High recovery system in seawater reverse osmosis plants

Reverse Osmosis (RO) desalination has gained wide and increasing acceptance around the world as a straightforward undertaking to alleviate the alarming water crisis. An enhanced monitoring of the quality of the water feeding in seawater RO (SWRO) plant through the application of an effective pretreatment option is one of the keys to the success of RO technology in desalination plants. Over the past 10 years, advances in ultrafiltration (UF) membrane technologies in application for water and wastewater treatment have prompted an impetus for using membrane pretreatment in seawater desalination plants. By integrating SWRO plant with UF pretreatment, the rate of membrane fouling can be significantly reduced and thus extend the life of RO membrane. With the growing importance and significant advances attained in UF pretreatment, this review presents an overview of UF pretreatment in SWRO plants. The advantages offered by UF as an alternative of pretreatment option are compared to the existing conventionally used technologies. The current progress made in the integration of SWRO with UF pretreatment is also highlighted. Finally, the recent advances pursued in UF technology is reviewed in order to provide an insight and hence path the way for the future development of this technology.

Objectives The production cost of reverse osmosis (RO) seawater desalination plant is determined by the CAPEX (Capital expenditure) and OPEX (Operating expenditure). In detail, CAPEX and OPEX are composed of direct cost, overhead cost, electricity cost, and other O&M costs. However, CAPEX and OPEX may vary by country and region. Therefore, this study tries to estimate the production cost by calculating the construction and maintenance costs depending on production capacities based on the operation results such as TDS concentration and the energy consumption from a seawater desalination plant in Korea. Methods A two-stage RO based seawater desalination plant with a capacity of 10 MIGD (45,000 m3/d) was used in this study. The plant consists of a 2 MIGD (9,000 m3/d) unit having DABF (Dissolved air bio-ball filter) and UF (Ultrafiltration) as pretreatment processes, and another 8 MIGD (36,000 m3/d) unit having DABF and DMF (Dual media filtration) as pretreatment processes. To estimate the production cost, construction and maintenance costs were calculated by using GWI's Desaldata cost estimator. CAPEX (Capital expenditure) was calculated based on production capacity, recovery rate, TDS concentration and temperature of seawater, while OPEX (Operating expenditure) was calculated based on production capacity, country, energy consumption, and electricity unit price. Results and Discussion The energy consumptions from EMS (Energy Management System) were 5.48 kWh/m3 at SLC (9,000 m3/d) and 3.4 kWh/m3 at MLC (45,000 m3/d), respectively. In the CAPEX, MLC was reduced by 395,954 ￦/m3 compared to SLC, and the LLC was lower by 192,019 ￦/m3 than MLC. Overall, CAPEX decreased as the production capacity increased. The CAPEX of small plants with production capacity between 10,000 and 50,000 m3/d was significantly different; however, there was no significant difference in larger plants having a capacity above 100,000 m3/d. The OPEX for the annual production capacity showed a sizable difference with 742.3 ￦/m3, 636.5 ￦/m3 and 580.3 ￦/m3 for SLC, MLC, and LLC, respectively. The electricity cost was a substantial portion of OPEX. Also, the production costs based on the interest rates (3% and 5%) were 1,326-1,384 ￦/m3, 1,163-1,209 ￦/m3, and 1,023-1,070 ￦/m3 for SLC, MLC, and LLC, respectively. The results were consistent with 1.0 US$/m3, which is the average production costs presented from other references. Conclusions The production cost estimated using the Desaldata cost estimator based on the CAPEX and OPEX tends to decrease as the capacity increases. However, when the capacity increased over 50,000 m3/d, the production cost decreased by an average of 40 ￦/m3. Thus the decrement of production cost reduced. From these results, the production cost of tap water through seawater desalination was estimated between 1,023 ￦/m3 and 1,070 ￦/m3 above 100,000 m3/d. Therefore, it is difficult to introduce a large-scale desalination plant in Korea, because the average tap water price was 834.6 ￦ in Korea in 2017. However, It is expected that the seawater desalination will be introduced as an alternative water source whenever drinking water price rises, or when the quantity of available drinking water sources reduce due to climate change and water pollution, or whenever energy consumption is reduced as a result of the steady development of the component technologies such as the reverse osmosis membrane, high-pressure pump, and energy recovery device. Key words: Reverse osmosis seawater desalination plant, Water price, Capital expenditure, Operating expenditure, Energy consumption

