A Wastewater Opportunity: Tech Advances Lead to Energy Rewards

by | Jul 25, 2012

Worldwide population growth is putting a predictable strain on crucial resources like water and energy. If we look at the US alone, our businesses and municipalities are creating 36 billion gallons worth of wastewater each day. Domestic and international demands for water make wastewater treatment and reuse essential, but we’re burning even more energy on treatment. Instead, we should be looking at wastewater as a resource in itself.

Operators have an opportunity to move beyond turning industrial wastewater around in reclamation. They should be generating electricity and related value-added products directly from the organic matter in wastewater. Before these organizations evaluate wastewater as a potential fuel source, they should keep these six points in mind:

1. Two to three percent of US electricity demand stems from wastewater aeration. American businesses must treat industrial waste to comply with legal and safety regulations. This often leads to treatment fees and electricity bills as high as hundreds of thousands of dollars per year, depending on the treatment method. Depending on the specific pollutant they need to remove, businesses use filtration, aerobic or anaerobic digestion, or chlorination to treat their wastewater. The most common approach in the US is aerobic digestion, which uses oxygen to treat water high in biological oxygen demand (BOD). All of these options require electricity, but the wastewater itself contains energy. Operators should use biological engineering to tap into that.

2. “Less energy-intensive” treatments are inadequate. To date, operators have looked at processes like anaerobic digestion (AD) as potentially better for treating solids and high-strength liquids that come from municipal and industrial wastewater streams. AD is less energy-intensive than aeration, and it generates biogas that can be combusted for energy generation. However, those biogas streams are often low quality (55 to 75 percent combustible gas fractions), and they require scrubbing or other expensive processes before the gas can be used to generate energy. Also, AD systems fail to adequately treat low levels of BOD ? operators face long hydraulic retention times and energy-intensive aerobic polishing to remove residual BOD. All of this puts a lot of strain on the operator, who must continually monitor and control elements within the reactors, including temperature, average BOD level and pH.

3. A bio-electrochemical system (BES) can generate energy and other value-added products from wastewater. These systems use exo-electrogens (electrically active microbes) to generate electricity directly from contact with electrodes. Traditional fuel cells or electrochemical systems use chemical catalysts that oxidize fuel (such as hydrogen) at anodes and reduce oxygen at cathodes. A circuit between the anode and cathode captures electrical energy released in the process. BES is like a fuel cell with a regenerative, living microbial catalyst. These microbes can oxidize and reduce a range of organic fuels, including wastewater. With a BES, operators can generate electricity, methane, hydrogen or related products from their wastewater while simultaneously offsetting costs. Meanwhile, they’re also supplying an alternative energy source, since the exo-electrogenic bacteria can respire through direct contact with electrodes. This can be used to power pumps and heat water, leading to a faster payback than a wastewater treatment process like AD.

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