Power Struggles

While not blessed with a constant power source like wastewater treatment plants, water plants have numerous ways to cut energy consumption and cost.

On the wastewater side they talk a lot about making treatment plants energy self-sufficient (or in the more popular language, reaching net zero energy).

They can talk that way largely because the water flowing into the plants brings an abundant and never-ending energy source, in the form of organic matter that can be converted to methane (biogas), a fuel for electric generators and boilers. They can even add materials like fats, oils, grease (FOG) and food waste to existing digesters and create even more fuel.

Water plants lack that luxury. They’re energy intensive but don’t have any obvious energy sources besides their utilities’ electric and gas lines. And yet, there’s room to reduce net consumption significantly, as shown by the Sustainable Practice features in WSO (this month we highlight Cedar Rapids, Iowa). Any of these actions taken alone will make a difference, and if done together they can have a substantial impact.

Consuming less

Many water plants are energy inefficient simply because their equipment is old.

Pumping is the greatest energy expense, and aging motors and pumps can be energy hogs. You can save substantial energy by switching to more efficient pumps and premium efficiency motors and adding variable-frequency drives. If it isn’t feasible to invest in new equipment, you can gain ground just by rebuilding old equipment to its original specifications.

Membrane treatment systems are more energy-intensive than conventional treatment, and an older membrane system may leave substantial room for savings. Manufacturers steadily improve their systems with membranes that operate at lower pressure and so use less energy.

In the same manner, older UV disinfection systems can be updated to more efficient units with superior lamp cleaning systems, and with lamps that achieve the same pathogen kill while using less electricity.

Then there’s good old-fashioned leak detection and repair. Water treated, pumped and lost through leaky distribution pipes boils down to energy wasted. Collectively, the nation’s water utilities lose billions of gallons to leakage daily. An investment in pipe condition assessment and leak detection, backed by an aggressive repair program, can pay quick dividends.

Using it intelligently

It’s also possible to do the same amount of work and use the same amount of energy — yet pay less for it — by taking advantage of your utility’s time-of-use pricing. For example, if you have ample storage, you can do the bulk of pumping to fill the tanks during the night hours when rates per kilowatt-hour are lower. This has the double benefit of reducing your total kilowatt demand — and utility demand charges — during peak times.

You can also follow the example of Cedar Rapids and sign up for your utility’s interruptible rate program, if available. In summer when air conditioning loads on the power grid are high, many utilities give major power users rate incentives to shed load when directed — usually for a several hours during the heat of the day. In exchange, the utility grants a substantial demand charge reduction all year long.

Your emergency generators can also help you earn special rate treatment. Your utility may offer incentives if you operate your generators when directed to reduce peak demands on the grid. The incentives typically are much larger than the cost of keeping the generators ready to run and paying for the fuel to operate them. In essence, you take load off the utility grid, without having to curtail your plant’s operations.

Making more

While raw water doesn’t contain energy-producing material, the water itself can be an energy source. For example, if you draw water from high elevations, a hydroturbine in the pipeline can generate electricity on the way down, under the same basic concept as a hydroelectric dam. Large utilities may find it feasible to deploy turbines with capacities up to 500 kW.

It’s even possible to get back some of the energy used to fill a water tower or reservoir — by adding smaller hydroturbines (50 to 100 kW) downstream. Small hydroturbines also can replace pressure-reducing stations, especially in remote locations where the electricity can help directly power a local building.

Finally, many water plants have ample properties and large rooftops that can lend themselves to renewable energy projects like wind and solar photovoltaic. These projects can be built under power purchase agreements and other innovative financing plans that require no up-front investment on the utility’s part.

Getting going

The utilities we feature prove that these things can be done, and done economically. We hope you find their examples useful. In the meantime, feel free to share your successes in energy savings and production. Send a note to editor@wsomag.com. I promise to respond, and we’ll present some of the most compelling stories in future editions.


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