Kinetic Modeling and Bio-energy Potential of Anaerobic Co-digestion: Cow Dung with Invasive Water Hyacinth Versus Agro-industrial Cassava Peels

Abstract

Third world areas are facing a twofold problem in terms of how the organic waste streams can be handled and how they can be provided with predictable and decentralized energy. This research paper is a comparative kinetic evaluation of the anaerobic co-digestion of cow dung (CD) with 2 different high-carbon feedstuffs, cassava peel (CP), a starch-based agro-industrial byproduct, and water hyacinth (WH), an invasive lignocellulosic weed in water. Three 1,000-L batch digesters were used with natural mesophilic conditions (25-32ºC) in 30-days of operation to compare stability of the process, biogas production and reaction rate. Cells were compared using an experimental design compared to a baseline mono-digestion of CD versus 50:50 co-digestion blends of CD+CP and CD+WH. The outcomes showed that co-digestion was much better than mono-digestion in yield and quality of methane. Knowing that CD+CP mix experienced the highest cumulative yield of 5,041.7 L (81.1 percent increase with the control), quick hydrolysis and short lag phase (3 days,) occurred in the CD and CP mix, respectively. On the other hand, (CD+WH) system yielded 4,810.3 and (72.8) increase, but the kinetic profile showed a slow-marathon profile because of lignocellulosic recalcitrance. In co-digestion systems, the concentration of methane increased to 61.0-62.0 percent as a result of improvement of 52.0 percent in the baseline. Moreover, an iron-oxide scrubber made locally effectively lowered raw hydrogen sulfide (H2S) concentration of a critical 5,000-8,000 ppM to the 0 ppM level, confirming an opportunity to use low-cost path of the purification. These findings suggest that while cassava peel offers rapid energy recovery suitable for systems with shorter retention times, water hyacinth remains a viable long-term substrate if retention times are extended. Future implementation, however, must critically assess the potential for heavy metal accumulation in water hyacinth digestate to ensure agricultural safety.