Moving away from aeration – utilising computational fluid dynamics modelling ofmechanical mixing within an industrial scale nature-based wastewater treatment system

The water treatment industry currently uses metal salt dosing (MSD) to precipitate the phosphorous into a sludge which can then be removed and disposed of. There has therefore been a massive increase in demand for ferric (the most used MS). The UK government's plan to achieve 'Net Zero' decarbonisation highlighted the need for WW operators to utilise alternative treatment processes, specifically nature-based solutions. UK WW companies are therefore creating 'nature-based solutions' portfolios. However, there is currently a shortfall in nature-based solutions that can be retrofitted into small rural sites.

Microalgae are single-celled aquatic organisms that can use the energy from light to take up simple nutrients from their environment along with CO2\. When used in a controlled system, microalgae can be used to remove contaminants from WW. Industrial Phycology (I-PHYC) have developed a unique process which exploits the ability of microalgae to quickly treat wastewater of multiple contaminants to low levels.

Mixing is a critical factor for achieving an efficient process in the algal systems because of its role in the distribution of light and nutrients, and diffusion of gases throughout the culture. I-Phyc currently uses aeration However, depending on the size of the process, the blowers can represent up to 34% of average operation electrical load during processing. An alternative to sparging is to provide mass transfer by mechanical mixing, potentially leading to decreased energy consumption and process complexity. In addition, to optimise the manufacturing and assembly of the I-Phyc product the contractors are recommending we move toward a _modularised_ system. This could have a high impact on the final product's quality and reduce the project cost by an estimated 20%.

However, the interaction of various factors including light location, a new tank geometry, and mixing methodology make this a complex system problem.

Through the support of Innovate UK's 'A4I' competition I-PHYC will collaborate with TÜV SÜD National Engineering Laboratory, a world leading modelling facility, to generate CFD models to improve mixing and lower power requirement within the I-Phyc process, while also understanding how mixing performs in the proposed _modularised_ design. Real-time measurements and CFD will link the complex relationship between physical (mixing method), biophotonics (number of lights) and algal biology (optical density (OD)) to reduce the process energy consumption. Once a robust model is created I-PHYC can then make informed multi-layered investment decisions, allowing the I-PHYC process to establish itself has a competitive, sustainable WW process.