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

摘要

Dairy wastewater can be concentrated by membrane technology to produce reusable water, and the retentate with high concentration could be reutilized as feed supplement for animals or substrate for biohydrogen production. Treatment of a model dairy wastewater (diluted skim milk) by nanofiltration (NF) with a rotating disk membrane (RDM) module was investigated using a NF membrane NF270 (Dow-Filmtec). Compared with the Desal-5 DK (Ge-Osmonics) membrane studied previously, the NF270 membrane gave much higher permeate flux, but same rejection. At a high enough shear rate for reducing concentration polarization, permeate flux and solutes rejection increased while specific energy per m~3 of permeate decreased when transmembrane pressure (TMP) rose from 10 to 40 bar. Because the RDM module could produce very high shear rates, concentration of dairy wastewater by NF could be operated under extreme hydraulic conditions that combined extreme TMP with high shear rate. Process efficiency and permeate quality were improved by operating under these condition, while membrane fouling was a little higher than when operating below critical flux. A real dairy wastewater was also treated by NF270 under same hydraulic conditions, and results were very similar to those of model solution. Membrane fouling was decreased by raising pH above 9. Irreversible fouling was almost removed using a commercial cleaning agent at high shear rate in a short time. The RDM module appeared to be a suitable technology to treat dairy waste without any biological and chemical treatments. Permeate qualities were suitable for reuse or discharge in river. These results from laboratory-scale tests can be very useful in the analysis of membrane process under extreme hydraulic conditions and can serve as valuable guide for process design in industrial application.