Production of biodiesel and water conservation through conversion of free fatty acids from a domestic wastewater drain

Abstract

ABSTRACT Wastewater discharge from restaurants, hotels, household kitchens, confectionaries, meat, fruits, and vegetable processing units contain free fatty acids (FFAs) from fats, oils, and greases (FOG). These FFAs are one of the major causes of sewer overflows and blockages that cause health and environmental issues. This study has investigated the use of sewer wastewater as a source of lipids for the production of alkyl esters (Biodiesel) and provides a characterization of the resulting processed water. Amberlyst A21 basic resin in a column reactor was used to recover the FFAs by adsorption from an oily layer collected from the domestic wastewater drain (Chakri drain, Rawalpindi, Pakistan) having a 33.0 ± 2.08% oily fraction with 59.7 ± 1.1% FFAs. The recovered ethanol washed FFAs from the Amberlyst A21 surface were then turned into Fatty Acid Ethyl Esters (FAEEs) in the presence of an acidic resin catalyst Amberlyst 15. The esterification reaction was studied at temperatures 50, 60, and 70°C, molar ratios of 1:2 to 1:3, acidic resin weight % of 2 to 6, and reaction time of 2 to 8 hr, respectively. A maximum FFAs conversion into esters of 91.38 ± 1.13% was noted at an esterification temperature of 70°C, molar ratio of 1:3, acidic resin weight of 6%, and a reaction time of 8 h. The fractional distillation of the esterified reaction product at 100°C improved the ester content in the reaction mixture up to 96.6 ± 0.18%, with a distilled biodiesel yield of 95.52 ± 0.21%. The collected top oily layer from sewer drain wastewater was found to have a density 947.31 kg/m3, kinematic viscosity 32.69 mm2/sec, flash point 283°C, and LHV and HHV of 26 and 28 MJ/kg, respectively, while for the produced biodiesel the density was 886 kg/m3, kinematic viscosity 4.3 mm2/sec, flash point 137°C, and LHV and HHV of 39 and 41 MJ/kg was noted, respectively. Only oily layer free wastewater after passing through PAC was found to meet Pakistan NEQS, with COD <150 mg/L, pH 6–8, Alkalinity <1000 mg/L, and Ammonia-nitrogen <40 mg/L. For every 1000 gallons of domestic sewer drain wastewater treated per 8 h work shift or 3 work shifts in a day with FFAs recovered and their conversion into biodiesel, a net profit of 54.89 and 93.32 million Pakistani rupees can be gained in the first year and then in successive years, respectively. Thus, this research provides a way to produce renewable energy fuel, biodiesel from the waste lipids (FFAs) of wastewater drains to meet the energy requirements and a solution for the conservation of water bodies.