The reverse osmosis (RO) method is a method obtaining the fresh water by using semi permeable RO membrane that does not percolate the low molecular weight material such as a salt. However, the RO method has to give continuous operation at high pressure in seawater desalination plants. In the present study, in order to improve the efficiency of RO desalination under low pressure conditions, the water treatment system is proposed by using microbubbles in salt water disposal and the effect of the microbubbles on the osmosis rate was investigated by measurements of the electric conductivity. It is confirmed that the fresh water is effectively produced for the system with microbubbles in contrast to that with no microbubbles, and the efficiency of desalination is significantly improved by microbubbles with a high electrical potential. The electric conductivity decreases with increasing the zeta potential of the microbubbles.

The scope of this paper will be to discuss the technical and economical aspects of utilizing reverse osmosis technology for desalination of seawater for offshore operations. This paper will introduce the basic concepts of reverse osmosis technology and some of the history concerning the technology. Factors influencing the design, shipment, operation, and maintenance of reverse osmosis systems for offshore installations will be presented. In addition, field data concerning the technical and economical aspects of the operation of reverse osmosis systems on offshore installations will be given. This paper will illustrate the significance and practicality of seawater desalination via reverse osmosis technology on offshore installations. INTRODUCTION A reliable and consistent supply of potable water is one of man's most basic needs. This need is especially critical for the operators and occupants of offshore platforms. Presently, the sources of potable water for these installations are either desalination by distillation or transportation from land via barge or helicopter. The water obtained from these sources can vary in quality and quantity and can also be costly. It will be the purpose of this paper to present a third alternative, desalination of raw seawater by reverse osmosis. THEORY AND DEFINITIONS When a salt water or saline solution is separated from pure water by a semipermeable membrane, the pure water molecules will pass through the membrane into the more concentrated saline solution. This process is defined as osmosis. Osmotic pressure can be defined as the pressure that must be applied to the saline solution to establish equilibrium. If the pressure applied to the saline solution is in excess of the osmotic pressure, the osmotic process is reversed. Water molecules will pass from the saline solution through the membrane into the purer water. This latter process is known as reverse osmosis. The processes of direct and reverse osmosis are shown by Figure 1. The desalination of seawater by the reverse osmosis process is illustrated in Figure 2. By supplying seawater to the membrane at a pressure greater than the osmotic pressure of the solution, water with a lower level of dissolved solids is produced. Materials such as colloids, organic compounds, dissolved solids, and bacteria that do not pass through the membrane are continuously discharged from the system. This continuous discharge prevents accumulation of these materials on the surface of the membrane. In the practical application of reverse osmosis, a small percentage of the dissolved solids do pass through the semipermeable membrane along with the water molecules. The ratio of the concentration of these dissolved solids in the product water to that of the feed water is defined as salt passage and is expressed as a percentage. Due to chemical and physical limitations of the process, only a portion of the seawater fed to the system is desalted. The ratio of the amount of water produced to the amount of feed water is defined as recovery and is also expressed as a percentage.

Live seawater experience in Japan with hollow fiber permeators

Cost analysis in RO desalination plants production lines: mathematical model and simulation

A comparative study of RO and MSF desalination plants

A comparative study of RO and MSF desalination plants

Hybrid systems in seawater desalination-practical design aspects, status and development perspectives

The ability to produce fresh potable water is an ever-growing challenge, especially with an increase in drought conditions worldwide. Due to its capacity to treat different types of water, reverse osmosis (RO) technology is an increasingly popular solution to the water shortage problem. The major restriction associated with the treatment of water by RO technology is the fouling of the RO membrane, in particular through biofouling. Membrane fouling is a multifaceted problem that causes an increase in operating pressure, frequent cleaning and limited membrane lifespan. The current paper summarizes the impact of biofouling of RO membranes used in seawater desalination plants. Following a brief introduction, the elements that contribute to biofouling are discussed: biofilm formation, role of extracellular polymeric substances (EPS), marine environment, developmental phases of biofouling. Following this, is a section on the implications of membrane biofouling especially permeate flux and salt rejection. The final section focuses on the new phenomenon of compression and hydraulic resistance of biofilms. Lastly, considerations on future research requirements on biofouling and its control in seawater reverse osmosis (SWRO) membrane systems are presented at the end of the article.

