The topic:   Troubleshooting, municipal wastewater treatment by MBRs

The client:  UK water consultancy

The brief

This job entailed the assessment of the design and O&M details to try and overcome a challenge imposed by severe permeability decline following a CIP (clean-in-place) at a small (~2,000 m³/d capacity) plant in Scotland. Two site visits and a number of communications with the client revealed that the recirculation rate through the membrane tank was too low for one of the plants, causing concentration polarisation problems, coupled with a strong clogging and ragging tendency. The ragging challenge was met by installing a rudimentary screen on the RAS. A second smaller plant (~400 m³/d capacity) was subject to severe fluctuations in water quality, demanding equalisation.

3 days

The cause of ragging generally was subsequently identified in a separate research project, the outcomes of which were published in the Journal of Membrane Science (Stefanski et al, 2011). This paper was the first research paper published which analysed and quantified ragging in MBRs, as well identifying the root cause.