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Wastewater Treatment

The size of the annual sugar beet crop is approximately 2,300,000 tons, of which 75% is water. This means that 1,600,000 gallons of water must be managed each day. Most of the water comes from the evaporation process as condensed steam from the evaporators. Much of this water is of a very good quality and can be re-used in the process. Excess condensate is sent to the holding ponds to await treatment at the wastewater treatment facility.

Some of the water is used to wash the beet as described in the section on “Handling”. The wash water is contained within a loop that involves a clarifier that allows the mud to settle out of the water. The clear water or clarifier overflow is returned to the wash water loop and reused many times. The underflow from the clarifier can contain as much as 20% mud. Horizontal solid bowl decanters separate the mud from the water using centrifugal force. The water is returned to the pond system and the mud may be land applied or used for covering in the lime storage unit.

The holding pond system consists of six individual ponds covering a total area of about 170 acres that can contain approximately 300,000,000 gallons when full. Storage of high strength wastewater during the summer months can be a significant source of odors when the ponds are in an anaerobic (without oxygen) condition. The wastewater from the pond system can be spray irrigated from late April through early October, on 1,000 acres of cropland that are used to grow reed canary grass as a forage crop for cattle.

The wastewater treatment facility utilizes both anaerobic and aerobic (with oxygen) biological processes, in conjunction with tertiary treatment to produce a wastewater effluent suitable for discharge to local surface waters. The up-flow anaerobic sludge blanket portion of the facility was designed for a wastewater flow of 1,500,000 gallons per day with a maximum waste loading of 125,100 pounds of BOD 5 per day. BOD 5 is an estimation of the amount of oxygen that will be used as the microbes break down the waste. To give some perspective to the organic loading on the treatment facility, 125,100 pounds of BOD 5 per day would be equivalent to a city with a population of about 735,000 people. A product of the anaerobic digestion process is digester gas. This digester gas will be about 70% methane and is used as a fuel to run a water heater that supplies heat for the wastewater entering the anaerobic system. This gas can supply up to 869,000,000 BTU per day back to the process.

The effluent from the anaerobic system is treated using a complete mix aerobic system that adds oxygen to the water to complete the treatment process. The effluent from the aerobic system is passed through another clarifier and then through sand filters to remove additional suspended solids. The final effluent flows through the post-aeration basin, where more oxygen is put into the water prior to discharging the water or returning the water to the holding ponds. The organic loading of the final effluent will be low enough that there will be no odors from the water during storage.

Both biological processes, the anaerobic and aerobic systems, treat wastewater by growing new microbes. Some of these unifrom microbes must be removed from the system by thickening with a gravity belt thickener that allows the water to return to the system and the resulting thickened biomass to be sent to a storage tank. The biomass is then land applied to cropland to provide an excellent source of organic matter, and both macro and micronutrients for plant growth.

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