Bioelectrochemical urine treatment and resource recovery using a haloalkaliphilic microbial consortium

Abstract

The discovery of electroactive microorganisms (EAMs) which possess the ability of extracellular electron transfer (EET) have brought considerable advancements to microbiological science. They have led to the invention of new and sustainable technologies, grouped under the name microbial electrochemical technologies (METs). METs have been applied in different fields such as environmental pollution remediation, low power generation, biosensing, and production of value-added chemicals and fuels. The possibilities of using extremophilic microorganisms for the development of sustainable technologies is huge. Ammonia oxidising bacteria have been found to significantly contribute to the global nitrogen cycle and play a major role in sustainable wastewater treatment. Out of them, anaerobic ammonia oxidising (ANAMMOX) bacteria which can convert ammonium (NH₄⁺) directly to nitrogen gas (N₂) using intracellular electron acceptors like nitrite (NO₂⁻) have gained a significant attention. Since their discovery, anammox bacteria have been studied and applied to develop novel and promising nitrogen removal biotechnologies. However, there have been only a few studies conducted on the EET capability of anammox bacteria i.e., electro-anammox, and even fewer on the ones coming from extreme environments, especially haloalkaline environments. The mechanism by which electrons can be directly transferred to an insoluble electron acceptor is known as EET mechanism. The findings of the EET capability of anammox bacteria could be promising in multiple fields of science and technology, such as in the context of implementing an electro-anammox process for energy-efficient treatment of waste streams which are high in nitrogen concentration, like treating source-separated urine which is high in nitrogen content. The type of extreme environment urine offers resembles to that of haloalkaline environment. In this context, my thesis work was focused on demonstrating the urine treatment in bioelectrochemical systems (BESs) using a haloalkaliphilic microbial consortium. An inoculum source from the Lonar Lake was used to enrich the haloalkaline bacteria on the anode. Hydrolysed human urine was used as a substrate to provide the haloalkaliphilic environment. In BESs, graphite electrodes were used as the terminal electron acceptors, and NH₄⁺ and organics present in hydrolysed urine served as energy and carbon sources. Duplicate MFCs were operated in a closed circuit with an external load of 160 Ω for two consecutive cycles of 26 days each. The results showed that the MFCs reached a maximum power density of