Increasing demand for freshwater and energy is pushing towards the development of alternative technologies that are sustainable. One of the realistic solutions to address this is utilization of the renewable resources like wastewater. Conventional wastewater treatment processes can be highly energy demanding and can fails to recover the full potential of useful resources such as energy in the wastewater. As a consequence, there is an urgent necessity for sustainable wastewater treatment technologies that could harness such resources present in wastewaters. Advanced treatment process based on microbial electrochemical technologies (METs) such as microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) have a great potential for the resources recovery through a sustainable wastewater treatment process. METs rely on the abilities of microorganisms that are capable of transferring electrons extracellularly by oxidizing the organic matter in the wastewater and producing electrical current for electricity generation (MFC) or H2 and CH4 production (MEC). Propionate is an important volatile fatty acid (VFA) (24-70%) in some wastewaters and accumulation of this VFA can cause a process failure in a conventional anaerobic digestion (AD) system. To address this issue, MECs were explored as a novel, alternative wastewater treatment technology, with a focus on a better understanding of propionate oxidation in the anode of MECs. Having such knowledge could help in the development of more robust and efficient wastewater treatment systems to recover energy and produce high quality effluents. Several studies were conducted to: 1) determine the paths of electron flow in the anode of propionate fed MECs low (4.5 mM) and high (36 mM) propionate concentrations; 2) examine the effect of different set anode potentials on the electrochemical performance, propionate degradation, electron fluxes, and microbial community structure in MECs fed propionate; and 3) examine the temporal dynamics of microbial communities in MECs fed with low or high concentration of acetate or propionate relating to the reactor performance. Overall, the findings from these studies provides new knowledge on propionate oxidation in MECs. The discovery of such findings may shed light on the development of an energy positive wastewater treatment process capable of producing a high quality effluent.

The disposal of large amounts of waste still containing energetic value is a central challenge in the waste management of the Brazilian sugarcane industry. As a sustainable solution, the biogas process appears to be a suitable technology for treating sugarcane waste products and for providing valuable commodities such as energy-rich biogas and digestate with fertilizer properties. Additionally, the proper treatment of the four major waste types (straw, bagasse, filter cake and vinasse) would avoid greenhouse gas emissions, air pollution and environmental contamination of soil and water. In order to investigate the feasibility and reliability of biogas production from sugarcane wastes, the microbial community dynamics of laboratory-scale reactors were assessed under different start-up strategies. Despite the promising results of the methane potential for all the waste products, chemical and physical pre-treatments were applied successfully to increase the methane yield of straw, bagasse and filter cake. The microbial community dynamics observed during co-digestion of filter cake and bagasse showed, together with the process parameters, that cattle manure can be effectively used as an inoculum for the start-up of a biogas process in the remote-located sugarcane industry. Monitoring methanogenic community dynamics at high organic loading rate of filter cake and bagasse demonstrated that the genera Methanosarcina and Methanobacterium are the major methanogens that produce biogas, even under process imbalances. Moreover, the results obtained from the process parameters and methanogenic community analyses revealed that the stable isotope fingerprinting technique may be a potential monitoring tool for quickly identifying changes in the methanogenic pathway, which indicates process disturbances. In conclusion, these studies established techniques for the efficient substrate processing and start-up procedure of a biogas process designed for the anaerobic digestion of sugarcane wastes, and by these means provided a highly detailed profile of the microbial community in relation to process parameters.

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