Chapter No. 17. Modelling Biofilms.
All biological treatment processes have the following two conditions in common: (i) they need a relatively high concentration of active microorganisms within the system and (ii) once a satisfactory degree of treatment is achieved the microorganisms have to be removed from the treated effluent before the water leaves the system. In activated sludge systems microorganisms grow in the water as suspended flocs and therefore solid-liquid separation is required to retain the biomass within the system (e.g. usually using a settling tank or a membrane). On the other hand, in biofilm reactors microorganisms are immobilized in a dense layer which grows attached to a solid surface. In biofilm systems, active biomass can be retained in the biofilm reactor without requiring a settler. In suspended growth systems bacteria can be washed out with the water flow, but in biofilms they are protected from washout and can grow in locations where their food supply remains abundant.
This course consists of 5 video lectures recorded by Prof. Dr. Eberhard Morgenroth currently at ETH Zurich Institute of Environmental Engineering and EAWAG in Switzerland. It presents an overview about biofilms and the motivation to model them. As such, it analyzes and discusses the most important and influencing operating conditions affecting biofilm systems (such as external mass transfer resistance with regard to electron donors and acceptors, biofilm detachment and thickness), which not only serve as a basis for the design of biofilm systems but also for the introduction of basic principles on 1-D biofilm modelling. Furthermore, it also presents a brief outlook of diverse advanced biofilm models (2-D/3-D models and fluid dynamics) which have helped to increase the understanding about the different microbial interactions and processes occurring within the biofilms.
Time Framework for the Course: 1 week
After the successful completion of this course, the student will be able to:
- Design and assess the operation of a biofilm system for wastewater treatment based on the conditions and factors affecting the microbial processes and interactions occurring within the biofilm.