With Aster Bio's increased work with molecular biomass testing (Environmental Genomics), we have found obligate anaerobic cultures in systems with DO meters reading above 3.0 mg/L in the aeration basin. How can this happen?
It is all about the biological solids - floc or biofilm. The graphic below represents MLSS from an aerobic granular sludge facility which is a most extreme case of aerobic/anoxic/anaerobic zones in a biofilm. However, depending upon your solids concentration, floc size, and biological polymer matrix - you can have similar environments in an extended aeration activated sludge or MBBR system. So while the water column may have a DO > 3.0, oxygen does not diffuse throughout the floc which enables anaerobic cultures to thrive inside. We have also noted that increased particulates in older sludges can increase the anaerobic effect - another reason to maintain a proper F/M or sludge age by wasting.
It is all about the biological solids - floc or biofilm. The graphic below represents MLSS from an aerobic granular sludge facility which is a most extreme case of aerobic/anoxic/anaerobic zones in a biofilm. However, depending upon your solids concentration, floc size, and biological polymer matrix - you can have similar environments in an extended aeration activated sludge or MBBR system. So while the water column may have a DO > 3.0, oxygen does not diffuse throughout the floc which enables anaerobic cultures to thrive inside. We have also noted that increased particulates in older sludges can increase the anaerobic effect - another reason to maintain a proper F/M or sludge age by wasting.
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