Acetate injection into anaerobic settled sludge for biological P-removal in an intermittently aerated reactor

Abstract

Injecting acetate into the sludge layer during the settling and decanting periods was adopted to enhance phosphorus release inside the sludge layer during those periods and phosphorus uptake during the subsequent aeration period in a KIST Intermittently Decanted Extended Aeration (KIDEA) process. The relationship among nitrification, denitrification and phosphorus removal was investigated in detail and analyzed with a qualitative floc model. Dependencies of nitrification on the maximum DO level during the aerobic phase and phosphorus release on residual nitrate concentration during the settling phase were significant. High degree of nitrification resulted that phosphorus release inside the sludge layer was significantly interfered with nitrate due to the limitation of available acetate and the carbon sources from influent. Such limitation was related to the primary utilization of organic substance for denitrification in the outer layer of the floc and the retarded mass transfer into the inner layer of the floc. Nevertheless, effects of acetate injection on both denitrification and phosphorus release during the settling phase were significant. Denitrification rate after acetate injection was two times as high as that before acetate injection, and phosphorus release reached about 14 mg PO4(3-)-P/g MLVSS/hr during the decanting phase after the termination of denitrification inside the sludge layer. Extremely low level of maximum DO (around 0.5 mg/L) during the aerobic phase may inhibited nitrification, considerably, and thus nearly no nitrate was present. However, the absence of nitrate increased when the phosphorus release rate was reached up to 33 mg PO4(3-)-P/g MLVSS/hr during the settling and decanting phase, and nearly all phosphorus was taken up during subsequent aerobic phase. Since the sludge layer could function as a blocking layer, phosphorus concentrations in the supernatant was not influenced by the released phosphorus inside the sludge layer during the settling and decanting period. Phosphorus removal was directly (for uptake) and indirectly (for release) dependent on the median and maximum DO concentration during the aerobic phase, and those optimal values may exist within the range from 0.2 to 0.6 mg/L and 0.4 to 1.2 mg/L, respectively.

ORGANIC CARBON SUPPLEMENTATION OF STERILIZED MUNICIPAL WASTEWATER IS ESSENTIAL FOR HETEROTROPHIC GROWTH AND REMOVING AMMONIUM BY THE MICROALGA CHLORELLA VULGARIS1

“…Wastewater plants employing an EBPR scheme used carbon supplements, mainly acetate, as part of the process of removing phosphate (Lemos et al. 1998, Ahn et al. 2001).…”

Nitrous oxide emissions and dissolved oxygen profiling in a full-scale nitrifying activated sludge treatment plant

“…These dynamic DO levels can create "micro-sites" within the same process, with oxygen availability changing considerably within the lane. This in turn can have a profound effect on the oxygen transfer from the liquid phase into the sludge floc (Ahn et al, 2001;Zeng et al, 2003;Hu et al, 2011). Under oxygen-limiting conditions, an outer aerobic region may be created within the floc, which benefits from an immediate interface with the bulk DO, where nitrification is most likely to take place (Hu et al, 2011).…”

“…Under oxygen-limiting conditions, an outer aerobic region may be created within the floc, which benefits from an immediate interface with the bulk DO, where nitrification is most likely to take place (Hu et al, 2011). An inner floc region is also created, where anoxic conditions prevail, allowing heterotrophic microorganisms to denitrify (Ahn et al, 2001;Zeng et al, 2003). Hu et al (2011) observed that an aerobiceanoxic interface was created within the floc, where N 2 O was mainly produced.…”