Performance of a UASB-Digester System Treating Domestic Wastewater

Abstract

The anaerobic treatment of raw domestic wastewater by a novel technology consisting of an Up-flow Anaerobic Sludge Bed (UASB) reactor combined with a completely mixed digester for the stabilisation of the UASB sludge was assessed. A pilot-scale plant of the so-called UASB-Digester system was located at the municipal wastewater treatment facility of Santiago de Compostela (Northwest of Spain). The main aim of the Digester was to enhance the biodegradation of influent solids retained in the UASB reactor at low temperatures, then increasing its specific methanogenic activity. The sludge drawn from the middle zone of the UASB entered the upper zone of the Digester and then circulated from the bottom of the Digester to the UASB bottom. Circulating in an automated semi-continuous way, the flow of this sludge stream was selected in order to set a previously defined hydraulic retention time (HRT) (16-27 d) in the digester. The Digester temperature was set at an optimum value ranging from 25 to 35 degrees C. The steady state efficiency of the UASB system, at 6-8 h of HRT, 15-16 degrees C of temperature and 330-360 mg l(-1) of influent total chemical oxygen demand (TCOD) was 79% of total suspended solids (TSS) removal, 52% of TCOD removal and 60% of biological oxygen demand (BOD5) removal. The hydrolysis of retained solids reached 85%, while excess sludge generation was only 7% of influent TCOD. A stable anaerobic (pre)treatment of diluted domestic wastewater was reached as the sludge concentration in the reactor remained mainly constant and the specific methanogenic activity showed a slight increase.

Enrichment of denitrifying methanotrophic bacteria for application after direct low-temperature anaerobic sewage treatment

“…Pilot-scale application of the combination of an upflow anaerobic sludge bed (UASB) reactor and a sludge digester, referred to as UASB-digester system, was successful for anaerobic sewage treatment at low temperatures [6][7][8]. In the UASB reactor (at 10-20 • C) dissolved COD is converted; solids are entrapped in the flocculent sludge bed and transported to the digester.…”

Treatment of low strength sewage with high suspended organic matter content in an anaerobic sequencing batch reactor and modeling application

“…These treatment conditions were significantly more advantageous for anaerobic digestion. Alvarez et al (2004) treated domestic wastewater (tCOD: 330 -360 mg/L) in an UASB reactor reaching total COD removal efficiencies of 60%. Lew et al (2004) reported COD removal efficiencies up to 75% in a two-phase system (UASB + anaerobic filter) operated at high OLR (around 5 kg COD/m 3 x d); however, solids accumulation in both reactors occurred.…”

The effect of sludge recirculation rate on a UASB-digester treating domestic sewage at 15 °C

“…The application of long SRT needs long HRT and therefore large reactor volume, which is economically not feasible. The combination of a UASB and a digester (U-D) has been shown to be successful to treat domestic sewage with high concentrations of suspended organic solids at low temperature (Mahmoud et al 2008, Mahmoud et al 2004, Álvarez et al 2004.…”