Studies on the physico-chemical and microbiological parameters associated with composting of brewers spent grains using different activators

Seven compost piles were formulated using brewer’s spent grains (BSG) as the bulk material amended with varied quantities of poultry droppings, soybean meal, cow dung and groundnut husks (activators). Composting was done through the static pile method in seven 30 × 25 cm containers. The process spanned 50 days during which temperature, pH, elemental profiles and microbial numbers were measured using standard procedures. Mature compost was pelletized with 22 mm extrusion pelletizer and applied to Zea mays in a randomized complete block design. The result showed 11.31% reduction in mean carbon content and 0.66% reduction in mean nitrogen content of composts at the end of composting. The most alkaline pH (10.66) and the highest temperature (55.7°C) were recorded in compost amended with poultry waste and soybean meal (BSGPS). Highest bacterial count in the first week of composting (5.8 × 107 cfu/g) was observed in compost pile amended with poultry waste alone (BSGP). Mean fungal counts were 2.0 × 103 cfu/g for compost pile amended with cow dung only (BSGC) and 5.0 × 103 cfu/g for the control compost pile (BSG). Composts from all seven piles had less than 10°C maximum rise in temperature over the ambient in Dewar self-heating assay and were deemed very mature. Pellets from BSGP and BSGPS compost showed 10% abrasion. Significant differences (p = 0.015) were observed in grain yield of compost-treated, NPK-treated, and untreated maize plants. The study concluded that compost made from brewer’s spent grains mixed with poultry droppings and soybean meal in equal ratio increased grain yield of maize plant in proportions that competed favourably with that of NPK fertilizer.