The present investigation studied the effectiveness of four types of agro-industrial wastes (cardboard, newspaper, sawdust and sugar-cane waste) as a carbon source in the batch anaerobic digestion of pig manure.
Pig manure with either sawdust or cardboard, especially sawdust, produced higher total volumes of biogas than with newspaper or sugar-cane waste. Mixtures in the ratio 4:1 pig manure: sawdust, and 4:1 and 3:1 pig manure: cardboard gave the highest yields of gas with the highest percentage of methane. The total solids, volatile solids and chemical oxygen demand of the digested materials showed that the organic material of the wastes had been substantially decreased by digestion.
The fertilizer values of the digested materials were tested by planting Lolium perenne (ryegrass) on sand amended with digested wastes. Pig manure with sugar-cane waste gave the highest crop yield, followed by manure plus cardboard or sawdust; pig manure with newspaper gave the lowest yield. Copyright © 1989 Published by Elsevier Ltd.