Nitrogen and phosphorus removal in an anaerobic (UASB)-aerobic (ABF) sewage treatment system

Anaerobic sewage treatment process using upflow anaerobic sludge blanket (UASB) coupled with aerated biofilter (ABF) was tested for the removal of nitrogen and phosphorus by recycling the final effluent and by adding alum to the influent. TCOD Removal efficiency was about 60% in UASB without recycling of the ABF effluent, while it increased to 90% at recycling ratio of 3. Complete denitrification had occurred in the UASB, and removal efficiencies of both total nitrogen (TN) and [GRAPHICS] -N were also improved to 74 and 96%, respectively, by recycling the nitrified ABF effluent. Total phosphorus (TP) removal was not improved by recycling of the ABF effluent. TP and soluble phosphorus were effectively removed in UASB by adding alum to the influent. 90% removal of TP was possible with alum dose at Al/P mole ratio of 2.6. In the final effluent, concentrations of TCOD, TN, and TP were below 14.0, 7.0, and 0.27mg/L, respectively, in the UASB-ABF sewage treatment system at recycling ratio of 3 with alum.