Deyin Hou

Experimental study of arsenic removal by direct contact membrane distillation

Arsenite (As(III)) and arsenate (As(V)) removal by direct contact membrane distillation (DCMD) were investigated with self-made polyvinylidene fluoride (PVDF) membranes in the present work. Permeability and ion rejection efficiency of the membrane were tested before the arsenic removal experiments. A maximum permeate flux 20.90 kg/m(2)h was obtained, and due to the hydrophobic property, the PVDF membrane had high rejection of inorganic anions and cations which was independent of the solution pH and the temperature. The experimental results indicated that DCMD process had higher removal efficiency of arsenic than pressure-driven membrane processes, especially for high-concentration arsenic and arsenite removal. The experimental results indicated that the permeate As(III) and As(V) were under the maximum contaminant limit (10 microg/L) until the feed As(III) and As(V) achieved 40 and 2000 mg/L, respectively. The 250 h simultaneous DCMD performance of 0.5mg/L As(III) and As(V) solution was carried out, respectively. The permeate arsenic was not detected during the process which showed the PVDF membrane had stable arsenic removal efficiency. Membrane morphology changed slightly after the experiments, however, the permeability and the ion rejection of the membrane did not change.

Boron removal from aqueous solution by direct contact membrane distillation

The removal of boron from aqueous solution by direct contact membrane distillation (DCMD) was studied with self-prepared polyvinylidene fluoride (PVDF) hollow fiber membranes in the present work. The effect of pH, boron concentration, temperature and salt concentration of the feed solution on the boron rejection was investigated. The experimental results indicated that boron rejection was less dependent on the feed pH and salt concentration. DCMD process had high boron removal efficiency (>99.8%) and the permeate boron was below the maximum permissible level even at feed concentration as high as 750 mg/L. Although the permeate flux was enhanced exponentially with the feed temperature increasing, the influence of feed temperature on the boron rejection could be neglected. Finally, the natural groundwater sample containing 12.7 mg/L of boron was treated by DCMD process. The permeate boron kept below 20 microg/L whether the feed was acidified or not, but pre-acidification was helpful to maintain the permeate flux stability. All the experimental results indicated that DCMD could be efficiently used for boron removal from aqueous solution.

Fabrication of asymmetric poly (m-phenylene isophthalamide) nanofiltration membrane for chromium(VI) removal

The feasibility of employing nanofiltration for the removal of chromium (VI) from wastewater was investigated. Poly (m-phenylene isophthalamide) (PMIA) was used to fabricate asymmetric nanofiltration membrane through the phase-inversion technique. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the obtained membrane, and the both confirmed a much smoother surface which could reduce membrane fouling. The PMIA membrane showed different rejections to electrolytes in a sequence of Na2SO4 > MgSO4 > NaCl > MgCl2, which was similar to the sequence of the negatively charged nanofiltration membranes. Separation experiments on chromium(VI) solution were conducted at various operating conditions, such as feed concentration, applied pressure and pH. It is concluded that chromium(VI) could be effectively removed from chromium-containing wastewater by the PMIA nanofiltration membranes while maintaining their pollution resistance under alkaline condition.

Fabrication and performance of PET mesh enhanced cellulose acetate membranes for forward osmosis

Polyethylene terephthalate mesh (PET) enhanced cellulose acetate membranes were fabricated via a phase inversion process. The membrane fabrication parameters that may affect the membrane performance were systematically evaluated including the concentration and temperature of the casting polymer solution and the temperature and time of the evaporation, coagulation and annealing processes. The water permeability and reverse salt flux were measured in forward osmosis (FO) mode for determination of the optimal membrane fabrication conditions. The optimal FO membrane shows a typical asymmetric sandwich structure with a mean thickness of about 148.2μm. The performance of the optimal FO membrane was tested using 0.2mol/L NaCl as the feed solution and 1.5mol/L glucose as the draw solution. The membrane displayed a water flux of 3.47L/(m(2)·hr) and salt rejection of 95.48% in FO mode. While in pressure retarded osmosis (PRO) mode, the water flux was 4.74L/(m(2)·hr) and salt rejection 96.03%. The high ratio of water flux in FO mode to that in PRO mode indicates that the fabricated membrane has a lower degree of internal concentration polarization than comparable membranes.

Desalination of brackish groundwater by direct contact membrane distillation

The direct contact membrane distillation (DCMD) applied for desalination of brackish groundwater with self-made polyvinylidene fluoride (PVDF) membranes was presented in the paper. The PVDF membrane exhibited high rejection of non-volatile inorganic salt solutes and a maximum permeate flux 24.5 kg m(-2) h(-1) was obtained with feed temperature at 70 degrees C. The DCMD experimental results indicated that the feed concentration had no significant influence on the permeate flux and the rejection of solute. When natural groundwater was used directly as the feed, the precipitation of CaCO(3) would be formed and clog the hollow fibre inlets with gradual concentration of the feed, which resulted in a rapid decline of the module efficiency. The negative influence of scaling could be eliminated by acidification of the feed. Finally, a 250 h DCMD continuous desalination experiment of acidified groundwater with the concentration factor at constant 4.0 was carried out. The permeate flux kept stable and the permeate conductivity was less than 7.0 microS cm(-1) during this process. Furthermore, there was no deposit observed on the membrane surface. All of these demonstrated that DCMD could be efficiently used for production of high-quality potable water from brackish groundwater with water recovery as high as 75%.

