Application of NF-RDM (nanofiltration rotating disk membrane) module under extreme hydraulic conditions for the treatment of dairy wastewater.

Nanofiltration using a rotating disk membrane (RDM) module was investigated as a method for the concentration of dairies waste waters. Filtration of diluted skim milk (a model dairy waste water) was performed using the module and the NF270 membrane (Dow-Filmtec), and results compared favourably with those obtained previously using the Desal-5 DK (Ge-Osmonics) membrane for filtration: membrane rejection was the same; however, the NF270 membrane achieved a much higher flux. When filtration was performed at a shear rate sufficient to reduce concentration polarization the filtration rate increased and the specific energy per m3 of permeate decreased with an increase in transmembrane pressure from 10 to 40 bar. These conditions of high shear and high transmembrane pressure that could be achieved with the RDM module improved efficiency of the waste water concentration as well as permeate quality, while a slight increase in membrane fouling occurred compared with that obtained following operation below critical flux. Concentration of a real dairy waste water was achieved using the system tested under identical hydraulic conditions, and results obtained were similar to those produced using the skim milk model waste water. Increasing the pH value to >9 was found to reduce membrane fouling. Treatment of the module with a commercial sanitizer under a high shear rate allowed almost complete removal of irreversible fouling with a short treatment time. The resultant permeate from the waste water nanofiltration was of sufficient quality to allow its reuse or disposal in a river. It is suggested that these results may assist in the design of industrial nanofiltration systems.