By Robert C. Brears
Since the industrial revolution, the total amount of waste has constantly grown as economic growth has been based on a ‘take-make-consume-dispose’ model. This linear model assumes that resources are abundant, available, and cheap to dispose of. In the U.S. and around the world, there is a move towards a ‘circular economy’ where products and waste materials are reused, repaired, refurbished, and recycled.
According to the International Water Association, water utilities need to understand the flow of resources in and out of cities and the relationship with the water and water cycle. The water cycle itself can be managed from watershed to consumer and back to watershed, and the transition towards a circular economy should consider the consumption and production of resources across this whole value chain.
Circular Economy Innovations
Already there are water utilities across the nation leading the way in transitioning towards a circular economy that promotes the reduction in water consumption, recycling of water, and recovery of energy from wastewater, with utilities in Tempe, San Diego, and Honolulu leading the way forwards.
City of Tempe Reducing Industrial Water Consumption
The City of Tempe has made water conservation a top priority with the city setting the ambitious goal of saving more than 600 million gallons of water a year by 2020. To encourage non-domestic water users to conserve the precious resource and lower their water and wastewater bill as well as their maintenance costs, the City of Tempe is offering industrial and commercial water users grants to install water saving technologies. Financial incentives will be offered to projects that are expected to result in significant reductions in water use (15 percent of more). The program targets three types of water use: industrial/commercial processes, landscape changes or retrofits, and cooling systems. Projects costing less than $10,000 can receive a rebate between 25 to 50 percent of the total project cost depending on the amount of sustained savings, while projects over $10,000 will be eligible for the same percentage funding with a rebate cap of $20,000
San Diego’s Energy-Neutral Recycling Of Water
With climate change projected to increase the number of hotter and drier days in San Diego and demand expected to increase by 20 percent by 2035, San Diego is developing alternative water supplies from potable reuse that will provide up to a third of the city’s water supply by 2035. The ‘Pure Water San Diego’ project will provide safe, reliable, and cost-effective drinking water supplies for San Diego in addition to the recycled water the city already produces for agricultural and industrial use. This 20-year project will involve the city’s North City Water Reclamation Plant pumping recycled water to the Advanced Water Purification Facility for membrane filtration, reverse osmosis, UV disinfection, and advanced oxidation before the purified water is either:
- Stored in the city’s San Vicente Reservoir before blending with runoff and imported water from the Colorado River or the Bay Delta followed by treatment at the Drinking Water Treatment Plant that involves coagulation, filtration, disinfection, ozone, and chlorine, or
- Directly pumped from the Advanced Water Purification Facility to the Drinking Water Treatment Plant before becoming potable water.
San Diego’s production of Pure Water is expected to increase energy consumption by the San Diego Public Utilities Department over and above current operations. However, because Pure Water will be replacing purchased imported water, the whole project will be energy-neutral for the most part in terms of the difference in the embedded energy in an acre-foot (AF) of purified water with that of existing supplies. According to the city’s 2013 Water Purification Demonstration Project, purified water produced at the city’s Reclamation Plant and pumped to the San Vicente reservoir would require approximately 2,500 kWh/AF compared to imported water requiring 2,000 to 3,300 kWh/AF of energy depending on the blend of water from the Colorado River or Bay-Delta
Hawaii Recovering Energy From Wastewater
The City of Honolulu has recently awarded a contract to Hawaii Gas — a state utility — to capture and process biogas at the Honouliuli Wastewater Treatment Plant (WWTP) and turn it into renewable energy. Previously, the WWTP flared the equivalent of 80,000 therms of biogas annually into the atmosphere. The new contract will allow Hawaii Gas to remove impurities from the raw biogas to produce a ready-for-market renewable natural gas (98 percent methane and 2 percent carbon dioxide), which Hawaii Gas will then blend with its synthetic natural gas. The price Hawaii Gas will pay to the city will be scaled to the quality of the biogas, which will be determined when it is extracted. Depending on these factors, it is estimated that the contract will generate for the city $1 million or more annually, along with environmental benefits. Overall, the project is estimated to take between 12 to 18 months to become operational.
In the transition towards the circular economy, water utilities need to develop innovative incentives to help customers reduce demand for water. Meanwhile, utilities, facing decreasing availability of water with rising demand, can explore developing alternative supplies with the aim of ensuring that increased supplies are energy-neutral. Finally, WWTPs in the circular economy will provide renewable energy to local communities, which will not only create additional revenue streams for the utility but also reduce carbon emissions.
Robert C. Brears is the author of Urban Water Security (Wiley). Urban Water Security argues that, with climate change and rapid urbanization, cities need to transition from supply-side to demand-side management to achieve urban water security.