Change of carbon substance characteristics during composting of waste packing and fungus chaff

Abstract: Aerobic composting is increasingly recognized as a viable treatment method for animal manure due to the possible recycling of its end-product (composts) in agriculture. However, carbon loss during composting may result in the formation of greenhouse gases. Thus, it is important to investigate changes of carbon during composting and to develop methods for conserving carbon and reducing potential negative environmental impacts. In this study, an experiment was conducted to study the carbon transformation and greenhouse gas emission in composting of waste packing and fungus chaff by using static forced-air composting boxes. Waste packing and fungus chaff were mixed according to the weight ratio (4:6 or 6:4) with or without EM microbial agent addition (MAA), respectively. The original composting materials were adjusted to the same C/N ratio (30:1) by adding urea, and then composted in a static forced-air composting box. Temperature was measured every day. Compost samples were taken on days 0, 10, 20, 25, 30, 35, 40 and 45 after the start of the experiment, respectively, and then used to determine total organic carbon (TOC), water-soluble organic C (WSOC), microbial biomass C (MBC), and humic acids concentrations. The results showed that during composting, for all treatments the TOC decreased rapidly in the first 20 days and then decreased gradually. This could be explained by the fact that microorganisms rapidly consumed the carbohydrates released during the degradation of carbon source. Interestingly, TOC were lower in the treatments with EM-MAA than the treatments without EM-MAA. The MBC gradually increased and peaked on day 20 after treatment, and then gradually decreased. However, it was significantly increased by 31.7%~73.4% for different treatments in the end-products compared to the initial mixed composting materials. In addition, the EM-MAA addition increased the MBC by 8.4%~7.2%, respectively. A similar trend in MBC was found in the WSOC compost. During composting, the humi?cation process resulted in increased humic acids and decreased fulvic acids. At the end of composting, humic acid contents in T3 and T4 treatments increased by 63.3% and 32.4% than those of T1 and T2 treatments, respectively. The humification index (HI) of T3 treatment was 95.2% higher than that of T1 treatment, and the HI of T4 treatment was increased by 222.8% than that of T2 treatments. It indicated that EM agents addition accelerated the organic matter mineralization and increased the HI of the composts. After 45 days, the degradation rates of original carbon were 5.7%~10.2%, and the humic acid, DOC, and MBC in the compost were increased by 56.0%~131.0%, 54.5%~81.5% and 31.7%~73.4%, respectively, compared to their initial values. Total carbon loss was significantly higher in the composts with waste padding than the composts with fungus chaff. It was concluded that the fungus chaff could be used to reduce carbon loss during composting.