Prevention of M-A-P-fouling using DLC in a sewage treatment plant

Abstract

This research deals with applications for coatings with amorphous carbon films, also called DLC (Diamond-Like Carbon) in the wastewater sector for the prevention of fouling with M-A-P (magnesium ammonium phosphate, MgNH4PO4, struvite). In a major sewage treatment plant a 300 mm long DN100 pipe was installed, which was coated inside with a-C:H:Si (hydrogenated amorphous carbon coating doped with silicon) coating of 5-10 µm thickness using a PACVD-reactor at the Wels Campus of University of Applied Science Upper Austria. The reactor technology comes from the company Rübig, Wels, Austria. The test campaigns (1 month, 5 months) showed in both cases heavy M-A-P fouling with uncoated test-tubes made of stainless steel (1,5 mm, 15 mm). In contrast DLC-coated tubes had no contamination at all. Further there is an economic discussion about using DLC-type coatings inside pipe-stocks which showed the need for further scale-up. The possible next steps of research and testing are in the field of DLC-coating in cavities, the loading capacity of reactors and the development of suitable plant technology to process longer pipe pieces. Of major interest is the development of a suitable welding technology, which would allow for the production of DLC-coated high pressure lines for up to 450 °C operating temperature.