Evaluation of Chemically Coagulated Swine Manure Solids as Value-Added Products

Abstract

The objective of this research was to evaluate the chemically coagulated swine manure solids as biofuel and/or compost feedstock. Three coagulants, namely agricultural lime [CaCO3], hydrated lime [Ca(OH)2], and lime slurry [Ca(OH)2], were added to fresh swine manure to coagulate manure solids. Four levels, i.e., 0.00 (0.0X), 4.89 (0.5X), 9.77 (1.0X), and 19.77 (2.0X) gm Ca⋅liter-1, were tested, in triplicates. Increasing the coagulant concentration increased the total solids, ash content, and pH of solid manure samples, whereas it decreased their volatile solids, chemical oxygen demand, and heating value. At the coagulant level of 2.0X rate, heating values of samples coagulated by agricultural lime, hydrated lime, and lime slurry were 2.64, 4.48, and 4.54 MJ⋅kg-1, respectively. The heating value of raw manure solids was as high as 13.49 MJ⋅kg-1. Increasing the coagulant concentration increased the O/C atomic ratio for all the studied coagulants. Accordingly, the high coagulant concentrations might reduce the acceptability of the feedstock as a biofuel that can be co-combusted with other feed stocks. The C/N ratio and the pH values of the solid separated swine manure increased by increasing agricultural lime and hydrated lime concentrations. The former might increase satisfactoriness for composting these solids, whereas the latter might hinder their use in the composting process. The maximum coagulant concentrations that allowed pyrolyzing the final product, based on the net energy values, were 48.80 (2.0X), 18.06 (1.0X), and 18.06 (1.0X) gm⋅liter-1 for agricultural lime, hydrated lime, and lime slurry, respectively. The maximum acceptable coagulant concentrations that allowed composting the final product, based on the pH values, were 48.80 (2.0X), 0.00 (0.0X), and 9.03 (0.5X) gm⋅liter-1 for the same three coagulants.