By Joel Stone, ConVergInce Advisers and member of Lee Enterprises Consulting
Special to The Digest
A unique and affordable membrane technology exhibiting extremely low fouling rates can offer significant benefits to dry mill ethanol operations, especially on streams containing protein and oil components.
First opportunity: Recover soluble protein, oil, and insolubles from stillage backset
The thin stillage stream, typically in the range of 6-8% total solids, is high in both protein and residual corn oil. In order to operate optimally in terms of water balance and energy conservation, up to 25% of the thin stillage “backset” is recycled to the front-end corn slurry process step, and ultimately back through the fermenters. Implementation of this new membrane technology by ZwitterCo would eliminate the endless recycle of insolubles, protein and oil in the thin stillage solids and would also remove all contaminating bacteria, yeast, or mold in the backset stream. Fermenter solids is a limiting factor in ethanol plant capacity, and removing these non-fermentable solids can result in an approximate 5-7% increase in available plant ethanol capacity. Recognizing its positive attributes, the concept of backset membrane filtration has been studied from time to time, but rapid membrane fouling from the protein and oil components has consistently been an economic showstopper. That issue is resolved with these new membranes.
Second Opportunity: Replace or reduce thin stillage evaporation
Depending on a plant’s design for energy utilization, rather than installing a unit sufficient to process only the ~25% backset, an attractive option could be to process the entire thin stillage stream through a ZwitterCo membrane system. Depending on the achievable retentate solids level exiting the membrane system, the evaporation step for concentration of the stillage to 60-65% solids “syrup” could be greatly reduced in its required energy input, or potentially even eliminated. A ZwitterCo membrane filtration system could reduce this energy requirement for concentrating the syrup by more than 80%, and potentially even 95%. An additional advantage is that the evaporation step results in some loss of nutritional value of the resulting feed co-products, and is not the case with the ZwitterCo membrane option. Historically, despite its potential advantages, membrane filtration has not to date been employed in the corn ethanol industry due to a major problem associated with membrane fouling and resulting rapid reduction of flux rate. Required chemical treatment with its inherent capex and operating costs required to return standard membranes to their original flux rate are another significant deterrent to their commercial deployment for this application using standard polymeric membranes. All of these issues are resolved with the breakthrough technology of the ZwitterCo membranes.
Third Opportunity: Facilitate high protein co-product production
With few exceptions, the 200+ ethanol plants in North America currently produce a single feed product consisting of all the non-starch components of the incoming corn plus some fermentation yeast. Over the past few years it has been shown conclusively that separating the fiber component of the “co-product” feed with as little protein and corn oil as possible from the protein component (along with other soluble or very fine fiber, ash, etc, and separately collecting as much of the corn oil as possible, provides a significantly higher overall co-product value. Given the commodity status (and resulting low margins) of the primary ethanol product, any increase in net value of the co-product components is critically important. The ZwitterCo membrane technology has significant potential for integration into new processes that are being developed for the purpose of producing these optimally separated products.
Fourth Opportunity: Wastewater BOD reduction/recovery of protein, oil and insolubles
Any ethanol plant internal recycle or plant discharge water containing levels of fine insolubles, protein, and/or oil deposits can be easily cleaned to near 100% removal of all these components, resulting in “clean” low BOD water for recycle or potentially direct discharge, as well as recovery of these valuable components for sale.
For more on ZwitterCo’s patented membrane chemistry and filtration, check out The Digest’s 2020 Multi-Slide Guide to ZwitterCo membranes here.
About the Author
Joel is the President of ConVergInce Advisers and serves as Executive Vice President Strategy for Lee Enterprises Consultants, the world’s premier bioeconomy consulting group. He has been a long-term visionary and respected leader in commercialization of industrial biotechnology. ConVergInce is presently providing services for fermentation and downstream recovery to develop and commercialize the emerging synthetic biology products including commercialization assistance for advanced technology clients in renewable chemicals, biochemicals, biofuels, and agricultural and biobased ingredients for food, fragrance and consumer products. Joel has twice been listed in Biofuels Digests top 100 in the bioeconomy. In 2019 he was selected as the inaugural “Champion for Industry” award from Thomas.net. Contact: firstname.lastname@example.org