Effects of ventilation modes on control of main odor substances in pig manure composting

During composting, a large number of odorous substances were produced, mainly containing ammonia, hydrogen sulfide and TVOCs (total volatile organic compounds). In order to control the odor produced during the composting process, composting experiment of pig manure and straw under different ventilation modes was carried out. The experiment has 3 treatments with the ventilation intensity of 0.1 m3/(min•m3), ventilated 5 min every other 30 min (T1), ventilated 5min every other 15 min (T2), continuous ventilation (T3) in a forced ventilation device with 50 L compost materials. Pig manure and straw were mixed in a mass ratio of 5:2. The C/N ratio of the composting materials was 29 and moisture content was 63%. The static chamber method was used to monitor the emission concentration of ammonia, hydrogen sulfide, TVOCs, dimethyl disulfide and dimethyl trisulfide during the composting. Data acquisition was started after 25 minutes of ventilation in T1, after 10 minutes of ventilation in T2, and data acquisition completed within 5 minutes. The optimal ventilation mode for reducing odor in composting was studied. The study showed that under the 3 treatments, the maximum emission concentration of ammonia in compost exceeded 150 mg/m3 for 22, 20 and 9 days; The maximum emission concentrations of hydrogen sulfide were 29.4, 18.89 and 10.3 mg/m3; The maximum emission volume fractions of TVOCs were 420.3×10-6, 382.7×10-6 and 326.5 ×10-6; The maximum emission concentrations of dimethyl disulfide were 1 730.1, 3 646.2 and 3 971.8 ng/L; The maximum emission concentrations of dimethyl trisulfate were 991.4, 6 678.8 and 1 883.4 ng/L, respectively. At the same time, the cumulative emissions of hydrogen sulfide per kilogram of dry pig manure and straw were 14.3, 13.5, 31.5 mg; The cumulative emissions of TVOCs per kilogram of dry materials were 1.26, 2.00 and 6.08 L/kg; The cumulative emissions of dimethyl disulfide per kilogram of dry materials were 1.5, 4.3 and 10.6 mg/kg; The cumulative emissions of dimethyl trisulfate per kilogram of dry materials were 0.37, 4.37 and 4.94 mg/kg, respectively. Increasing the frequency of ventilation during composting can reduce the maximum concentrations of hydrogen sulfide and TVOCs. However, high frequency ventilation can increase the cumulative emissions of hydrogen sulfide, TVOCs, dimethyl disulfide and dimethyl trisulfide, compared with the concentration of odor emission, the cumulative amount of odor emission can better characterize the degree of odor harm to the environment. In this experiment, the reduction of cumulative odor emissions was used as the optimization objective. It was found that the optimal ventilation modes was ventilated 5 min every other 30 min. This study provides a reference for controlling odor in organic fertilizer production by changing ventilation mode. © 2019, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.