최근 국내에서 세계 최초로 개발한 SWRO-PRO 복합해수담수화 시스템은 압력지연삼투(PRO) 기술을 활용하여 역삼투(SWRO) 해수담수화 플랜트에서 발생하는 고염도 농축수의 삼투에너지를 회수하는 기술이다. 고염도 농축수와 저염도 하수처리수를 각각 PRO 시스템의 유도용액과 유입수로 사용하며, 두 용액의 농도차에 의해 발생되는 삼투에너지를 압력교환장치(isobaric pressure exchanger)를 통해 회수하여 SWRO 고압펌프에서 필요한 에너지를 줄이거나, 터빈 형태의 에너지 회수장치(Pelton turbine)를 통해 전력을 생산하는 기술이다. PRO 시스템을 통해 회수된 에너지는 해수담수화 운영비를 절감하는데 기여하고, 고농도 농축수의 희석 방류로 해양생태계 영향을 최소화 시킬 수 있다.

본 사례는 최근 준공된 “구미하수처리장 하수처리수를 이용한 재이용시설”에 대한 것으로 이 시설은 구미하수처리장의 2차 처리수를 원수로, 응집침전시설, 전처리시설, 주처리시설과 재이용수 공급시설로 구성되어 있으며, 설비의 성능 확인을 위한 시운전을 완료하였다. 주처리시설로는 역삼투막(RO Membrane)을 적용하였으며, 하수처리수 내 잔류물질로 인한 역삼투막 성능저하방지와 수요처의 요구수질 충족을 위해 활성탄 주입을 포함한 응집침전공정과 정밀여과막(Micro Filter)을 전처리시설로 구성하였다. 사업 초기단계에 현재 시공된 것과 동일한 공정으로 구성된 Pilot Plant를 건설, 운영하여, 반영된 각 단계별 공정의 적정성과 주요 설계 인자를 확인하였으며, 일부 확인된 개선 사항은 실시설계시 반영하였다.

SWRO-PRO hybrid desalination technology is recently getting more attention especially in large desalination markets such as USA, Middle East, Japan, Singapore, etc. because of its promising potential to recover a considerable amount of osmotic energy from brine (a high-concentration solution of salt, 60,000 – 80,000 mg/L) and also to minimize the impact of the discharged brine into a marine ecosystem. By the research and development of the core technologies of the SWRO-PRO desalination system in a national desalination research project (Global MVP) supported by Ministry of Land, Infrastructure, and Transport (MOLIT) and Korea Agency for Infrastructure Technology Advancement (KAIA), it is anticipated that around 25% of total energy consumption rate (generally 3 to 4 kWh/m3) of the SWRO desalination can be reduced by recovering the brine’s osmotic energy utilizing wastewater treatment effluent as a PRO feed solution and an isobaric pressure exchanger (PX, ERI) as a PRO energy converter. However, there are still several challenges needed to be overcome in order to ultimately commercialize the novel SWRO-PRO process. They include system optimization and integration, development of efficient PRO membrane and module, development of PRO membrane fouling control technology, development of design and operation technology for the system scaling-up, development of diverse business models, and so on. In this paper, the current status and progress of the pilot study of the newly developed SWRO-PRO hybrid desalination technology is discussed.

최근 국내에서 연구개발중인 SWRO-PRO 복합해수담수화 기술은 SWRO 해수담수화 플랜트에서 발생하는 고염도 농축수와 저염도 하수처리수를 각각 PRO 시스템의 유도용액과 원수로 사용하여, 두 용액의 농도차에 의해 발생되는 삼투에너지를 압력교환장치를 통해 회수하여 RO 고압펌프에서 필요한 에너지를 줄이거나, 터빈 형태의 에너지 회수장치 적용을 통해 전력을 생산하는 기술이다. PRO 시스템을 통해 회수된 에너지는 해수담수화 운영비를 절감할 수 있고, 고농도 농축수 방류로 인한 해양생태계 영향을 최소화 시킬 수 있다. 또한, 농축수 처리 비용 및 해수담수화 전력시설 비용을 절감시키는 효과를 기대할 수 있다.

