S caling control of RO membranes and direct treatment o f surface water

i ssues 2 and 3. F rom 1993 until 1997 the optimization of the a ntiscalant and acid dose to avoid scaling was i nvestigated. As shown in Fig. 3, the water q uality is such that scaling may affect the o peration of the RO units. From the beginning it w as evident that the feed water was already s upersaturated with BaSO4 by a factor of 1-2. E specially precipitation of CaCO3 and BaSO4 in t he concentrate will affect the operation as the m aximum solubility of these low soluble salts w ill be exceeded [1]. Two operation modes were s uccessful in preventing scaling problems. These a re summarized in Table 2. I n mode A sulfuric acid was dosed up to a L angelier saturation index (LSI) in a concentrate o f 2.0, and antiscalant (Flocon 100) was dosed i nto the RO feed water in a concentration of 2 mg/I. The RO unit could be operated with a r ecovery of 90% without any scaling problems e ven though the concentrate was supersaturated w ith BaSO4 by a factor of 75. In mode B h ydrochloric acid was dosed up to a LSI in the c oncentrate of 0.0 to avoid CaCO3 precipitation. S caling of BaSO4 was avoided by lowering the r ecovery to 85%. This reduced the Ba 2+ and SO~c oncentrations in the concentrate by a factor 2 as c ompared to mode A. Moreover, sulphate was r educed further by adding HCI. This resulted i n a decrease of the BaSO4 ion product from

• • 6. Inhibition duration time P arallel with the increasing recovery experim ent, the duration of the active antiscalant for i nhibition was investigated. For this the concent rate produced with increasing recoveries was d irectly passed through a 180m-long polye thylene tube (i.d. 10 mm) and sampling points e very 30m. The total residence time was l h. O ver the total length the barium mass balance w as analyzed. Over a period of 2 weeks no s caling was found with concentrate with 87% r ecovery. This means that with a recovery of • R eferences