Comparative performance of FO-RO hybrid and two-pass SWRO desalination processes: Boron removal

Boron removal in seawater desalination presents a particular challenge. In seawater reverse osmosis (SWRO) systems boron removal at low concentration (<0.5 mg/L) is usually achieved by a second pass using brackish water RO membranes. However, this process requires chemical addition and important additional investment, operation and maintenance, and energy costs. Electrocoagulation (EC) process can be used to achieve such low boron concentration. In this work, the removal of boron from aqueous solution was carried out by EC process using aluminum and iron electrodes. Several operating parameters on the removal efficiency such as initial pH, current density, initial boron ion concentration, feed concentration, gap between electrodes, and electrode material, were investigated. In the case of bipolar electrocoagulation (BEC), an optimum removal efficiency of 96% corresponding to a final boron concentration of 0.4 mg/L was achieved at a current density of 6 mA/cm² and pH = 8 using aluminum electrodes. The concentration of NaCl was 2,500 mg/L and the gap between the electrodes of 0.5 cm. Furthermore, a comparison between monopolar electrocoagulation (MEC) and BEC using both aluminum and iron electrodes was carried out. Results showed that the BEC process has reduced the current density applied to obtain high level of boron removal in a short reaction time compared to MEC process. The high performance of the EC showed that the process could be used to reduce boron concentration to acceptable levels at low-cost and more environmentally friendly.

Enhanced boron removal using polyol compounds in seawater reverse osmosis processes

Boron in the desalinated water produced by the seawater reverse osmosis (SWRO) system is one of the most challenging issues for drinking or irrigation water uses. In recent years, many post-treatment methods and designs for boron elimination have emerged and attracted lots of attention, but only a few cases have demonstrated high performance and economic efficiency. The main aim of this work was to evaluate the efficiency of boron removal from seawater using a two-pass SWRO system employing different RO membranes at Qingdao Jiaozhou Bay, the Yellow Sea of China. In this study, HYDRANAUTICS SWC3+ and ESPAB were chosen as the first and second pass membrane, respectively. The impact of feed properties including temperature, pH, salinity, boron concentration, and operational conditions such as feed pressure on boron rejection and permeate flux was determined. In addition, a relative long term run of the two-pass SWRO system was investigated and compared with performance of system that uses Filmtec membrane as reported in the literature. Although the pilot system in this study experienced more severe feed conditions with lower pH, higher feed boron concentrations and lower operational pressures: all potential negative factors for boron rejection, it still achieved good performance for boron reduction. The results of three-month long term operation indicated that, at optimum conditions, two-pass SWRO system at Qingdao Jiaozhou Bay achieved a high performance and stability without anti-scalants to produce permeate which has much a lower boron concentration than the World Health Organization (WHO) guideline.

This study aimed to enhance boron removal through powdered activated carbon adsorption (PAC) and application of a micro-filtration (MF) process as a pretreatment of a seawater reverse osmosis (SWRO) process. Batch and continuous experiments were conducted to investigate the effect of membrane filtration as well as PAC addition on boron removal in reconstituted seawater. In batch test, two kinds of polyvinylidene fluoride (PVDF) hollow fiber membrane, Module A and Module B, were used to assess the influence of pH and PAC on boron removal, whereas in continuous mode, two MF systems with submerged PVDF flat-sheet membrane were run in parallel. Modules A and B obtained the highest percentage boron removal at pH 9 in the batch experiment with an average value of 47.33%, and their concentration of boron was further reduced after addition of PAC increasing the removal to 51.33 and 69.33%, respectively. For the continuous operation, PAC addition decreased the boron concentration by 20–30 and 40% in the reactor and effluent, respectively. On the other hand, only 5% reduction was obtained inside the reactor and 30–40% in the effluent for the system without PAC. Thus, operating the system at high pH with PAC addition could enhance the performance of the adsorption-MF system, which can be used as a pretreatment for the SWRO process.

Linked to potential health problems and toxicity to crops, boron is present in seawater at concentrations of ranging from 4 to 7 mg/L, and not readily removed by reverse osmosis technology. Commercially available seawater reverse osmosis (SWRO) membranes possess a wide range of rejection characteristics for boron in seawater under ambient temperature and pH, ranging from approximately 50% for low-energy membranes to greater than 90% for the newest high rejection membranes. This level of rejection is typically insufficient to reduce boron concentrations in natural seawater to less than recommended levels. Current World Health Organization (WHO) drinking water concentrations for boron are limited to 0.5-mg/L. Two techniques utilized to mitigate boron concentrations are (1) increasing the dissociation of boric acid by increasing pH prior to SWRO; and, (2) utilizing a second pass reverse osmosis system, potentially coupled with pH adjustment. Utilizing these techniques, the authors tested commercially available SWRO membranes from three different manufacturers utilizing feed water alkalization, coupled with a second pass system. Utilizing feed water alkalization alone, the authors found that all three SWRO membranes were able to produce permeate complying with WHO regulations. Using second pass RO, a boron concentration of less than 0.5 mg/L was achieved for feed pH greater than 6, and less than 0.1-mg/L for pH of 10.

