Anaerobic digestion of primary winery wastewater sludge and evaluation of the character of the digestate as a potential fertilizer

Abstract

Sludge is generated from settling of winery wastewater from seasonal cellar activities. Most primary winery wastewater sludge is generated during the crush season and is often disposed to landfill. This practice is an economic and environmental burden and ignores the potential for valorization. In this study, a series of biochemical methane potential tests were conducted using seasonal batches of sludge with and without the addition of selected micronutrients (Co, Cu, Ni) at different inoculum to substrate ratios and temperatures (ambient vs 37 °C). The highest specific CH4 yields were obtained at an inoculum to substrate ratio of 4 with the addition of micronutrients from sludge collected during (206±2.7 mLCH4/gVSadded) and after (177±1.4 mLCH4/gVSadded) the crush season at 37 °C and ambient temperatures (15.3 to 27.1 °C), respectively. In some instances, digestion at 37 °C appeared to promote inhibited steady-state conditions leading to lower CH4 yields than at ambient temperatures. This suggested that the sludge could be easily digested without heating, particularly during the warmer months of grape harvesting and crushing. The composition of the digestate indicated that it may be suitable as an agricultural fertilizer, with high concentrations of N (21.5 to 27.7 g/kg dry weight) and C (229 to 277 g/kg dry weight), as well as the presence of all essential micronutrients.