Acetogenesis and methanogenesis liquid digestates for pretreatment of rice straw: A holistic approach for efficient biomethane production and nutrient recycling

Abstract The present work investigated the potential of acidogenesis digestate rich in volatile fatty acids (Bio-D Acid ) and methanogenesis digestate rich in ammonia (Bio-D Meth ) as a green method for the pretreatment of rice straw and biomethane production. After pretreatment with Bio-D Meth for 48 h, a maximum hemicellulose reduction of 22.4% was recorded, while 48 h of Bio-D Acid showed the lowest reduction of 15.7%. In addition, pretreatment for 48 h with Bio-D Meth and Bio-D Acid showed significant removal of lignin by 16.6 and 11.0%, respectively. SEM and FTIR confirmed major increase in straw porosity and degradation after all applied pretreatments. The highest significant biomethane content of 71.2% was recorded in 24 h Bio-D Acid -pretreated straw. However, the highest significant yield of 249.1 L kg −1 VS was recorded from the 48 h Bio-D Meth -pretreated straw, which was 9.8, 19.6, and 27.0% higher than 24 h Bio-D Meth -, 24 h Bio-D Acid and 48 h Bio-D Meth -treated straw, respectively. Importantly, pretreatment with Bio-D Meth for 24 h showed the highest estimated net bioenergy output of 7.37 GJ ton −1 dry straw, which represented 28.6 and 0.13% increase over that of the control and 48 h Bio-D Meth -pretreated straw, respectively. The present study suggested application of Bio-D Meth for 24 h as an efficient eco-friendly pretreatment method for efficient AD of rice straw.