Developing the Circular Water Economy

Water utilities are beginning to promote the circular water economy to not only mitigate greenhouse gas emissions but also enhance resilience to climate change.

By Robert C. Brears

In our current economic model, manufactured capital, human capital, and natural capital all contribute to human welfare by supporting the production of goods and services in the economic process, where natural capital — the world’s stock of natural resources (provided by nature before their extraction or processing by humans) — is typically used for material and energy inputs into production and acts as a ‘sink’ for waste from the economic process. This economic model can be best described as ‘linear’ which typically involves economic actors (people or organisations) harvesting and extracting natural resources, using them to manufacture a product, and selling a product to other economic actors, who then discard it when it no longer serves its purpose.

In the linear economy, following this ‘Take-Make-Dispose’ model, the water sector typically employs the ‘Take-Use-Discharge’ strategy. In this strategy, water is ‘withdrawn’ from streams, rivers, lakes, reservoirs, oceans, and groundwater reservoirs as well as harvested directly as rainwater. Water is then ‘used’ by municipalities, industries, agriculture, the environment, etc. within the water cycle, including for consumptive and non-consumptive uses. Non-consumptive used water is ‘returned’ to the river basin directly or via a municipal treatment facility. Depending on the location within the basin this returned water could then be used downstream or lost to the basin. 

While the current linear economic model has generated an unprecedented level of growth, the model has led to constraints on the availability of natural resources in addition to the generation of waste and environmental degradation. In response to climate change, increasing resource scarcity, and environmental degradation, governments around the world are implementing a variety of policies to encourage the transition towards the ‘circular economy’ that focuses on reducing material consumption, reusing materials, and recovering materials from waste.

The Circular Water Economy

In the context of water resources management, water utilities are beginning to promote the circular water economy that reduces water consumption, reuses and recycles water and wastewater, and recovers materials, including heat and minerals, from water and wastewater to not only mitigate greenhouse gas emissions but also enhance resilience to climate change.

Reducing Water Usage with Smart Meters in Singapore

To meet future demand for water with today’s technologies, Singapore’s Public Utilities Board’s (PUB) energy footprint will need to quadruple from the current 1,000GWh/year to 4,000GWh/year. To reduce this demand, PUB is trialling a smart water network that will collect detailed data on household water consumption to build customer consumption profiles and identify consumption patterns and trends. The data will then be analysed and provided to customers enabling them to monitor their water usage patterns and better manage water consumption. PUB will also enable customers to set water-saving goals and track their performance. This is part of an experiment to see if game playing is more effective at engaging and motivating customers to conserve water rather than increasing water prices.

Reusing Water in New York City

New York City’s Department of Environmental Protection has launched its On-Site Water Reuse Grant Pilot Program to provide commercial, mixed-use, and multi-family residential property owners with incentives to install water reuse systems. Grants are available for water reuse systems at the individual building and district level, with district-scale projects involving two or more parcels of land such as a housing development, where the project reduces demand in the shared distribution system. Individual building-scale projects can receive up to $250,000 in reimbursement for a system designed to save at least 32,000 gallons per day (gpd), and district-scale projects are eligible to receive up to $500,000 in reimbursement for a system designed to save at least 94,000 gpd. The NYC Construction Code regulates two types of on-site water reuse systems that can be installed: wastewater reuse systems (black water, greywater, rainwater) for non-potable uses including flushing of toilets and urinals, laundry, and subsurface drip irrigation systems and rainwater reuse systems for non-potable uses including subsurface drip irrigation.

Recovering Biogas in Stockholm

In Stockholm, the two sewage treatment plants, Henriksdal and Bromma, serve more than one million people and industries in the city plus surrounding municipalities. Rather than viewing the city’s wastewater as waste, it is being turned into a resource. During the sewage treatment process, the organic material is separated in the form of sludge from the water. In total, the two plants produce around a million tons of sludge per year. When the sludge is digested biogas is formed, providing a steady stream of vehicle fuel: currently, around 17 million cubic meters of crude gas is produced which is sold to Scandinavian Biogas, who then transform the raw gas into vehicle gas. The gas that is not converted to vehicle gas is used for heating and electricity generation. Most of the gas produced at Henriksdal is used by SL’s inner-city buses. Meanwhile, vehicle gas from Bromma is sold, partly from a tank outside the plant and partly at other filling stations in the city, to taxis, private cars, buses, and waste trucks. Overall, the biogas mitigates more than 22,000 tons of carbon dioxide emissions annually.

Conclusion

A range of innovative technologies is available to close the loop and create a circular water economy.