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K-water's endeavor to tackle water shortage problem : seawater desalination and water reuse

Sea water desalination

INTRODUCTION

  • K-water is carrying out two pilot projects to overcome water shortage problem: high-recovery seawater reverse osmosis (SWRO) system and reuse of wastewater treatment plant (WWTP) effluent using RO system. The main objectives of the projects are to obtain design factors and optimized operation and management (O&M) techniques of full-scale reverse osmosis systems for seawater desalination and wastewater reuse.
  • Seawater desalination pilot plant is being operated in Sokcho, an eastern coastal city of South Korea and wastewater reuse pilot plant will be constructed in a wastewater treatment plant in Ulsan which is a famous city for the huge industrial complex. Key point of the seawater desalination project is a high recovery ratio of 60% and the wastewater reuse project focuses on the low fouling system.
  • From 2016, K-water has participated a national R&D project funded by Ministry of Land, Infrastructure and Transport (MOLIT). As a 4-year project with the budget of $ 2,700 in terms of government fund, the final goal is to develop the low-energy desalination technologies. This project could promote more business opportunities in Middle East for the Korean companies. In addition, K-water is conducting the preliminary researches to relive the water stress of industrial complex in western area of Chungnam province.

HIGH-RECOVERY SWRO SYSTEM

  • There are two benefits of higher recovery ratio of seawater reverse osmosis (SWRO) system: decreases in pretreatment capacity and concentrate discharge rate. Recovery ratios for common SWRO systems and the high-recovery SWRO system are 40% and 60%, respectively. The pilot plant was designed to compare the performance of both systems as shown in Figure 1.
  • Seawater of 500m3/d is taken from the intake point close to estuary. Ultrafiltration (UF) and dual media filtration (DMF) are used as two options for pretreatment processes. Higher pressure and water flux of RO systems are essential to obtain higher recovery ratio. Higher flux means the higher fouling potential of RO membrane, which is the reason why rigorous pretreatment method like UF is needed for high-recovery SWRO system as shown in Figure 1.
  • Figure 1. Process flow diagram and pictures of SWRO pilot plant, Sokcho, South Korea
  • Since the intake point is close to estuary, the seasonal change of total dissolved solid (TDS) concentration and turbidity are expected to be large. In summer, the pilot plant meets lower TDS concentration and higher turbidity, and vice versa in winter. UF system also assures a constant water quality for the varied seawater quality. Because of the varied TDS value, an automatic operation control system was introduced to maintain the constant permeate flow rate and recovery ratio. The pilot plant operation started from April, 2009 and the project will be ended by December, 2010.

LOW-ENERGY DESALINATION SYSTEM

  • In the national R&D project started from 2016, K-water works as a lead agency of the 3rd group who is in charge of designing, constructing and operating the 1,000-2,000 m3/d SWRO pilot plant in United Arab Emirates(UAE). In this project, two targets such as mitigation of the energy consumption of the desalination plant down to 3.3 kWh/3 and 30% reduction of water production costs by UAE standards should be achieved. To do so, several technological advancements are required; Energy saving pretreatment for algae control, energy saving RO system with the world’s best RO membrane, and low-energy technologies which can replace the 2nd pass RO. Besides, development of the optimal design and O&M technologies has the highest priority to efficiently confront the high temperature and TDS conditions in the Middle East. In particular, K-water will develop an operation program to efficiently and economically manage the desalination plant until the first half of 2018. since then, K-water will take the responsibility of O&M of UAE pilot plant.
  • Figure 2. Schematic of the low-energy desalination process researched in the national R&D project

WASTEWATER REUSE RO SYSTEM

  • Water reuse can be a good alternative water source. A good example for water reuse is to treat wastewater treatment plant (WWTP) effluent and reuse it as an industrial use. When the WWTP effluent has high TDS concentrations, RO system should be introduced to produce industrial water from the WWTP effluent.
  • The key feature of the WWTP effluent is highly concentrated organic matter, which is a potential source of RO membrane fouling. Hence the key point of the project is to design low fouling RO system and develop a periodic cleaning methodology to maintain the constant performance of RO system.
  • The first procedure to design low fouling system is to select the lowest fouling RO membrane module. The fundamental method to find the fouling potential of a RO membrane for specific foulants is to analyze the interfacial forces between membrane and foulants surfaces using the material characterization data, which is difficult to be applied to complex foulants in WWTP effluents.
  • Therefore a field RO membrane fouling test procedure is developed to select membrane module resulting in the lowest fouling characteristics as shown in Figure 2. Pilot test using the lowest fouling membrane selected from the field RO membrane fouling test, will be carried out in 2010.
  • Figure 2. Schematic of the field RO membrane fouling test system
  • Figure 2. Schematic of the field RO membrane fouling test system
  • Dept: K-water Convergence Institute
  • Name: Kim Ji Hye