| Municipal wastewater treatment plants play a vital role in the treatment of wastewater.In the process of wastewater treatment,a large number of odorous gases are often produced,which are mainly ammonia and volatile sulfide compounds(including hydrogen sulfide,methyl mercaptan,methyl sulfide,carbon disulfide,and dimethyl disulfide).There are little researches on quantitative analysis and human health effects of odorous gases discharged from wastewater treatment plants.Therefore,it is urgent to study the emission characteristics,influencing factors and diffusion rules of odor gas in wastewater treatment plants,and to evaluate its influence on human senses and health.In this thesis,the odor gas emissions from municipal wastewater treatment plants with three typical processes of A~2/O,oxidation ditch,and SBR were monitored using the static chamber and the polytetrafluoroethylene bag.It is found that the emission fluxes of ammonia and volatile sulfur compounds decreased gradually from the pretreatment unit to the biochemical treatment unit and finally to the deep treatment unit.The main odor gas discharged from wastewater treatment is ammonia,accounting for 60%-98%.The total nitrogen,total sulfur,and chemical oxygen demand influence discharge of ammonia and volatile sulfur compounds in wastewater treatment processes.The odor gas emission factors(mg/t wastewater)in the A~2/O wastewater treatment plant are ammonia(22.24),hydrogen sulfide(0.80),methyl mercaptan(0.19),methyl sulfide(0.08),carbon disulfide(0.10),and dimethylene disulfide(0.34).The odor gas emission factors(mg/t wastewater)in the oxidation ditch wastewater treatment plant are ammonia(18.22),hydrogen sulfide(0.17),methyl mercaptan(0.08),methyl sulfide(0.04),carbon disulfide(0.03),and dimethylene disulfide(0.11).The odor gas emission factors(mg/t wastewater)in the SRB wastewater treatment plant are ammonia(28.54),hydrogen sulfide(0.44),methyl mercaptan(0.15),methyl sulfide(0.06),carbon disulfide(0.02),and dimethylene disulfide(0.19).In this thesis,the exposure concentrations of odor gas in the municipal wastewater treatment plant’s ambient air were monitored.The odor intensity,odor activity value,and hazard index were used to evaluate the exposure concentration.The results showed that the exposure concentrations of hydrogen sulfide,methyl mercaptan and carbon disulfide reached the maximum values in the pretreatment unit,which were 0.1299,0.1912 and 0.0911 mg/m~3,respectively.In the biochemical treatment unit,the exposure concentrations of ammonia,dimethyl sulfide,and dimethyl disulfide reached the maximum values,which were 1.0720,0.1196,and 0.0937 mg/m~3,respectively.The pretreatment unit has the highest total odor activity value(1207.92),which is the main pollution point of odor gas in wastewater treatment plant.Ammonia is the main chemical concentration contributor to odor gases,while hydrogen sulfide,methyl mercaptan,and dimethyl sulfide are the main odor contributors.Each treatment unit’s odor gas will cause more than mild odor sensory impact on the human body and cause non-carcinogenic risk to the human body.Still,it will not cause the effect of reducing working life and generating the corresponding diseases.The diffusion characteristics of odorous gases discharged from municipal wastewater treatment plants in the atmosphere were studied by on-site monitoring and AERMOD(American Meteorological Society/Environmental Protection Agency Regulatory Model)calculation.The results show that the odorous gases released from the wastewater treatment plant meet the relevant national standards.The pre-treatment unit emission is the main source of hydrogen sulfide and methyl mercaptan in the atmospheric environment.Emission from the biochemical treatment unit is the main source of ammonia,dimethyl sulfide,carbon disulfide and dimethyl disulfide in the atmospheric environment.Odorous gases discharged from wastewater treatment plants can have a sensory impact on the surrounding areas up to a strong odor level and cause non-carcinogenic risks to the people in the surrounding areas,but reduce the working life of the human body and cause-related diseases.Wastewater treatment plants can implement dosing chemicals and control aeration intensity and select targeted deodorization processes to collect and treat the discharged odorous gases,which can achieve emission reduction in wastewater treatment. |
PDF Full Text Request