Combining Wastewater-To-Energy Processes Could Power Large Cities

According to Louisiana State University (LSU) Civil and Environmental Engineering Assistant Professor Xiuping Zhu, there is enough energy in U.S. wastewater to power 13 percent of U.S. households. And by harnessing the energy from wastewater alongside seawater and river water, Zhu believes that large cities could effectively be powered by extracting energy from these water sources.

“Energy contained in U.S. wastewater is 150 billion kWh per year, which is six times the amount of energy demand for wastewater treatment,” Zhu said. “This is enough power to light 285,171,000 60-watt bulbs and 13,932,000 households.”

Zhu is currently working on five research projects that revolve around energy and water. She has proposed a new approach to harvesting the salinity gradient (SG) energy from seawater and river water based on alternatively Na+/Cl– (sodium chloride) intercalation with the electrode in seawater and deintercalation with the electrode in river water. This approach relies on two waters of different salt concentrations combining to release energy driven by the difference in chemical potentials.

Zhu estimates that the potential power production from estuarine SG energy between seawater and river water could equal current worldwide demand for electrical power (~2 terawatts).

In another project, Zhu has proposed using a microbial concentration cell (MCC) to recover energy from wastewater through biological processes that will be used to power the treatment cycle’s membrane processes. This system can not only remove organic pollutants, but also recover salts, nitrates and phosphorus.

Wastewater-to-energy systems typically capture methane gas when organic waste decomposes in an oxygen-free environment. In sludge-to-energy systems, the sludge undergoes a pretreatment process called thermal hydrolysis to maximize the amount of methane it can produce. After breaking down in an anaerobic digester, the resulting product is a biogas, which can be used for on-site energy needs, or processed further and used in place of natural gas.

“This is a good demonstration on development of energy-sustainable wastewater treatment processes by using energy contained in wastewater,” Zhu said.