Preparation of hydrophobic PVDF hollow fiber membranes for desalination through membrane distillation

Fabrication of polyvinylidene fluoride (PVDF) hydrophobic asymmetric hollow fiber membranes was studied by introducing inorganic salt LiCl and water soluble polymer polyethylene glycol (PEG) 1500, using N,N-dimethylacetamide (DMAc) as solvent and tap water as the coagulation medium. The membranes properties also were tested and characterized. It is found that the non-solvent additive can increase membranes porosity, ether LiCl or PEG 1500. Because of the addition of PEG 1500, the PVDF membranes obtained a rough topography on the membrane surface and the contact angle of the PVDF membranes increased to 113.50 degrees compared to 89.82 degrees of the PVDF membranes spun without an additive. During direct contact membrane distillation (DCMD) of 0.6 M sodium chloride solution, the PVDF membranes spun with PEG 1500 as a non-solvent additive achieved higher water permeation flux compared to the membranes spun from PVDF/DMAc and PVDF/DMAC/LiCl dopes, but the latter two membranes exhibited higher salt rejection rate.

Hydroxyl carboxylate based non-phosphorus corrosion inhibition process for reclaimed water pipeline and downstream recirculating cooling water system

A combined process was developed to inhibit the corrosion both in the pipeline of reclaimed water supplies (PRWS) and in downstream recirculating cooling water systems (RCWS) using the reclaimed water as makeup. Hydroxyl carboxylate-based corrosion inhibitors (e.g., gluconate, citrate, tartrate) and zinc sulfate heptahydrate, which provided Zn(2+) as a synergistic corrosion inhibition additive, were added prior to the PRWS when the phosphate (which could be utilized as a corrosion inhibitor) content in the reclaimed water was below 1.7 mg/L, and no additional corrosion inhibitors were required for the downstream RCWS. Satisfactory corrosion inhibition was achieved even if the RCWS was operated under the condition of high numbers of concentration cycles. The corrosion inhibition requirement was also met by the appropriate combination of PO4(3-) and Zn(2+) when the phosphate content in the reclaimed water was more than 1.7 mg/L. The process integrated not only water reclamation and reuse, and the operation of a highly concentrated RCWS, but also the comprehensive utilization of phosphate in reclaimed water and the application of non-phosphorus corrosion inhibitors. The proposed process reduced the operating cost of the PRWS and the RCWS, and lowered the environmental hazard caused by the excessive discharge of phosphate. Furthermore, larger amounts of water resources could be conserved as a result.

Fluoride removal from brackish groundwater by direct contact membrane distillation

The direct contact membrane distillation (DCMD) applied for fluoride removal from brackish groundwater is presented. The self-prepared polyvinylidene fluoride membrane exhibited high rejection of inorganic salt solutes and a maximum permeate flux 35.6 kgm(-2) h(-1) was obtained. The feed concentration had no marked impact on the permeate flux and the rejection of fluoride. The precipitation of CaCO3 would clog the hollow fiber inlets and foul the membrane surface with the increase of concentration factor when natural groundwater was used directly as the feed, which resulted in a rapid decline of the module efficiency. This phenomenon was diminished by acidification of the feed. The experimental results showed that the permeate flux and the quality of obtained distillate kept stable before concentration factor reached 5.0 with the acidified groundwater as feed. The membrane module efficiency began to decline gradually when the feed continued to be concentrated, which can be mainly attributed to the formation of CaF2 deposits on the membrane surface. Finally, a 300 h continuous fluoride removal experiment on acidified groundwater was carried out with concentration factor at 4.0, the permeate flux kept stable and the permeate fluoride was not detected.

The effects of operating parameters on spiramycin removal by nanofiltration membrane

Spiramycin removal from wastewater using four nanofiltration (NF) membranes (NF270, NF90, ESNA1-K1 and ESNA1-LF2-LD) was studied. The effects of operating pressure, feed temperature, feed concentration, cation and anion ions on the permeate flux rate and spiramycin rejection were investigated. The results show that increasing operating pressure resulted in the increase of both permeate flux and spiramycin rejection. The flux rate increased almost linearly with temperature, while the spiramycin rejection decreased. The permeate flux rate declined relatively with increasing feed concentration of spiramycin for NF270 and ESNA1-LF2-LD membranes compared with NF90 and ESNA1-K membranes. The presence of cations reduced spiramycin rejection, with the strength of influence for the NF270 NF membrane following the order Mg(2+)>Ca(2+)>K(+). The presence of anions also resulted in decreased spiramycin rejection, the strength of the effect following the order NO(3)(-)>Cl(-)>SO(4)(2-) for the NF270 membrane.

Domestic wastewater treatment by forward osmosis-membrane distillation (FO-MD) integrated system

In this study, real domestic wastewater treatment by forward osmosis-membrane distillation (FO-MD) integrated system was investigated in laboratory scale. The integrated membrane system presented a good separation performance and the removal efficiency of most contaminants in the domestic wastewater was higher than 90%. High molecular weight contaminants were completely removed, while a few low molecular weight contaminants permeated through the membrane. The FO membrane fouling layer mainly consisted of organic substances like polysaccharides and proteins, and was very loose and could be effectively removed by rinsing the membrane surface with tap water. By comparison, the MD membrane fouling was mainly induced by inorganic salts and was not as severe as that of the FO membrane. During 120 h continuous operation, the FO-MD integrated system exhibited satisfying performance stability and maintained a high water yield and high product water quality. The results indicated the potential of the FO-MD integrated system for municipal wastewater treatment in coastal cities, water purification and desalination.