TS and VS contents determined according to Standard Method 1684 [12]. Total alkalinity (TA) and total volatile fatty acids (TVFA) were measured according to the standard protocol EPA-430/9-77-006/March1977. COD was calculated using a test kit (Hach Lange GmbH) according to the manufacturer's instructions and a spectrophotometer (DR/2010, Hach). A pH meter (HI991001, Hanna Instruments) was used to measure the pH. The biogas production was determined by means of water volume displacement. The concentrations of CH4 and CO2 were quantified by a micro gas chromatograph (single channel 2-stream selector system, Thermo Fisher Scientific equipped with a chromatographic column (PLOTU)with Helium as carrier gas at a total flow of 10 mL min1. A gas standard consisting of 50% (v/v) CH4, 20% (v/v) CO2 and 30% (v/v) N2was used for calibrating gas chromatographic results. All the results represent the mean value of experiments conducted in triplicatewith an accuracy of 10%.