Optimal Conditions for Phosphorus Leaching from the Incineration Ash of Night Soil Sludge by Shaking Cultures of Sulfur-Oxidizing Bacteria

Abstract

Shaking of cultures was carried out to examine the maximum P elution concentration of night soil sludge incineration ash and the effective factor for concentration using the technique of bacterial leaching (BL) with sulfur-oxidizing bacteria. The highest P elution concentration in incineration ashes from 14 facilities was 5,700 mg-P L⁻¹ with an addition rate of 6 %. The incineration ashes with high P elution concentrations had high addition rates, P elution yields and P concentrations. The ashes with low P elution concentrations had extremely low values. In the ashes with high elution yields, instead of Fe-based flocculant, Al-based was used, and it was thought that phosphate was contained more as Al(PO₄) than Ca₉Al(PO₄)₇. Discriminant analysis to distinguish high-concentration elutions (≧3000 mg-P L⁻¹) from low-concentrated elutions (<3000 mg-P L^-1) was carried out. The significant discriminant function was obtained with a 92.6 % discriminant rate for high-concentration elutions. It was revealed that the higher the P in the elution from ash samples, the less Ca, K and Al they contained. The phosphorus elution unit cost of BL elution, calculated from use agent cost, was from 1/4 to 1/3 that of chemical elution by sulfuric acid.