Used to Useful

UsedtoUseful is an online channel offering industry insight to impact the industrial and municipal sectors, with a focus on water reuse in the areas of energy efficiency, tough-to-treat water and monitoring. UsedtoUseful takes a broader look at the world of wastewater treatment and technology. The stories and opinions do not necessarily reflect the views of GE.

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Wastewater treatment plants in the U.S. consume a large amount of energy. Listen as Senior Product Manager, Jeff Peeters, explains how water treatment plants can achieve energy neutrality by increasing their energy production and decreasing their energy consumption to ultimately demand no energy from the grid.

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Treating mixed waste

Recover water; generate biogas & electricity; reduce GHG

Dr. Stephen Vasconcellos, Consulting Engineer for GE Water & Process Technologies

The United States, as well as other regions, have not traditionally focused on mixed waste biogas plants as a way to use anaerobic digestion (AD) to drive alternative energy.  But, given all the issues around fossil fuel and their environmental impact, perhaps they should?

Thanks to academic, and industrial research and development, AD technology has been optimized to allow for the treatment of high-solids wastes. An advantage of high-solids systems is that they can process “mixed municipal solid waste (MSW)” as well as biowaste. “Mixed MSW” is all material set out as garbage excluding recyclables, compostables or waste diverted from garbage by some other means. “Biowaste” is source separate household waste. Mixed MSWs also can promote Central Effluent Treatment plants which optimize land usage and facilitate downstream applications (E.g. electricity generation) for the bio-gas produced.

A typical configuration has these digesters receiving waste from local industries, dairy farms and waste recyclers. AD Technology takes the waste and generates biogas. That biogas from the digester can then fuel a gas engine to generate up to ~ 5 MWh of renewable electricity. This renewable energy could replace traditional energy use at the local industries, which in turn reduces greenhouse gas emissions, (by the equivalent of tens of thousands of metric tons of CO2 each year), as well as reduces waste odors.

But, the benefits do not stop there. The waste from the AD can be further treated to recover more value. Efficient dewatering – using high speed centrifuges – achieves higher solids (which can be land-applied) and cleaner water (for reuse in the industry). New polymer technology that sustains the high shear in the centrifuge can deliver reuse water containing less than 2% solids, and typically between 0.2 – 0.8%. Cake solids range from 35-45% and can be land-applied on site so there are no hauling costs.

All this can be achieved by reviewing operating conditions, such as bowl speed and speed differential to optimize torque. Polymer dosages need not be very high and can match those used in traditional municipal plants.

By looking to a historically untapped market and by combining advanced technologies – Anaerobic Digestion; Dewatering; Gas Engines; Chemicals – industries (particularly food manufacturers) can find new value in their waste management solutions and create renewable energy alternatives.

http://ch4biogas.com/projects/napoleon-biogas/

http://wst.iwaponline.com/content/41/3/283.abstract

http://www.seas.columbia.edu/earth/vermathesis.pdf

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