Treatment of wastewater results in the removal of organic components measured as BOD/COD/TOC and the final conversion of organics into carbon dioxide, water, and new microbial cells. The new cells form the mixed liquor suspended solids in activated sludge or the biofilm in fixed film systems. In any case, normal operation includes keeping a fixed amount of microbial biomass to treat influent loading. So some of the cells must be wasted (keep a stable food/microorganism (F/M) or sludge age (MCRT).
How must wasting needs to be done is calculated based on cell yield per unit of organic treated. Using BOD5 or soluble BOD as the influent loading, we often plug in 0.5 g of new cells per gram of BOD5. However, this is not a constant or fixed number and can easily vary from 0.3 - 0.7. What causes variation in cell yield? I will list a few:
Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.
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