The operation performance of a single and two (in series) laboratory UASB reactors (working volume of 2.7 l, recycle ratio varied from 1:1 to 1:18) treating diluted wine vinasse was investigated under psychrophilic conditions (4-10°C). For a single UASB reactor seeded with granular sludge, the average organic loading rates (OLR) applied were 4.7, 3.7 and 1.7 g COD/l/d (hydraulic retention times (HRTs) were around 1 d) at 9-11, 6-7 and 4-5°C, respectively. The average total COD removal for preacidified vinasse wastewater was around 60% for all the temperature regimes tested. For two UASB reactors in series, the average total COD removal for treatment of non-preacidified wastewater exceeded 70% (the average OLRs for a whole system were 2.2, 1.8 and 1.3 g COD/l/d under HRTs of 2 days at 10, 7 and 4°C, respectively). In situ determinations of kinetic sludge characteristics (Vm and Km) revealed the existence of substantial mass-transfer limitations for the soluble substrates inside the reactor sludge bed. Therefore an application of higher recycle rations is essential for enhancement of UASB pre-treatment under psychrophilic conditions. The produced anaerobic effluents were shown to be efficiently post-treated aerobically - final effluent COD concentrations were around 0.1 g/l.

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