Effect of Oxygenation Level on Yard Trimmings Composting Rate, Odor Production, And Compost Quality In Bench-Scale Reactors

Abstract

Oxygen availability has a profound effect on composting rate, and properties of the final compost. However, the effect of a defined range of oxygenation rates on organic matter conversion, volatile organic acid (VOA) production, ammonia emission, and various compost properties that affect plant growth is not known. In this study, yard trimmings (2:1 leaves:grass) were composted in a set of four-liter laboratory scale reactors oxygenated at four rates (0, 0.1, 1 and 10 ml O₂/min). These rates corresponded to a range from no oxygenation (0 ml O₂/min), to a rate exceeding the peak oxygen uptake rate of the compost (10 ml O₂/min). The results showed that as oxygenation rate increased, the rate of conversion of initial carbon to CO₂, and ammonia emission increased, while VOA production decreased. Oxygenation rate also had a dramatic effect on various properties of the final compost including pH, nitrogen content, and the concentration of soluble salts, ammonia, and available phosphorus. At low oxygenation rates (0 and 0.1 ml O₂/min) composts had a low pH (< 5.0), and high levels of soluble salts (>7 mS), phosphorus, and ammonia. In contrast, at the highest rate of oxygenation (10ml O₂/min), the final compost had an alkaline pH (8.6), no VOAs, an acceptable level of soluble salts, and was stable (O₂ uptake rate < 0.1 mg O₂/g OM/hr). In conclusion, these results demonstrate that oxygenation markedly influences the rate of composting, odor problems related to VOA and NH₃ production, and selected properties of the final composts.