Effects of Phosphate-Containing Additives and Zeolite on Maturity and Heavy Metal Passivation During Pig Manure Composting

Abstract

This study investigated the effects of the combination of phosphogypsum and calcium oxide (PPG+CaO), superphosphate and calcium oxide (SSP+CaO) and zeolite on composting maturity and heavy metal passivation in pig manure composting. The results showed that all treatments reached the maturity requirements and the calcium phosphate amendment treatments had higher final germination index. All treatments enhanced the compost maturity when compared with the control by promoting volatile fatty acids decomposition (26.4%–30.5%) and formation of stable humus substances. The additive amendment treatments increased humic acid-like substances by 20%, and the PPG+CaO treatment had the highest level of humus. The composting process reduced the bioavailability of Cu (49.2%), Cd (5.0%), Cr (54.3%), and Pb (26.6%). The PPG+CaO treatment further increased the passivation rate of Cu (65.6%), Cd (21.7%), and Pb (48.7%), and decreased the mobilization of Zn. Correlation analysis found that the heavy mental passivation rate was significantly negatively correlated with volatile fatty acids and nitrogen-containing substances, and positively correlated with the pH, germination index, humic acid content and the humic:fulvic acid ratio. Therefore, the PPG+CaO treatment improved the heavy metals passivation rate by promoting maturity and humification during composting.

Keywords: Composting, phosphate-containing additives, zeolite, maturity, heavy metals, humification