Influence of support medium height on the optimization of performance of an Upflow Anaerobic Hybrid Reactor (UAHB) treating synthetic wastewater

The support media of upflow anaerobic hybrid reactors (UAHB) facilitates the formation and retention of microbial biofilm and the contact between the influent and microorganisms. Previous studies demonstrated the importance of support media height (SMH) to organic matter removal; however, the influence of this parameter in the UAHB reactor performance under varying conditions is still a gap. The Central Composite Design (CCD) method was applied to optimize the removal of organic matter by varying the cross-sectional area and height of the reactor based on 42 studies. The modelling indicated 72-87% COD removal efficiencies with 0.007 m² cross-sectional area and 0.75 m height, with 5.5 L total volume. Thus, three pilot-scale UAHB reactors, filled with Corrugated Polyvinyl Chloride (PVC) rings at different heights (6, 15, and 24 cm), were operated with a hydraulic retention time of 10 h, treating synthetic effluent with a COD of 490 mgO₂ L^-1. Unlike previous studies, this study evaluated identical UAHBs operating in parallel under controlled conditions. The UAHB reactors presented stability, buffering capacity, and neutral pH during the operation. The reactor with higher SMH (24 cm) achieved higher removal efficiencies of turbidity (90%), COD (72.6%), and TS (63%). Variations in SMH affected reactor performance, as corroborated by the negative and 'very strong' correlation for turbidity, COD, and TS and a 'moderate' correlation for fixed and volatile solids. The novelty of this study lies in its comprehensive assessment of how varying SMH affects UAHB reactor performance, guiding future advancements in its design for efficient wastewater treatment.