Effect of organic shock loading on membrane fouling without DO control

Using the experimental setup shown in Fig. 1, impact of high organic loading on membrane fouling was investigated. As summarized in Table 1, steady steady condition was developed for about two months to obtain baseline data. During the shock organic loading tests, F/M ratio was quadrupled to 1.04 g COD/g VSS/d by adding molasses solution to the feed. As a consequence of the shock organic loading, aeration system could not keep up with oxygen demand and as a consequence dissolved oxygen dropped to 0.2 mg/L as shown in Fig. 2. After the 8 hour duration of the shock organic loading, DO slowly increased, but it took 20-40 hours until it was recovered to the original 3 mg/L.

   During the organic peaking event for 8 hours, TMP jumped from 13 kPa to 21 kPa. More importantly, the TMP was not recovered fully after the organic peaking event was over. It was found that SMP level increased significantly during the event as shown in Fig. 3 and it is believed that the SMP caused irreversible fouling.

   Although this experiment revealed a possibility of accelerated membrane fouling at high F/M ratio, it is not clear whether the similar irreversible membrane fouling occurs, if DO was maintained at a sufficient level, e.g. 1-2 mg/L. As discussed here, DO is one of the critical parameters that affect membrane fouling.

Shocki10 (1)aaaFig. 1. Experimental setup (Syed, 2009).

                         Table 1. Experimental condition of organic shock loading tests  (Syed, 2009)             

Parameters Unit Steady state Organic peaking condition
F/M ratio gCOD/gVSS/d 0.26 1.04
DO mg/L 2 0.20-3.0
SRT days 15
HRT hours 8 8
MLSS g/L 10±0.5
Test duration hours ~1,400 8

Shocki15Fig. 2. Organic shock loading effect on MLSS, pH, and DO.

Shocki16Fig. 3. Effect of organic peaking on soluble microbial products (SMP)

 

© Seong Hoon Yoon