Effect of dissolved organic carbon on leaching of copper and zinc from swine manure compost

Swine manure was comprehensively characterized with respect to Cu and Zn due to feed additives. Separated swine manure (SSM) composts were collected from five pig farms at Tainan County. The total content, base extractability, synthetic acid rainwater (SAR) solubility, and leachability at varying pH of Cu and Zn were determined to assess its environmental hazard. The influence of dissolved organic carbon (DOC) from compost on leaching of these elements was evaluated. The SSM composts were enriched with Cu (208-1380 mg/kg) and Zn (847-2840 mg/kg). The SAR and neutral pH leachable fractions of Cu, Zn, and organic C were generally low (< 6% of their total content). Copper leachability in F2 compost, however, was high (14%), resulting from immaturity and associated substantial dissolution of organic C (11%). Most of Cu (86% on average) while small portion of Zn (14% on average) were distributed on humic substances (HS) which comprised about 40% of total compost organic C. Extracted Cu increased rapidlyand was highly correlated to the increase of organic C concentration as the pH raised above pH 8, while extracted Zn remained low. High leachability of Cu at alkaline pH and during HS extraction was due at least in part to complexation with DOC.