Wastewater Treatment Challenges from an Ethanol Plant Recycle System

This paper was authored by Thomas Lawry prior to joining McKim & Creed. Tom joined McKim & Creed in 2015 as vice president of industrial and alternative project delivery. ©IWC 2009 

Several types of water are required to support the production of ethanol, including production process water, boiler feed water, and cooling tower makeup water.  A base process of filtration, reverse osmosis (RO), and ion exchange is typically used to produce this water.  Most of the water is recycled within the plant while a portion is discharged in a blowdown stream combining the RO reject, cooling tower blowdown, filter backwash, and softener regeneration.  This presentation describes the challenges faced by a particular 110 million gallon per year ethanol plant that utilizes groundwater with fluoride contamination as source water.  This plant discharges the blowdown to a nearby stream and was granted an NPDES permit with low permissible fluoride levels. Similar challenges exist for ethanol plants using a fluoridated municipal water supply as makeup to their water system.

To meet the strict discharge limits, a fluoride treatment system employing innovative technology was installed to treat the RO reject stream, which contains the highest fluoride level of the various blowdown streams.  The reject stream is pH adjusted before passing through activated alumina (AA) filters.  The AA filter effluent combines with the other blowdown streams in an equalization pond prior to discharging through the outfall.  The wastewater produced during AA filter regeneration has a high fluoride concentration and is treated with a more conventional calcium fluoride precipitation system prior to discharge.

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