Role of microparticles on the filamentous bulking of activated sludge

Abstract With the cancellation of primary sedimentation tanks, a large number of particles have entered the biochemical treatment units of wastewater treatment plants. Based on the more common problem of filamentous bulking in wastewater treatment plants, the paper investigates the effect of particles on activated sludge filamentous bulking, using polyethylene terephthalate (PET) microparticles as test particles. The results showed that the particles could significantly reduce the number of filamentous bacteria in activated sludge, and had a significant effect on its growth morphology. The role of 0.5 mm and 1.0 mm particles on filamentous bacteria was more obvious than that of 0.1 mm particles, and 0.1 mm particles were easily adsorbed by activated sludge and became biofilm carriers. Its improvement in the settling ability of filamentous expanded activated sludge is more significant than that of particles with 0.5 mm and 1.0 mm. The addition of 0.1 mm PET particles to the Anaerobic-Anoxic-Oxic (AAO) reactor promoted the coalescence of loose bacterial agglomerates under the combined effects of hydraulic shear, impact, friction, and extracellular polymeric substances (EPS) adhesion, which had a positive role on the settling properties of the activated sludge. The test abundance of particles in activated sludge at 4000 particles/L had no significant effect on the removal of COD and total phosphorus, but the removal of ammonia nitrogen decreased by 5–7%, showing some inhibition of nitrification; the sludge volume index (SVI) decreased from 358 mg/L to 198 mg/L, which had a significant control on filamentous bulking.