Parts of the USA are facing impending shortages of freshwater. One proposed solution is the construction of desalination plants to turn seawater into freshwater. Although seawater desalination plants are widely used in the Middle East, especially Saudi Arabia, there are few desalination plants in the USA. In 2003, Tampa Bay Water built the largest desalination plant in North America. Persistent operating problems and escalating costs have caused the utility to re-evaluate its reliance on the seawater desalination plant as part of a long-term regional water supply strategy. In addition, environmental effects of the plant are uncertain. Advances in reverse osmosis technology have significantly reduced desalination costs. However, desalination of seawater is still more expensive than other freshwater supply sources and demand management measures. With time and research, seawater desalination may prove to be a sustainable, cost-effective source of new freshwater supplies, especially if plants are coupled with renewable energy sources. Until then, the development of small-scale groundwater desalination plants, the re-use of water, water conservation, and a more efficient allocation of water through higher prices and rising block rates will be important strategies in meeting growing water demand. Moreover, it is important to improve the coordination between water supply planning and land use planning as populations continue to increase.

Hybrid systems in seawater desalination—practical design aspects, present status and development perspectives

Investigation of efficient corrosion inhibitor during acid cleaning of reverse osmosis (RO) desalination plant

The anaerobic ammonium oxidation (anammox) process is one of the most cost-effective technologies for removing excessive nitrogen compounds from effluents of wastewater treatment plants. The study was conducted to assess the feasibility of using ion exchange (IE) and reverse osmosis (RO) methods to concentrate ammonium to support partial nitritation/anammox process, which so far has been used for treating only wastewater with high concentrations of ammonium. Upflow anaerobic sludge blanket (UASB) reactor effluents with 40.40, 37.90 and 21.80 mg NH4─N/L levels were concentrated with IE method to 367.20, 329.50 and 187.50 mg NH4─N/L, respectively, which were about nine times the initial concentrations. RO method was also used to concentrate 41.0 mg NH4─N/L of UASB effluent to 163 mg NH4─N/L at volume reduction factor 5. The rates of nitrogen removal from respective RO pretreated concentrates by partial nitritation/anammox technology were 0.60, 1.10 and 0.50 g N/m2day. The rates were largely influenced by initial nitrogen concentration. However, rates of RO concentrates were 0.74, 0.92 and 0.81 g N/m2day even at lower initial NH4─N concentration. It was found out from the study that higher salinity decreased the rate of nitrogen removal when using partial nitritation/anammox process. Dissolved oxygen concentration of ∼1 mg/L was optimal for the operation of the partial nitritation/anammox process when treating IE and RO concentrates. The result shows that IE and RO methods can precede a partial nitritation/anammox process to enhance the treatment of wastewater with low ammonium loads.

Reverse osmosis (RO) technology requires high energy input in order to extract freshwater from seawater. Improvements in RO technology have led to seawater RO (SWRO) becoming the dominant form of large scale desalination around the world. However, the specific energy consumption (SEC) of SWRO remains substantially higher than that for surface water treatment and indirect potable recycling, making SWRO less cost effective than other alternatives for producing potable water. Furthermore, where non-renewable energy sources are used to supply SWRO energy demand, higher levels of greenhouse gas are emitted compared with lower energy alternatives. The purpose of this paper is to review the RO process configurations currently available and their impact on reducing SWRO energy consumption. This paper highlights the main factors contributing to SWRO energy consumption and presents some of the commonly adopted approaches to reducing SEC in SWRO plants. The use of energy recovery devices (ERDs) in SWRO is explored and the relative effectiveness of the various types of ERDs in reducing SEC presented.