Activated sludge process versus rotating biological contactors in WWTPs: Evaluating the influence of operation and sludge bacterial content on their odor impact

Abstract

Two municipal wastewater treatment plants (WWTPs), based on activated sludge process (ASP) and rotating biological contactors (RBC) as biological treatments, were comparatively evaluated in terms of their operational conditions, bacterial content and physicochemical characteristics of their derived sludge (SL) to determine their influence on odor impact. The average values of influent wastewater flow, inlet chemical oxygen demand (COD) and COD removal efficiency were (ASP-WWTP vs. RBC-WWTP): 447 vs. 689 m3/d, 300 vs. 423 mg/L and 88.28 vs. 83.17%, respectively. Regarding the global odor emissions, ASP-WWTP and RBC-WWTP had a similar odor emission rate (11,177 ouE/s and 12,784 ouE/s, respectively), with sludge thickening and dewatering being the major sources of odor in both facilities. Proteobacteria, Bacteroidetes and Firmicutes were the three predominant phyla in both WWTPs, representing the 83% in ASP-SL and the 97% in RBC-SL. RBC-SL showed lower bacterial biodiversity than ASP-SL. The higher odor concentration from the sludge handling activities in RBC-WWTP were linked to the significative increments in the abundance of Porphyromonadaceae, Clostridiales, Lachnospiraceae (obligate anaerobe) and Moraxellaceae (aerobic) families compared to ASP-WWTP. However, when odor emissions were evaluated per equivalent inhabitant (EI), a higher value was obtained for ASP-WWTP (16.22 ouE/s·EI) compared to RBC-WWTP (6.84 ouE/s·EI).