Urban Wastewater: One Man's Waste Is Another Man's Treasure
By Lulu Almana, SCE/EI ’12
For the first time in history, more than half of the human population now lives in urban environments. In the United States alone, there has been substantial urban population growth since the nineteenth century; in 1820, less than 5 percent of Americans lived in cities, however today, almost 200 years later, the percentage of urban dwellers in the United States increased to 82 percent.
This drastic multiplication in urban population in the United States and specifically in New York City in the past century has demonstrated to policy makers and scholars the urgency to develop new systems that are capable of handling the pressures of a large and dense population. A population that is in need of better water management, secure food systems and efficient energy usage.
How can we overcome the main challenges we face in our urban wastewater systems today? Are there opportunities to improve sustainability in water treatment systems in U.S. cities to support local food security?
This article aims to investigate various urban wastewater systems in the United States and how they correspond to today’s food security threats. Current limitations of wastewater and water treatment systems are a challenge in that they are energy intensive, available in limited locations and require transporting water to far distances. In Southern California, pumping water alone (without treating it) accounts for over 30 percent of their energy bill. The systems examined in this article look at technologies from the early 1800s till today, and include decentralized privy vault-cesspool systems, centralized separate-sewer systems and today’s closed loop localized systems.
According to research published in the Journal of Urban Technology, decentralized wastewater systems, which were popular in the early 1800s in the U.S., became overtaxed and subsequently no longer utilized when the American population started to form large cities and demand public services. That is because the decentralized privy vault-cesspool wastewater management systems became unable to support heavy demand or handle large amounts of wastewater. Which is why centralized water-carriage sewer systems were introduced and were designed as part of a master plan for wastewater treatment plants in cities to meet the needs of a growing population. They were promoted as the ideal management alternative for urban areas with large populations.
However, those wastewater treatment facilities are limited in size and quantity in U.S. cities because they are expensive to build and require a great amount of energy to operate. They are also difficult to control and accommodate changes in natural supply and therefore create many unnecessary risks. These risks and limitations overwhelm their performance, especially during storms and heavy rainfall when the demand increases. As cities grow both in size and density, they tend to overwhelm their existing treatment facilities and resort to discharging wastewater into existing natural water bodies. The need for an efficient wastewater treatment system in the city is not only an urgent conservation priority, but also a means of advancing health and providing local food security.
Today, although centralized separate-sewer systems remain the most common technology used in U.S. urban areas, the idea of developing a localized inter-connected system in newly urbanizing areas has been gradually increasing. “There are an encouraging number of innovative technologies, systems, components, processes and management approaches emerging for localized water treatment, including new filtration and disinfectant technologies, treatment systems, business models and approaches to effectively managing regional water,” says Sarah Slaughter in a recent article on innovation in waste water systems. This paradigm is increasing in popularity because it has proven to be easier to control risks related to such technologies, reduce impact on ecosystems and existing water bodies, have fewer operation and maintenance costs compared to large-scale treatment facilities, and allow on-site operation of energy generation systems. Creating a relationship between localized treatment plants and on-site energy generation not only reduces costs, but also creates new jobs, increases energy efficiency and promotes renewable energy.
Cities such as Seattle, Washington and Portland, Ore., have become leaders in proposing and implementing urban design approaches for wastewater systems. They have come up with new standards that changed the way cities now deal with wastewater and especially rainwater runoff. “Each roof, driveway, roadway and parking lot can be designed to produce a much lower net change in the amount of runoff it produces, and can be designed to act as its own ‘kidney’ ” writes Kristina Hill in The Water Environment of Cities. Many other communities within cities in the United States have also begun to allow or encourage experimentation with these design approaches, referred to as low-impact development or natural drainage systems.
A local example is the 2012 Green Infrastructure Grant Program unveiled by Bloomberg in September 2011. Funds up to $4 million were made available by the city to build green roofs, rain gardens and similar methods for managing storm-water on private property and public sidewalks in combined sewer areas of New York City. Under this agreement, the Department of Environmental Protection will use green infrastructure to reduce amounts of storm water from entering the city’s combined sewer system from 10 percent of available impervious surfaces in combined sewer drainage areas by 2030. According to a study led by Stuart Gaffin, a scientist at Columbia’s Center for Climate Systems Research, if New York City’s 1 billion square feet of roofs were transformed into green roofs, it would be possible to keep more than 10 billion gallons of water a year out of the city sewer system.
Most of these initiatives in U.S. urban areas are used to support existing large centralized water treatment systems and are often linked within a larger network. However, many projects are installing small decentralized local systems to supplement the larger networks and be able to perform independently within a closed loop. This approach is not yet widely spread locally due to several challenges, such as the difficulties in meeting nutrient removal permits and the lack of automation in these smaller projects.
According to a report by the United Nations Environment Programme, “there is no option but to consider wastewater as part of the solution. To be successful and sustainable, wastewater management must be an integral part of rural and urban development planning.” By developing such ideas and technologies of smart infrastructure and improving supportive policy, well-managed wastewater can no longer be a problem in urban areas but an important element that supports the ecosystem and an integral part of the cycle toward improving health and food security.