission characteristics and the harm to human of typical odors,including NH₃,H₂S,CH₃SH,CH₃SCH₃,CH₃S₂CH₃,and CS₂.This paper took a WWTP with sludge thermal hydrolysis-anaerobic digestion process in Beijing as the research object,where the on-site sampling analysis were conducted.The emission amounts of NH₃and voltatile sulfur compounds?VSCs?during the sludge thermal hydrolysis-anaerobic digestion process were identified,as follows?g/t dry sludge?:741.60?NH₃?,270.67?H₂S?,6.23?CH₃SH?,0.19?CH₃SCH₃?,0.12?CS₂?,and 0.064?CH₃S₂CH₃?.In addition,the exposure concentrations of six odors in the ambient air from the different sludge treatment units were monitored,and their sensory impact,health risk,and odor contribution were assessed.Results showed that NH₃could reach a degree of 5?unbearable odor?in the sludge pump room and sludge pre-dehydration workshop;H₂S and methyl mercaptan could reach a degree of 4?strong odor?in the sludge pump room and sludge pre-dehydration workshop,respectively.According to the evaluation results of odor activity values,H₂S and methyl mercaptan contributed the most to the sensory impact in the sludge pump room and sludge pre-dehydration workshop.Based on evaluation results of the permissible concentration-time weighted average and non-carcinogenic risk,odors would harm health to the on-site employees in the sludge pump room and pre-dehydration workshop,and corresponding protective measures were necessary.In view of the influence of intake air load,residence time and filler type on the deodorization effect of biological trickling filter tower,a lab-scale test of biological trickling filter deodorization was carried out.In the lab-scale test,activated carbon and polyurethane foam were selected as fillers,in order to identify the deodorizing effect of the two fillers running alone or been mixed together with different proportions.Results showed that a low comprehensive removal rate and poor stability during the deodorization process occurred at the group of pure polyurethane foam filler;the best removal effect for CH₃SH occurred at the group mixed with activated carbon and polyurethane foam filler at a mass of ratio of 1:2,but the comprehensive removal effect and stability of the six odors were general for this group;the best comprehensive removal effect and stability for six odors occurred at the group of the pure activated carbon filler.Its comprehensive removal efficiency could be maintained above 90%,and met Level one standard of the requirements specified in the"Emission standards for odor pollutants"?GB1554-93?and Beijing local standard"Integrated emission standards of air pollutants"?DB11-501-2017?.For the combined deodorization process of biological trickling filter tower and chemical washing tower,the influence of their sequence on the deodorizing effect was studied using the pilot test.Results showed that the chemical washing-biological trickling process had a better removal effect on thioethers?CH₃SCH₃and CH₃S₂CH₃?,and NH₃and H₂S at an unstable air intake with the low-concentration;the biological trickling-chemical washing process had a better removal effect on CH₃SH,and NH₃and H₂S at a stable air intake with the high-concentration.