Abstract
Traditional wastewater treatment methods have become aged and inefficient, meaning alternative methods are essential to protect the environment and ensure water and energy security worldwide. The use of microbial electrolysis cells (MEC) for wastewater treatment provides an innovative alternative, working towards circular wastewater treatment for energy production. This study evaluates the factors hindering industrial adoption of this technology and proposes the next steps for further research and development. Existing pilot-scale investigations are studied to critically assess the main limitations, focusing on the electrode material, feedstock, system design and inoculation and what steps need to be taken for industrial adoption of the technology. It was found that high strength influents lead to an increase in energy production, improving economic viability; however, large variations in waste streams indicated that a homogenous solution to wastewater treatment is unlikely with changes to the MEC system specific to different waste streams. The current capital cost of implementing MECs is high and reducing the cost of the electrodes should be a priority. Previous pilot-scale studies have predominantly used carbon-based materials. Significant reductions in relative performance are observed when electrodes increase in size. Inoculation time was found to be a significant barrier to quick operational performance. Economic analysis of the technology indicated that MECs offer an attractive option for wastewater treatment, namely greater energy production and improved treatment efficiency. However, a significant reduction in capital cost is necessary to make this economically viable. MEC based systems should offer improvements in system reliability, reduced downtime, improved treatment rates and improved energy return. Discussion of the merits of H2 or CH4 production indicates that an initial focus on methane production could provide a stepping-stone in the adoption of this technology while the hydrogen market matures.
Highlights
Growing populations and expanding infrastructure have led to a rapidly changing climate and the depletion of global resources
Hydrogen produced per electrode surface area was four times larger in the small microbial electrolysis cells (MEC) (2 L m2 of anode) than in the large MEC (0.5 L m2 of anode). Scale up in this manner did not seem to be detrimental to performance, but these findings demonstrate that further understanding is needed when scaling up to real-world applications as the effects of scale up are not well understood [63]
This review aimed at identifying the barriers hindering the progression of MEC use from lab-scale investigations to pilot-scale systems and beyond to inform future research aims
Summary
Growing populations and expanding infrastructure have led to a rapidly changing climate and the depletion of global resources. The water crisis is listed in the top five risks to humanity by the World Economic Forum with the global demand for water set to rise by 55% from 2000 to 2050 [1]. 80% of global wastewater is expelled into 4.0/). The environment untreated; this includes industrial, agricultural and municipal waste [2]. The large volumes of untreated waste and the increase in demand for water dramatically increases the strain on the environment and existing ageing infrastructure. The transition would see wastewater become a sustainable source of water, bioenergy and nutrients, providing security for generations to come
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