Study On H2S And NH3Emission And Control In Landscaping Waste Composting

As the increasing of city’s landscaping area, people are more and more paying attention to city pollution caused by the landscaping wastes. Using high-temperature aerobic composting technology to dispose landscaping wastes is an effective way to achieve resource recovery and safety disposal. But the obnoxious gas generated by composting process by landscaping wastes can’t meet the regulated effluent standard of the country, which are becoming important factors in holding back the development of mass-production and industrialization of composting technology. To solve this problem, we conducted researches on H2S and NH3discharged by the landscaping wastes composting process, performed the box-type thermophilic aerobic composting experiments, explored the discharge rules of H2S and NH3during the process of landscaping wastes composting and the relationship with impact factors C/N, temperature, pH, ventilation, and biological deodorization bacteria, and studied ways to control H2S and NH3discharge. These activities were performed in Beijing Fragrant Hill Park using prunings and litter as composting target. The results are as follows:(1) Different C/N have impact on megathermal period days and duration. The megathermal period is the shortest when C/N is30, and the highest temperature65℃of the compost is appeared at the third day, and it has the longest duration period of12days at the temperature of above55℃. The C/N can also affect the pH and EC rangeability and the final value of pH and EC of the compost. The rangeability of pH and EC is obvious when C/N is30during the composting period and it has the lowest EC in dealing with the composting products, and the pH is the lowest when C/N is40.(2) Different C/N of composts have impact on the decline of C/N during the composting process, the product’s C/N, and the value of T. The compost’s C/N is the lowest when the C/N is20, and it has the largest rangeability and smallest value of T, which is less than0.6, when C/N is30. It also affects the seeds’ germination index. It has a germination index of78.88%for the seeds when C/N is20, indicating not decomposed yet; it has a germination index of98.47%when C/N is30, indicating totally decomposed; it has a germination index of81.82%when C/N is40, indicating mainly decomposed.(3) Different C/N have an effect on release concentration and cumulative release amount of H2S and ammonia during the decomposting process. The lower C/N for the compost, the more H2S and ammonia discharged. The rules of the H2S discharge are that rise at the beginning then decline at the warming up phase, rise at the beginning then slightly decline in the megathermal period, and rise to the highest in the catathermal period. The laws of the accumulative release amount is megathermal period> catathermal period> warming up phase, so the H2S control measures can be concentrated in the megathermal period and catathermal period. The rules of ammonia discharge are that rise continuously at the warming up phase, rise to the peak then decline gradually during the megathermal period, and decline to flat during the catathermal period. The laws of the accumulative release amount is megathermal period> warming up phase> catathermal period, and ammonia control measures can be concentrated in the megathermal period and warming up phase.(4) Different ventilation time affect the product’s condition of composting and the release concentration and accumulative release amount of H2S and ammonia. If the ventilation time is long, it will cause the discharge of H2S and ammonia at the same time and take longer time to achieve totally decomposed; if the ventilation time is short, it will take shorter time to become totally decomposed and make the discharge of H2S and ammonia a slower pace with a low accumulative release.(5) Adding biological deodorization bacterium agent can not only lower H2S accumulative release during landscaping wastes decomposting process, but also reduce the total discharge amount to a level lower than samples without handling.(6) The pH is positively correlated with the release concentration of H2S and negatively correlated with the release concentration of ammonia during the landscaping wastes decomposing disposal process. Therefore, the ph value must be adjusted to make the emission of H2S and NH3reach the lowest point.