Water is a vital resource for human beings, not only for consumption, but also for all kinds of industrial processes and production of goods. Human activity alters its natural state and pollutes it, causing serious environmental damage to rivers and seas. It is therefore essential to ensure correct water treatment for its reuse and return to the environment. At the WWTP, purification processes are carried out that allow treated water to be returned to the environment with optimum quality conditions.

WWTPs can help in the decarbonisation processes by transforming the energy contained in the organic matter eliminated in the purification process into green H2. Green H2 from renewable sources, due to its high energy density and clean combustion, would replace fossil fuels and contribute to increasing the circularity of these facilities.

ACCIONA has designed and built more than 330 wastewater treatment plants globally. The total capacity of the 330 WWTPs is 27 million m3/day, which represents a population equivalent of more than 100 million inhabitants. The production of H2 in WWTPs is considered a clean energy source, as H2, when burned or used in a fuel cell, only emits water as a by-product, thus contributing to the reduction of greenhouse gas emissions. The possible production of H2 in WWTPs is in line with European and national policies that seek to promote renewable energy and reduce dependence on unsustainable energy sources. The European Union, for example, in its Green Deal, has set targets to reduce greenhouse gas emissions, and the production of H2 in WWTPs is part of these policies. In addition, the injection of H2 into the electricity grid, self-consumption at the WWTP itself, and the use of H2 to power vehicle fleets, can represent a source of significant revenue and savings.

ACCIONA is launching this challenge to identify solutions and/or technologies that allow the production of H2 to be included in the conventional operation of a WWTP without the need for pre-treatment, for example, a biological reactor that produces H2 in addition to purifying the water. The solution must meet the following requirements:

• H2 production from one of the aqueous (non-gaseous) streams or sludge from the sewage treatment plant, without involving prior purification similar to that required to operate conventional electrolysers.
• The solution should present a positive energy balance of the treatment and help decarbonisation of the sector.
• The technology must be at TRL 5 or higher.