Aerating Recycled Water on Mushroom Composting Sites Affects Its Chemical Analysis and the Characteristics of Odor Emissions

Recycled water (RW) containing compost leachate can be a potent source of foul odor on mushroom composting sites. Samples of RW were repeatedly collected from storage tanks and pits of 14 mushroom composting sites in England and Ireland. Relationships between the effects of submerged aeration of the RW, the chemical and microbial characteristics of the RW, and the odors emitted were investigated. Recycled water samples were analyzed for pH, electrical conductivity (EC), redox potential, and dissolved oxygen concentration after 7 to 14 d cold storage. Freeze-dried material from the RW samples was chemically profiled by pyrolysis gas chromatography-mass spectrometry (GC-MS), and the content of odor precursor compounds was determined by the ninhydrin colorimetric method. The headspace air of containerized RW samples was analyzed by thermal desorption GC-MS and with gas detection tubes and assessed for odor intensity (OI) and concentration by panelists and serial dilution olfactometry. The predominant odorants in the headspace and freeze-dried residues of RW samples were volatile sulfur-containing compounds and carboxylic acids. The headspace OI, EC, dry matter content, and redox potential of RW were interrelated. The headspace OI and combined concentration of hydrogen sulfide (H2S) + dimethyl sulfide of RW were correlated (R2 = 0.635; P < 0.001). Prediction of the OI of RW by measuring RW EC and the concentration of headspace sulfides using gas detector tubes enables rapid and low-cost monitoring of RW from mushroom composting sites. Submerged aeration of RW in storage tanks or pits reduced the RW headspace air OI and the combined H2S + dimethyl sulfide concentration by 88%.