by Andrew Green
(Editor’s note: We have published numerous posts on this important and popular subject in the past, including water-energy co-dependence, the water-energy nexus, and the effects on your plant. We’d love to hear about your plant’s successes in reducing energy consumption and/or improving energy recovery. Send your story to revere@reverecontrol.com or use the Contact Us function on this site.)
The water/wastewater treatment sector is said to account for 3% of the total United States energy load. The reason for this is that a large amount of energy is required for the respective treatment processes. According to the Water Environment and Reuse Foundation, “Behind labor costs, energy is often the second-highest operating cost at a water resource recovery facility (WRRF).” It is for this reason that many municipalities are working towards a state of energy neutrality.
According to Water Online, “A plant that has reached energy net-zero, or neutrality, generates all of the energy needed for operation solely from what’s available in the water and waste that it treats.” With a commodity as valuable as electricity, the benefits of a plant that has reached energy neutrality cannot be understated. As it relates to wastewater treatment, having a process that is self-sustaining to treat and reuse waste equates to, basically, free energy and electricity. In a world where more energy is being consumed than ever, sustainability is how companies, municipalities, etc. will continue to stay relevant in the days ahead with the rising energy costs.
But that begs the question: Does the sector lend itself to being energy neutral, in the first place? The Water Environment Research Foundation reported, “Pumping, aerating, heating, and cooling – it all adds up, making energy the largest controllable cost for facilities that provide wastewater services. But new technology and new ways of thinking are putting some facilities on track to not only cut consumption of energy, but also to generate it – offsetting their use and moving them towards an energy-neutral sweet spot.” Currently, there are a couple of areas in the process that are being pursued for the potential to steer the plant closer to energy neutrality.
Primary Treatment
In the wastewater treatment process, non-soluble solids are filtered out in the very beginning stages. Depending on the size and makeup of the solids, some may make it further through the treatment process. This relates to energy consumption because those solids end up having to be filtered out in the bio treatment part of the process – the highest energy consumer in the entire plant. Increasing the effectiveness of primary treatment will help to save more energy downstream.
Digestion
The digestion process produces a large amount of biogas which can be reclaimed and converted into electricity. Unfortunately, many facilities are not taking the initiative to recapture the biogas that is produced by their respective processes. This allows relatively free energy to escape into the environment. Numerous companies are working on solutions to capture, convert, and reuse the biogas produced in these facilities.
Revere has designed several control systems for reclaiming fuel from the digestion process to contribute to a reduction of energy costs. Most notably, a water and sewer department in South Florida were provided with a control system for adding two, new generators that run on various combinations of methane from the sludge digesters, the landfill, and natural gas. The control system controlled fuel feed, fuel selection, cooling water, thermal oil heat transfer, adsorption chillers, standard chillers, and digester heating loops. The scope also included programming of the SCADA system to ensure full visibility and control were given to the metrics of success for these generators. Oftentimes, all that is needed to make a leap closer to net zero energy consumption is a simple change in how the process is fueled and powered – like adding generators that can run with methane from the digestion process. As a company, we are very fortunate to have been able to participate in these efforts by the South Florida water and sewer department. It’s also notable that this project, performed using design-build delivery, received an award from the Design-Build Institute.
The industry is gradually working towards a point of energy neutrality. Rising costs of electricity in the US make now a more critical time than ever to operate as efficiently as possible. Several are leading the way and the water/wastewater treatment sector has recognized the need. Energy neutrality – here we come.
If you need help identifying aspects of your plant’s operations that are candidates for energy reduction or energy recovery, whether it be as simple as saving energy by improving pump sequencing and speed or as complex as bio-gas recovery and reuse, please contact us.
Update-031017: The Midwest Energy Research Consortium has released a public summary of their report titled, “Strategic Roadmap on the Energy Water Nexus“. We have made available a copy of the summary.