Differences in Aeration and Air Scour Energy Requirements between Membrane Bioreactors, Conventional Activated Sludge (CAS), Ifas and MBBR following Process Optimization

Hollow fiber membrane bioreactors (MBRs) were evaluated in full scale to study methods of reducing their aeration and air scour energy requirements. The changes were modeled to determine methods to optimize the aeration and air scour energy consumption and compare the total to the aeration energy requirements of conventional activated sludge (CAS), IFAS and MBBR systems. The research found that the aeration and air scour energy required for an MBR can be reduced to within 33% above conventional activated sludge (CAS) systems operating with 50 percent more volume (Aeration Optimized Mode, AOM). It can be reduced further to within 20% with automated DO and ammonium-N monitoring and control in the aerobic zone and the membrane cell, or at facilities which can discharge effluent ammonium-N above 0.5 mg/L during some weeks (Aeration Constrained Mode, ACM). The optimization techniques included reduction of the DO set point in the main reactor to 1 mg/L for AOM and 0.5 mg/L for ACM; reduction in the air scour on time from 100% to 25%. The air scour air flow rate was controlled such that it was just above 18 mm/sec during the on time. The combination of these two changes reduced the DO levels in the membrane cell from greater than 6 mg/L to less than 4 mg/L. The energy requirements for MBRs were then compared to other compact solutions such as IFAS and MBBRs. In the MLE process configuration and ACM, the MBR consumed 4 to 7% more aeration and air scour energy than IFAS and MBBR, respectively. In the Enhanced Nutrient Removal (ENR) mode, in which methanol is added to the post-anoxic cells to increase denitrification, the MBR consumed similar amounts compared to IFAS and MBBRs, with all processes achieving 4 mg/L Total Nitrogen (TN).