ACTIVATED SLUDGE DIFFUSION FOR COST EFFECTIVE BIOLOGICAL TREATMENT OF ODORS FROM WASTEWATER TREATMENT WORKS

The odor treatment efficiency and wastewater treatment process performance of activated sludge (AS) being sparged with hydrogen sulfide (H2S) was studied. H2S removal in a pilot scale system with a fine bubble diffuser in a deep aeration tank was compared with removal in a system with a coarse bubble diffuser in a shallow tank of the same volume. The results showed that the AS continued to treat the wastewater to an acceptable level, with removals of up to 81%, 76% and 60% being achieved for Biological Oxygen Demand (BOD5), Chemical Oxygen Demand (COD) and ammonia (NH3), respectively. BOD5 removal during higher (25 ppmv) dosing was actually better than during lower (5 ppmv) dosing. The impact of diffuser depth and bubble size on H2S removal rate indicated that diffuser depth was not as important as bubble size. The system with fine bubble diffusers achieved 94–99% H2S removal, while the coarse bubble diffusers achieved 85–98% H2S removal rates. The increases in filamentous organisms reported in previous studies were not observed, however, selective agar plates showed that the population dynamics within the aeration tanks changed during the course of each experiment. This indicated that acclimation via selection pressure was taking place. The data were fitted into a modelling package and H2S degradation rates under differing conditions were calculated. The model predictions reflected the trends observed in H2S removal efficiency with respect to changes in bubble size, tank depth and H2S concentration, but failed to predict removals efficiencies accurately.