Spatial and temporal distribution of pore gas concentrations during mainstream large-scale trough composting in China

With the advantages of high treatment capacity and low operational cost, large-scale trough composting has become one of the mainstream composting patterns in composting plants in China. This study measured concentrations of O₂, CO₂, CH₄ and NH₃ on-site to investigate the spatial and temporal distribution of pore gas concentrations during mainstream large-scale trough composting in China. The results showed that the temperature in the center of the pile was obviously higher than that in the side of the pile. Pore O₂ concentration rapidly decreased and maintained <5% (in volume) for 38 days or more in both the center and side of the pile and effective O₂ diffusion occurred at most in every two contiguous layers. Pore CO₂ and CH₄ concentrations at each measurement point were positively correlated (0.436 ≤ r ≤ 0.570, P < 0.01) and the concentrations in the side of the pile were obviously lower than those in the center. The top layer exhibited highest pore O₂ concentration and lowest CO₂ and CH₄ concentrations, and the bottom layer was on the contrary. No significant differences in pore NH₃ concentrations between different layers or between different measurement points in the same layer were found. Therefore, mixing the center and the side of the pile when mechanical turning and adjusting the height of the pile according to the physical properties of bulking agents are suggested to optimize the oxygen distribution and promote the composting process during large-scale trough composting when the pile was naturally aerated, which will contribute to improving the current undesirable atmosphere environment in China.