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

This long-term investigation provides a step-wise optimization of a pilot-scale continuous flow reactor (CFR, total volume similar to 200 L) using aerobic granular sludge (AGS) to treat municipal wastewater (MW) at temperatures of 18.2 +/- 1.8 degrees 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 mu m in diameter and sludge volume indexes of similar to 40 mL.g(-1). Following a start-up and optimization period of 187 days, the system was stably operated with similar to 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).

Automated summary

This long-term investigation presents the optimization of a pilot-scale continuous flow reactor using aerobic granular sludge to treat municipal wastewater. The reactor achieved complete granulation and stable operation with high MLSS concentration and efficient NH4+-N removal. The study provides insights into the effect of operating parameters on the performance of the reactor.