Microorganisms produce extracellular polymeric sub-
stances (EPSs), and the production of EPSs plays an
important role in aggregation and settling of microor-
ganisms because they could form a crosslink to connect
microbial cells. They can also create granules by binding
cells between microorganisms (Ross, 1984; Shen et al.,
1993). In general, EPSs can be classified into bound
EPS and soluble EPS. The bound EPSs are located close
to cells, while the soluble EPSs are weak in coherence
between cells or dissolved in a solution.