The Upflow Anaerobic Clarification Tank (UACT) is of interest as a post-treatment step for high-rate anaerobic wastewater treatment systems. The UACT contributes to extra capture of methane from the raw wastewater. It also significantly facilitates the reuse of the treated water. The efficiency of the UACT process is demonstrated in this study using laboratory-scale reactors. The water produced by the UACT had a low total COD, in most cases below 145 mg/L and a soluble COD below 60 mg/L at surface loading rates between 0.1–0.4 m3/(m2 h) and hydraulic retention times between 5–6 h. The sludge bed of the UACT was characterised by 6–10 times higher substrate affinity (for ethanol, acetate and propionate) compared to the parent UASB and similar specific activity. The results suggest that a UASB followed by the UACT can, upon subsequent application of a rapid filtration, qualify as a total COD removal, no longer necessitating aerobic treatment.

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