Alkaline pretreatment of food waste and grass clippings for the enhancement of methane production in anaerobic digestion processes

Abstract

This study evaluated the biochemical methane potential (BMP) of co-digestion of food waste and grass clippings pretreated with 3% sodium hydroxide (NaOH) for 12, 24, and 48 h. BMP tests followed German standard VDI 4630 (2006) for 31 days at 37 °C ± 1. Parameters such as total and volatile solids, chemical oxygen demand, total Kjeldahl nitrogen, total organic carbon, carbon/nitrogen ratio, carbohydrates, cellulose, hemicellulose, and lignin were analyzed. The substrate and co-substrate ratio was 1:1, with an inoculum-to-substrate ratio of 0.5. Co-digestion enhanced nutrient balance, increasing the carbon/nitrogen ratio to 25. The highest biogas and methane production occurred in the 12-h pretreated sample, which also achieved the greatest solids reduction. Alkaline hydrolysis reduced lignin content by 40.95% and improved substrate conversion and methane production rates by 1.25 and 1.05 times, respectively. Digestibility improvements were observed across all configurations. Grass clippings pretreated with 3% NaOH for 12 h proved to be the most effective co-substrate with food waste, enhancing methane production and overall anaerobic digestion performance. This process represents a novel integration of biochemical optimization strategies, leveraging nutrient balance and structural pretreatment to enhance the efficiency of biogas production from lignocellulosic substrates.