Simultaneous biological nutrients removal from wastewater with high ammonium and phosphorus loading using aerobic granular sludge
Elsayed Mady, Jan A. Oleszkiewicz, Qiuyan Yuan
Abstract
In this study, two SBRs were inoculated with biomass from a flocculant biological nutrient removal facility and operated for the biological treatment of synthetic wastewater to explore the impact of low influent COD/TN/TP ratio on the start-up, performance, and development of stable, matured AGS. AGS maturation and simultaneous nutrient removals were investigated for 422 days under applying limited DO (1.5–2.0 mg L−1); after that, an optimization period was performed till day 558 to study the influence of applying high DO levels (5.0–8.5 mg L−1). Initial observations at day 118 indicated high settling velocities for granules with a size ≥1.5 mm, with 90 % COD removal achieved since day 35, while exhibiting moderate levels of ammonium (68–71 %) and phosphorus removal (42–44 %). By day 422, the maturation of granules continued, reaching sizes exceeding 3 mm, with a 70 % increase in biomass growth (14.3 g L−1). P-release and P-uptake rates of 52 and 12 mg-P/g-MLVSS·h, respectively, resulted in reduced effluent PO4−3-P (1.5 ± 0.2 mg-P L−1). TN removal performance reached 82 % (NH4-N removal of 88 %), and SND of 99 % was achieved by matured granules maintaining effluent nitrite/nitrate concentrations ≤0.5 ± 0.3 mg-N L−1 (days 330–422). The optimization period was conducted by enhancing biomass mixing conditions and increasing DO, resulting in improved nitrification, with oxidation rate reaching 19.2 mg-NH4/g-MLVSS·h at DO 6 mg L−1. However, DO > 6.5 mg L−1 adversely affected EPS secretion, and granules exhibited poor settleability.