Sustainable scenarios for alkaline protein extraction from leafy biomass using green tea residue as a model material

Leaf protein can be extracted cost-efficiently using 0.1 mol dm-3 NaOH, but this process is less sustainable due to the generation of large amounts of sodium salts. KOH or Ca(OH)2 are considered as replacements for NaOH, as these salts can be reused. This work evaluates the economic and environmental sustainability of weak alkaline pectin extraction followed by KOH enhanced protein extraction, and Viscozyme® L-aided pectin extraction followed by Ca(OH)2 enhanced protein extraction. The evaluations are made for green tea residue and are compared to related processes using NaOH. The predicted profits using KOH are comparable to those using NaOH. Environmental sustainability improves for all impact categories in the case of KOH extraction. Further environmental benefits are obtained by substituting conventional K fertilizer with the K-rich salty waste water from the extraction process. The profits of the process using Ca(OH)2 are highly dependent on the extraction yield of the protein product. Protein extraction yields using Ca(OH)2 need to be higher than 70% to be more profitable than the same process with NaOH. The environmental benefits of Ca(OH)2 extraction include the absence of salty waste water and the net production of heat. This is accompanied by increased electricity consumption. Thus, the impact categories of climate change, fossil and water depletion, and particulate matter formation worsen. Photochemical oxidant formations remain the same, while the other impacts improve. This work has shown the potential and bottlenecks of NaOH, KOH and Ca(OH)2 protein extraction on different types of biomass in terms of environmental and economic sustainability