The encouragement of attached microbial growth in oxidation ponds is an apparent practical solution for maintaining biological populations while still obtaining the treatment desired. Although baffles are considered useful primarily to ensure good mixing and to eliminate the problem of short-circuiting, they behave similarly to the biological disks in that they provide a substrate for bacteria, algae, and other microorganisms to grow (Polprasert and Agarwalla, 1995; Reynolds et al., 1975). In general, attached growth surpasses suspended growth if sufficient surface area is available. In anaerobic or facultative ponds with baffling or biological disks, the microbiological community consists of a gradient of algae to photosynthetic, chromogenic bacteria and, finally, to nonphotosynthetic, nonchromogenic bacteria
(Reynolds et al., 1975). In these baffle experiments, the presence of attached growth on the baffles has been the reason for the higher efficiency of treatment than that in the nonbaffled systems. Polprasert and Agarwalla (1995) demonstrated the significance of biofilm biomass growing on the sidewalls and bottoms of ponds. A model for substrate utilization in facultative ponds was presented using first-order reactions for both suspended and biofilm biomass.
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