Limited filamentous bulking in order to enhance integrated nutrient removal and effluent quality

Limited filamentous bulking has been proposed as a means to enhance floc size and make conditions more favorable for simultaneous nitrification/Denitrification (SND). Moreover a slightly heightened SVI is supposed to increase the removal of small particulates in the clarifier. Integrated nitrogen, phosphorus and COD removal performance under limited filamentous bulking was investigated using a bench-scale plug-flow enhanced biological phosphorus removal (EBPR) reactor fed with raw domestic wastewater. Limited filamentous bulking in this study was mainly induced by low DO levels, while other influencing factors associated with filamentous bulking (F/M, nutrients, and wastewater characteristics) were not selective for filamentous bacteria. The optimum scenario for integrated nitrogen, phosphorus and COD removal was achieved under limited filamentous bulking with an SVI level of 170–200 (associated with a DO of 1.0–1.5 mg/L). The removal efficiencies of COD, TP and NH4+–N were 90%, 97% and 92%, respectively. Under these conditions, the solid–liquid separation was practically not affected and sludge loss was never observed. A well-clarified effluent with marginal suspended solids was obtained. The results of this study indicated the feasibility of limited filamentous bulking under low DO as a stimulation of simultaneous nitrification/denitrification for enhancing nutrient removal and effluent quality in an EBPR process.

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► To utilize limited filamentous bulking induced by low DO, but not to fear for it.
► Limited filamentous bulking could enhance nutrient removal and achieve well effluent.
► Removal efficiencies of COD, TP, NH4+–N were 90%, 97% and 92% with an optimum SVI.
► Solid–liquid separation was not affected and no sludge loss was observed.
► Dominant and minor filaments were identified as Haliscomenobacter hydrossis and S. natans.