Three UF-systems were tested for the drinking water treatment of karstic spring water. The pilot plants were operated in Marmagen, which is located in North-Rhine Westfalia (Germany). One of the two tested capillary UF-systems (in-out mode) was backflushed with filtrate and with filtrate and hydrogen peroxide. The other one could be flushed with air and raw water (forward flush) before a backflush was performed. The third system was an immersed UF-system (out-in) where negative pressure on the filtrate side is applied. The capillary UF-systems were operated at high flux and long backflush intervals when turbidity was low. At high turbidities the permeability declined and could only be restored by chemical cleaning. For this particular water the immersed system showed also a permeability decline, which was less pronounced. The permeability recovered in normal operation, when the turbidity declined. Using SEM and EDX the fouling could be mainly attributed to small particles (well below 3 μm). Qualitative element analysis showed that silica is the main component of the formed cake layer.

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