Effects of turning frequency on compost stability and some chemical characteristics in a rotary drum composter

Effect of turning frequency on quality, namely some chemical characteristics (temperature, moisture content, pH, electrical conductivity, total organic matter, nitrogen dynamics, phosphorus and trace elements) and stability of compost (biochemical oxygen demand, chemical oxygen demand, rate of oxygen consumption and carbon dioxide evolution) in a rotary drum were studied. Composting was stimulated by three turns of rotary drum at different time intervals i.e. at the gap of 6 h (Run A), 12 h (Run B), 18 h (Run C) and 24 h (Run D) for 15 d. It was observed that Run D (24 h turning frequency) caused longer thermophilic phase (4 d) with a higher rise at temperature 58 C; consequently, peak of maximum temperature was shifted along with the increase of turning frequency. Around 23% of available carbon in Run D was utilized by micro-organisms and contained lower final electrical conductivity (1.32 dS m(-1)) possibly causing lesser phytotoxicity effects on the growth of plants. The percentage increase in total nitrogen and total phosphorus (organic and inorganic) in Run D was found to be 45% and 37% as compared to 7% and 17%. 6% and 32% and 18% and 30% in Run A, B, and C, respectively, indicating higher mineralization. The final values of respiration rates (CO2 evolution and oxygen uptake rate) for Run D was found to be the lowest, nevertheless, other runs also provided relatively stable compost. (C) 2008 Elsevier Ltd. All rights reserved.