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Preparing Wastewater Effluent for Membranes

Ethanol is a love hate issue in America today. Grain farmers love it while poultry and livestock ranchers hate it; American isolationists love it while globalists hate it, and it goes on and on. Regardless of one stand on the subject, ethanol plants are in operation all over the United States. Today, 143 biorefineries are producing 8.2 billion gallons of ethanol per year (bgy). Presently, 57 new facilities are under construction with seven major expansions of existing facilities that will soon add another 5.2bgy.

Infrastructure is a big issue with local ethanol plants. Hundreds of big trucks go in and out taking their toll on local roads and bridges. Noise becomes a nuisance to surrounding neighbours. Electrical services must often be upgraded. About 2-3 gallons of water are needed for each gallon of ethanol produced. Where is this “extra” water going to come from?

Facility

The 1700 people in the rural community are contributing to renewable energy in a big way by producing 110 million gallons of fuel ethanol per year from locally grown corn. This facility is state-of-the-art for converting corn grain to fuel grade ethanol. Water usage at this location is 600 gallons per minute (gpm) 20 hours per day. This facility has two sources of water available, both being six miles away. The first is water supply reservoir that provides water to the community and surrounding area.

The second is effluent from the local municipal wastewater treatment plant, also stored in a reservoir.Both sources needed onsite treatment for uses in the production of ethanol. Hollow fiber ultra filtration (UF) membrane systems were chosen for this task. Water at the rate of 400gpm was to be drawn from the fresh water reservoir and feed one of the UF membrane systems. Part of the permeate from this system would feed a reverse osmosis (RO) membrane system for further treatment for boiler feed water and other critical uses while the remaining permeate went to cooling tower make up and other less critical uses. Another 200gpm would be drawn from effluent reservoir and supplied to a second UF membrane system also for cooling tower, wash-down stations, and other miscellaneous.

Initial Problem

It was quickly realised that neither waste water source could be fed directly to the UF membranes without some form of pretreatment. The fresh water reservoir supported a teaming population of fish, turtles, insects and some vegetation. Pumping from this reservoir six miles away entrained all of these critters and more into the supply water. The effluent reservoir, though recently treated to safe standards at the wastewater treatment plant and further treated by more filtration and disinfection was still in a reservoir standing as an open body of water. Being more nutrient rich, algae and other phytoplankton grew quickly. Some form of additional treatment was necessary at the ethanol plant to remove these solids before introducing the water to the UF membrane.

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