Aeration and control of slurry odours by heterotrophs

In continuous-culture aeration, heterotrophic activity varied with mean treatment time and treatment temperature but was unaffected by the level of dissolved oxygen provided it was maintained above 1% of saturation. At temperatures from 15 to 50°C most of the slurry odorants were removed even after very short treatment times. Below 1% of dissolved oxygen saturation, heterotrophic activity, in particular the oxidation of odorants and other BOD₅ material, varied with the oxygen concentration as well as mean treatment time and temperature. The oxygen concentration was no longer detectable by the Mackereth-type electrode and was controlled and measured indirectly through redox potential within the range −500 to 0 mV E_cal (pH 7·8). At 35 and 50°C total residual COD and BOD₅ were both similarly related to changes in redox potential. At 15°C only the total residual BOD₅, not the total residual COD, was related to redox potential. This could indicate that at lower temperatures some fermentative activity occurs at low aeration rates. Treatment times must normally exceed 7 days and redox potential during treatment must be higher than −200 mV E_cal (pH 7·8) if the rapid regeneration of odorants after treatment is to be avoided.