Characteristics Of Gas Emission During Composting Of Manure And Dead Pigs And Effect Of Biofilter Technology

Composting is not only the main way to treat livestock and poultry waste,but also the important emission sources of NH₃,GHG and VOCs.The existing research on composting mainly focused on pig manure.However,the research on the gas emission and reduction technology during the composting process with a low C/N ratio and co-fermentation of manure and dead pigs is limited.This study used box composting with dead pigs and manure as the feedstock,based on contrasts of the emission characteristics of NH₃,GHG and VOCs in the composting process of dead pigs and manure,the influence of biofilter-residence time on the removal efficiency of NH₃,GHG and VOCs during the composting of dead pigs was explored.It provides important reference value for controlling NH₃,GHG and VOCs in fecal disposal of pig farms.The main conclusions obtained are as follows:When compost materials were under conditions of C/N=13.2,and with pig manure after 31 days of aerobic fermentation,the daily average temperature inside composing bin over 50℃was more than10 days,which could secure pathogen inactivation and meet the non-hazardous requirement of national standards.NH₃ emission mainly focused on the first week of composting and after remixing,accounting for 31.09%and 36.15%of the total emissions,respectively.The GHG emission mainly focused on the fourth week,accounting for 30.9%of the total emissions.Without regard to CO₂,Nitrous oxide（N₂O）is the main contributor to GHG emission which is responsible for 72.02%.The proportion of N loss via NH₃ and N₂O during the whole composting process was 23.81%and 0.54%relative to the starting material TN.The loss of CH₄ and CO₂ account for 0.17%and 35.83%of the initial raw material TC.There were 81 kinds of VOCs which could be detected during the aerobic composting of manure,VOCs with high detection rates and concentrations far exceeding their olfactory thresholds include trimethylamine,dimethyl sulfide,dimethyl disulfide and dimethyltrisulfide,and VOCs emissions occurred mainly in the first two weeks of composting.After 45 days of aerobic fermentation,the degradation rate of dead pigs in each box was over 95%,and the number of days for the daily average temperature of the box over 50℃was over 10 days,which could secure pathogen inactivation and meet the non-hazardous requirement of national standards.Similar to manure composting,NH₃ emission was mainly concentrated on the first week of composting,accounting for 30.02%of the total emissions.Without regard to CO₂,GHG emissions were mainly concentrated on the fifth week of composting,accounting for 33.21%of the total emissions,in which N₂O is the main contribution of greenhouse gases,accounting for 65.01%.But due to the longer composting time,cumulative emissions of NH₃,N₂O,CH₄ and CO₂ in the composting process were increased by 2.06%,31.81%,82.64%and-4.46%,respectively compared with the pig manure composting.During the composting process,a total of 82 kinds of VOCs were detected.Compared with the pig manure composting,Freon 114 was only detected in dead pigs composting.Compared with pig manure composting,the main volatile organic substances（trimethylamine,dimethyl sulfide,dimethyl disulfide and dimethyltrisulfide）are the same,but OVA（maximum value）is 2.34,1.34,1.20 and 1.25times,respectively.The experiment results of effect of biofilter technology in dead pigs composting on gas emission showed that,for 3 retention time of biofilter which was designed to 30s,60s and 100s,the removal rate of NH₃ was more than 80%in the composting process of dead pigs.The removal rate of CH₄ reached85%,but the removal rate of N₂O was negative to the biofilter in the early stage,whereas in the late stage the removal rate remained at 50-60%.There was great uncertainty for the treatment of VOCs,with the removal rate of trimethylamine on the first 23 days more than 85%for 3 treatments.For the sulfur compounds,dimethyl disulfide and dimethyl trisulfide was removed mainly in the first 10 days,and dimethylsulfide was removed mainly latter.