Upgrading Stillage Processing Section of Dry Grind Corn-Ethanol Plants.

摘要

The focus of this study was to investigate the possibility of upgrading the stillage processing section to mitigate both the environmental (high phosphorus (P) content of animal feed coproducts) and resource (energy and water) consumption issues associated with dry grind corn-ethanol plants.;Thin stillage was determined to be the main P contributor in all of the animal feed coproducts. Centrifugation followed by chemical treatment with coagulants (lime, alum, ACH) and flocculants (anionic and cationic polymers) resulted in the removal of both inorganic phosphates and organic P. A significantly (p0.05) higher P removal was achieved with lime treatment (85%) than Al-based coagulants (70%) while anionic polymers resulted in better flocculation (bigger and more stable flocs) compared with cationic polymers. An optimum treatment combination of lime with anionic polymer was selected for safe and effective recovery of phosphorus from thin stillage. In addition, both centrifugation and chemi-cal treatment resulted in new coproducts: the secondary distillers grains (a low P, high crude protein feed component) and P-rich sludge (11.32% as P2O5).;Treated thin stillage (centrifugation and chemical treatment) is determined to have improved characteristics compared to raw thin stillage leading to a higher biogas yield of 793 mL/g VS added. Analysis at various ISR levels revealed alkalinity was a critical factor effecting digestion of treated thin stillage and an organic loading corresponding to ISR≥2 was recommended. A COD removal of 80.63% was achieved at ISR level of 2. The digester supernatant at this ISR level was not found to pose inhibitory effects upon its recycle based on the parameters tested with the exception of possible inhibition from sodium concentration.;Overall, energy efficiency would result from both the energy contained in biogas and the elimination of the evaporation step as a result of recycling treated thin stillage. In addition, the application of sludge as fertilizer to corn fields would result in the recycling of nutrients such as P and Ca. Moreover, analysis with 31P NMR indicate that the ethanol industry coproducts is not a significant contributor of the unavailable P (phytate P content 36.5% of total P) for all the coproducts analyzed.