3.8. Evolution
CO2 evolution is the most direct technique to evaluate compost stability because it measures carbon derived directly from the compost being tested. CO2 evolution directly correlates to aerobic respiration. Higher CO2evolution rate (9 mg/g VS (volatile solids)/day) observed at inlet zone during initial days of waste loading into the drum subsequently reduced up to 6 mg/g VS/days due to further degradation achieved at inlet zone during the later phase of experiments (Fig. 5). This could be possible when material retained at inlet zone (almost 30–40%) after turning serve as an inoculum for the incoming material. After 115 days of wastes loading, CO2 evolution rate was stagnant at around 5.8 mg/g VS/day may be due to maximum possible degradation condition achieved inside the drum. The greatest decrease in CO2 evolution (>40%) was observed at outlet zone after 40 days of operation. The decrease in CO2 evolution rate at outlet zone was very high during initial days as similar to inlet zone. The lower final values of CO2 evolution (3.5 mg/g VS/day) strongly recommended that the institutional wastes could produce stable and quality compost using drum composting. Solvita results based on CO2 evolution increased from 3.6–5.2 to 4.8–6.4 indicated that the composts enter into the maturation phase and required few more days for reduction of CO2 evolution.
Table 4 shows the trend of CO2 evolution rate during maturation in different ambient temperatures. Results indicated that highly stable compost with Solvita maturity index of 8 obtained from vermicomposting compared to windrow, which indicated that it was ready for usage as a soil conditioner. Therefore, it is concluded that for primary stabilized compost earthworm efficiency was not affected the variation in ambient temperature.