Water. Desalination + reuse
Issue link: https://fhpublishing.uberflip.com/i/107143
TECHNOLOGY FI start of operation, the frequency of cleaning could be reduced to one-third. The use of IK-110 is considered to be an effective way to suppress adhesion of microbes to the membrane surface and of breaking away any adhering microbes and their metabolic products. FI 4 inch RO membrane P CF HPP FI Fig 1. Flow scheme for test unit Pump Cartridge filter High pressure pump Flow indicator Table 1. RO permeability test data Feed Chemical Feed pH Permeate Recovery Dosage conc. Combined Free chlorine Combined Free chlorine ratio % (mg/L) chlorine (mg/L) (mg/L) chlorine (mg/L) (mg/L) 12% sodium 5 29 25 2.3 2.3 2.6 2.6 hypchlorine 7.8 31 25 2.3 2.3 3.3 3.3 8.8 39 25 1.6 1.6 2.6 2.6 7.5 30 20 1.68 ND ND Kurivert IK-110 ND ND: below limit of detection Table 2. Conditions at seawater desalination RO plant 1 Category Power plant 2 Intended use of product water Feedwater to boiler 3 Type of feedwater Seawater of Bo Hai Bay 4 Feedwater flow rate 250 m3/h × 3 units 5 Type of membrane Dow AW30HRLZ-400 PA membrane 6 Recovery ratio 40% 7 Bank composition 2nd bank composition 8 No of 1st bank lines 4 lines 9 No of 1st bank vessels 30 vessels/line 10 No of membranes contained 7 membranes/vessel Before application of IK-110, flux had dropped to 60 m3/h in one month because of biofouling. Accordingly, cleaning was done every two months. In this test, IK-110 was added to the feed water line immediately prior to RO. Table 2 shows the conditions for this plant. FLOw OF RO pLaNT The flow of the RO plant operation is shown in Figure 2. REsuLTs OF appLiCaTiON OF iK-110 Permeate flow As shown in Fig 3, the flow in the Blank line (without any biocide before the RO membrane) dropped to 60 m3/h on the 35th day and was therefore cleaned. However, a flow level of 95 m3/h was maintained by the 35th day in the case of the line to which IK-110 was added. On the other hand, the Blank line had to be cleaned twice, on the 35th and 58th days. This was because of a drop in the permeate flow. The line to which IK-110 was added could be operated continuously without cleaning for 80 days or more. Therefore, it was confirmed that cleaning frequency could be reduced to one-third by adding IK-110. As is evident from the above results, the use of IK-110 enabled maintenance of a permeate flow that was twice as high as the case of the line without the addition of IK-110. Also, within two months after the Figure 2. Plant flow Seawater (1) NaCIO (2) PAC Mixing tank Filter (coarse) Flux As shown in Fig 4 and similarly to the case of the permeate flow, the flux dropped from 0.28 m/d to 0.18 m/d within 35 days for the Blank line, but flux was maintained at 0.30 m/d, the level at the start of operation, 35 days after the start in the case of the line with IK-110 added. Filter (fine) | 38 | Desalination & Water Reuse | August-September 2012 CF (3) NaHSO3 (4) Kuriverter N-500 (5) IK-110 RO MBP Differential pressure Fig 5 shows changes in differential pressure. Differential pressure increased gradually in both lines with IK-110 added and in the Blank line. No remarkable difference could be observed in differential pressure during a 35-day period between the two lines. Note however that the Blank line suffered a decrease in differential pressure as cleaning was done on the 35th day due to a decrease in flux. This cleaning caused recovery of the differential pressure to the initial value, but not recovery of flux. The probable cause could be failure to remove materials (microbes' metabolic products, such as glycoproteins several tenthousands in molecular weight) adhering to the membrane surface, even though materials adhering to the flow channel were removed. In other words, the cleaning proved to be insufficient. Recovery rate As shown in Fig 6, the recovery ratio decreased to 30% in 35 days for the Blank line and was maintained at the planned value of 40% in the case of the line with IK-110 added. As described above, compared with the Blank line, the line to which IK-110 was added could maintain a high recovery ratio while maintaining high flux. In other words, in spite of high load conditions caused by addition of IK-110, adding IK-110 suppressed adhesion of slime and helped to maintain flux. Water quality As shown in Table 3, an analysis of RO feedwater quality proved that, judging from Ca, Fe, Al, and other scale components, scales were not among the factors responsible for membrane fouling. In addition, 22 items subject to quality analysis were almost constant, meaning that the