analyzer (MF-DMA) counting technique to determine suspended particles and dissolved solids in water

Suspended particles and dissolved solids in seawater during desalination process have been known to cause colloidal fouling in membranes. The membrane filtration-differential mobility analyzer (MF-DMA) counting technique has been developed to quantify suspended nanoparticles and dissolved solids in water in real time. Various types of suspended particles (PSL, CaCO3, and MgCO3) and dissolved solids (artificial seawater, NaCl, KCl, MgCl2, and CaCl2) were used to evaluate the MF-DMA method. By using PSL particles of known sizes and numbers in water, a linear relationship between particle number concentrations in air (particles/cm3) and in water (particles/ml) was established, which was valid independent of particle size. This relationship was used to determine number concentrations of CaCO3 and MgCO3 particles in water, showing good agreements with the calculated values within ∼19%. By using artificial seawater, a linear relationship between mass concentration of dissolved solids in air (μg/m3) and in water (ppm) was also found. Mass concentrations of dissolved solids (NaCl, KCl, CaCl2, and MgCl2) in water estimated by the MF-DMA method were in good agreements with those measured with the TDS meter within ∼15%. The current real time technique can be applied to monitor both suspended particles and dissolved solids in pretreated seawater during RO membrane desalination process.

Quantitative performance of the MF-DMA counting technique to determine number concentration of suspended particles and mass concentration of dissolved solids in water was evaluated by using suspended particles (PSL, CaCO3, and MgCO3) and dissolved solids (artificial seawater, NaCl, KCl, MgCl2, and CaCl2) in water. Relationships between concentrations of particles and dissolved solids in air measured with the MF-DMA method and those in water were established by using PSL particles of known sizes and numbers and artificial seawater of known concentrations. The relationships were applied to determine number concentration of suspended particles and mass concentration of dissolved solids in water. Results showed that the MF-DMA method was able to estimate particle number concentration in water within 19% for suspended CaCO3 and MgCO3 particles and mass concentration of dissolved solids (NaCl, KCl, CaCl2, and MgCl2) within 15%. Furthermore, we determined dissolved solids which passed through the UF and RO membranes. We found that mass concentration of dissolved solids in the UF membrane-filtered seawater was 26,358 ppm and after RO membrane filtration it decreased to 469 ppm. Also, we observed that the geometric mean diameters (GMD) of dissolved particles passed through MF, UF and RO membranes were 102.81 nm, 102.94 nm, and 69.18 nm, respectively.