Fig. 5 shows the CE including the effect of US application comparing
the US application submerging the membrane module
inside the US bath and applying US to the cleaning solution for
UH030, UP005, Inside Céram 50 kDa and Inside Céram 15 kDa
membrane. In general terms, for all the membranes, for tests 1, 2
and 4 (for organic membranes) and 5, 6 and 8 (for inorganic membranes),
no significant differences were observed with the exception
of tests number 1 and 5, in which US application
submerging the membrane module does seem to be more effective
than applying US to the cleaning solution (excepting for membrane
Inside Céram 15 kDa). Tests number 1 and 5 was carried out with
Renylat 45 solution. As previously commented, inorganic agents
(as calcium cation) had influence on the membrane fouling. US
application to the cleaning solution was less effective than submerging
the membrane module in the US bath for removing calcium
cations remaining on the membrane surface since the
generated microbubbles remove more easily organic molecules
(weekly bond to the membrane surface) than inorganic ones as calcium
cations that drive to stronger interactions between proteins
and membranes because of the bridges formed between them, as
described in Section 3.1. Similarly, Chen et al. [35] applied US to
the cleaning of UF membranes fouled by natural organic matter
and silica particles and they concluded that the presence of calcium
cation increases fouling and reduces the effect of US on the
CE.