Humans have been harnessing water’s energy for thousands of years. Archaeologists have discovered trip hammers powered by a water wheel—dating back to 202 BC and 9 AD—that were used to grind grain, break ore, and press paper in early China.
Today, we continue to rely on water to generate energy. Modern hydropower represents about 20% of our current global energy production. Water’s energy potential is harnessed too in oil, gas, and coal power plants when it is converted to steam. So why is it that have we have overlooked the latent thermal, hydraulic, and chemical energy found in wastewater?
I learned recently that the energy potential of wastewater is 10 times the energy needed to treat it. That’s a significant margin. Some wastewater treatment plants, I understand, are capable of producing 100% or more of the energy they need to operate. Studies show that if all US wastewater treatment plants produced power, they could potentially meet 10% of the national electricity demand. It seems like the perfect opportunity for wastewater facilities to shift from energy consumers to energy producers. I wonder: could we be at the tipping point of wastewater energy recovery?
I attended the OneWater Leadership Summit in Atlanta, Georgia last week. One of the more compelling workshops was an exploration of the Water-Energy Nexus in the Wastewater Sector led by Albert Cho of Xylem. Directors of several major utilities shared their experiences in making their plants more energy efficient and, as you might expect, energy recovery from wastewater was a recurring topic.
It seems that there are a multitude of strategies to increase plant efficiency. Plant managers reported converting their digestion from aerobic to anaerobic and cleaning bubblers to make aeration less energy intensive, since it can amount to as much as 60% of a facility’s energy consumption. Each did extensive energy modeling to improve process operations and lower the plant’s carbon footprint. Some incorporated nutrient recovery and pelletization, while others succeeded with water reclamation and gas-to-energy conversion. One utility (DC Water) is exploring the development of a microgrid to help with plant redundancy.
Each of these agencies currently derives energy from wastewater but reported a lack of incentive as often inhibitive for others, explaining how hard it is to spend money on something that isn’t urgent. As we all know, budgets are restrictive these days. At the plant level, repairing in-use equipment and providing water treatment takes priority over purchasing new assets. In addition, low fuel prices have simply not provided the necessary economic push to reach for more efficient technologies. It seems, the environmental impetus is alive but has not sufficiently motivated policymakers to support with adequate funding.
