Accelerated Composting of Grass Clippings By Controlling Moisture Level

Grass clippings were composted with an autothermal packed bed type laboratory-scale reactor in which a desired temperature (60°C) is maintained by controlling air flow rate. Effects of controlling moisture level on composting of grass clippings were examined by measuring changes in CO₂ evolution rate, conversion of carbon, HPLC pattern of water soluble organic matter and concentrations of organic matter constituents in the composting solid, during the composting process. Time courses of CO₂ evolution rate and conversion of carbon, corresponding to total amount of organic matter decomposed, differed substantially among the experimental runs with controlled different moisture levels. The moisture level yielding the most rapid decomposition of organic matter in the grass clippings was around 50% (W/W). Analyses of HPLC pattern of water soluble organic matter and concentrations of organic matter constituents in the composting solid also indicated that the composting rate could be accelerated by keeping the adequate moisture level. Approximately 75% of cellulosic materials such as cellulose and hemi-cellulose were decomposed during a 194 h composting period under 50% moisture conditions. Rather rapid decomposition of cellulosic materials, which is characteristic of the composting of grass clippings, was observed.