Effect of Peanut Shell Biochar on Dynamic Changes of Nutrient Elements and Heavy Metals during Sewage Sludge Composting

The effect of peanut shell biochar (PB) addition on thermophilic compost of sewage sludge (SS) with wheat straw was investigated. Four treatments were designed with different concentrations of PB0% (CK), PB10% (H1), PB20% (H2), PB30% (H3) (on dry weight of compost basis). The pH value, electrical conductivity (EC), total nitrogen (TN), total phosphorus (TP), total potassium (TK), and the different speciation of Cu and Zn were determined. After 30-days of compost, the growth rate of EC values of four treatments were 113.20%, 98.98%, 89.62% and 79.82%, respectively, and they were1.31%, 4.63%, 5.06% and 6.51%, respectively for pH value, the loss rate of TN was 18.96%, 16.25%, 12.51% and 12.44%, respectively, the growth rate of TP were 19.72%, 42.03%, 62.26% and 89.99%, respectively, and they were 63.59%, 81.21%, 91.14% and 94.05% of the TK. The maximum passivation rate of Cu was 9.72%, when PB adding was 30%. As for Zn, only 30% PB adding can reduce the activation of Zn. Treatments with PB had a lower value of EC and a higher value of pH than CK, and contributed to the increase of the contents of TN, TP and TK, relatively. Bioavailability of Cu and Zn decreased with the increase of PB addition. It is suggested that in the range of the study, the addition of 30% PB was the optimal choice which had the most effective effect on improving composting nutrient and reducing the bioavailability of heavy metals Cu and Zn.