Optimizing Water Use
Water is an essential natural resource and an important input to our materials management processes. As part of the environmental solutions we offer to our clients, we recycle millions of gallons of wastewater through pretreatment and discharge to POTWs every year. And as part of our commitment to environmental stewardship, we also strive to minimize freshwater use and wastewater discharge in our own operations as much as possible by recycling and reusing water. In addition to benefiting the environment, these steps frequently help us conserve costs too.
All thermal power plants—including our EfW facilities—use water to generate electricity. In the boiler, water is heated to generate steam, which runs the turbine to generate electricity. Most of this water is condensed and reused in the process of producing power. At some of our plants (such as the Covanta Niagara facility), we also generate steam that we export to communities and local businesses. While steam generation is a very efficient use of the waste resource, it can increase water withdrawal because the condensed water produced by the steam that is exported may not be returned to the facility to produce additional steam. At some of our facilities, water is also used in the cooling towers to condense the steam exhausted out of the turbine back into water for return to the boiler cycle. We also operate two once-through cooling plants, both of which use non-potable saline water.
The use of alternative, non-potable sources of freshwater continues to grow at our facilities. In 2018, the York County facility installed a roof rainwater collection tank, saving over three million gallons. Alternative water sources, including reclaimed wastewater (which now makes up nearly 30 percent of our freshwater consumption, up from 11 percent in 2007), made up 33 percent of our 2018 freshwater consumption.
*Does not total to 100% due to rounding
|Total Freshwater Use (millions of gal.)||8,919||8,251||8,967|
|Percent Alternative (Non-potable) Water Sources||34%||32%||33%|
Minimizing water consumption is also a key objective. In addition to the thermal cycle, a key use of water at our EfW facilities is for ash quenching. After the combustion process, the non-hazardous ash is quenched with water to reduce dusting. To reduce water consumption, we look for ways to use water more efficiently. For example, at our Delaware Valley facility, engineers identified an opportunity to reduce water consumption in the pugmill, an ash mixing device, by reducing process variability through a new automatic control system. With lower variation, we can lower the setpoint of water addition closer to its theoretical requirement, reducing excess water consumption. Annually, the facility expects to reduce potable water consumption by 14 million gallons.
In addition to minimizing our water consumption, we also minimize our wastewater discharge, using water internally as much as possible. A total of 19 of our facilities are zero process water discharge facilities, meaning that only sanitary wastewater is discharged to the local wastewater treatment plant.