The reason why residual proteins in the membrane did not
affect the permeate flux was probably due to the fact that the
amount of residual proteins was not high enough to block the
pores. Argüello et al. (2005) observed the same behavior using
enzymatic cleaning for membranes fouled with whey proteins.
They concluded that residual enzymes could lead to a self-cleaning
mechanism. Nevertheless, this phenomenon was also observed
with acidic cleaning (Paugam et al., 2013). On the contrary, this
phenomenon was not observed by the same authors with NaOH
using skim milk as foulant.
It is important to remark that quantification results from PierceBCA
method were lower than results from FTIR–ATR analysis. This
could be attributed to the fact that methods are completely different
and experimental errors in the calibration line (FTIR–ATR,
R2 = 0.97) due to accuracy in the weight of the membrane pieces
with very low protein amount. However, both methods showed
similar results in terms of percentage of BSA removal with the
cleaning solutions. Thus, it can be concluded that both methods
can be valid from a qualitative point of view for determining the
efficiency of the cleaning solutions.
Taking into account the results showed in Table 6, it can be
observed that the cleaning with Ultrasil was the most efficient.
The cleaning with NaOH for UH030 membrane led to protein
removal efficiencies of 42.7% and 37.34% for FTIR and Pierce-BCA
methods, respectively. For UP005 the values were 10.05% and
12.06% for FTIR and Pierce-BCA methods, respectively.