Modelling biological processes in water treatment: the integrated biofiltration model

Biofiltration is a form of biofilm process used to make drinking waters biologically stable, which means that the water does not support excessive bacterial growth when it is distributed. Biofiltration avoids the many quality problems associated with biological instability: high chlorine doses, disinfection by-products, accelerated corrosion, taste and odours, high turbidity, and increased plate counts or coliforms. Most designs of biofilters have been empirical. However, using a mechanistic model as a design tool can improve process reliability and the effectiveness of pilot and laboratory studies on biofiltration. Unfortunately, models that include the critical phenomena have been quite complex; they are good research tools, but are not easily used for routine design and analysis. The Integrated Biofilm Model (IBM) is a spreadsheet program that includes all the key phenomena for biofiltration of drinking water, but is simple to use. Specifically included in the model are the consumption and production of chemical species (input substrates, end products and soluble microbial products); heterotrophic and nitrifying bacteria; inert biomass; physical processes, such as transport and detachment; and the relationships between all of the different organisms and chemical species. An example shows the inputs to the model and the kind of trends that it predicts for original substrates, soluble microbial products, and biofilm biomass. The IBM makes iterative design and analysis of biofiltration processes straightforward.