Growing up in China, Yuanzhi Tang has directly experienced the recycling of human waste. In the building where she lived, the toilets discharged to an underground tank, where the waste mixture was digested anaerobically, a process that produces methane. Through gas lines, the fuel went back to the stove in the kitchen.

Tang says she didn’t think much of the recycling she experienced every day when she lived in China. Now, Tang is an assistant professor in the School of Earth and Atmospheric Sciences. One big question she addresses is recovery of resources from wastes – and not just carbon-based waste that yields methane as an energy source. She’s aiming for a system that also will recover wastewater and nutrients such as nitrogen and phosphorus, while performing other tasks. “When we’ve figured this out,” she says, “I can think of many ways to apply it to wastewater treatment plants, farm sites, or even community buildings.”

Tang has partnered with scientists in Georgia Tech and beyond to attack the problem of integrated contaminant elimination and resource recovery from biological wastes. The National Science Foundation has awarded Tang and her collaborators over $2.4 million over three years to figure out how to integrate and optimize multiple technologies to recover energy, water, and nutrients from biological wastes, while simultaneously reducing waste volume and removing the heavy metals, pathogens, and organic contaminants.

The system Tang envisions sounds like a giant machine. Wastes would enter at one end. Various products could emerge on the other side, including methane, nitrogen- and phosphorus-containing slow-release fertilizer, clean water, and biochars for use as solid fuel or soil conditioner. In addition, the machine would perform key environmental services, such as degrading waste-borne pathogens, organic contaminants, and toxic metals; reducing waste volume; and discharging clean water.

According to Tang, the individual technologies to treat wastes to environmental standards or to obtain a particular product are already available. These include hydrothermal reactors, anaerobic digesters, membrane distillation units, and a wastewater treatment system enabled by magnetic nanoparticles. What’s different is the integration, which would require a lot of new science and engineering, she says. Tang also intends to develop a database and models that can be used to predict the best combination and operating conditions of technologies for particular waste characteristics and treatment goals. 

To get started, Tang and her colleagues are conducting experiments with various types of wastes, including sludge from the F. Wayne Hill Water Resources Center, a Gwinnett County wastewater treatment facility; cow dung and pig waste slurry from Mountain Valley Farm, in Ellijay, Georgia; and poultry litter from a family-owned farm near Atlanta. They also have tested the methane production system and are growing corn with the produced fertilizers. “The results look promising,” Tang says.

Tang will work with four co-principal investigators.

• Shihong Lin, an assistant professor at the School of Civil and Environmental Engineering and School of Chemical and Biomolecular Engineering at Vanderbilt University, brings expertise in membrane distillation, which can utilize low grade heat to transform wastewater to high-quality distilled water.
• Spyros Pavlosthatis, a professor in the Georgia Tech School of Civil and Environmental Engineering, will lead the research on anaerobic digestion.
• Baoshan Xing, a professor of soil science and agriculture at the University of Massachusetts, Amherst, will spearhead the plant growth tests and soil characterization using the produced slow release fertilizers and soil conditioners.
• Jie Xu, a principal research scientist at Georgia Tech Research Institute, brings expertise in wastewater treatment using magnetic nanoparticle system.

Five other Georgia Tech personnel will contribute to the project:

• Hailong Chen, an assistant professor in the George W. Woodruff School of Mechanical Engineering
• Thomas DiChristina, a professor in the School of Biological Sciences
• Ching-Hua Huang, a professor in the School of Civil and Environmental Engineering
• Rixiang Huang, a research scientist in the School of Earth and Atmospheric Sciences
• Alexander Samoylov, a senior research scientist at Georgia Tech Research Institute

Tang sees applications of this research within Georgia Tech itself. “In designing new buildings at Georgia Tech,” she says, “we can incorporate small-scale recycling modules to recover energy or achieve specific goals.”