Monitoring extracellular enzyme activities and microbial population numbers during composting of winery solid waste
Waste management in winery and distillery industries faces numerous disposal challenges as large volumes of both liquid and solid waste by-products are generated yearly during cellar practices. Composting has been suggested a feasible option to beneficiate solid organic waste. This incentivized the quest for efficient composting protocols to be put in place. The objective of this study was to experiment with different composting strategies for spent winery solid waste. Compost materials consisting of chopped pruning grape stalks, skins, seed and spent wine filter material consisting of a mixture of organic and inorganic expend ingredients were mixed in compost heaps. The filter material component varied (in percentage) among five treatments: T1 (40%) lined, T2 (20%) lined, T3 (0%) lined, T4 (40%) grinded material, lined and T5 (40%) unlined. Composting was allowed to proceed in open air over 12 months, from autumn to summer. Indicators such as temperature, moisture, enzyme activities, microbial counts, pH, and C/N ratio, were recorded. Generally, season (df =3, 16, P < 0.05) had significant effects (df =1, 3, P < 0.05) on heap temperature and moisture in all treatments. Similarly, microorganisms (actinobacteria and heterotrophs) varied significantly in all treatments in response to seasonal change (df = 3, 16; P < 0.05). Enzyme activities fluctuated in accordance with seasonal factors and compost maturity stages, with phosphatases, esterases, amino-peptidases, proteases and glycosyl-hydrolases being most prominent. Compared to treatments T2 and T3, compost treatments with higher percentage waste filter materials (T1, T4 and T5) had higher N (16100-21300 mg/kg), P (1500-2300 mg/kg), K (19800-28200 mg/kg), neutral pH, and lower C/N ratios (13:1-10:1), which were also comparable with commercially produced composts. Filter materials therefore, appears to be a vital ingredient for composting of winery solid waste.