Co-composting of filter cake and bagasse; by-products from a sugar mill.

Thailand has nearly 2 million tonnes of filter cake waste containing 1.8% total N from the sugar cane industry to dispose of annually. Compost studies were conducted to determine how rapidly this material can be converted to a stable product that may be useful in crop production, and to characterize the N transformations. Two kinds of sugar mill by-products were composted, filter cake and filter cake mixed with bagasse, at a 2:1 ratio to reduce the C:N ratio in an attempt to reduce N loss during composting. Materials were mixed manually at 3-5 day intervals during the composting process. Both composts were analyzed at least weekly to measure temperature, pH, NH4+, NO3-, total N content, C loss, and germination index. For both mixtures, the thermophilic stage lasted 15-20 days and was higher than ambient for nearly 80 days. The degradation of organic matter (OM) was rapid in both mixtures to approximately 40 days, after which it began to stabilize. Both mixtures achieved maturity at approximately 90 days as indicated by a stable C/N, low NH4+/NO3-, lack of heat production and a germination index higher than 80%. Mixing filter cake with bagasse helped conserve N during composting. Because N was in excess, approximately 12-15% was lost from the composts. Mixing more bagasse with the filter cake may result in further reduction in N losses. Both composts have potential for use in crop production.