Application of nanofiltration pretreatment to remove divalent ions for economical seawater reverse osmosis desalination

To minimize scale formation potential in the applications of reverse osmosis (RO) membranes as a pretreatment unit, relatively loose nanofiltration (NF) membrane systems coupled with ultrafiltration (UF) were used to remove divalent ions from seawater. However, the UF did not reject any ions because of pore size. The rejection of divalent ions by NF was in order of sulfate (>95%), magnesium (>60%), and calcium (>30%) in every rejection experiment based on water recovery rate (40, 50, 60, 70, and 80%). In the UF/NF/RO hybrid pilot system, most of the divalent (>99%) and the monovalent (>97%) ions were effectively rejected with slightly increased divalent ion rejection compared to the UF/RO system. Seawater temperature influenced rejection of ions with regards to either the diffusion- or convection-dominant transport of ions through the membrane pores. Electric power consumption was also compared between the UF/NF/RO process and the UF/RO process. For different salinity conditions (28,000 and 45,000mg/L of total dissolved solids), the lowest energy consumption by NF/RO was 3.3 and 6kWh/m(3) with recovery of 80% for NF and 40% for RO, respectively.close

Synthesis Mechanism and Thermal Optimization of an Economical Mesoporous Material Using Silica: Implications for the Effective Removal or Delivery of Ibuprofen.

Mesoporous silica materials (MSMs) were synthesized economically using silica (SiO2) as a precursor via a modified alkaline fusion method. The MSM prepared at 500°C (MSM-500) had the highest surface area, pore size, and volume, and the results of isotherms and the kinetics of ibuprofen (IBP) removal indicated that MSM-500 had the highest sorption capacity and fastest removal speed vs. SBA-15 and zeolite. Compared with commercial granular activated carbon (GAC), MSM-500 had a ~100 times higher sorption rate at neutral pH. IBP uptake by MSM-500 was thermodynamically favorable at room temperature, which was interpreted as indicating relatively weak bonding because the entropy (∆adsS, -0.07 J mol(-1) K(-1)) was much smaller. Five times recycling tests revealed that MSM-500 had 83-87% recovery efficiencies and slower uptake speeds due to slight deformation of the outer pore structure. In the IBP delivery test, MSM-500 drug loading was 41%, higher than the reported value of SBA-15 (31%). The in vitro release of IBP was faster, almost 100%, reaching equilibrium within a few hours, indicating its effective loading and unloading characteristics. A cost analysis study revealed that the MSM was ~10-70 times cheaper than any other mesoporous silica material for the removal or delivery of IBP

Isotherm parameters obtained by fitting equilibrium data with the Freundlich and Langmuir isotherms for the adsorption of IBP on MSMs.

<p>^a<i>k</i>_F in mg^1–1/n L^1/n g^–1, <i>K</i>_L: Langmuir constant, <i>k</i>_F and <i>n</i>: Freundlich constants, <i>q</i>_max: maximum amount of adsorbate.</p><p>Isotherm parameters obtained by fitting equilibrium data with the Freundlich and Langmuir isotherms for the adsorption of IBP on MSMs.</p

Synthesis Mechanism and Thermal Optimization of an Economical Mesoporous Material Using Silica: Implications for the Effective Removal or Delivery of Ibuprofen - Fig 2

<p>(A) Adsorption isotherms of the MSMs calcined at different temperatures. (B) Kinetics of IBP uptake by MSMs calcined at different temperatures.</p

Temperature effect of IBP adsorption onto MSM-500.

<p>Temperature effect of IBP adsorption onto MSM-500.</p

IBP uptake by MSM-500 at several recycles: (A) kinetics, (B) <i>q</i>_<i>eq</i>, (C) <i>K</i>_<i>2</i>, and (D) <i>v</i>_<i>0</i> according to the number of recycles.

<p>IBP uptake by MSM-500 at several recycles: (A) kinetics, (B) <i>q</i>_<i>eq</i>, (C) <i>K</i>_<i>2</i>, and (D) <i>v</i>_<i>0</i> according to the number of recycles.</p