Comparison of different chemical cleaning reagents on fouling recovery in a Self-Forming dynamic membrane bioreactor (SFDMBR)

Self-forming dynamic membrane bioreactor (SFDMBR) using large pore size (> 5 mu m) membrane material is regarded as a cost-effective technology with less fouling and high permeate flux. However, no successful long-term operation without chemical cleaning is achieved. Therefore, an optimum chemical cleaning reagent needs to be explored with the understanding of foulants structure. This study compared the cleaning effects of three typical chemical cleaning reagents, i.e. sodium hydroxide (NaOH), sodium hypochlorite (NaClO), and sodium dodecyl sulfate (SDS), using a lab-scale SFDMBR. NaClO is identified as the most effective cleaning reagent in view of its trans-membrane pressure (TMP) reduction and permeability recovery efficiency. NaClO could achieve 99.0% of permeability recovery and full TMP reduction, while NaOH and SDS could only recover 87.7% and 76.5% of initial permeability and showed limited efficiency in TMP reduction, although all three reagents can achieve over 70% of extracellular polymeric substances (EPSs). The major foulant of the SFDMBR was a complex mixture of sludge flocs with EPS. NaClO cleaning can largely remove the flocs and EPS by oxidization effects while NaOH and SDS were only effective in EPS removal, which explained why NaClO cleaning showed the best performance. beta-polysaccharide attached on the mesh fibers and acted as the binding substance between the foulants and mesh fibers is the main reason for irremovable inner pore fouling, which only could be significantly removed with NaClO cleaning. These results well explain the difference of filtration performance after three types of chemical cleaning.