The use of coal fly ash and vinegar residue as additives in the two-stage composting of green waste.

Composting is an attractive way to recycle organic wastes because the product (compost) can be used as an organic fertilizer or a culture substrate. This study assessed coal fly ash (CFA; at 0, 15, and 35%) and/or vinegar residue (VR; at 0, 35, and 55%) as additives in the green waste (GW) composting process. Compost maturity was assessed based on the following indicators: water-holding capacity, pH, total organic carbon, electrical conductivity, total Kjeldahl nitrogen, and germination index. Other important compost properties that were determined included germination percentage and root length of seeds in a germination assay, crude fiber degradation, specific UV absorption, E4/E6 ratio, microbial numbers (culturable bacteria and volatile fatty acid-degrading bacteria), enzyme activities (dehydrogenase, β-glucosidase, acid-phosphatase, urease, and ortho-diphenol oxidase), and available nutrients. When added together, CFA and VR improved all of these properties. As indicated by the maturity indicators and other properties, the best treatment (the combined addition of 15% CFA and 55% VR) required only 23 days to produce a mature and high quality compost.