Low temperature calcium hydroxide treatment enhances anaerobic methane production from (extruded) biomass

Abstract Ca(OH) 2 treatment was applied to enhance methane yield. Different alkali concentration, incubation temperature and duration were evaluated for their effect on methane production and COD conversion efficiency from (non-)extruded biomass during mesophilic anaerobic digestion at lab-scale. An optimum Ca(OH) 2 pretreatment for grass is found at 7.5% lime loading at 10 °C for 20 h (37.3% surplus), while mild (50 °C) and high temperatures perform sub-optimal. Ca(OH) 2 post-treatment after fast extrusion gives an additional surplus compared to extruded material of 15.2% (grass), 11.2% (maize straw) and 8.2% (sprout stem) regarding methane production. COD conversion improves accordingly, with additional improvements of 10.3% (grass), 9.0% (maize straw) and 6.8% (sprout stem) by Ca(OH) 2 post-treatment. Therefore, Ca(OH) 2 pretreatment and post-treatment at low temperature generate an additional effect regarding methane production and COD conversion efficiency. Fast extrusion gives a higher energy efficiency ratio compared to slow extrusion.