Effect of Oxygen Concentration on the Composting Process and Maturity

The goal of this research was to investigate the effects of oxygen concentration on the composting process in China. The compost system was composed of cattle manure, chicken manure, and wheat straw combined at a ratio 1:3:6 for a period of 60 days. Microaerobic treatment was attained by manual turning, while aerobic treatment was performed by forced air plus turning. The fermentation parameters such as C/N ratio, composting temperature, lginocellulose content and O2concentration were determined. Results showed that oxygen concentration of compost in the microaerobic treatment was always lower than 1.5% during composting periods except for the first four hours and oxygen concentration was more than 4.0% in the aerobic treatment at all times. The duration of the thermophilic phase above 50°C under microaerobic treatment was 23 days, compared to 15 days under the aerobic treatment. However, the composting temperature at the later phases declined more slowly under aerobic conditions than under microaerobic conditions. The hemicellulose content decreased from 13.9% to 8.0% in the microaerobic treatment, compared to 8.5% in the aerobic treatment. The cellulose content decreased from 21.5% to 16.1% in the microaerobic treatment, compared to 18.0% in the aerobic treatment at the end of composting process. When C/N ratio, NO−3content and composting temperature were used as indexes to evaluate compost maturity, the compost matured in 35 days in the microaerobic treatment, compared with 45-50 days in the aerobic treatment. Laboratory culture experiment with compost samples taken at the thermophilic phase corroborated that cellulose degradation was more rapid under microaerobic conditions.