Development of an automated, multi-vessel respirometric system to evaluate decomposition of composting feedstocks

Abstract

Aerobic respirometry, which involves measuring the carbon dioxide (CO 2 ) evolved during decomposition, is an invaluable metric for evaluating biomass decomposability, characterising compost feedstocks, and studying decomposition dynamics over time. However, respirometric systems and CO 2 sampling methods can be expensive, operationally cumbersome, and produce temporally low-resolution data. This paper details the technical development and validation of an automated, multi-vessel respirometric system using off-the-shelf microcontrollers and miniature non-dispersive infrared (NDIR) CO 2 sensors to produce temporally high-resolution and accurate CO 2 data generated from decomposing biomass. The accuracy of the NDIR CO 2 sensors, as given by the cumulative CO 2 (g), was validated through an acetic acid-sodium bicarbonate reaction test. In this test, a mean cumulative CO 2 evolution of 0.99 g ( n = 8) was measured with the sensors from an expected stoichiometric yield of 1 g CO 2 , with a standard deviation of ±0.137 g. The operation, reliability, and reproducibility of the system were tested through a series of biomass decomposition experiments. Through these experiments, an airflow rate of 0.25 L min −1 was found to be most effective at preventing the excessive drying of biomass at an initial moisture content of 50%. The system sensed, per 5-s sampling event, a peak CO 2 concentration of ∼28,000 ppm at a temperature of 35 °C, which resulted in the largest mean cumulative CO 2 evolution of 27.93 g from 200 g dry biomass. As indicated by the CO 2 curves, the system can produce reliable and high-resolution CO 2 datasets on an individual vessel basis, making it a useful tool for respirometric studies. • An aerobic respirometric system with high-resolution CO 2 sampling was developed. • The reproducibility of the data in organic matter decomposition trials was high. • Accuracy of the CO 2 sensors was shown through acetic acid-sodium bicarbonate test. • The system produced reliable CO 2 data for aerobic decomposition of organic waste.