Enhanced treatment of water with low turbidity:Combined effects of permanganate, PAM and recycled sludge

The effectiveness of enhancing treatment of water with low turbidity through combined effects of permanganate oxidation, PAM aiding coagulation and sludge recycling was investigated through continuous bench scale studies. In comparing with ferric chloride coagulation, only recycling sedimentation sludge was ineffective in enhancing treatment of water with low turbidity. PAM with recycled sludge showed positive effects, and the additional permanganate dosing exhibited the best potential of favoring coagulation, which leaded to much lower effluent turbidity and CODMn. Additionally, it was observed that the optimal permanganate dosage was 0.4 mg/L and the higher permanganate dosage exhibited inhibiting effects for pollutants removal. SEM analysis indicated that the flocs were loosely formed and the particle diameter was critically low for ferric chloride coagulation process. Comparatively, the addition of PAM and permanganate with recycled sludge facilitated the aggregation of tinny particles onto compact PAM polymer chains, therefore contributing to the formation of compact flocs with high particle diameter. The combined employment of recycled sludge, PAM and permanganate showed the best potential of favoring coagulation, mainly through synergistic effects between seeding, polymer bridging and increasing effective collision in mechanism. Additionally, the variation of Fe and Mn concentration after recycling and sedimentating units was studied for the processes, and the main species was also investigated for elements Fe and Mn. Sludge recycling and permanganate addition did not increase Fe and Mn concentration in the sedimented water.

Metal cation removal by P（VC-r-AA） copolymer ultrafiltration membranes

A series of amphiphilic copolymers containing poly（vinyl chloride-r-acrylic acid） （P（VC-r-AA）） was synthesized and used to prepare membranes via a non-solvent induced phase separation method. The prepared membranes were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and water contact angle and zeta potential measurements. The copolymer P（VC-r-AA） chains did not dissolved in a coagulation bath, indicating that the AA segments were completely retained within the membrane. Enriching degree of AA segments in surface layer was 2 for copolymer membrane. In addition, the introduction of AA segments made the membrane electronegative and hydrophilic so that the membrane was sensitive to the solution pH. The fouling resistance, adsorption of Cu（II）, Cr（III） and Ce（IV） ions and the desorption properties of the membranes were also determined. The copolymer membranes exhibited good antifouling performance with a fouling reversibility of 92%. The membranes also had good adsorption capacities for Cu（II）, Cr（III） and Ce（IV） ions. The optimal pH for Cu（II） adsorption was 6 and the copolymer membrane has potential applications for low concentration Cu（II） removal.

Thin-film composite forward osmosis membranes with substrate layer composed of polysulfone blended with PEG or polysulfone grafted PEG methyl ether methacrylate

To advance commercial application of forward osmosis （FO）, we investigated the effects of two additives on the performance of polysulfone （PSf） based FO membranes： one is poly（ethylene glycol） （PEG）, and another is PSf grafted with PEG methyl ether methacrylate （PSf-g-PEGMA）. PSf blended with PEG or PSf-g- PEGMA was used to form a substrate layer, and then polyamide was formed on a support layer by interfacial polymerization. In this study, NaC1 （1 mol·L^-1） and deionized water were used as the draw solution and the feed solution, respectively. With the increase of PEG content from 0 to 15 wt-%, FO water flux declined by 23.4% to 59.3% compared to a PSf TFC FO membrane. With the increase of PSf-g-PEGMA from 0 to 15 wt-%, the membrane flux showed almost no change at first and then declined by about 52.0% and 50.4%. The PSfwith 5 wt-% PSf-g-PEGMA FO membrane showed a higher pure water flux of 8.74 L·m^-2·h^-1 than the commercial HTI membranes （6-8 L·m^-2·h^-1） under the FO mode. Our study suggests that hydrophobic interface is very important for the formation ofpolyamide, and a small amount of PSf- g-PEGMA can maintain a good condition for the formation of polyamide and reduce internal concentration polarization.

Effect of adding a smart potassium ion-responsive copolymer into polysulfone support membrane on the performance of thin-film composite nanofiltration membrane

Thin-film composite (TFC) nanofiltration (NF) membranes were fabricated via the interfacial polymerization of piperazine (PIP) and 1,3,5-benzenetricart)oiiyl trichloride on polysulfone (PSf) support membranes blended with K^+-responsive poly(N-isopropylacryamideco- acryloylamidobenzo-15-crown-5)(P(NIPAM-co- AAB15C5)). Membranes were characterized by attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscope, scanning electron microscope, contact angle, and filtration tests. The results showed that:(1) Under K^+-free conditions, the blended P(NIPAM-co-AAB15C5)/PSf supports had porous and hydrophilic surfaces, thereby producing NF membranes with smooth surfaces and low MgSO4 rejections;(2) With K^+ in the PIP solution, the surface roughness and water permeability of the resultant NF membrane were increased due to the K^+-induced transition of low-content P(NIPAM-co-AAB15C5) from hydrophilic to hydrophobic;(3) After a curing treatment at 95℃, the improved NF membrane achieved an even higher pure water permeability of 10.97 L·m^-2·h^-1 - bar1 under 200 psi. Overall, this study provides a novel method to improve the performance of NF membranes and helps understand the influence of supports on TFC membranes.

PVDF ultrafiltration membranes of controlled performance via blending PVDF-g-PEGMA copolymer synthesized under different reaction times

Polyvinylidene fluoride grafted with poly（ethylene glycol） methyl ether methacrylate （PVDF-g- PEGMA） was synthesized using atomic transfer radical polymerization （ATRP） at different reaction times （9 h, 19 h, and 29 h）. The corresponding conversion rates were 10%, 20% and 30%, respectively. PVDF was blended with the copolymer mixtnre containing PVDF-g-PEGMA, solvent and residual PEGMA under different reaction times. In this study, we explored the effect of the copolymer mixture additives with different synthesis times on cast membrane performance. Increasing the reaction time of PVDF-g-PEGMA causes more PVDF-g-PEGMA and less residual PEGMA to be found in the casting solution. Incremental PVDF-g-PEGMA can dramatically increase the viscosity of the casting solution. An overly high viscosity led to a delayed phase inversion, thus hindering PEGMA segments in PVDF- g-PEGMA from migrating to the membrane surface. However, more residual PEGMA contributed to helping rnore PEGMA segments migrate to the membrane surface. The pure water fluxes of the blended membrane with reaction times of 9 h, 19 h, and 29 h are 5445 L. m 2.h I 1068 L- m 2.h land 1179 L.m 2.h I respectively, at 0.07 MPa. Delayed phase inversion can form smaller surface pore size distributions, thus decreasing the water flux for the membranes with PVDF-g-PEGMA at 19 h and 29 h. Therefore, we can control the membrane pore size distribution by decreasing the reaction time of PVDF-g-PEGMA to obtain a better flux performance. The membrane with PVDF-g-PEGMA at 19 h exhibits the best foulant rejection and cleaning recovery due to its narrow pore size distribution and high surface oxygen content.