OXYGEN RESPIROMETRY TO ASSESS STABILITY AND MATURITY OF COMPOSTED MUNICIPAL SOLID-WASTE

The stability and maturity of compost prepared from municipal solid waste (MSW) at a full-stale composting plant was assessed through chemical, physical, and biological assays. Respiration bioassays used to determine stability (O-2 and CO2 respirometry) were sensitive to process control problems at the composting plant and indicated increasing stability with time. Radish (Raphanus sativus L.) and ryegrass (Lolium perenne L.) growth bioassays revealed that immature compost samples inhibited growth. Growth of ryegrass in potting mix prepared with cured compost not amended with fertilizer was enhanced as compared to a peat control. Garden cress (Lepidium sativum L.) seed germination, used as an indicator of phytotoxicity, revealed inhibition of germination at all compost maturity levels. The phytotoxicity was thought to be salt-related. Spearman rank-order correlations demonstrated that O-2 respirometry, water-soluble organic C, and the water extract organic C to organic N ratio, significantly correlated with compost age and best indicated an acceptable level of stability. Oxygen respirometry also best predicted the potential for ryegrass growth, and an acceptable level of compost maturity.