• Wastewater Treatment


View Staff


September 7, 2012
The engine generator employs a 4‑cycle, 12-cylinder, 1,650 cu in turbocharged engine with a 450 kW, 4,160 V generator manufactured by Caterpillar. The co-generation system is designed to continuously deliver up to 560 kVA of three-phase power. Electrical power will be used within the plant. Switch gear will allow paralleling in the plant with power provided by Alliant Energy. Engine generator heat will be used to heat the anaerobic sludge digester system, the hauled waste storage tanks, and to pre-heat building ventilation air. Any excess heat will be exhausted through radiators in the plant yard area.

We produce biogas through the anaerobic digestion process or fermentation of biodegradable materials such as municipal sludge.

In addition to that we receive high strength wastes which are hauled in by tanker truck from local industries that we pump directly into the digesters for increased biogas production.

High strength waste will be received and stored in two heated and mixed 304 stainless steel tanks each with a volume of 20,000 gallons prior to pumping to either the thermophilic or mesophilic digesters.

This biogas needs to undergo cleaning before it can be used to prevent damage and corrosion to our biogas engine. First, the highly corrosive hydrogen sulfide is removed utilizing a biological system where a controlled environment is maintained inside of a tank for microorganisms to consume the hydrogen sulfide.

Through fermentation biogas is produced. Biogas comprises primarily methane and carbon dioxide along with a few other trace gases. We produce approximately 200,000 cubic feet of biogas each day. There are other things that are produced in the digestion process that need to be removed to ensure beneficial reuse of the biogas. Hydrogen sulfide, siloxanes, and moisture are items that need to be removed from the gas.

Next, the biogas flows through a siloxane removal system. Siloxanes come from silicone based products such as cosmetics and some cleaning agents that end up down the drain and to the plant. Siloxanes are produced in the digestion process when these products are broken down and gas is produced. Imagine fine black sand and that is what siloxanes look like. The cleaning system uses media to drop out the siloxanes from the gas.

Finally moisture can be another problem with biogas utilization. There is a lot of moisture in the gas and in order for the biogas engine to run efficiently the moisture needs to be removed.  The now cleaned biogas can be utilized as fuel for our biogas engine which we use to produce approximately half of our energy consumption.

We also use the waste heat off of the engine to help maintain digester temperatures which are crucial for biogas production.

Methane gas production also varies with the concentration of the organic matter and the total amount of gallons of sludge pumped to the digesters per day. On average, we pump 40,000 gallons of sludge every day to the digesters and the methane gas production averages 127,000 cubic feet per day.

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