The Potential of Biogas Recovery from Anaerobic Co-digestion of Fecal Sludge and Organic Waste

Abstract

This article presents a comprehensive comparative assessment of the reac- tion conditions employed in the heterogeneous and homogeneous catalytic hydroly- sis of waste lignocellulosic biomass (WLB) for the production of fermentable sugar (FS) for its subsequent conversion to renewable bioethanol. The effects of catalyst type and reaction conditions on the selectivity of FS in catalytic hydrolysis of low- cost WLB have been meticulously assessed. Moreover, representative radar plots demonstrating FS (substrate for bioethanol) yield in both homogeneous and hetero- geneous catalytic protocols have been elucidated. An intensive global attention has recently been paid for the improvement of catalytic technologies pertaining to effi- cient pretreatment and hydrolysis for conversion of WLB to FS. Cellulose [(C6H10 O5 )n ], the foremost component in WLB materials, is a biodegradable polymer of simple carbohydrates, consisting of $β$ (1, 4)-linkage of d- glucose units, which can be depolymerized to FS for the subsequent sustainable synthesis of renewable biofu- els. In this article, a critical assessment of the production of FS through catalytic pretreatment and subsequent hydrolysis of WLB resources has been elucidated. The abundant presence of low-cost WLB and their potential application for synthesis of FS (d-glucose) and other derivatives (xylose) for subsequent bioethanol, biobutanol, bio-H2 production can provide an economically sustainable and environmentally benign avenue to mitigate energy crisis and global climate change. The present study reveals the effects of important process parameters, viz. hydro- lysis time, catalyst concentration, temperature and water to WLB ratio on the selec- tivity of d-glucose in both homogeneous and heterogeneous catalytic hydrolysis of WLB along with various advanced pretreatment intensification protocols. In order to improve the existing drawbacks, recent efforts have been made to develop advanced methods through utilization of ionic liquid, microwave, and infrared irra- diation as well as ultrasonication to make the overall process more efficient and environmentally benign.