Complex but intriguing iron sulfide-based autotrophic denitrification

The University of Galway, located on the west coast of Ireland, was established in 1845. The original building, depicted here, housed only six students, providing ample space for their studies and accommodations. Over the years, the University has significantly expanded into a large campus. The campus layout includes various facilities, with the primary academic buildings situated in one corner, while additional areas are designated for sports, including soccer pitches, a hockey pitch, and running tracks. The Engineering building, shown in green, is positioned adjacent to the picturesque C River, one of the shortest rivers in Europe, which is particularly enjoyable during the summer months. My office offers a view of this river.

Today, I will present research on iron sulfide-based autotrophic denitrification, a concept we developed approximately 50 years ago. Traditional wastewater treatment plants primarily focus on the removal of organic matter, nitrogen, and phosphorus. The removal process typically involves heterotrophic bacteria oxidizing organic matter, or chemical oxygen demand (COD), to carbon dioxide. Nitrogen removal occurs through nitrification, where ammonia is oxidized to nitrite, followed by the reduction of nitrate to nitrogen gas by heterotrophic bacteria. Phosphorus is removed through phosphorus-accumulating organisms that absorb phosphorus from the water.

This slide illustrates the fundamental processes for nitrogen and phosphorus removal, utilizing both aerobic and anaerobic methods. However, these traditional processes face several challenges. The requirement for oxygen during COD oxidation and nitrification leads to high energy consumption and increased operational costs. Additionally, the energy stored in organic matter remains untapped, resulting in no energy recovery from wastewater. The reliance on autotrophic bacteria for sulfate oxidation and denitrification can also result in excessive sludge production, complicating subsequent sludge treatment. While these methods effectively reduce nitrogen and phosphorus levels, achieving very low concentrations in the effluent remains a significant challenge.