Emission characteristics of volatile organic compounds during vegetable residues and livestock manure combined aerobic fermentation

Abstract: The aerobic fermentation process will emit a trace of volatile organic compounds (VOCs), although the VOCs content is less, the effect on human health cannot be neglected. VOCs are not a single substance, but a class of compounds. However, the emission characteristics of VOCs and key odor substances during vegetable residues and livestock manures combined aerobic fermentation process is relatively limited at present. In order to investigate the characteristics of VOCs and key odor substances, vegetable residues and livestock manures combined aerobic fermentation was carried out, and the experiment lasted for 20 days in November 2018 at the Key Laboratory of Technology and Model for Cyclic Utilization from Agricultural Resources. The water content of leaf vegetable residues-pig manures-straw mixes for aerobic fermentation was 65%, and the ratio of carbon to nitrogen was 25:1. During the aerobic fermentation process, the forced ventilation was used, and the ventilation rate was 0.25 m3/(min·m3). The temperature inside the fermentation pile rose and exceeded 55 ℃ within 3 days, and kept above 50 ℃ for 7 days, kept above 55 ℃ for 6 days, which could secure pathogen inactivation and meet the non-hazardous requirement of national standards. The experiment to monitor volatile gas emission from the aerobic fermentation process, the VOCs concentration at different phases were analyzed and detected by GC-MS, and the odor concentration was determined by three-point comparative odor bag method. The results showed that 34 kinds of VOCs were detected, besides ammonia and hydrogen sulfide. The detected VOCs included carbonyl sulfide, methyl sulfide, carbon disulfide, dimethyl disulfide, butyl acetate, ethyl acetate, ethanol, isopropanol, acetaldehyde, acetone, 2-butanone, 2-hexanone, methyl isobutyl ketone, chloroform, dichloromethane, 1,2-dichloroethane, 2-methylbutane, pentane, 2-methylpentane, 3-methylpentane, methylcyclopentane, N-hexane, octane, a-pinene, limonene, 2-methyl-1,3-butadiene, toluene, ethylbenzene, m-xylene, p-xylene, styrene, o-xylene, 1,2, 3-trimethylbenzene, benzene. There were sulphur compounds, esters compounds, aldehyde compounds, ketone compounds, alcohol compounds, halohydrocarbons, alkane compounds, aromatic compounds were 4, 2, 1, 4, 2, 3, 7 and 11, respectively. The highest odor concentration was 72 443 during the mesophilic phase, however the most variation of VOCs was up to 29 during the cooling phase. The correlation analysis between importance to smelly gases and odor concentration showed that the hydrogen sulfide and dimethyl disulfide were significantly positively correlated with odor concentration (P<0.01). Carbon disulfide was significantly positively correlated with odor concentration (P<0.05). The relationships between dimethyl sulfide, ammonia with ordor gas were not strong, but the concentration of dimethyl sulfide and ammonia were high and had a strong pungent odor. Beyond that, it contributed a lot to the odor concentration, and should be monitored and controlled. Therefore, the smelly and odor-causing matters of vergetable residues and livestock manures combined aerobic fermentation were mainly disulfide dimethyl, hydrogen sulfide, carbon disulfide, dimethyl sulfide and ammonia. In order to monitor the key odor substances and provide reference for making control strategy in the vergetable residues and livestock manure combined erobic fermentation, we recommended disulfide dimethyl, hydrogen sulfide as a foul odor pollution indicator. Next, we need to study the emission of VOCs from vergetable residues with different feedstocks and different fermentation conditions. The study provides data support for mitigating VOCs gas emissions during the composting of agricultural wastes aerobic fermentation.