Biogas Generation from Co-Digestion Waste Systems: The Role of Water Hyacinth

Using biomass as a renewable energy source has earned tremendous interest from researchers in recent decades, especially because the technology is environmentally benign. This article reviews the recent methods for generating biogas from water hyacinth (WH, Eichornia crassipes), arguably the world’s most evasive aquatic macrophyte. Therefore, various economic, environmentally benign, and renewable procedures that enhance biogas production from WH biomass are reviewed. WH has been co-digested with numerous waste types, including poultry droppings, municipal wastes, animal tissue wastes, pig wastes, cow dungs, etc., recording varying success degrees. Other studies focused on optimizing the operation parameters, such as mixing ratio, contact time, pH, temperature, organic loading rate, etc. We observed that most attempts to generate biogas from WH alone were not promising. However, when co-digested with other biomasses or wastes, WH either increases the process rate or improves the methane yield content. Also, the potential of WH as a phytoremdiator-cum-biogas source was investigated. This chapter provides mathematical models, scale-up installation models, and specific experimental results from various studies to guide future study plans toward optimizing CH4 generation from WH co-digestion.

Evaluation of Levels of Cadmium, Chromium and Lead in Bio Fertilizer from Various Feed Stocks and in Inorganic Fertilizers Used in Kenya

This study was conducted to compare the levels of selected heavy metals (Pb, Cr and Cd) in inorganic fertilizers and bio slurry from different feed stocks. Bio slurry samples from chicken droppings, cow dung and pig wastes were analyzed for levels of selected heavy metals. Inorganic fertilizers for analysis DAP, CAN, Urea and NPK were procured from local market in Juja town next to Jomo Kenyatta University of Agriculture and Technology (JKUAT). Bio slurry samples were collected from Githunguri Sub County in Kiambu County and from mini digesters set up at JKUAT. Concentrations of Cd, Cr, and Pb were determined by Flame Atomic Absorption Spectrophotometer (Shimadzu 6200). Inorganic fertilizers were found to contain detectable amounts of lead metal. DAP had the highest amount of Pb at 0.03 mg/l followed by CAN (0.02 mg/l) Urea and NPK had 0.01 mg/l each. Bio slurry samples contained lower amounts of lead which was below detectable limit in chicken litter and pig wastes. Inorganic fertilizers contained Cd with the highest levels being in the phosphorous containing fertilizers DAP (0.41 mg/l) and NPK (0.48 mg/l). All samples contained Cr with the highest in bio slurry samples being 0.09 mg/l in cow dung collected from Githunguri. CAN had the highest level of Cr (0.08 mg/l) among the inorganic fertilizers. Bio slurry is a better alternative fertilizer in reducing heavy metal uptake and their subsequent bioaccumulation.

Valorization of Solid Wastes from Biomethanisation of Pig Breeding Effluents

The biomethanisation of pig wastes produces a significant amount of biogas and reduces the organic load of the effluent. This effluent contains an important amount of nutrients that may be recuperated by coagulation-floculation, with cationic polymers. The optimization of this process was studied and the characteristics of the solid wastes produced determined. This product is a typical protein concentrate whose value is discussed, as well as possible reutilizations for feeding purposes.