Efficiency Of Pilot-scale In-situ Mechanical Composting Equipment For Treating Community Biodegradable Waste And Its Odor Emission Characteristics

Community-based in-situ mechanical compost is considered as an effective resourceful treatment-technology of biodegradable waste,which is also suitable for treating urban domestic garbage under current garbage classification model in China.However,poor fertilizer quality of the products,high energy consumption and severe malodor pollution have been the bottlenecks in developing mechanical composting equipment.To solve these problems,an investigation was conducted in typical communities of Hangzhou to figure out the basic characteristics of the biodegradable waste.After that,a set of pilot scale plug flow high-temperature aerobic fermentation machines was designed for community-based disposal of biodegradable waste..The operation efficiency of the pilot equipment was analyzed along with the components and emission of the odor during the composting process.The results could provide a theoretical basis for improving the biodegradable waste mechanical composting equipment and controlling the malodor pollution.The main findings are as follows:（1）Aiming at the characteristics of the biodegradable waste in typical communities,an in-situ resource reduction treatment process（including biodegradable waste crushing and dehydration,continuous push flow high-temperature mechanical composting fermentation,mechanical screening and odor decontamination）and the relevant pilot equipment were initially developed.According to the field investigations and experimental analysis of 13 typical urban communities in 8 districts（counties,cities）of Hangzhou,it was found that the proportion of biodegradable waste in community domestic waste was as high as 58.21±5.12%while the salt content was only 11.06±1.56 g Na Cl/kg.The size of biodegradable waste generated from classification was large（62.4±49.1 mm）and the moisture content was high（80.08±7.58%）.Based on the characteristics of the targeted biodegradable waste,a set of treatment technology was developed by combing crushing and dehydration,continuous plug flow high-temperature mechanical composting fermentation,mechanical screening and odor decontamination processes.Moreover,a new pilot equipment for intelligent biodegradable waste mechanical composting was designed with the integration of"plug-flow+agitation"structure,partitioned aeration method,infrared temperature measurement and feedback,negative pressure induced deodorization,underground lift system,programmable logic control module,etc..To meet the requirements of oxygen,temperature control and dehumidification,a dynamic model of oxygen supply and microbial oxygen consumption was built based on the kinetics of microbial and hot water vapor.The optimal operating strategy for the pilot equipment treating 240 kg of biodegradable waste was partitioned aeration at fan air volume of 80 m³/h for 4.90 min with an interval of 6.60 min,and stirring 5 times per hour.（2）The on-site experiment showed that the pilot equipment can operate normally,and the products meet the standard for maturity of the Technical Specifications for Domestic Waste Composting（CJJ52-2014）.The aerobic fermentation temperature in the pilot equipment can be stably maintained at 50～60℃,and the low C/N of the biodegradable waste had no significant effect on the fermentation.After 15 days of aerobic fermentation,the moisture content of the substrate can be reduced to less than 30%,and the germination index（GI）of the plant seeds can reach to higher than 80%.Correlation analysis of the physic-chemical properties and GI showed that the p H value of about 8.5 and the electrical conductivity（EC）drop below 4.0 m S/cm can be used as a preliminary basis for judging the maturity of composting products in pilot equipment.When the NH₄⁺-N content dropped below 400 mg/kg,the product can be further judged as well matured.（3）The components and emission characteristics of the odor in the process of biodegradable waste composting were quite complex.According to the detection of volatile organic compounds（VOCs）and ammonia gas,108 kinds of VOCs can be qualitatively detected during the process of mechanical biodegradable waste composting.Altogether,56 substances（55VOCs+ammonia gas）were quantitatively detected.It was obvious that the types of malodorous gases in the process of pilot mechanical composting were changed along the time,and the components of the odor were more complicated at the later stage.In addition,as the concentrations of ammonia,2-butanone,acrolein,and 2-hexanone were close to or even exceeded the detection threshold,these malodorous gases should be considered as key components in odor pollution control.