Biomass waste-to-energy valorisation technologies: a review case for banana processing in Uganda

Abstract

BackgroundUganda’s banana industry is heavily impeded by the lack of cheap, reliable and sustainable energy mainly needed for processing of banana fruit into pulp and subsequent drying into chips before milling into banana flour that has several uses in the bakery industry, among others. Uganda has one of the lowest electricity access levels, estimated at only 2–3% in rural areas where most of the banana growing is located. In addition, most banana farmers have limited financial capacity to access modern solar energy technologies that can generate sufficient energy for industrial processing. Besides energy scarcity and unreliability, banana production, marketing and industrial processing generate large quantities of organic wastes that are disposed of majorly by unregulated dumping in places such as swamps, thereby forming huge putrefying biomass that emit green house gases (methane and carbon dioxide). On the other hand, the energy content of banana waste, if harnessed through appropriate waste-to-energy technologies, would not only solve the energy requirement for processing of banana pulp, but would also offer an additional benefit of avoiding fossil fuels through the use of renewable energy.Main bodyThe potential waste-to-energy technologies that can be used in valorisation of banana waste can be grouped into three: Thermal (Direct combustion and Incineration), Thermo-chemical (Torrefaction, Plasma treatment, Gasification and Pyrolysis) and Biochemical (Composting, Ethanol fermentation and Anaerobic Digestion). However, due to high moisture content of banana waste, direct application of either thermal or thermo-chemical waste-to-energy technologies is challenging. Although, supercritical water gasification does not require drying of feedstock beforehand and can be a promising thermo-chemical technology for gasification of wet biomass such as banana waste, it is an expensive technology that may not be adopted by banana farmers in Uganda. Biochemical conversion technologies are reported to be more eco-friendly and appropriate for waste biomass with high moisture content such as banana waste.ConclusionUganda’s banana industrialisation is rural based with limited technical knowledge and economic capability to setup modern solar technologies and thermo-conversions for drying banana fruit pulp. This review explored the advantages of various waste-to-energy technologies as well as their shortfalls. Anaerobic digestion stands out as the most feasible and appropriate waste-to-energy technology for solving the energy scarcity and waste burden in banana industry. Finally, potential options for the enhancement of anaerobic digestion of banana waste were also elucidated.

Comparison of pretreatment methods that enhance biomethane production from crop residues - a systematic review

“…Chemical pretreatments were reported to be expensive due to high costs of disposal of digestion residues ( (Rouches et al, 2017). Other studies reported chemical methods with respect to alkali pretreatment to be inexpensive (Song et al, 2014;Amin et al, 2017;Gumisiriza et al, 2017;Ismail et al, 2017;Kumar and Sharma, 2017). The benefit of Ca(OH)2 pretreatment is the low disposal costs as Ca can be easily recovered from the hydrolyzate (Amin et al, 2017).…”

“…(2014) who posited that short duration time is an advantage of mechanical pretreatment. Conversely, Gumisiriza et al (2017) reported that irradiation processes are slow.…”

“…Two studies Li et al, 2015) reported that chemical pretreatment is a fast process, and three studies reported that it is a slow process (Amin et al, 2017;Gumisiriza et al, 2017;Kumar and Sharma, 2017). This can be explained in terms of variation in treatment conditions.…”

“…show that combined processes are high energy-consuming methods(Gumisiriza et al, 2017;Speda et al, 2017;Perendeci et al, 2018). High temperatures and limited heat recovery during steam explosion (SE) pretreatment may lead to high energy use and reduced methane yield(Gumisiriza et al, 2017). Extrusion pretreatment also consumes high energy of about 10 to 15 kW of power to pretreat a tone of substrate (Montgomery and Bochmann, 2014).…”

Wastewater remediation via combo-technology

“…Dewatering is an energy consumptive process, sometimes taking even weeks for complete sludge drying through incineration, pyrolysis, or gasification [13]. Even excreta collected from toilets either on-site (e.g., in a pit latrine or septic tank) or transported off-site in sewer systems are also termed sludge.…”