Anaerobic prefermentation and primary sedimentation of wastewater in a sequencing batch reactor

Abstract

This research was carried out with the aim of evaluating the solubilisation and acidification capacity of fermenting organisms in suspension in a sequencing batch reactor (SBR), which had a volume of 1 800 ℓ. Using 8 h cycles with 340 min of anaerobic
reaction time, the wastewater fed to the SBR presented an average of total and dissolved COD of 315 and 230 mg/ℓ. The experiment was divided into three phases: In Phase 1 the organic load was decreased from 1.46 to 0.27 kgCOD/kgTSS·d, as total COD, during a period of 154 d. If the acidification is defined as the fraction of organic substrate that is transformed to volatile fatty acids (VFA) then the highest acidification percentage (80%) of the dissolved COD (CODD) was obtained for the organic load runs of between 0.62 and 0.72 kgCOD/kgTSS·d. Within this range of organic load the 2nd and 3rd experimental phases were achieved at the same time after 130 d while the pH and temperature were the control parameters: pH from 5.5 to 7.5 and temperature from 22 to 31ºC. Finally, the higher production level of the dissolved COD during the fermentative reaction period was 35 mg/ℓ. The acidification of the dissolved influent COD was increased from 50 to 60% by decreasing the pH from 7.0 to 5.5 and this percentage was doubled from 33 to 66% when the temperature was increased from 22 to 31ºC. All of the dissolved effluent COD was in the form of VFA, when an organic load of 0.62 kgCOD/kgTSS·d was used or when the temperature was increased up to 31ºC. The VFA production rate that was achieved after 80 min diminished by half when the solids retention time (SRT) was decreased from 8 to 2 d or when the temperature was lowered from 31 to 24ºC.

Water SA Vol.32 (4) 2006: pp.577-583