Simultaneous biological nutrients removal from wastewater with high ammonium and phosphorus loading using aerobic granular sludge

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.