Use of an aerobic selector to overcome filamentous bulking in an activated sludge wastewater treatment plant

Abstract

An urban wastewater treatment plant (WWTP) with two different parallel lines of treatment and located in the north of Portugal was studied during four months, following recurrent episodes of filamentous bulking caused by Sphaerotilus natans and eventual occurrences of Nocardioforms and Type 1863. An aerobic selector was introduced in both lines in the beginning of the studied period, suppressed in one of the lines during six weeks, and then put into operation again until the end of the study. A total of 14 filamentous bacteria morphotypes were identified. The results showed that the presence of an aerobic biological selector in continuous operation prevented the overgrowth of the filamentous Type 1863, of Nocardioforms and, in particular, of S. natans. Simultaneously, it allowed lowering the oxygen levels in the aeration tanks without negative consequences in the overall performance of the WWTP, namely bulking occurrence. Dissolved oxygen (DO) in the aeration tank varied initially between 2 and 3 mg/L, but the introduction of the selector enabled to lower it to 1-1.5 mg/L in the aeration tank and around 0.5 mg/L in the selector. A significant energy save was allowed, even considering the aeration of the selector. The results are more relevant if one considers the fact that the main cause of the bulking problems in this WWTP was the overgrowth of S. natans, a filamentous bacterium known to be stimulated by low DO levels.

Potential Inhibition of Filamentous Microorganisms in Sludge Bulking by Static Magnetic Field

“…When the normal balance of these biological communities is disturbed, filamentous microorganisms tend to proliferate, causing various problems. Sludge bulking phenomena is one of the major problems referred usually resulting in poor settleability and low quality of the final effluent [2,9]. There are more than 20 types of filamentous morphotypes presence in activated sludge biomass [1,13].…”