Modelling respirometric tests for the assessment of kinetic and stoichiometric parameters on MBBR biofilm for municipal wastewater treatment

Moving Bed Biofilm Reactor (MBBR) technology is a suitable option for up-grading and retro-fitting wastewater treatment plants. Although being introduced in late 80s, design and operational guidelines of MBBR are mainly based on empirical approaches. This work was aimed to assess the biokinetics on both detached and undisturbed biofilm samples from a large pilot-scale MBBR treating pre-settled municipal wastewater. Experimental OUR profiles of heterotrophic biomass in detached and undisturbed biofilm have been obtained with respirometric tests and then modelled with an extended version of ASM3 which assumes biomass growth to take place on both readily biodegradable substrate and storage products. Results indicated the storage mechanism to be prevalent for heterotrophic biomass growth, with a 80% fraction of soluble substrate converted into storage products. The active heterotrophic biomass in the film was estimated in detached biofilm samples; on average, it corresponded to a 39% fraction of particulate COD. Tests on undisturbed biofilm were carried out to quantify autotrophic ammonia and nitrite removal, showing an effective specialisation of the nitrifying biomass. The parameters obtained could support a more rational design approach for the moving-bed biofilm process.