Long-term monitoring reveals improvements in nitrogen removal and energy efficiency with MABR upgrade at full scale

Membrane aerated biofilm reactors (MABR) are emerging to be a popular alternative for intensifying wastewater treatment. However, the performance of the technology has not yet been investigated at full-scale where mixing conditions and biofilm thickness control strategies differ from those employed in smaller-scale MABRs. This study investigated the long-term performance of one of the largest MABR installations in North America and reported key performance metrics related to nitrogen removal, aeration tank operations, and electricity consumption. Upgrading of the plant from a conventional activated sludge to a hybrid MABR configuration improved nitrification from seasonal to year-round performance. Denitrification in the hybrid MABR doubled the total nitrogen removal in the plant from 30 to 40 % before upgrade to 70–80 % afterwards. Operation at reduced MABR airflow (4.5 NL m −2 h −1 ) resulted in lower nitrification rates due to insufficient biofilm thickness control that led to diffusional limitations. Temperature was found to impact nitrification in the MABR with a 22 % decrease in nitrification rate from 1.8 ± 0.2 g-N m −2 d −1 during warm weather to 1.4 ± 0.2 g-N m −2 d −1 during cold weather conditions. The hybrid MABR denitrification efficiency was not substantially impacted by ammonia loading, process airflow, or wastewater temperature. Operation at a higher biofilm scouring intensity increased the NH 4 -N removal efficiency in the aeration tank during cold weather conditions suggesting increased nitrifier seeding due to enhanced sloughing of biofilm into the suspended sludge. Aeration related electricity consumption decreased by 50 % after the upgrade due to the efficiency of oxygen supply by the MABR and the reduction of aeration requirements in the downstream aeration basin. Overall, the improved nitrogen removal under reduced electricity consumption at full scale demonstrated the potential of MABR as a process intensification technology. • Upgrading a CAS plant with a hybrid MABR improved the winter nitrification. • MABR process air that controlled biofilm thickness influenced nitrification rate. • MABR denitrification efficiency was >80 % and independent of operations. • Higher MABR air flow led to a greater extent of nitrification in aeration tank. • Aeration related electricity consumption reduced by half post MABR upgrade.