VOLATILE FATTY-ACID PRODUCTION AND UPTAKE IN BIOLOGICAL NUTRIENT REMOVAL SYSTEMS WITH PROCESS SEPARATION

In this research, the relative rates of volatile fatty acid (VFA) prod uction and VFA uptake were quantified through separation of fermentati on step from the phosphorus-accumulating bacteria (Bio-P removal proce ss). Furthermore, the effect of prefermentation of raw wastewater on B io-P removal was evaluated. Degritted raw wastewater was fermented und er different conditions in bench-scale anaerobic sequencing batch reac tors called primary acid fermenters (PAFs). Specific rates of VFA prod uction 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 t o 6.4), two regimens of mixing (6 h/cycle versus 0.25 h/cycle), and hy draulic retention times of 9 and 12 hours. Experiments were conducted at room temperature (20 +/- 2 degrees C). Specific rate of VFA product ion ranged from 0.3 to 3.0 mg VFA/g VSS . h under investigated conditi ons 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 up take was measured in a subsequent biological nutrient removal sequenci ng batch reactor fed with fermented wastewater. The rate was 28.5 mg V FA/g VSS . h. Phosphorus release was found to be 18.5 mg ortho-P/g VSS . h (primary release) during the period of VFA uptake and 1.8 mg orth o-P/g VSS . h (secondary release) when VFA were depleted in the enviro nment. Bio-P removal improved significantly as the result of prefermen tation of degritted raw wastewater.