Effect of compost inoculation on pig manure composting

Abstract: Microbial inoculation is often performed to accelerate the process of composting and improve the quality of the compost, but its effect is controversial. The effectiveness of inoculants in composting mainly depends on the properties of the raw material and microorganisms applied. It is therefore important to propose a strategy of inoculation based on the evolution of biochemical and microbiological characteristics at different composting stages. In this study, two composting piles with pig manure (CK) and pig manure inoculated with 3% (w/w) matured compost (T) were composted for a total of 11 days. Various biochemical and microbiological parameters were analyzed during the process of composting. The experimental results indicated that windrow temperature in the inoculated pile was 5℃ higher than CK at 24 h of composting (P<0.05). The inoculated pile reached peak temperature six hours earlier than non-inoculated. However, the average temperature of the inoculated pile was 8℃ lower than CK in the thermophilic stage of composting, and the maintenance of high temperature (>50℃) in inoculated pile was four days shorter. The degradation of organic matter, as indicated by the reduction of C/N ratio and the organic matter loss rate, was higher in the inoculated pile in the early composting stage. The dynamic of microbial evolution was similar between the inoculated and non-inoculated. The number of mesophilic microorganisms increased in the initiation phase but decreased in the thermophilic phase of composting, while the number of thermophilic microorganisms in the two piles increased with the increase of the temperature. Inoculation of pig manure compost increased the multiplication rates of mesophilic bacteria, thermophilic bacteria and cellulose degradation microorganisms in the initiation phase. Compared with CK, the numbers for mesophilic bacteria, thermophilic bacteria and cellulose degradation microorganisms in the inoculated pile were increased by 12.2%, 152.6%, 60.3%, respectively. The peak values of dehydrogenase activity and cellulase activity were brought forward and the protease activity was enhanced by 4.9% in the inoculated pile. However, the populations of thermophilic cellulytic bacteria was 22.5% lower and the cellulose activity as well as the degradation of organic matter was 25.8% and 6.1% lower in the inoculated pile than the control in the thermophilic phase. Above all, compost inoculation was able to accelerate the initiation rate at the early stage of pig manure compost, however, inoculated was neither effective to prolong the thermophilc stage nor increase the peak temperature during composting, because of the decreased number of cellulytic microorganism and cellulose activity in the thermophilic stage. As a result, we proposed that inoculation of thermophilic cellulose decomposition microorganism at the thermophilic stage of the process would be necessary in order to facilitate decomposition of pig manure.