Union Carbide, a subsidiary of Dow Chemical, says it saved energy and reduced capital and operational expenses by using constructed wetlands to treat wastewater near Seadrift, Texas — one example of how companies are using green infrastructure solutions to achieve economic and environmental benefits, according to a whitepaper.
The Case for Green Infrastructure recommends that green infrastructure become part of the standard toolkit for engineers. Dow Chemical, Shell, Swiss Re and Unilever, working with the Nature Conservancy, evaluated the assumption that green infrastructure can provide more opportunities than gray infrastructure to increase the resilience of industrial business operations against disruptive events such as mechanical failure, power interruption, raw material price increases and floods.
Green infrastructure employs elements of natural systems, while traditional gray infrastructure is man-made. Examples of green infrastructure include creating oyster reefs for coastal protection, and reed beds that treat industrial wastewater.
The research team concluded that hybrid approaches, utilizing a combination of green and gray infrastructure, may provide an optimum solution to a variety of shocks and improve the overall business resilience.
The white paper highlights Union Carbide’s 110-acre engineered wetland, designed to meet regulatory requirements for water discharge from the manufacturing plant, which has operated successfully for more than a decade.
The green infrastructure, which was implemented in half the expected time for the gray infrastructure alternative, was fully operational in 18 months. The capital expense was between $1.2 million and $1.4 million, compared to an expected $40 million for gray infrastructure. The wetlands also require no electric power and very little operations and maintenance support as opposed to the energy-intensive gray infrastructure alternative requiring 24/7 support.
Another example is Petroleum Development Oman, which uses constructed wetlands to treat produced water from oilfields in Oman. The Nimr oilfields, in which Shell is a joint venture partner, produce oil and more than 330,000 m3 of water per day. PDO built the world’s largest commercial wetland, and it treats more than 30 percent (or 95,000 m3 per day) of the total produced water.
This volume would normally require extensive infrastructure to treat and inject the water into a subsurface disposal well. Gray infrastructure would thus result in a high-cost facility, requiring large amounts of electric power and producing greenhouse gas emissions.
Instead, the company selected a four-tier gravity-based wetland system. As gravity pulls the water downhill, reeds act as filters, removing oil from the water. The oil is eaten by microbes that naturally feed on hydrocarbons underground. Oil content in the produced water is consistently reduced from 400 mg/l to less than 0.5 mg/l when leaving the wetlands.