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BioRtration Process related to the size of the media bed and the recirculation rate. If-aspecific amount of waste needs to be reduced then a specific tank size is required. Time consideration is regulated by the recirculation rate. Because the recirculated flow passes back over the media with its zoogleal mass, the organisms have another opportunity to absorb food and the water has greater opportunity to absorb oxygen that will be used for cell growth. Ventilation supplies the oxygen the organisms need to live. The organisms in the zoogleal mass are aerobic organisms. This means they rely on dissolved oxygen (DO) to sustain life. DO levels should be adequate to theoretically sustain the organisms throughout the treatment process including the secondary clarifier. The DO level should be excessive so that the required amount will be used and a residual amount will remain. DO residuals in the secondary clarifier should be maintained between lA and 3.0 mg/1 and never fall below 0.5 mg/1. Oxygen is introduced into the treatment process by the water falling over the media, splashing through the air and flowing up into the spaces between the media. The increased surface area creates high oxygen transfer into the water, thus increasing Do. Microbiology and Biochemistry of BioFiltration The process of biofiltration provides 'an ideal environment for numerous microorganisms including bacteria, fungi, protozoa and nematodes. Bacteria are the significant organism'consuming the waste. Microbiology Biofiltration focuses on the dominant species of microorganism. The success of the biofiltration process depends on how well the operation.can maintain the perfect environmental conditions that keep the good settling and working bacteria dominant. The dominant culture will remove and consume (assimilate) waste material, grow and reproduce, and settle well, thus producing a good clear effluent. Indicator organisms that perform the above consistently are Rotifer, Stalked Ciliates, Free Swimming Ciliates, Flagellates, Amoeboids, and Nematodes. Biochemistry The biochemical reactions in biofiltration occur through the stabilization of organic and inorganic compounds. Heterotrophic bacteria are those that use 7H Technical Services Group Operation &Maintenance Manual BioFiltration Process Page 8 of 26 Rev991215 1