In a typical day, 900 pounds of methane gas are produced and burned off as a greenhouse gas and waste product of the wastewater treatment process at the McAlpine Creek Wastewater Treatment Plant in Pineville. But the City of Charlotte, with its mission of environmental sustainability, has committed to harnessing the potential of this gas by turning it into a powerful source of renewable energy.
In March 2017, the City of Charlotte opened the Combined Heat and Power (CHP) facility at the McAlpine Creek Wastewater Treatment Plant. The facility is one of the largest producers of renewable energy in the Charlotte area and the only facility of its kind at a wastewater treatment plant in North Carolina. This important work by city staff was honored by the American Council of Engineering Companies of North Carolina as the best engineering project in the state and given the 2018 Henry A. Stikes Grand Conceptor Award.
“This CHP facility is science fiction turned into reality,” said Will Rice, Charlotte Water’s project coordinator. “We take dirty water, the things people put down their drains and in their toilet, and in the process of cleaning that water, we generate power. As long as people are using water, we can make power from it.”During a process called anaerobic digestion, bacteria break down organic materials from wastewater and create their own waste — methane gas. The CHP facility burns methane gas in a specialized engine that runs a generator and produces power and heat off of the engine. The heat is then recycled back to the anaerobic digestion system, which needs the heat much like human stomachs need to be kept at a certain temperature. At the same time, power generated by the CHP is also sold back to Duke Energy, offsetting the plant’s energy costs.
To illustrate the impact of the facility, think of an average house. Between washers and dryers, microwaves, televisions, lighting and other sources of energy consumption, that house will use about 897 kilowatt-hours of energy per month. The CHP generator creates about 656,000 kWh of energy every month. Therefore, energy generated by the facility could power about 731 homes in a month. To date, more than 5.3 million kWh of energy have been produced by around-the-clock generation at the Combined Heat and Power facility. For comparable energy production, a solar energy facility would need 5-10 acres of land, and would still only generate energy when the sun is out.
A 20-year, zero-interest loan from the state of North Carolina’s Clean Water Revolving Fund financed the project, which is expected to pay for itself in less than 13 years. In the future, the city could also explore introducing this technology at its other four wastewater treatment plants, thereby increasing the impact of this action for sustainability.
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