Abstract:
Anaerobic digestion (AD) technology has become a promise manner of choice because of its application in sustainable management of industrial and agricultural wastes and high value bioenergy generation in the form of Biomethane. Various strategies have been adopted to improve the efficiency of this process and one of them is to immobilize the microbial consortia on low cost porous carrier materials to create Biofilms. This thesis investigated the technique of using low cost lignocellulosic materials like luffa sponge, coconut coir and wood chips as support materials for bacterial cell immobilization with potential benefits of improved degradation of organic matter, high biogas yield and reactor stability. Anaerobic batch mode bioreactors comprising of carrier materials for biofilms and control bioreactor were run in parallel at mesophilic temperature (35⁰C) for 55 days. A combination of various techniques like chemical characterization of substrate, electron microscopy and kinetic models were opted for this study to understand the phenomena of biofilm formation and its impact on gas yield. The results depicted that introduction of porous, fibrous support can play an important role in microbial retention. In current study luffa sponge reactor provided the best performance in terms of gas yield and reactor efficiency. Furthermore, results of Scanning electron microscopy (SEM) confirmed the main cellular morphologies of methanogenic bacteria in Luffa sponge. Among the Kinetic Models logistic growth and modified Gompertz model provided the best fit with the experimental gas yield. Hence selection of immobilization support is a key design feature to achieve the high microbial density within AD reactors and should be incorporated in future design framework for anaerobic fix bed reactors. Furthermore, a part of this thesis also comprised of policy study of bio digestion technology using TIS approach to understand its diffusion dynamics and barriers that affected the widespread adoption of this renewable energy technology in Pakistan.
