Acclimation of denitrifying activated sludge to a single vs. complex external carbon source during a start-up of sequencing batch reactors treating ammonium-rich anaerobic sludge digester liquors

Abstract

In this study, denitrification of ammonium-reach anaerobic sludge digester liquor was investigated during start-up periods of two laboratory-scale "fill-and-draw" reactors. One reactor was fed with a single carbon source (ethanol), whereas the other reactor was fed with a complex carbon source (fusel oil). During two acclimation experiments, the structure of microbial community involved in denitrification was analyzed using 16S rDNA polymerase chain reaction-denaturing gradient gel electrophoresis fingerprints and fluorescent in situ hybridization. The characteristics of the mixed liquor were additionally supported by regular measurements of nitrate uptake rates. The addition of fusel oil and ethanol resulted in a significant enhancement of the denitrification rate and efficiency combined with the increasing volumetric addition of sludge digester liquor up to 15 % of the reactor volume. The microbiological analyses revealed that the addition of sludge digester liquor as well as both external carbon sources (fusel oil and ethanol) did not affect the structure of microbial communities in a severe way. In both reactors, Curvibacter sp. and Azoarcus sp. were found as the most abundant representatives of denitrifiers.

Adaptation of the Activated Sludge to the Digestate Liquors During the Nitrification and Denitrification Processes

“…In the lab-scale experiments (Figure 2a-2b), a nearly constant NH 4 + concentration (≈ 30 mg N/L) was maintained by dosing the digestate liquors in the range of 5-10% of the reactor working volume.…”

“…Before applying biological treatment, suspended solids were removed from digestate liquors by coagulation with ferric (III) chloride preceding sedimentation. The studied digestate liquors exhibited a high NH 4 + variation (300-1200 g N/m 3 ) due to the different substrates for anaerobic digestion. In the lab-scale experiments, the dosing amount of the digestate liquors varied in the range of 5-10% of the reactor working volume to maintain a constant NH 4 + concentration (≈ 30 mg N/L).…”

“…The studied digestate liquors exhibited a high NH 4 + variation (300-1200 g N/m 3 ) due to the different substrates for anaerobic digestion. In the lab-scale experiments, the dosing amount of the digestate liquors varied in the range of 5-10% of the reactor working volume to maintain a constant NH 4 + concentration (≈ 30 mg N/L). As far as the pilot-scale experiment is concerned, the dosing amount of the digestate liquors ranged from 5to 7.5% of the reactor working volume to maintain a constant NH 4 + concentration (≈ 15 mg N/L).…”

“…In the lab-scale experiments, the dosing amount of the digestate liquors varied in the range of 5-10% of the reactor working volume to maintain a constant NH 4 + concentration (≈ 30 mg N/L). As far as the pilot-scale experiment is concerned, the dosing amount of the digestate liquors ranged from 5to 7.5% of the reactor working volume to maintain a constant NH 4 + concentration (≈ 15 mg N/L). The lab-scale experiments were carried out during a period of 22 days in a plexiglass sequencing batch reactor (SBR) with a working volume of 10 L equipped with electrodes and probes (Endress+Hauser, Switzerland) for continuous monitoring of pH (CPS471D), temperature and dissolved oxygen (DO) (COS22D) (Figure 1a).…”

“…A single operational cycle lasted for 12 hours and consisted of the nitrification phase (from 4 h to 5 h), denitrification phase (from 7 h to 6 h) as well as settling and decantation phase (1 h). The durations of the nitrification and denitrification phases were designed for the adaptation of the activated sludge under the increasing loads of the digestate liquors (increasing NH 4 + concentrations) to ensure full nitrification. During the nitrification phase, the DO concentration was set above 2.0 g O 2 /m 3 by using PI control system and the pH was controlled above 6.8 by automatic dosing sodium hydroxide (NaOH) (6 mole/ L).…”