Wastewater BOD Removal
Aerobic BOD (Biochemical Oxygen Demand) removal is accomplished by direct removal of particulate organics and indirectly through the biological activity of the filter. AST’s bead filters can be configured to do both.
Bead Filters as Biological Filters
A floating bead media filter acts as a fixed film reactor with bacteria growing on the surface of the beads in a layer that is a hundreds of microns thick. If biological activity is desired, the filter must be managed to encourage the culture of heterotrophic bacteria. Typical control issues include flowrate, substrate concentration, oxygen supply, backflush frequency, temperature, and pH. Fortunately, development of a heterotrophic fixed film is a natural process easily accomplished in an expandable granular format. All PolyGeysers used as biological filters should employ EN media which displays a better porosity and provides protection for the biofilm during high frequency backwashing events. The units display a high specific surface area for biofilm development in the range of 1100-1200 m2/m3.
Frequent Backwashing Prevents Biofouling
Bead filters can be operated in a wide variety of BOD concentration regimes. The PolyGeyser units are virtually impervious to biofouling, and with a high backwashing frequency, they can be effectively used as roughing filters reducing particulate BOD of raw wastes with high BOD and TSS concentrations. Roughing filters are managed with a high frequency of backwashing (down to about once an hour) to prevent clogging of the bed. Peak conversions on waste streams with CBOD5 levels below 100 mg/L typically fall in the 3-6 hour backwash interval range. Rapidly growing biofilms uptake dissolved organics producing biomass that is then removed before the demand can be fully expressed reducing oxygen demand.
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Pilot RCPG System for Facultative Lagoon Polishing
In order to meet increasingly strict discharge standards, AST provided a trailer mounted pilot scale test unit to pull a side stream off of the current waste stream.
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