Evaluation of Stability Parameters in In-vessel Composting of Municipal Solid Waste

Composting is a reliable technology for production of stabilized organic matter that is suitable for agriculture, but this process should be carefully monitored with appropriate indices. Quality of compost is important from maturity and stability viewpoint, but in most compost factories proper attention is not paid to it. This study was designed to evaluate the stability indices in municipal solid waste composting, for selecting the best index in quality monitoring of the wastes. Processed and shredded municipal solid waste from Isfahan compost plant was used as raw material in an in-vessel composting process. A cylindrical reactor with 1 m height and 50 cm diameter made of Pyrex glass was designed. Air was supplied at a specifically flow rate 0.2 L/min.kg to maintain aerobic condition. NH4 +/ NO3 ratio, dehydrogenase enzyme activity (DA), pH, oxidation reduction potential (ORP or Eh) and specific oxygen uptake rate (SOUR) were used as stability indices. These parameters were measured during 40 days of composting process. Changes in these parameters during this period were surveyed and analyzed. Statistical analysis was carried out to choose best of them. Results showed that among the indices, SOUR can show the different stages of microbial decomposition and a numerical value for compost stability also SOUR value less than 2 mg O2/gVS.h can show the full stability of compost.