Process kinetics of inoculation composting of municipal solid waste

A method was used to improve the composting efficiency by seeding with Inoculum A (a blend of Bacillus azotofixams, Bacillus megaterium and Bacillus mucilaginosus), Inoculum B (a blend of effective cellulolytic strains, i.e. Trichoderma koningii, Streptomyces cellulosae, and White-rot fungi), and Inoculum C (a mixture of Inoculum A and Inoculum B). There were four runs: the control run (not inoculated), Run A, Run B and Run C. During the runs, parameters such as temperature, O2, CO2 and H2S emissions, and microbial concentration were investigated to study the efficiencies of inoculation composting. The maximum oxygen uptake rates in the control run, Run A, Run B and Run C were calculated as 0.22, 0.32; 0.28 and 0.34 mol/h kg while the corresponding total O2 quantities accumulated were 511.18, 684.57, 659.74 and 778.47 g/h kg, respectively. In addition, odorous gases were highly reduced by inoculation. In order to understand the mechanisms of inoculation composting process, two stages kinetics equations were developed from the viewpoint of microbial kinetics. These equations showed that, in the first stage, microbial concentration was the main limiting factor of the degradation rate. The degradation rates in control, Run A, Run B and Run C were 10.5, 13.61, 13.08, and 15.671 g/kg h, respectively. In the second stage, the degradation rate was mainly affected by substrate concentration. Although the degradation rates were at almost the same level for both with and without inoculation, inoculation could reduce the half velocity coefficient Km and in turn stabilize the composting products efficiently. Therefore, inoculation could improve the efficiency of the composting process.