Treatment of Naval Ship Hull Cleaning Waste Residual by High-Shear Rotary Ultrafiltration

The effectiveness of the high-shear rotary ultrafiltration (HSRUF) system for concentrating sludge from ship waterborne underwater hull cleaning effluent processing operations was examined. The sludge was a mixture of material removed from the ship hull that did not settle in the primary settling chamber, and iron oxide solids. The sludge solids concentration was approximately 5%. Two membranes, a 0.1 um Ti-Al oxide membrane and a 3 um sintered metal membrane were tested. Each membrane had 1 ft2 of membrane area and was rotated at 1100 rpm. Temperature was not controlled but was monitored. Permeate flux, turbidity, temperature and pH were measured frequently. Samples of permeate and feed tank contents were taken at whole number values of the hydraulic concentration factor and at the end of each run. Samples were tested for turbidity and copper concentration (permeate), and solids concentration (feed tank). Both membranes were effective in concentrating the sludge - from about 5% to 32% for the 0.1 um membrane and from 5% to 42.5% for the 3 um membrane. The permeate flux for the 0.1 um membrane ranged from 59 gal/ft2 -d at 5% solids to 33 gal/ft2 -d at 32% solids. The permeate flux for the 3 um membrane ranged from 63 gal/ft2 -d at 5% solids to 235.8 gal/ft2 -d at 42.5% solids. For the 0.1 um membrane, pressure excursions were conducted at feed tank solids concentrations of 5% and 20%. For both concentrations, the flux versus transmembrane pressure relationship was linear. For the 3 um membrane the pressure excursion was conducted at a solids concentration of 10% and was also linear. Based on these data, it appears that system had not reached the pressure independent stage and higher fluxes could be realized with increases in transmembrane pressure. Permeate turbidities for both membranes were about 0.02 NTU and were not a function of temperature or feed concentration. The permeates were relatively clear and aqua blue in color. After sitting overnight, a greenish precipitate formed. It is hypothesized that the copper in the permeate either desorbed from the ferric hydroxide solids or was leached from paint particles under the elevated temperature and pressure conditions in the membrane chamber. The aqueous phase copper passed through the membrane with the permeate and when the temperature decreased to ambient levels Cu(OH)2(S) (or some other Cu solid) formed. In an actual system, the permeate from the HSRUF process would be returned to the head of the US Filter process and should not adversely affect the performance of the ACTIFLO.