Biofiltration - the treatment of fluids by microorganisms immobilized into the filter bedding material: a review

Biofiltration is distinguished from other biological waste treatments by the fact that there is a separation between the microorganisms and the treated waste. In biofiltration systems the microorganisms are immobilized to the bedding material, while the treated fluid flows through it. In recent decades, a vast amount of literature has been written on single experiments involving the treatment of fluids by immobilized microorganisms. Several artificial immobilization methods have been examined and impressive results have been achieved in the treatment of fluids with one of the artificial immobilization methods - the entrapment of microorganisms within polymer beads. This method, even though it needs to be improved, seems to have a future potential in commercial biofiltration systems. The methods of artificial immobilization of microorganisms within biofiltration systems have several advantages, but also suffer from several disadvantages in comparison to the treatment of fluids by naturally attached microorganisms. Understanding the mechanisms and forces responsible for the attachment of microbes to the bedding material, in attempt to improve this attachment, is of the utmost importance. Further improvement of the artificial entrapment of microorganisms within polymers will allow the exploitation of the advantages of this method in the treatment of fluids. The aim of this review essay is to introduce the main principles of two immobilization processes - the self-attachment of microorganisms to the bedding material and the artificial entrapment of microorganisms within polymer beads. Both treatments of liquids and gases with each immobilization process are discussed. The advantages and disadvantages of each immobilization process are pointed out and different aspects of the fluid treatment with the two immobilization processes are compared. (C) 2001 Elsevier Science Ltd. All rights reserved.