Contents I. Introduction
Bioflocculant is a kind of macromolecular flocculant secreted by microorganisms which is easily degradable. Owing to the nontoxic, harmless characteristic of bioflocculant and without secondary pollution, they have a great potential for use in wastewater treatment. At the present time most of research focused on screening for microorganisms, culture conditions, mechanism of flocculation, chemical structure, and so on [1]–[3]. However, high production costs associated with relatively expensive substrates, such as glucose, fructose and glutamate limit their practical application [4]. Seeking for low-cost substrates to reduce the production cost was also investigated. The excess biological sludge was generated from the biological treatment process of wastewater. The sludge management is the major issue of wastewater treatment plant, as it costs 60% of the total plant capital cost and the laws for sludge disposal are becoming increasingly stringent. Excess biological sludge contains various fractions of water associated with sludge solids, most of which are made up of microorganisms. The main constitutes of the microorganisms were macromolecules compounds such as polysaccharide, protein, cellulose and so on. These macromolecules compounds have flocculating activity. Tenney and Stumm [5] had shown that macromolecules could be viewed as naturally produced flocculants. Thus excess biological sludge is believed as a source of bioflocculants and could be recycled to prepare bioflocculant.
