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Effects of mixing velocity on anaerobic fixed film reactors
Authors:Dhandapani Thirumurthi
Abstract:Four laboratory-model upflow anaerobic fixed film reactors (AFFR 1, 2, 3 and 4) treating landfill leachate were subject to identical volumetric organic load (7 kg COD m−3 d−1) and hydraulic retention time (3d), but the contents in each unit were continuously recirculated for 10 months at four different velocities, respectively, of 21, 66, 680 and 3063 cm h−1. The objective was to assess the effects of such mixing velocities (ν) on COD removal efficiencies (E), mean cell residence time (MCRT) and substrate utilization rate (U expressed as g COD removed d−1 g−1 VSS). The results showed that the relationships between E and ν and MCRT and ν were inverted U-shaped curves. The two middle reactors (AFFR 2 and 3) had near-optimum velocities (ν2 and ν3) with maximum E values of 88–89%. AFFR 4 had a high value of ν scouring biofilm on the biorings, resulting in higher concentrations of SS, VSS and COD in the effluent. All four reactors had nearly similar values of U (1.85–2.14 g COD d−1 g−1 VSS). The value of ν1 (AFFR 1) was too low to enhance performance and ν4 was too high to retain the biomass. The optimum recycle velocity, under the test conditions, was in the range of 66–680 cm h−1.
Keywords:leachate treatment  anaerobic fixed film reactor  mixing velocity  recycle velocity
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