Membrane fouling biological

Fig. 23. Visualization of membrane fouling by scanning electron microscopy (A) inorganic fouling dne to calcinm carbonate, calcium sulfate, silica, iron, barium and strontium sulfate (35,000x) (B) organic fonling dne to humic acid (35,000x) (C) flow channels in membrane fouled with biological growth.

In order to have a better understanding of membrane fouling, UV spectrophotometry can be useful. Figure 23 presents the UV spectra evolution of a secondary effluent, from a biological treatment plant, before and after microfiltration. The decrease of the flux is due to membrane fouling. The stabilised flux is obtained after about 60 min of filtration. 

Surface alteration of the membrane to reduce the likelihood of dqrosition and adhesion by biologically treating membranes has been used [Hall and Protheroe, 1991]. In microfiltration the nature of the membrane has less significance than in ultrafiltration, however, the flux decay and membrane fouling may be due to q>edes other than the major constituent of the process fluid. Under these circumstances the membrane chemistry may be significant even in microfiltration. 

Treatments of landfill leachate in a two-stage RO system with biological pre-treatment have been also proposed (Linde et al., 1995). In this case tubular membranes were used in the first step to reduce membrane fouling of RO spiral wound membranes used in the second stage. An improvement of this process can be obtained by replacing the RO unit in the first stage by a NF unit with a consequent decrease in operating costs (Peters, 1998). 

The reasons for fouling of RO membrane are reported as consisting of chemical fouling, biological fouling, and scale precipitation. 

One of the standard FilmTec products (FT-30) is based on the interfacial polymerization of m-phenylenediamine chain extended and cross-linked with trimesoyl chloride. Sulfonated polysulfone and sulfonated poly(ether sulfone) have also been utilized, as they offer the advantage of chlorine resistance (which is desirable, as chlorine is often employed to remove biological deposits causing membrane fouling). Newer versions of sulfonated polysulfones demonstrating excellent chlorine resistance have recently been reported in the literature. Reverse osmosis is also relevant for organic mixture separations, of which a few have been commercialized such as solvent recovery from lube oil. ... 

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