BIOLOGICAL COATING OF FINE BUBBLE DIFFUSERS WITH EPDM-MEMBRANES
Biological coatings on EPDM-membranes are a problem on many wastewater treatment plants in Europe, as the oxygen supply of the micro-organisms is no longer guaranteed. Studies prove that the pressure loss and the Shore A-hardness of the EPDM-membranes increase while on the other hand
their softener content decreases accordingly. The detected coatings on the membrane surfaces and in the slits or holes of the membranes show extracellular organic substances (EPS), which, compared with fibrillar/filamented EPS usually found on surfaces in wastewater treatment plants, are
viscous to a much greater extent. As, besides primary organic parts (carbon), the coatings on the membranes as well as in the slits or holes also consist of inorganic constituents (magnesium, silicium, and others), the authors assume that, the separating agent (and also inactive filler) talcum
(magnesium silicate), used when producing the membranes, support at least a first beginning of the coating. Superfine dust constituents and fibres, input via the compressed air, will build up inside the coating and consequently lead to a gradual clogging of the holes or slits. Besides chemical
cleaning measures, the exchange of the EPDM-membranes against membranes of silicone would also be a possible measure to solve this problem. The market will decide, if, in the future, a cleaning or an exchange of the EPDM-membranes against membranes of silicone will be applied, but it has to
be considered that the loss of softener is irreversible.
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