Desalination is getting more attention as an alternative to solve a global water shortage problem in the future. Especially, a desalination technology is being expected as a new growth engine of Korea’s overseas plant business besides one of the solutions of domestic water shortage problem. In the past, a thermal evaporation technology was a predominant method in desalination market, but more than 75% of the current market is hold by a membrane-based reverse osmosis technology because of its lower energy consumption rate for desalination. In the future, it is expected to have more energy efficient desalination process. Accordingly, various processes are being developed to further enhance the desalination energy efficiency. One of the promising technologies is a desalination process combined with Pressure Retarded Osmosis (PRO) process. The PRO technology is able to generate energy by using osmotic pressure of seawater or desalination brine. And the other benefits are that it has no emission of CO2 and the limited impact of external environmental factors. However, it is not commercialized yet because a high-performance PRO membrane and module, and a PRO system optimization technology is not sufficiently developed. In this paper, the recent research direction and progress of the SWRO-PRO hybrid desalination was discussed regarding a PRO membrane and module, an energy recovery system, pre-treatment and system optimization technologies, and so on.

Recently, reverse osmosis (RO) is the most common process for seawater desalination. A common problem in both RO and thermal processes is the high energy requirements for seawater desalination. The one energy saving method when utilizing the osmotic power is utilizing pressure retarded osmosis (PRO) process. The PRO process can be used to operate hydro turbines for electrical power production or can be used directly to supplement the energy required for RO desalination system. This study was carried out to evaluate the performance of both single-stage PRO process and two-stage PRO process using RO concentrate for a draw solution and RO permeate for a feed solution. The major results, were found that increase of the draw and feed solution flowrate lead to increase of the production of power density and water permeate. Also, comparison between CDCF and CDDF configuration showed that the CDDF was better than CDCF for stable operation of PRO process. In addition, power density of two-stage PRO was lower than the one of single-stage. However, net power of two-stage PRO was higher than the one of single-stage PRO.

역삼투(RO) 해수담수화 공정에 필요한 많은 에너지를 절감하기 위해 최근에 다양한 연구개발이 추진 중이다. 그 중에서 농도차에 의해 발생하는 삼투현상을 이용한 정삼투(FO)와 압력지연삼투(PRO) 기술을 접목한 하이브리드 해수담수화 공정들이 대표적이다. 특히, PRO 기술은 해수담수화 플랜트에서 배출되는 농축수와 하수처리수를 PRO 시스템의 유도용액과 원수로 각각 활용하여 두 용액의 염도차에 의해 발생되는 에너지를 회수함으로써, 기존 역삼투 해수담수화 공정 대비 25% 이상의 에너지 절감이 가능하며, 해수담수화 플랜트의 고농도 농축수를 희석 방류함으로써 해양생태계 파괴 방지 및 농축수 처리비용 절감 등의 효과를 기대할 수 있다.

In this study, we have investigated leaching characteristics of heavy metals and alkalinity centering around steel mill slags by several extraction methods, for the purpose of risk assessment that exert influence on environment and offer of the foundation data of reuse by slags. Korean standard method, U.S.EPA Extraction Procedure, alkalinity extraction test and 9 step sequential fractionation experiment by Miller et al. were carried out for investigating leachability of steel mill slags. As a result of this experiment, heavy metals were little detected and it was considered that alkalinity does not exert a bad effect around environment in slags with large particle size. By the result of 9 step fractionation experiment, heavy metal contents in slags were not plentiful, in addition, even comparatively plentiful contended heavy metals, for the most part, were likely to detained or bonded in silica matrix. Therefore, in case of slags with large particle size, it seems that leachability of heavy metals were next to impossible that is existed as a safety condition.