Introduction

Pure fixed-film processes, as used for industrial wastewater treatment, generally take the form of towers containing a fixed plastic media having a specific surface area of about 30 sq.ft./cu.ft. (100 m2/m3).  In this case, wastewater is dosed to the top of the tower using a fixed or rotating distributor and trickles downward over the surface of the media.  Microorganisms attached to the media degrade the organic constituents of the wastewater as it passes through the tower.  

Advantages of fixed-film processes are their ease of operation and low power requirements.  

Disadvantages include low loading rates and large reactor volumes, stripping of volatile organic chemicals, and release of odors.  Accumulation of microorganisms in the media bed provides the solids retention time necessary for treatment.  The media may be washed occasionally to remove excess biomass.  

Trickling filters built in the US over the past several years have been deep (8 +/- m) with high rate distributors.  Trickling filters are OK for instances in which only roughing treatment is needed

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