H₂O may be the chemical formula for water, but it should also stand for ‘How To Optimize’.
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More than a third of municipal energy budgets are taken up by water and wastewater utilities.
Hardware upgrades such as high efficiency blowers can cut plant electricity consumption by 50%.
Exploiting in-pipe kinetic energy can help power water utility operations, and recovered waste heat from grey water can be used to heat district energy systems.
Harvesting biogas from waste treatment can power plant operations and be sold (e.g. for biofuel vehicles) to generate additional income.
Increasing energy efficiency, reducing emissions, and optimizing water facilities is an important goal that municipalities should be working towards. These facilities not only have substantial potential for upgrades, they also account for a significant chunk of municipal energy expenditures, so even small improvements can lead to substantial savings.
In the U.S., 35% of a typical municipal energy budget is used by water and wastewater utilities. Overall, water facilities account for 3-4% of total energy consumption in the United States, releasing 45 million tons of greenhouse gases (GHG) each year.
Electricity accounts for 25-40% of the operating budgets of wastewater facilities, and a whopping 80% of the budget of drinking water processing and distribution systems. Due to more stringent safety and environmental regulations, between 1998 and 2008, the number of facilities employing processes greater than secondary treatment has increased by 48%. This means that more energy-intensive processes are being used in many facilities.
In the U.S., 35% of a typical municipal energy budget is used by water and wastewater utilities.
According to the Environmental Protection Agency (EPA), “the most effective way for communities to improve energy efficiency in their water and wastewater facilities is to use a systematic, portfolio-wide approach that considers all the facilities within their jurisdiction.” Fortunately there is a lot of potential energy in the very water that these facilities deal with, energy which can be captured and utilized to reduce costs and emissions.
In terms of equipment upgrades, solutions can be as simple as adding plastic balls to cover oxygen production vaporizers to prevent evaporation and heat loss.
More complex upgrades including switching to high efficiency blowers, as aeration systems typically account for about half of plant energy use. Upgrading blowers can allow for more precise operations, with variable frequency drivers ensuring appropriate pump speeds based on flow conditions.
This is what the treatment plant in Green Bay, Wisconsin did. By installing high efficiency blowers in its first-stage aeration process, the plant reduced electricity consumption by 50% and now saves more than 2.1 million kWh annually.
Installing SCADA (Supervisory Control and Data Acquisition) software can also increase operational efficiency and process monitoring, which together with IoT sensors can provide plant operators with valuable insights and avenues for further savings. While installing smart systems is a great way to save money, sometimes the biggest savings come from not having to spend money in the first place. As the EPA notes:
“The most compelling argument in favour of energy efficiency improvements is that they represent an opportunity to free up resources that would otherwise be spent on energy costs […] communicating these benefits to the appropriate managers and obtaining their commitment from the beginning is crucial.”
Take Indianapolis for example; the city has to deal with 7.8 billion gallons worth of sewer outflows every year. Upgrading the sewer system was set to cost the municipality $3.8 billion over 20 years, but after talking to experts, city hall was convinced that by identifying sustainable solutions (green roofs, rain gardens, and bioswales) the city could divert nearly half of the run-off entering the storm water system, while also saving $740 million at the same time.
Capturing kinetic and thermal energy
Alongside reducing electricity consumption, proactive municipalities can benefit from utilizing waste energy and waste products to generate electricity and revenue. One simple way to do so is to capture the kinetic energy of water moving downhill in pipes. Gravity-fed systems save energy by using far less electricity to pump water, and can use in-pipe turbines to generate electricity. As long as the pipe system is gravity-fed with excess head pressure, systems like LucidPipe can be installed.
For example, one mile of 48 inch diameter pipe can potentially produce up to 3MW of energy. When installed in a 60 inch pipe with a flow velocity of 7ft/s and 40 psi of excess head pressure, one LucidPipe turbine can generate up to 100kW.
The city of Seattle installed four such in-pipe turbines in 2017, which are expected to generate 1,100MWh annually and $2 million in renewable energy capacity over 20 years. Alternatively, unused space can be converted into solar installations. This is what the plant in Oroville, California did. The 60 acre site with a daily processing capacity of 6.5 million gallons installed 520kW worth of solar panels which now provide 80% of the facilities energy needs.
Thermal energy (from showers, laundry machines, dishwashers etc) can be harnessed to reduce emissions and costs.
Alongside kinetic energy, wastewater also contains thermal energy (from showers, laundry machines, dishwashers etc) that can be harnessed to reduce emissions and costs. This is what Vancouver’s False Creek utility did back in 2010 when it became the first utility in North America to extract heat from untreated municipal wastewater.
The utility is connected to a district energy system that is expanding from 5.7 million square feet to service 22 million square feet in the city. The extracted heat is used for space heating in buildings, and this recycled energy has led to a 60% decrease in GHG emissions associated with heating buildings in the service area.
The East Bay Municipal Utility District in California has saved $1.7 million on its annual energy costs by using a biogas and natural gas turbine co-generation system, with waste heat from the turbines recovered to maintain the optimal temperature for the facilities anaerobic digesters and to provide building heating.
This brings us to a third way to capture extra value from water systems; namely, by using biogas produced by anaerobic digesters in a combined heat and power system to generate electricity and provide space heating. Specifically, one million gallons of wastewater flow can, via anaerobic digesters, produce enough biogas to generate 26kW and 2.4 Btus per day.
The Washington Suburban Sanitary Commission is developing a bio-energy project set to come online in late 2021 that accepts all biosolids from surrounding plants in order to capture methane. The gas is then sold to a facility for fueling buses generating revenue. This gas harvesting process also generates annual renewable energy credits to the tune of $2-2.5 million.
A related tactic that water facilities can use to increase biogas generation is to process fats, oils, and grease (FOG) that would otherwise enter the wastewater system and lead to extra maintenance. Millbrae, California chose to divert grease from its water system by offering daily FOG pickups: the resulting biogas now provides 80% of the plant’s energy needs. Gresham, Oregon is another municipality that has implemented a FOG program.
Gresham noticed that biowaste facilities were charging the private haulers removing FOG from thousands of restaurants up to 21 cents per gallon in tipping fees. The utility decided to offer haulers an 8 cent tipping fee, an offer that was quickly taken up.
This in turn led to a 60% increase in biogas generation and the utility is raking in $350,000 in tipping fees each year. Overall, Gresham is saving $500,000 on its energy costs and the Gresham Wastewater Treatment Plant became a net-zero facility in 2015.