Comparison of a gas detection tubes test with the traditional alkaline trap method to evaluate compost stability

Compost stability is an important parameter of compost quality. Among tests proposed to evaluate compost stability, microbial respiration is one of the better accepted tests. Variations in rates of CO2 evolution during composting were studied in two pilot pruning waste piles using a windrow composting system. To measure the CO2 production rate, two methods were compared: the alkaline trap test and gas detection tubes. Both respiration tests indicated increasing compost stability with processing time, but CO2 evolution rates from the alkaline trap method were higher than values from the gas detection tube method. A first-order kinetic equation was used to describe CO2 evolution over time. A linear relationship (r=0.81, p < 0.01) was found between the two methods. Although both methods could distinguish unstable compost from stable compost, CO2 detection tubes were easier to use and gave results in a shorter period of time.