NaClO-assisted maintenance cleaning for fouling control in membrane bioreactors

A novel in situ chemical backflushing method, utilising NaClO (sodium hypochlorite) as the principal reagent, has been developed by Chinese researchers to control fouling in membrane bioreactors (MBRs).

The results demonstrate that, compared with a control MBR with water backflushing, the use of low NaClO loads has few adverse effects on nutrient removal. On the contrary, the exposure to NaClO enhanced the denitrification performance of the MBR as a result of the formation of sludge granules.

Measurements of transmembrane pressure (TMP) showed that an NaClO backflush at 0.2 ppm could achieve effective membrane fouling control in MBRs. Ex situ backflush tests showed that an NaClO backflush enhanced the detachment of biopolymers from the fouled membranes compared with a water backflush.

Comparative 16S rRNA sequencing showed differing bacterial community composition in the fouling layers of the two MBRs. Specifically, the NaClO backflush could suppress filament-caused membrane fouling, i.e. it lowered the abundance of Thiothrix eikelboomii in the fouling layers.

Both the water and NaClO backflushing resulted in significant increases in the pure water permeability of the membranes as a result of enlarging the membrane pores.

The results of Fourier transform infrared spectroscopy (FTIR) indicate that frequent NaClO backflushing does not significantly change the functional groups of the active layer of the membranes.

Water Research, Volume 53, 15 April 2014, Pages 1–11.