It has been well known that ozonation of mixed liquor can increase the average particle size due to the unproportional destruction of small particles. It is perhaps because the highly active ozone reacts with any organic substances on its way while the small particles have larger surface to volume ratio that provide better chance to contact with the radicals produced by ozone. Therefore, partial ozonation of mixed liquor in MBR potentially reduces membrane fouling potential.
Using the experimental setup shown in Fig.1, where two MBR systems were run with and without ozonation, side-by-side comparisons were performed (Hwang, 2010a; Hwang, 2010b). A venturi injector called turbulent jet flow ozone contactor (TJC) was used to enhance the ozone reaction with sludge. The cavitation in the venturi injector did not affect sludge reduction significantly when the venturi was operated without ozone.
Following are the summary of the findings.
- While the total extracellular polymeric substances (ECP) remained relatively unchanged, loosely bound extracellular polymeric substances (LB-ECP) defined in a literature (Li, 2007) were significantly reduced with ozonation.
- Average zeta potential of particles increased from -20 mV (control MBR) to -8 mV (TJC-MBR). One interesting finding was the ozonated sludge had a positive zeta potential (+12mV). When this disintegrated sludge was recycled to the membrane tank of TJC-MBR, particle size grew perhaps due to the particle aggregations induced by charge interaction.
- Particle size also grew from 167 micron to 213 micron on average (Fig. 2).
- The membrane fouling rate measured by TMP increasing rate was lower in TJC-MBR with ozonation (Fig. 3).
Fig. 1. Experimental setup of two MBR with and without turbulent jet flow ozone contactor (TJC) (Hwang, 2010b)
Fig. 2. Comparison of particle sizes with and without ozone (Hwang, 2010a)
Fig. 3. Effect of ozonation on membrane fouling (Hwang, 2010b)
© Seong Hoon Yoon