Wastewater sludge is the by-product of wastewater treatment plants. Currently, 13.5 million tonnes of dry sludge are produced in Europe annually, 1.5 million tonnes in the UK, and further increase has been projected with population growth. Sludge management poses several challenges due to its high liquid-to-solid ratio, which requires thickening and mechanical dewatering and the presence of toxic and environmental pollution compounds. However, sewage sludge is also an interesting feedstock for energy production due to its high organic content. Nevertheless, the sewage sludge environmental impact when not correctly disposed of, the unsustainability of current disposal techniques (like landfilling, storage, and composting), and the health concern towards some of its components for agriculture applications such as fertilisers make it necessary to rethink sludge management in a more sustainable and circular economy framework.
The present research focuses on producing hydrogen from sewage sludge from direct biomass electrolysis. Hydrogen has been defined as a critical fuel to decarbonise the UK and the EU energy sectors by 2050. Therefore, advancement in direct biomass electrolysis for hydrogen production from sludge is of interest to the water and energy industry.
Direct biomass electrolysis can produce hydrogen from biogenic content, like biomass and biowaste. Although the TRL of direct biomass electrolysis is still low (1-3), it has key advantages compared to existing technologies: i) potential high yield of hydrogen (e.g. 0.2 mg of H2 for 1 mg of wasted raw material -Hibino et al., 2018; 15.76 mL hydrogen at a constant current density of 40mA/cm2 after 1 hour from 0.2 gram of corn straw powder- Liu et al., 2016) (ii) low energy demand of about 0.69 kWh per m3 of hydrogen (17% of the energy required by water electrolysis) (Liu et. Al., 2016); (iii) small treatment device footprint; (iv) limited requirement for waste pre-treatment, compared to pyrolysis and gasification; (v) little or no post-treatment requirement for the gas produced (e.g., hydrogen separation, purification).
Furthermore, the CO2 produced at the anode is ready to be used and captured (Chen et al., 2019).
The PhD student will:
· Develop an in-depth literature review of the state of the art of electrochemical technologies, with a focus on direct biomass electrolysis to produce hydrogen from sewage sludge
· Process modelling
· Run a series of experiments using an electrolysis system and real wastewater sludge to assess the potential hydrogen production from sewage sludge and the main parameters influencing the reactions
· Model validation
· Case study analysis to assess the techno-environmental performance of the system for wastewater facilities compared with other existing technologies