Quantalux Blog

News, events, observations, industrial and otherwise, from a Quantalux point-of-view.

Biogas/Water = Win/Win

There’s been plenty of recent attention on energy prices since the price of a barrel of oil topped $100. Less recognized (but also important) is the long term availability of water. For arid parts of the US, water sources are as important as energy sources. Not all water needs to be drinkable – reclaimed water can be used for all sorts of uses ranging from toilet flushing, irrigation on golf courses and parks, and landscaping /wetland enhancement. Toilet flushing is particularly water-intensive: even after the adoption of building codes that mandate low-flow toilets, flushing alone consumes 30% of the water used in a residence.1

 

Waste-to-energy technology based on anaerobic digesters is an interesting solution for both energy and water. Anaerobic digesters not only extract biogas energy from organic waste materials, but can also reclaim water for non-potable use. Every day, we humans produce all kinds of organic waste, including carbon-rich water waste from food preparation/disposal (grey water), water from washing/cleaning (also called grey water) and nitrogen-rich human waste (black water). Anaerobic digesters are processing vessels that break down this organic matter in the absence of oxygen, producing biogas and (with suitable temperatures) a pathogen-free digestate. Biogas is approximately 65% methane, and can be uses as a heating fuel, or to power electrical generators. Water in the organic waste can be extracted from the digestate, filtered and used for a variety of non-potable uses.

 

It may be a surprising to think of using black water waste for reclamation, but by digesting waste at higher temperatures (70C), anaerobic digestion can destroy common fecal pathogens such as E. Coli, Giardia Lamblia, and Cryptosporidium that commonly exist in black water. Consequently, the digested effluent from the digester has a low (or zero) level of pathogens, and substantially lowers the risk of contaminating nearby water sources. The remaining nutrients in the water are particularly beneficial for irrigation of landscaped plants.

 

President Obama issued an Executive Order for Sustainability Targets for a wide range of government operations 2, and waste-to-energy technology is well suited to meet these targets. But the US Military (a typical early-adopter for new technologies) was already thinking along these lines in order to save money. For base camps in arid areas, they see the potential to capture all waste generated by soldiers and feed this waste into a potable digester system. Shipping materials to and from facilities is terribly expensive, so using waste-to-energy technology can make the base more self-sufficient and save tax-dollars. Municipalities and smaller entities benefit in the same way. Community digesters are emerging in the US as towns and cities see the value in both energy and water recovery from the waste stream.

1 Water Conservation Systems, April 2010, Building Codes Division, Oregon Smart Guide, http://www.cbs.state.or.us/external/bcd/pdf/0990.pdf

2 Executive Order 15413,

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