ERI: Alkaline Thermal Pretreatment to Improve Anaerobic Digestion of Sewage Sludge through Mitigating Volatile Sulfur Compounds: Reactor Performance, Pathways, and Mechanisms

Anaerobic digestion uses microbes to turn organic waste into clean energy, such as methane gas, in the absence of oxygen. Sewage sludge can be converted anaerobically to methane gas, which is used to generate heat and electricity. However, sewage sludge contains a high amount of sulfur. During anaerobic digestion, this sulfur turns into volatile gases making the energy-producing process less efficient. Sulfur gas also corrodes metal pipes and equipment. This project develops a new strategy to fix the issues caused by sulfur in organic waste such as human sewage. The project tests a treatment that uses heat and lime to stop the sulfur gases from forming in the first place. This method helps recover more clean energy in the form of methane gas from organic waste while protecting the environment and people’s health. The results give cities and companies a more reliable way to create green energy from waste. This project also helps the next generation of scientists and engineers by training students in engineering and technology. The team works closely with local wastewater treatment plants to convert the research outcomes to real-world technology. This project investigates how calcium-oxide-assisted (CaO-assisted) alkaline thermal pretreatment modifies sulfur transformation pathways and microbial activity during anaerobic digestion of sewage sludge as well as other types of organic waste with a relatively high content of sulfur. Controlled batch and semi-continuous reactor experiments quantify biomethane production, volatile sulfur compound formation, sulfur speciation, enzyme activities, and microbial community responses under multiple operating conditions. Integrated chemical analyses, molecular biotechnology tools, kinetic modeling, and statistical analysis are used to identify mechanisms responsible for suppressing sulfate reduction and transformation, stabilizing sulfides through mineral interactions, inhibiting organic sulfur biotransformation, and promoting microbial sulfide oxidation. The research generates predictive relationships linking pretreatment conditions with biomethane yield and sulfur emissions. The work also establishes a mechanistic framework for optimizing pretreatment-digestion coupling in advanced anaerobic bioreactor systems. The results advance fundamental understanding of sulfur cycling in anaerobic environments and support the design of more efficient and resilient waste-to-energy technologies applicable to municipal sludge and other organic residuals. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria. NSF Award ID: 2552624 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Chiqian Zhang | Institution: Arkansas State University Main Campus, JONESBORO, AR | Award Amount: $177,108 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2552624 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2552624.html