Enhanced biomethane potential from wheat straw by low temperature alkaline calcium hydroxide pre-treatment

A factorially designed experiment to examine the effectiveness of Ca(OH)(2) pre-treatment, enzyme addition and particle size, on the mesophilic (35 degrees C) anaerobic digestion of wheat straw was conducted. Experiments used a 48 h pre-treatment with Ca(OH)(2) 7.4% (w/w), addition of Accellerase (R) - 1500, with four particle sizes of wheat straw (1.25, 2, 3 and 10 mm) and three digestion time periods (5, 15 and 30 days). By combining particle size reduction and Ca(OH)(2) pre-treatment, the average methane potential was increased by 315% (from 48 NmL-CH4 g-VS-1 to 202 NmL-CH4 g-VS-1) after 5 days of anaerobic digestion compared to the control. Enzyme addition or Ca(OH)(2) pre-treatment with 3, 2 and 1.25 mm particle sizes had 30-day batch yields of between 301 and 335 NmL-CH4 g-VS-1. Alkali pre-treatment of 3 mm straw was shown to have the most potential as a cost effective pre-treatment and achieved 290 NmL-CH4 g-VS-1, after only 15 days of digestion. (C) 2015 Elsevier Ltd. All rights reserved.