MICROBIAL ADAPTATION, PROCESS PERFORMANCE AND A SUGGESTED CONTROL STRATEGY IN A PRE-DENITRIFYING SYSTEM WITH ETHANOL DOSAGE

Biological nitrogen removal in activated sludge processes is dependent on sufficient supplies of easily metabolized carbon compounds for the denitrifying bacterial population. An external carbon source can incr ease denitrification rates and compensate For deficiencies in the infl uent C/N ratio. Plant performance and microbial adaptation were studie d in a pre-denitrifying pilot-scale activated sludge plant with and wi thout ethanol. Total nitrogen removal efficiency was 67 and 35% for th e ethanol and reference line, respectively. The process responded rapi dly to ethanol but one sludge age was necessary for Full bacterial ada ptation. An initial rapid increase suggests enzyme induction rather th an alterations in bacterial species composition. increased enzyme acti vity was explained by an increase in turn-overrate of biomass. Low eff luent nitrate concentration was a result of the simultaneous use of in fluent COD and ethanol. Fluctuations in influent COD did not affect de nitrification capacity with ethanol. Sludge settling properties were m oderately better in the process without ethanol addition. An automatic control strategy for carbon dosage using feedforward from influent ca rbon and nitrate in the recirculated now was simulated. Simulations wi th an adaptive linear quadratic controller demonstrated that the desir ed nitrate concentration at the end of the anoxic zone could be mainta ined despite relatively large disturbances. Copyright (C) 1996 IAWQ.