Sewage sludge is primarily water combined with the solids (both organic and inorganic) that are removed through physicochemical processes (settling/filtration) during the wastewater treatment process. Future global quantities of sewage sludge are expected to rise significantly due to increasingly strict effluent requirements for wastewater-treatment-plants, and the building of more wastewater treatment plants in developing countries. This increased sludge production necessitates an economic and environmentally sustainable treatment process. Sludge disposal/handling is challenging not only because of the large volumes produced, but also because of its high concentration of microplastics, other harmful pollutants, pathogens and heavy metals. Currently, most of the sewage sludge produced by water treatment plants is stabilized via biological processes (e.g. anaerobic digestion) or chemical processes (e.g. liming) with the resultant product used as a fertilizer. Microplastics/PFOAs/pathogens finding their way into the agricultural landfill via sludge has adverse impacts on human health and the environment.

Given the ongoing climate crisis, concerns about microplastics and an increasingly competitive outlet market, use of alternative novel technologies such as pyrolysis is being actively investigated by water treatment companies and others stake-holders to thermally treat sewage sludge with the following aims:

* Energy recovery to help minimize carbon emissions and drive the water companies towards their net zero targets.
* Destruction of microplastics and other potential contaminants to minimize any perceived risk to the environment.
* Reduction in the disposal risk and costs.
* Recovery of phosphorus and other high value elements.

This 18months industrial-research project aims to develop a pyrolysis gasifier demonstrator (equipment and methodology) 'PyroPlus' which responds to all of the above described needs of water industry. PyroPlus brings a step change in the sewage sludge handling by producing clean, high Calorific Value (~20MJ/m3) hydrogen laden syngas and eliminating microplastics through their thermal cracking into smaller hydrogen and carbon (C1, C2 and C3) compounds free from sulphur and nitrogen acids, and heavy metals. The project also aims to develop a 5kg/hr continuous coating method to valorise pyrolytic char through surface functionlisation.

All competing primary, secondary and tertiary sludge treatment solutions (screening/sedimentation/ultrafiltration) fail to completely eliminate microplastics and other solid pollutants from the sewage sludge. Competitive technologies focus on separating the microplastics rather than thermally crack them into smaller compounds, a key reason of their failure.

PyroPlus will help meeting the UK's renewable energy targets and climate change management obligations but will also help safeguarding the role of existing waste treatment assets in the water industry.