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.

Automated summary

This study evaluates the viability and impacts of four alternatives for utilizing acai seeds waste in the Brazilian Amazon. The option of co-production of polyphenols and electricity shows good economic and environmental performances, while complete combustion for power generation is the least profitable.