Biomass Valorization to Bioenergy: Assessment of Biomass Residues’ Availability and Bioenergy Potential in Nigeria

The bioenergy sector in Nigeria currently lacks a proper assessment of resource availability. In this study, we investigated the bioenergy potential of agricultural residues and municipal solid and liquid waste using data from 2008 to 2018, and we applied a computational and analytical approach with mild assumptions. The technical potential for the production of cellulosic ethanol and biogas was estimated from the available biomass. It was discovered that higher energy was generated from biogas than cellulosic ethanol for the same type of residue. The available crop residue technical potential of 84 Mt yielded cellulosic ethanol and biogas of 14,766 ML/yr (8 Mtoe) and 15,014 Mm3/yr (13 Mtoe), respectively. Biogas has diverse applications ranging from heat to electric power generation and therefore holds great potential in solving the current electricity crisis in Nigeria. It will also position the nation towards achieving the 7th sustainable development goal (SDG 7) on clean and affordable energy.

Dynamic and equilibrium precipitation of struvite from the concentrated cellulosic ethanol stillage

The phosphate rock mineral is the main source of P-fertilizer production. It is estimated to become depleted in next century. Thus, the recovery of phosphorus from waste streams have attracted great interest. The cellulosic ethanol production is seen more and more important in future. During the production of cellulosic ethanol, the phosphorus element is released from lignocellulosic biomasses and end up dissolved as phosphate ions in the stillage stream. In this study, the struvite (MgNH4PO4 · 6 H2O) recovery from the concentrated cellulosic ethanol stillage (ES) was conducted under room conditions with an initial pH at 7–9. The effect of Mg2+, PO43−, NH4+ and Ca2+ during struvite precipitation testes are investigated. The optimized pH value for struvite recovery is estimated at 8.5, by which 85% of PO43− and 46% of Mg2+ are removed from the liquid stream. The mass fraction of struvite in recovered crystal sample reaches 82 wt.%. The economic evaluation of struvite recovery from ES was also investigated. This work proves that the struvite is potentially to be recovered with high purity from the concentrated cellulosic ethanol stillage.

Net Energy Analysis and Techno-Economic Assessment of Co-Production of Bioethanol and Biogas from Cellulosic Biomass

Co-production is a process based on the biorefinery concept that maximizes the benefit of biomass by reusing residue from the production of one product to produce others. In this regard, biogas is one of the most researched second products for the production of ethanol from cellulosic biomass. However, operating this scheme requires additional investment in biogas processing equipment. This review compiles data from research studies on the co-production of bioethanol and biogas from lignocellulosic biomass to determine which is more worthwhile: leaving the residue or investing more to benefit from the second product. According to previous research, ethanol stillage can be converted to biogas via anaerobic digestion, increasing energy output by 2–3 fold. Techno-economic studies demonstrated that the co-production process reduces the minimum ethanol selling price to a level close to the market price of ethanol, implying the possibility of industrializing cellulosic ethanol production through this scheme.