ERI: alkaline thermal pretreatment to improve anaerobic digestion of sewage sludge through mitigating volatile sulfur compounds: reactor performance, pathways, and mechanisms

The National Science Foundation Division of Chemical, Bioengineering, Environmental, and Transport Systems awarded Arkansas State University $177,108 on July 1, 2026, under the Engineering program (CFDA 47.041) to investigate calcium-oxide-assisted alkaline thermal pretreatment as a method to improve anaerobic digestion of sewage sludge.

The project addresses sulfur-related inefficiencies in converting organic waste to methane gas. During anaerobic digestion, sulfur compounds in sewage sludge produce volatile gases that reduce methane recovery and corrode metal equipment. The research uses heat and lime pretreatment to suppress volatile sulfur compound formation, enabling higher biomethane yields while protecting equipment and human health. Controlled batch and semi-continuous reactor experiments will quantify biomethane production, volatile sulfur compound speciation, enzyme activities, and microbial community responses across multiple operating conditions. The team will employ chemical analysis, molecular biotechnology tools, kinetic modeling, and statistical methods to identify the mechanisms governing sulfur transformation pathways and microbial activity during digestion of sewage sludge and other sulfur-rich organic wastes. Work occurs at Arkansas State University in Jonesboro, Arkansas with collaboration from local wastewater treatment plants to transition research outcomes to operational technology. The project runs through June 30, 2028, and includes student training in engineering and technology.

Abstract

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.- subawards are not planned for this award.