Physical cleaning initiation controlled by transmembrane pressure set-point in a submerged membrane bioreactor

The application of physical cleaning methods such as backflushing or relaxation is an essential part of the operation mode in submerged membrane bioreactors (SMBRs) applied to wastewater treatment. However, the strategy usually applied for pre-set fixed value of the cleaning frequency involves a loss of water production. This paper deals with the validity of a control system for cleaning initiation by monitoring transmembrane pressure using both physical cleaning methods. To evaluate the effect of the key operational parameter (transmembrane pressure set-point, TMPsp) on membrane fouling and process productivity, sludge samples from a pilot-scale SMBR were filtered under different filtrate flux values (J = 20–40 l h−1 m−2) in bench filtration unit. From this study, it was found that this system automatically adjusts the cleaning frequency as a function of the membrane fouling which results in an increase in the net permeate produced. Cleaning efficiency, described in terms of residual fouling resistance, and the cake fouling rate can be significantly affected by the value of TMPsp selected and the cleaning method performed. A maximal net permeate flux can be achieved when backflushing is used, a filtrate flux above the threshold value of 30 l h−1 m−2 is imposed and intermediate TMPsp values are applied.

► Applicability of a control system for physical cleaning initiation in a MBR.
► Effect of the TMP set-point for backflushing and relaxation on process productivity.
► Determination of residual fouling resistance, cake fouling rate and net permeate flux.