| Abstract: | Experimental studies of the growth of a natural microbial population on a synthetic liquid effluent containing sugar, sodium alginate, and nutrients showed that: (I) the concentration of substrates in the feed to an activated sludge process exerts a significant effect upon its effluent chemical oxygen demand (COD) and (ii) there is an optimum sludge age for achieving minimum effluent COD, given by the relationship: optimum growth rate ∝ (feed COD)0.5. These were explained by incorporating the concept of product formation into existing activated-sludge theory, which showed that at sludge ages longer than optimum, effluent COD increased due to product formation; at shorter sludge ages, the effluent COD increased owing to an increased concentration of degradable substrates. |
