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.