Phosphorus fractionation in membrane-assisted biological nutrient removal processes

A comparison between a patented novel membrane bioreactor (NMBR) and conventional University of Cape Town adapted MBR (UMBR) was conducted using two different municipal wastewaters at a total bioreactor hydraulic retention time of 6 h and sludge retention time of 10 d. Total nitrogen removal efficiencies were 73–80% and 70–77% for the NMBR and UMBR, respectively, with 1–1.7 mg L−1 lower effluent nitrates in the NMBR. The average effluent P in the NMBR and UMBR were 0.5 and 0.8 mg L−1, respectively. P uptake by denitrifying phosphate accumulating organisms (DPAO) accounted for 37–40% of the total uptake in both systems and DPAOs were 40% of PAO. Sludge P fractionation substantiated that poly-P content increased from 27–37% to 57–59% of the total phosphorus, with P increasing from around 3% to 6% by weight upon the supplementation of the wastewater volatile fatty acids.