Can WWTPs go from Energy Drain to Energy Gain?
As many of us know, the wastewater treatment process uses a lot of energy, and with increasing economic pressures on wastewater utilities, facility managers are looking for high strength waste to help them become energy neutral — even net energy producers. The creation of energy would not only provide relief from normal operational expenses, it could help demonstrate sustainability to the surrounding communities.
One such utility, Milwaukee Metropolitan Sewerage District, cleans billions of gallons of wastewater every year at two reclamation facilities that serve 1.1 million people in 28 communities. MMSD wants to achieve energy neutrality by 2030 and they see food waste as an integral part of it.
This isn’t another fantasy. In the first quarter of 2016, MMSD received over 200,000 gallons of high strength food waste slurry at one of their two facilities.
The slurry is virtually contaminant-free and readily biodegradable, which enables water resource recovery facilities like MMSD to make more biogas to produce onsite energy. As a result, they are able to help offset operational expenses by reducing their dependence on purchased electricity.
The slurry is high in solids compared to sludge pumped into municipal digesters – about 10-12% TS. But it is pumpable and contains very high volatile solids — over 90% on average. The high COD content and readily biodegradable composition is a result of the food waste being held in a storage tank at the waste generator for 7-10 days.
Plants say, “Keep it coming”
The treatment plants already accepting food waste slurry say, ‘We want more of this!’ It has very high volatile solids content (more than 90 percent) and it’s rapidly biodegradable. The methane potential testing we’ve done in-house shows that the organics are converted to methane in five to 10 days. It doesn’t take the normal 20- to 30-day detention time that a digester requires to process wastewater sludge.
If you’re thinking it’s too good to be true, you should take a look at this video. Feel free to drop me a note if you have questions or need convincing you’re not dreaming.