Bioavailability and species transformations of micronutrients in (bio)reactors used for resource recovery and water reuse

Anaerobic digestion is often used for the treatment of industrial, municipal or agricultural wastewaters and can be considered as the key technology regarding renewable energy production from wastewater. It is known that metals are needed as essential cofactors for a variety of enzymes involved in methane production and their absence can cause a serious decrease in biomass activity. However, detailed knowledge on the fate of metals in anaerobic digesters is still in its infancy. Recent studies have shown that metals dosed as soluble salts (which is the industrial practice) do not remain in bioavailable form during their passage through anaerobic digesters. They may precipitate or may adsorb on the surfaces present in the reactors (e.g. anaerobic granules). Furthermore, organic complexes present in the reactors (humic acids, siderophors etc.) play a very important role in rendering metals unavailable for microorganisms by binding them in stable organic complexes that cannot be transported across cell membranes. The proposed project aims to develop a new method that with help with supplementation strategies of trace metals. The method will be based on determining a bioavailable fraction of trace metals and relating this fraction to methanogenic activity. The bioavailable fraction in the digestates will be assessed by diffusive gradients in thin film (DGTs). Special attention will be paid to the hydraulic patterns inside the reactors and their effect on the retention of trace metals in the reactor.