Compact pilot-scale aerobic granular sludge system treating real wastewater continuously for over 500 days

Abstract

This long-term investigation provides a step-wise optimization of a pilot-scale continuous flow reactor (CFR, total volume ∼ 200 L) using aerobic granular sludge (AGS) to treat municipal wastewater (MW) at temperatures of 18.2 ± 1.8 °C and with organic loading rates of 1.39 ± 0.89 kg COD·m−3·d−1. Short settling times of about 10 min which led to a high selection pressure allowed for a complete granulation after day 47 — i.e., >80 % of the mixed liquor suspended solids (MLSS) larger than 200 μm in diameter and sludge volume indexes of ∼40 mL·g−1. Following a start-up and optimization period of 187 days, the system was stably operated with ∼6.1 g MLSS·L−1 over one year. The best-performance was achieved with an aerobic/anaerobic volume ratio of 2/1 and intermittent aeration. Furthermore, for most of the time a NH4+-N removal of 99 % was possible with low oxygen concentrations (2.0 to 2.5 mg·L−1), and despite the high‑nitrogen ratios of CODt:TN:TP (100:15:1.7).