Biological nutrient transformation during composting of pig manure and paper waste

Composting of pig manure is a challenging task that requires appropriate co-substrate and bulking agent to provide optimum composting conditions and reduce nitrogen loss. In this study, paper waste is co-composted with pig manure as well as wood chips as the bulking agents. These raw materials were mixed at three different ratios of paper: pig manure: wood chips = 1:1:0 (pile 1), 3:2:1 (pile 2) and 3:1:1(pile 3), respectively. Each composting pile was about 11 m³in size equipped with negative-pressure forced aeration. The temperature of all the three piles ranged between 43 and 76°C and therefore produced pathogen-free compost. The overall total carbon reduction of 39%, 36% and 36% were achieved from pile 1, 2 and 3, respectively. The NO₃⁻− N increased with the composting period, indicating the transformation of ammoniacal-N into nitrate by nitrification activity. However, all three piles showed significant variations in soluble PO₄³⁻at different stages of composting, which could be due to the microbial assimilation and mineralization. The results revealed that the co-composting of pig manure, paper along with wood chips was optimum under the mixing ratio of 3:2:1 (pile 2).