EFFICIENT CONTAMINANT REMOVAL FROM LIQUID DIGESTATE OF PIG MANURE BY CHEMICAL PRECIPITATION AND CO2 MINERALIZATION USING ALKALINE ASH

Chemical precipitation is a widely applied approach for a liquid fraction of digestate(LFD) of agricultural waste but its large-scale application requires low-cost and efficient precipitating agents and novel process design. This study evaluated novel approach for the efficient removal of contaminants from the LFD using fly ash-based chemical precipitation, followed by filtration and CO2mineralization. The technical feasibility of this approach was evaluated using p H and electrical conductivity(EC), and removal efficiencies of total phosphorus(TP), chemical oxygen demand(COD) and heavy metals during the treatment. The fly ash used in this study showed a promising performance as a chemical precipitation agent for COD and TP removal from the treated LFD involving complex effects of precipitation and adsorption. CO2bubbling after fly ash-based chemical precipitation provided further COD and TP removal by carbonation reactions between CO2and the excessive alkaline minerals in fly ash. Although addition of fly ash to untreated LFD increased p H from 8.3 to12.9 and EC from 7.01 to 13.7 m S·cm-1, CO2bubbling helped neutralize the treated LFD and reduce the EC, and concentrations of toxic ions by carbonation reactions. The fly ash-based chemical precipitation and CO2mineralization had > 93% COD and > 98% TP removal efficiencies, and resulted in an EC of < 2 m S·cm-1and a neutral pH in the treated LFD, as well as the high purity calcite product.