Impacts of Hydraulic Retention Time on Treatment Performance and Biofilm Formation in Moving Bed Biofilm Reactor

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Abstract
Moving bed biofilm reactors (MBBRs) are compact and high-performing wastewater treatment technology preferred for their effectiveness in treating both domestic and industrial effluents. Despite the widespread application of MBBRs, the literature lacks comprehensive investigation into the influence of key design parameters, such as attached biomass concentration and sludge retention time (SRT) of biofilm, on treatment performance across varying operational conditions. This study explored the impact of varying hydraulic retention time (HRT) and organic loading rates (OLRs) on the process performance, amount of heterotrophic bacteria attached to plastic carriers and SRT of the biofilm in an aerobic MBBR (with a 50% fill ratio of plastic carriers) treating synthetic wastewater. The MBBR exhibited robust performance, maintaining a high average COD removal efficiency of 97%, even when operated at an HRT of 3 h and a COD loading rate of 13.3 g/(m2⋅d). However, reducing the HRT to 1 h and increasing the OLR to 40 g/(m².d) resulted in a decrease in COD removal efficiency to 65%. This study also demonstrated that HRT and OLR values have a significant effect on the amount of attached heterotrophic biomass and the biofilm SRT. Decreasing the HRT value from 24 to 1 h (and increasing the OLR from 0.1 to 40 g/(m².d)) in MBBR increased the attached biomass concentration by 62% and decreased biofilm SRT by 3.5 times. These findings highlight the fact that high-rate MBBRs can perform well even at high loading rates and low HRT values. However, future pilot-scale studies are needed for the sustainable and widespread use of high performing energy efficient high rate-MBBR processes.
Funding Information
  • Türkiye Bilimsel ve Teknik Araştırma Kurumu (1919B012314958)

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