Financial and Process Performance of a Wastewater Reuse System in the Upper Midwest

摘要

A new 100 million gallon ethanol plant was recently constructed approximately 25 miles west ofrnthe City of Fargo in eastern North Dakota. Finding a suitable water supply for the ethanol plantrnwas a challenging task that involved unsuccessful exploration of private wells, regional waterrnsystems, and municipal drinking water. However, with persistence and open minds, stakeholdersrnturned their attention to recycled wastewater from the City of Fargo. After fast-tracking a waterrnsupply/diversion permit for the water supply system, the City, Ethanol Plant, and Cass RuralrnWater Users District (CRWUD) developed a thorough Memorandum of Understanding (MOU)rnthat defined the project requirements and responsibilities for each party. An Effluent ReusernFacility (ERF) capable of producing 1.4 million gallons per day (MGD) of reverse osmosis (RO)rnquality water was designed and the construction was completed in the fall 2008. The ERFrnstarted delivering RO water to the ethanol plant since December 2008 and more than 700 millionrngallons RO water has been provided so far. Due to the seasonal fluctuation of influent waterrnquality, such as temperature and TSS, the ultrafiltration (UF) process in the ERF has experiencedrnrapid fouling in the last two and half years and the original designed chemical cleaningrnprocedure cannot remove the biological fouling of the UF membranes. The City conducted anrnintensive study of cleaning solutions and processes for the UF membrane fouling issues andrnconcluded that an enzyme cleaner and a detergent are most effective. The RO process has beenrnrunning stably at the design operational conditions over the last two and half years. The Cityrnestimated operations and maintenance (O&M) costs of $1.02 per 1,000 gallons duringrndevelopment of the MOU. Over the first two and a half years, the actual average O&M cost perrn1,000 gallons has been $1.50. The costs of chemicals and energy contribute more than 70rnpercent of total O&M. As the ethanol plant is quickly expanding its designed productionrncapacity and increasing its water demand, the City is generating increasing revenue. Encouragedrnby the overall success of this wastewater reclamation project, the City of Fargo is continuing tornconsider potential options for expanding its wastewater reuse system.