Integrating computational fluid dynamics and biological models to assess wastewater reactor design

Current design of reactors for biological wastewater treatment is focused on the development of new processes with optimised removal capacity, low consumption of raw materials and energy, and minimum environmental impact. Mathematical models and simulation can help to determine and validate key design parameters and shorten the duration of experimental RDI works. Still, the computational capacity of these tools has to be expanded and models’ limitations like the assumption of a “perfect blend” should be overcome.

The thesis entitled “Integrating computational fluid dynamics and biological models to assess wastewater reactor design” by Albert Vilà Rovira has integrated biological models – concretely, activated sludge models “ASM” – with simulation tools of computational fluid dynamics “CFD”, and has applied them to the design of two advanced technologies for wastewater treatment: “Microbial Fuel Cells” and the “Anammox” process. Wastewater treatments based on Microbial Fuel Cells use the catalytic bioelectrochemical activity of certain microorganisms to oxidise organic compounds and produce electricity without needing additional chemical compounds. In Anammox process (Anaerobic Ammonium Oxidation) microorganisms play a main role in the autotrophic removal of nitrogen compounds. This reduces sludge and aeration needs. The researcher has carried out his doctoral thesis at LEQUIA group of University of Girona, with a strong track of records in experimental research projects and technology transfer projects focused on these technologies. This has allowed him interacting with experienced researchers and getting to know implementation at industrial scale.

Results obtained show that the potential to integrate computational fluid dynamics and biological models to design biological reactors for wastewater treatment is very high. Among the parameters studied, there is the influence of the reactor configuration in substrate distribution and nutrients removal rate. For Microbial Fuel Cells, different materials for the electrode have been assessed, and its geometry, composition and electrical properties have been considered. The use of granular graphite and stainless steel mesh favoures the flux distribution through the anodic chamber, being the best option the latest thanks to its electrical properties and low cost. For Anammox process, it has been demonstrated that the use of internal plates favours the flow distribution and that the introduction of lateral feeding streams along the column reactor would increase the nitrogen removal rate. To obtain more reliable simulation results, a solid phase representing the sludge involved in the biological process should be included.