Volatile fatty acid production and uptake in biological nutrient removal systems with process separation

Abstract

In this research, the relative rates of volatile fatty acid (VFA) production and VFA uptake were quantified through separation of fermentation step from the phosphorus‐accumulating bacteria (Bio‐P removal process). Furthermore, the effect of prefermentation of raw wastewater on Bio‐P removal was evaluated. Degritted raw wastewater was fermented under different conditions in bench‐scale anaerobic sequencing batch reactors called primary acid fermenters (PAFs). Specific rates of VFA production were measured under different solids retention times (4, 8, 12, and 13 days), two pH levels (natural pH of wastewater and pH of 6.1 to 6.4), two regimens of mixing (6 h/cycle versus 0.25 h/cycle), and hydraulic retention times of 9 and 12 hours. Experiments were conducted at room temperature (20 ± 2°C). Specific rate of VFA production ranged from 0.3 to 3.0 mg VFA/g VSS · h under investigated conditions while the volumetric rate of production varied from 4 to 54 mg VFA/L · d depending on the conditions of the reactors. The rate of VFA uptake was measured in a subsequent biological nutrient removal sequencing batch reactor fed with fermented wastewater. The rate was 28.5 mg VFA/g VSS · h. Phosphorus release was found to be 18.8 mg ortho‐P/g VSS · h (primary release) during the period of VFA uptake and 1.8 mg ortho‐P/g VSS · h (secondary release) when VFA were depleted in the environment. Bio‐P removal improved significantly as the result of prefermentation of degritted raw wastewater.

Mixed Liquor Fermentation and Other Alternatives for Providing VFA to EBPR Processes

“…During the experiments very little conversion of organic-P to PO 4 -P was observed, but significant conversion of organic-TKN occurred even at the 0.5 hour HRT. Danesh and Oleszkiewicz (1997) used an in-line SBR prefermenter to generate VFA for a pilot SBR system. Operation of the SBR prefermenter at a pH of 7 to 7.6 showed an increase in VFA production from 38 to 48 mg/L/day as the SRT increased from 4 to 13 days.…”

Comparative Evaluation of Longitudinal Dispersion of Liquid in Non-Biological and Anaerobic Fixed Film Reactors

“…At an HRT of 30 hours and 70% removal of BODs was achieved. Prefermentation of degritted raw wastewater significantly improved biophosphorus removal in benchscale ASBRs (Danesh andOleszkiewicz, 1997a and. The relative rates ofVFA production and uptake were quantified through separation of the fermentation step from the phosphorus-accumulating bacteria.…”

Acid Sludge Fermentation Products Vary with the Type of Sludge

“…Adequate supply of short-chain volatile fatty acids volatile fatty acids (VFA) is necessary for successful performance of the phosphorus accumulating organisms (PAO) (Chu et. al., 1994;Oleszkiewicz and Barnard, 2006;Danesh and Oleszkiewicz 1997). For low organic content (weak) wastewater, external carbon/ VFA addition is necessary to satisfy the demand for rbCOD and to meet increasingly more stringent effluent nutrient limits.…”