Acai waste valorization via mannose and polyphenols production: techno-economic and environmental assessment

A critical environmental problem in the Brazilian Amazon-rainforest region is the annual generation of 1.4 million tons of acai seeds as a waste from acai-pulp production. This work evaluates the techno-economic viability and environmental impacts of four alternatives to avail acai seeds: complete combustion for power generation, integrated production of polyphenols and electricity, and co-production of mannose, polyphenols, and electricity by two different routes. Incineration is the least profitable alternative and requires long-term payback for the considered capacity of 6000 kg/h of seeds. The alternative that prescribes co-production of polyphenols and electricity has sound economic and environmental performances but misses the opportunity to avail the mannan content of acai seeds to produce mannose. The comparison of mannose-producing processes unveiled lower capital and operational costs in the single-step oxalic acid hydrolysis than the sequential sulfuric acid and enzymatic hydrolysis, resulting in a payback time of 2.7 years and an internal rate of return of 34.8%. It further evinces lower aquatic toxicity and acidification potentials, but greenhouse gas emissions are slightly higher than in the sulfuric acid case. The biorefinery is shown as a viable and sustainable waste valorization pathway for acai seeds, which could help develop a circular bioeconomy in the Amazon region.