Hybrid membrane system for desalination and wastewater treatment : Integrating forward osmosis and low pressure reverse osmosis

Boron removal efficiency from Red Sea water using different SWRO/BWRO membranes

Boron removal in brackish water desalination systems

Removal of boron in a multistage SWRO system with pre-crystallization

Objectives : The objective of this study is to investigate the potential for the removal of boron(B) from synthetic wastewater through chemical precipitation using microwave heating to identify the optimal conditions for the removal of boron.Methods : Synthetic wastewater was prepared using boric acid(H3BO3) and distilled water. The range of variables that exert an influence on boron removal included the initial pH 3-13, the calcium hydroxide(Ca(OH)2) dosage of 0.5-10 g per 30 mL(17–333 g/L), and the boron concentration of 100-1,500 mg/L. A face-centered design in response surface method was employed to identify the optimal conditions for boron removal in a continuous scale and to ascertain the interaction of the factors.Results and Discussion : In discontinuous conditions, the maximum removal efficiency was observed at initial pH 3, Ca(OH)2 of 2 g, and the boron concentration of 1,500 mg/L. As the pH value decreased, the removal of boron increased. The greatest removal efficiency was observed when the dosage of Ca(OH)2 was 2-5 g. It was also found that the higher the concentration of boron, the greater the removal efficiency. In the continuous scale, the optimal conditions for boron removal were identified as initial pH 3.3, the dosage of 6.2 g Ca(OH)2, and the boron concentration of 1,500 mg/L, with the removal efficiency of 93%. All independent variables exerted a statistically significant influence on chemical precipitation removal(p&lt;0.05). In comparison to pH(p=0.047), boron concentration(p&lt;0.001) and Ca(OH)2 dosage(p&lt;0.001) demonstrated a more pronounced impact on boron removal. The interaction between boron concentration and Ca(OH)2 dosage was also identified as statistically significant(p&lt;0.001).Conclusion : Chemical precipitation using microwave heating was effective in removal of boron from wastewater, and the optimal conditions in continuous scale through response surface analysis were initial pH 3.3, boron concentration 1,500 mg/L, and Ca(OH)2 dosage 6.2 g(207 g/L).

Surface engineering design of polyamide membranes for enhanced boron removal in seawater desalination

Treatment and reuse of produced water has become increasingly attractive. The complicated nature of produced water, however, and its variability make it challenging to reuse. Boron (B), a common component in produced water, is a concern when reusing produced water for hydraulic fracturing fluids. Excess boron in water can interfere with the timing of crosslinking reactions in hydraulic fracturing fluids, and premature crosslinking can increase friction pressure (horse power) when the fluid is being pumped. Lowering the boron concentration in produced water, therefore, will help to prevent or reduce formation damage and increase the stability of the hydraulic fracturing fluid. This paper presents a patent-pending and environmentally preferred process for boron and hardness removal from produced water. The traditional approach to boron removal has been to add chemicals (like activated alumina (Al2O3) or cerium oxide (CeO2)) or a chemically impregnated material (activated carbon) and clay as sorbents for boron removal from produced water, but these techniques have seen limited success. In these conventional approaches, sorption efficiency was affected by solution pH, initial boron concentration and other contaminants in the water. The method presented in this paper, however, is an environmentally preferred and simple process of adding liquid sodium silicate (Na2SiO3) to produced water for boron and hardness reduction. Efficient boron removal from more than 150 mg/L to less than 30 mg/L was achieved using this process, while at the same time, total hardness (as CaCO3) was reduced by more than 80%. While the waste solids that were created do contain high levels of calcium and magnesium silicate, it is proposed that they could be used for cementing material for oil industry applications thereby reducing the environmental impact of the process. Compared with other methods such as boron-selective resin, reverse osmosis (RO) or chemical sorption, this process exhibited better performance in the efficient removal of boron and hardness from produced water.

Co-precipitation and absorption methods were investigated for removal of boron from produced water, which is groundwater brought to the surface during oil and natural gas extraction. Boron can be toxic to many crops and often needs to be controlled to low levels in irrigation water. The present research focused on synthetic reverse osmosis (RO) concentrate modeled on concentrate expected from a future treatment facility at the Arroyo Grande Oil Field on the central coast of California. The produced water at this site is brackish with a boron concentration of 8 mg/L and an expected temperature of 80°C. The future overall produced water treatment process will include lime softening, micro-filtration, cooling, ion exchange, and finally RO. Projected boron concentrations in the RO concentrate are 20 to 25 mg/L. Concentrate temperature will be near ambient. This RO concentrate will be injected back into the formation. To prevent an accumulation of boron in the formation, it is desired to reduce boron concentrations in this concentrate and partition the boron into a solid sludge that could be transported out of the area. The primary method explored for boron removal during this study was adsorption and co-precipitation by magnesium chloride. Some magnesium oxide tests were also conducted. Jar testing was used to determine the degree of boron removal as a function of initial concentration, pH, temperature, and reaction time. Synthetic RO concentrate was used to control background water quality factors that could potentially influence boron removal. The standard synthetic RO concentrate contained 8 g NaCl/L, 150 mg Si/L and 30 mg B/L. After synthetic RO concentrate was prepared, amendments (e.g. sulfate, sodium chloride) were added and the pH adjusted to the desired value. Each solution was then carried through a mixing and settling protocol (5 min at 200 RPM, 10 min at 20 RPM, followed by 30 min settling and filtration). Boron concentrations from the jar tests were determined using the Carmine colorimetric method. Boron removal with magnesium chloride was greatest at a pH of 11.0. At this pH 87% of boron was removed using 5.0 g/L MgCl2◦6H2O at 20°C. Mixing time did not greatly affect boron removal for mixing periods of 5 to 1321 minutes. This result indicates equilibrium was achieved during the 45-min experimental protocol. Maximum boron removal was observed in the temperature range of 29°C to 41°C. At 68°C boron removal decreased five-fold compared to the reduction observed at 29°C to 41°C.

Full-scale simulation of seawater reverse osmosis desalination processes for boron removal: Effect of membrane fouling

Optimal Design of SWRO Desalination Processes with Boron Level Considerations