HOMETechnologyPreparing for the futureExpertise
Membrane filtration for Water Supply
1. Introduction of Membrane Filtration Technology for Water Treatment
- The use of microfiltration(MF) and ultrafiltration(UF) for the production of drinking water has arisen within the last 20 years and these technologies recently have become more popular in drinking water treatment. Thus, to improve water qualities, the government of South Korea is actively trying to introduce membrane system in drinking water treatment plant(WTP).
- K-water has developed a model project for application of membrane system to large scale WTP since 2002. Demonstrative application was tested at two plants: one at the 300 ㎥/day scale in Ji-Rye waterworks as an example of small scale waterworks(2002~2005), and the other at the 3,600 ㎥/day scale in Siheung water treatment plant as an example of middle scale water treatment plant(2004~2008).
- Finally, K-water has adopted large scale membrane filtration WTP of 30,000 ㎥/day capacity in 2009 at Gonju. The water produced in Gongju WTP has been suppling to Gongju citizens from July 1, 2009. And also, the design for introducing the ceramic membrane system of 16,000 ㎥/day was completed for retrofitting Yeoncho conventional WTP in Sep. 2009. This WTP will be built by December 2011.
2. Gongju Membrane Filtration Water Treatment Plant
- Initially, Gongju WTP was designed as conventional water treatment plant including powdered activated carbon contactor, coagulation and flocculation, sedimentation and rapid sand filtration. However, the membrane process was introduced as a strategic to improve water technology and development of domestic water industry according to the global trend in 2004.
- Sedimentation and sand filtration processes were replaced by microfiltation membrane process as fallows. Thus, Gongju WTP became the first large scale membrane filtration WTP in South Korea.
- Design Change of Gongju WTP
- Schematic diagram of Gongju membrane WTP
- Bird's-eye-view of Gongju membrane WTP
- The pilot study has been conducted from 2005 to 2009 in order to determine design parameters and to develop the optimal operation technology for Gongju membrane process in Hyeondo intake facility.
- Gongju membrane facility consists 4 trains having 6 units in each train. As one unit has 20 membrane modules, total 480 modules of microfiltration membrane with the nominal pore size of 0.05 ㎛, manufactured by Toray were installed in Gongju WTP.
Memberane spec List
|Type of membrane
||Microfiltration(Hallow fiber pressurized membrane), Toray
||L2, 160㎜, OD216㎜, 72㎡
|No. of module
||480 modules(4 trains, 6 units/train, 20 modules/unit)
- Membrane Speculations in Gongju WTP
- The design filtration velocity and recovery rate were 0.95 ㎥/㎡·day and 95%, respectively. Backwash is performed every 30 minutes for 30 seconds by membrane filtrate containing 5~10 mg/L NaOCl at the flow rate of 1.5 times of filtration flux. Air flushing with 0.1~0.2 N㎥/min/module was performed simultaneously with backwash. Before filtration, there is a water flushing step with raw water for 50 seconds. To check defect of membrane, pressure decay test(PDT) is performed once a day as integrity test.
- Gongju membrane facility is currently operating reliably at 0.98 ㎥/㎡·day and 94.6% of recovery rate and the turbidity of filtrate meets water quality standard of 0.05 NTU.
3. Yeoncho Membrane Hybrid Water Treatment Plant
- Yeoncho water treatment plant(WTP) which was built in 1979 was temporarily suspended operations since September 2004. The raw water quality of this plant was relatively high concentration of organic materials, iron and manganese. Also, taste and odor problem frequently occurred. Thus, K-water determined to retrofit this old conventional WTP for satisfying the strengthened water quality standards before reactivating this plant.
- However, post-ozonation and granular active carbon (GAC) processes were difficult to be introduced because of a limited area. Therefore, the integrated ceramic membrane system consisted of pre-ozonation, coagulation, membrane filtration, GAC processes were selected among several alternatives for retrofitting Yeoncho WTP.
- Especially, ceramic microfiltration membrane was chosen instead of polymeric hollow fiber membranes used widely because of higher flux and less frequent cleaning, the longer lifetime of the ceramic membranes, and their inherent mechanical and chemical stability.
The selected ceramic membrane system was evaluated for 6 months in pilot plant to verify the performance of the membrane under suggested operation conditions by vendor. During verification periods, the performance of ceramic membrane depending on the variation of flux and water qualities was confirmed.
Memberane spec List
|Type of membrane
||Microfiltration(Monolith type, pressurized membrane ), NGK
||L1, 1500㎜, OD180㎜, 25㎡
- Membrane Speculations in Yeoncho WTP
- Yeoncho membrane facility of 16,000 ㎥/day was designed 4 trains having 7 modules in each train. One module consists 10 ceramic membrane elements and total 280 elements of microfiltration ceramic membrane with the nominal pore size of 0.1 ㎛ will be installed in Yeoncho WTP. This plant will become the first ceramic membrane WTP in Korea and treated water will be supplied to Geoje from January 2012.
- Schematic diagram of Yeonch membrane WTP
- Bird's-eye-view of Yeonch membrane WTP
- The membrane system is operated in a dead-end mode with filtration velocity (flux) of 2.5 ㎥/㎡-day excepting several days. A backwash interval was 2 hours and one time of chemically enhanced backwash (CEB) with sulfuric acid(H2SO4, 0.3%) and sodium hypo-chloride (NaOCl, 200 ppm) was conducted after 11 times of backwash by turns.
- Backwashing of membrane was carried out for 15 seconds by backwash water pressurized to 5 kgf/㎠ by compressed air to break off the cake layer from the membrane surface. A tangential air flushing for 3 seconds through the feed channel was followed by compressed air of 2 kgf/㎠ to discharge detached cake which was retained in each channel. Chemical cleaning (CIP, clean in place) is conducted using citric acid of 1% and sodium hypochlorite (NaOCl) of 0.3 % when measured trans-membrane pressure (TMP) exceeded 1.5 kgf/㎠.