The Urban Water-Energy-Food Nexus: Three Mini Case Studies
With rising demand for water, energy, and food, leading cities and water utilities have created synergies between the water-energy-food nexus sectors while reducing trade-offs in the development of a green economy.
Water-Efficient Urban Farms
Kansas City is cultivating a locally sustainable food system to ensure local food access for all, especially the needy, and ensure food is integrated into the civic life of the community. A key aspect of the city’s sustainable food system is that it is democratic where people take ownership of the local food system, as a whole and in their own lives, the environmental and personal health and well-being of local residents are prioritized, and that the food system is resilient and adaptable.To ensure the local food system is resilient, the KC Grow: Water Access Program has been established to help Kansas City community groups and farmers access water for their gardens and farms. Increased water access makes it easier to grow more food in the city, increasing the amount of nutritious food available in the community. The program, with a budget of USD 100,000, sponsored by the City of Kansas City, and administered by Kansas City Community Gardens, assists community gardens and farms in Kansas City. Urban gardeners and farmers turning vacant lots and lawns into productive growing space can apply for funding from the program to assess the amount of water required to sustain the garden or farm, evaluate water access options, connect the farm to local resources that best meet the garden or farm’s water needs, and provide small grants to help implement recommended water access strategies.
Before small grants can be provided to implement recommended water access strategies, a water audit will be conducted to analyze the garden’s or farm’s water use, plot size, and the area’s average annual rainfall. The completed audit will recommend ways to increase water access and affordability for the garden or farm. It will also provide soil improvement and conservation recommendations, best mulching practices, and water budget estimates. Once the audit has been completed, KC Grow Small Grants can then be disbursed to applicants to implement their water audit recommendations including installing rainwater and stormwater catchments systems, water pumping systems, and drip irrigation systems.
Energy Crops and Food Waste Powering a Water Utility
The UK’s water utility Severn Trent is aiming to generate 50% of its own energy by 2020, up from 38% today. To reach this goal, the utility has developed one of the largest energy crop plants in the UK as well as opened its second food waste plant.
To reach its goal, Severn Trent has developed a new crop digestion plant near Nottingham. At the plant, crop materials are fed into anaerobic digesters. Inside, bacteria are added and the mixture is kept at 42°C. As the crops break down, methane is released for use in gas engines, from which the heat is used to keep the digesters or adjacent sewage works at their efficient temperatures and make electricity which can be used onsite or exported to the national grid. A combination of maize, wheat, rye, and energy beet is used in the digesters, with the energy beet being a special hybrid form of sugar beet that produces a large amount of gas in digesters. Crops for use are also grown on Severn Trent land adjacent to the plant. In the past, contaminated materials were added to the land, making it unsuitable for food production for 900 years.
To further meet the renewable energy goal, Severn Trent’s second food waste plant at Stourbridge recently opened. The plant accepts food waste from a variety of sources including food and drinks manufacturers, food processing companies, hospitality and food service outlets, local authorities, schools, supermarkets, and retail stores. With a capacity of 48,500 tons of both packaged and unpackaged food waste, the plant generates energy output of 2.4 MW, the equivalent to the amount of electricity required to power over 4,000 homes for a year.
Wastewater is not Waste: DC Water’s Bloom
DC Water has created Blue Drop, a non-profit organization, to market products and services as well as provide ratepayer relief from tariff increases due to rising operating expenses, capital investments, and declining water consumption. A key program of Blue Drop is Bloom, which is DC Water’s brand name for its EPA certified Exceptional Quality biosolids product. After water is used in homes and businesses in the District of Columbia, and portions of adjacent counties in Virginia and Maryland, it is sent to DC Water’s Blue Plains Advanced Wastewater Treatment Plant: A resource recovery facility. On average, Blue Plains treats nearly 300 million gallons of wastewater and can treat over 1 billion gallons a day at peak flow.
Rather than viewing wastewater as just waste, solid materials are separated from the liquid and sent to DC Water’s new state-of-the-art thermal hydrolysis process and anaerobic digesters. This equipment adds heat, pressure and helpful bacteria to the solids to remove harmful pathogens and reduce odor. The output is Bloom, a biosolids product that can be used in any area, from large farms to backyard gardens and lawns. Currently, Fresh Bloom is on sale for USD 3.50 per cubic meter. The product has been dewatered and contains around 30% solids and can be used to increase crop growth or even used on sporting fields.
The benefit of Bloom is that it helps capture carbon and prevents it from being released into the atmosphere. Biosolids application also recycles nutrients like phosphorous and nitrogen back into the soil instead of releasing them into the Potomac River and the Chesapeake Bay. Finally, to offset the costs to ratepayers in providing water-related services, Bloom provides an additional revenue stream enabling DC Water to mitigate the impacts of rising tariffs on its customers.
Conclusions
From the mini-cases, water-efficient urban farms can contribute to inner-city food security, the water utility of the future will be carbon-neutral, generate renewable energy from multiple sources, and be at times a net exporter of that renewable energy, and water utilities can offer a variety of products including biosolids to provide rate relief.