Supercritical oxidation of Water work sludge From Ringsjöverket
This paper presents how super critical water oxidation (SCWO) performs on the iron rich sludge from the drinking water treatment plant Ringsjöverket. The pilot-test shows that the SCWO-technique is capable of treating the sludge from Ringsjöverket. During the pilot- test all organic material were oxidized while the rest precipitated as ferric oxide crystals. Chromium and nickel in elevated concentrations were found in the ferric oxide. The nickel probably comes from corrosion of the pilot plant while most of the chromium probably comes from the raw water and pilot plant. Problems with scaling also occurred during the pilot-tests. These problems may be smaller in a full-scale plant solely constructed for treating sludge from Ringsjöverket.
The annual cost for a full scale SCWO-plant was estimated to be approximately 4.9 million SEK which include a saving of 1.3 M SEK in heating costs due to the surplus of energy produced by the process. The annual cost can be lowered with about 1 M SEK if the iron oxide can be reused for producing a new coagulant. If the iron oxide can be sold as a pigment the savings might be even greater.