Fixed-film systems

The reac tor concepts described above can be utilized with any of the electron acceptor systems previously discussed, although some reactor types perform better with specific electron acceptors. For example, suspended growth systems are generally superior to fixed film systems when molecular oxygen is the electron acceptor because it is easier to supply oxygen to suspended growth systems. 

Packed-Bed Fixed-Film Systems These systems were originaUy termed anaerobic trickhng filters because the first systems were submerged columns filled with stones run under anaerobic conditions (Fig. 25-57). A wide variety of packed media is now used ranging in size from graniiles 40 mesh to 7.5-cm (3—in) stones. Many systems use open structure plastic packing similar to that used in aerobic trickhng filters. 

Residuals Produced As with the suspended growth and fixed-film systems, some biomass is produced which will require disposal. The pretreatment and disposal practices required will depend on site-specific requirements. 

Attached-growth (or fixed-film) systems rely on the ability of microorganisms to attach themselves to inert surfaces. Contaminated water is passed through a bioreactor that houses such media, where the resulting microbial growth attaches and forms a thick film called biofilm. The biomass remains in the reactor except for the part that sloughs off the supporting media. 

V. R. Borregaard, Experience with Nutrient Removal in a Fixed-Film System at Full-Scale Wastewater Treatment Plants, Wat. Sci. Tech., 36(1), 129-137 (1997). 

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