Enhanced degradation of waste grass clippings in one and two stage anaerobic systems

The present work investigated the use of a simple rumen-fluid-inoculated anaerobic treatment system for the degradation of organic waste. Fresh rumen fluid collected from a fistulated sheep was used as the inoculum and fresh grass clippings were used as the waste material for treatment. Studies were carried out on both a one-stage system where the ligno-cellulosic fraction breaks down into a mixture of soluble products including volatile fatty acids and a two- stage system where these products are subsequently mineralised to biogas. In the one stage system about 70% of the organic waste was solubilized and in the two stage system about 60% waste material was solubilized in a week. About 50% of the degradation was achieved in a 4 day period, showing that a 4 day solids retention time would be a suitable operating regime. The maximum volatile fatty acid production rate was 327 mg COD l(-1) h(-1). A higher loading rate of 30 g l(-1) d(-1) was achieved in these systems compared to anaerobic digesters. Microbiological studies showed an increase in the number of fungal spores as well as a decrease in the number of protozoa in the treatment system. These numbers attained stable values over the duration of the experiments. The system developed is superior to conventional composting or anaerobic digestion and can be applied for the treatment of ligno-cellulosic agricultural residues.