Hyperthermophilic pretreatment device and its application on improving decomposition effect for chicken manure and rice straw aerobic composting

Abstract: Composting is a process of controlling and enhancing the biological decomposition of organic residues into usable end product such as organic fertilizer. However, the disadvantages of malodor problems, long processing cycle and N loss caused by traditional composting plants, and are particularly problematic in countries with high population densities. The particle size, moisture content, C/N ratio and temperature are the key parameters influencing the process. In this study, we established a novel hyperthermophilic pre-treatment (HTPRT) method that used a temperature-adjustable HTPRT reactor for pre-heating of feedstocks, and then the in-vessel post-composting (IPC) process to mature composts. The feedstocks for composting were mainly chicken manures and rice straw. Three treatments included the control (conventional composting, CK), HTPRT (85℃, 4 h) followed by an IPC process (HPC), the HTPRT process (85 ℃, 4 h) followed by an IPC process inoculated with fresh chicken manures (0.5%, dry weight basis) (I-HPC). The composting treatments were in triplicate and lasted for 62 days. Temperature, pH value and moisture dynamics and organic material decrement were determined. C/N ratio, dissolved organic carbon (DOC), NH4+-N, NO3--N, humification index (HI) and germination index (GI) had been chosen for the determination of compost stability and maturity, and the comparison among the three composting techniques. HTPRT accelerated organic matter degradation during the thermophilic phase and prolonged the thermophilic phase in the IPC process. The maximum composting temperature in HPC and I-HPC treatments were 13.6 and 12.8 ℃ higher than that in CK. The thermophilic period of composting (≥50 ℃) in HPC and I-HPC treatments lasted 2 and 3 days longer than that in CK. The IPC process was reduced significantly in comparison with the traditional composting process. However, addition of the fresh chicken manure did not accelerate HTPRT-IPC process, no significant difference was found in composting cycle between HPC and I-HPC. After HTPRT, the bulk density of the residues was reduced from 0.81 to 0.72 g/cm3 and the pH value was declined by 1-2. However, the content of DOC was increased from 106 to 124 g/kg, and total volatile fatty acids (TVFAs) and ammonium N contents were increased by 3.2 and 2.45 folds, respectively. The organic matter degradation rate constants in I-HPC and HPC were 0.0501, 0.0534 d-1, significantly larger than that in CK (0.00143 d-1). Consequently, the total organic carbon content in the mature product of HPC and I-HPC (182.1, 192.1 g/kg) were 11.3% and 6.4% lower than that in CK (205.3 g/kg). TN contents in the mature product of HPC and I-HPC (19.70, 21.28 g/kg) were 9.7% and 18.5% higher than that in CK (17.96 g/kg). The humification indice (HI) in the mature product of HPC and I-HPC (0.77, 0.71) were 20.3% and 10.9% higher than that in CK (0.64). The humification indices of HPC and I-HPC were 20.3% and 10.9% higher than that in CK. The study suggested HTPRT-IPC as a novel method for shortening the composting cycle and improving the quality of compost, and had great potential for practical use.