Corn grain is one of the main sources for bioethanol production. However, corn bioethanol plants consume a significant amount of energy and water, compete with food supply chain for feedstock and may lead to eutrophication as the result of high nitrogen and phosphorous content of waste streams. All of the above issues challenge the sustainability of bioethanol from corn grain in terms of energy, water and arable lands. Each liter of ethanol produced can generate up to 20 L of stillage. The conventional practice for treatment of this byproduct is evaporation and drying to produce animal feed, accounting for approximately 47% of total energy consumption of the bioethanol plant. In this study, an integrated anaerobic digestion of thin stillage, coupled with microalgae production is proposed in which starch-rich microalgae produced using the digestate of thin stillage will be recycled into the front end corn-ethanol plant to reduce the reliance on corn feedstock. Additionally, nutrients present in thin stillage will be partially assimilated by microalgae and will be recycled back to the fermenters to grow yeast. To evaluate the feasibility of the proposed integrated process, thin stillage is digested in a 30L anaerobic baffled reactor (ABR) under various operating conditions to determine the optimum contaminant removal efficiency and methane production yield. Digestate of thin stillage will be used to cultivate microalgae under various nutritional and environmental conditions to determine the optimum carbohydrate cellular content and productivity. In our preliminary assessment, several microalgae species that are capable of growth on thin stillage digestate are identified. Research is in progress to determine the performance of the ABR at higher organic loading rate and to produce digestate for cultivation of carbohydrate rich-microalgae under various nutritional and environmental conditions.

Integrated system for thin stillage remediation coupled with microalgae cultivation for carbohydrate production

255th National Meeting (2018)

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