Post-treatment of submerged membrane bioreactor effluent by coagulation/flocculation: color, organic matter, and phosphorus removal

ABSTRACT

Submerged Membrane Bioreactors (SMBRs) produce high-quality effluents, however, for some situations of water reuse or discharge into water bodies, additional colloids and phosphorus removal may still be necessary. In this study, the removal efficiency of true color, organic matter, and total phosphorus of a treated sewage effluent by MBR process, that treated domestic sewage from the student housing and restaurant of the University of São Paulo, was evaluated through physical-chemical method (coagulation/flocculation). In all tests, an efficiency between 17 and 35% was observed for true color removal, with lower removal in the flocculant presence. However, there was no organic matter removal, measured as dissolved organic carbon (DOC), suggesting that the low concentration of particulate matter in the MBR permeate and the applied dosages used did not allow the formation of flocs capable of removing such compounds. Phosphorus removal was higher than 90% in all trials, resulting in an effluent with residual concentration between 0.2 and 0.4 mgP.L^-1, even with the lowest coagulant metal molar ratio per phosphorus concentration. The results indicate that coagulant application in the MBR system effluent requires significantly lower dosages, up to three times, than the direct application in mixed liquor (suspended biomass in the aerobic tank), being, therefore, an attractive strategy to reduce costs related to the use of coagulants for phosphorus and color removal.

Keywords:
color removal; membrane bioreactor; organic matter removal; phosphorus removal