Evaluation of medical stone amendment for the reduction of nitrogen loss and bioavailability of heavy metals during pig manure composting

The purpose of this research was to evaluate the effect of medical stone (MS) on nitrogen conservation and improving the compost quality during the pig manure (PM) composting. Five treatments were designed with different concentrations of MS0%, 2.5%, 5%, 7.5% and 10% (on dry weight of pig manure basis) mixed with initial feed stock and then composted for 60 days. The results showed that MS amendment obviously (p < 0.05) promoted the organic waste degradation and prolonged the thermophilic phase as well as enhanced the immobilization of heavy metals Cu and Zn. With increasing the amount of MS, the NH3 loss and N2O emission were significantly reduced by 27.9-48.8% and by 46.6-85.3%, respectively. Meanwhile, the MS amendment could reduce the NO2−-N formation and increase the NO3−-N content. Finally our results suggested that 10%MS addition could significantly reduce the nitrogen conservation as well as improve the quality of compost.