Application of a pilot-scale solar still for wine lees management: characterization of by-products and valorization potential

Abstract

Wine lees is a heavily contaminated by-product of wine making process. A pilot-scale solar still, equipped with an underfloor heating system, was used for dewatering the wine lees and recovering the evaporated water. Two solar distillation experiments were conducted, and the average distillate productivity rate ranged between 1.43 L/d·m2 and 3.86 L/d·m2. The higher productivity was observed at Experiment B when the daily maximum wine lees temperature in the still was 34.3 °C. The collected distillates were characterized by acidic pH and low conductivity while the average concentrations of COD and total phenols were ranged up to 82.5 g/L and 10.7 mg/L, respectively. UPLC-QToF-MS analysis revealed the existence of eighteen and five bioactive compounds in the wine lees and produced distillate, respectively, at concentrations up to 183 mg/kg and 12 mg/L for ethyl hydrogen succinate. Target screening analysis of the solid residuals allowed the quantification of seven bioactive compounds while four extra substances were identified via suspect screening. Ethyl hydrogen succinate was measured at the highest concentration (10.8 mg/kg) while the highest recovery was observed for 4-hydroxy-benzaldehyde (23.8%). The calorific values of the solid residuals exceeded 28 MJ/kg indicating their potential use as solid biofuels. Batch experiments showed that Chlorella sorokiniana can be grown in diluted distillates of the still. The higher average biomass productivity was observed for a dilution factor of 1:5 and it was equal to 31.4 mg/L per day. Analysis of the collected biomass indicated high lipid and starch content ranging up to 38.8% and 56.9%, respectively.