Jian-Jun Qin

Hollow fiber ultrafiltration membranes made from blends of PAN and PVP

Polyacrylonitrile (PAN) hollow fiber ultrafiltration (UF) membranes have been made from a new dope solution containing PAN/N,N-dimethylformamide (DMF)/poly(vinyl pyrrolidone) (PVP 360K)/1,2-propanediol by using a dry-jet wet spinning process. The as-spun fibres were post-treated by means of hypochlorite solutions with different concentrations. The experimental results showed that water flux of a membrane decreased but retention for the same solute increased with increasing air gap. The flux of a treated membrane was about twice higher than that of an untreated membrane. Retentions of an untreated membrane and a treated membrane for PEG 35K were 94 and `1%, respectively. There was an optimum hypochlorite concentration for the treatment to achieve a PAN membrane with a pure water flux of over 200 x 10(-5) l m(-2) h(-1) Pa(-1). The experimental results also showed that the treated membranes experienced higher fouling tendencies than the untreated membrane, mainly due to an increase in contribution of fouling resistance from surface adsorption and pore plugging to the total relative flux reduction

Experimental studies and modeling on concentration polarization in forward osmosis

Concentration polarization (CP) is an important issue in forward osmosis (FO) processes and it is believed that the coupled effect of dilutive internal CP (DICP) and concentrative external CP (CECP) limits FO flux. The objective of this study was to distinguish individual contribution of different types of DICP and CECP via modeling and to validate it by pilot studies. The influence of DICP/CECP on FO flux has been investigated in this study. The CP model presented in this work was derived from a previous study and evaluated by bench-scale FO experiments. Experiments were conducted with drinking water as the feed and NaCl/MgSO(4) as draw solutions at different concentrations and velocities. Modeling results indicated that DICP contributed to a flux reduction by 99.9% for 0.5 M NaCl as a draw solution although the flow pattern of both feed and draw solutions was turbulent. DICP could be improved via selection of the draw solution. The modeling results were well fit with the experimental data. It was concluded that the model could be used for selection of the draw solution and prediction of water flux under similar situation. A draw solution with greater diffusion coefficient or a thinner substrate of an asymmetric FO membrane resulted in a higher flux.

Preliminary study of osmotic membrane bioreactor: effects of draw solution on water flux and air scouring on fouling.

Preliminary study on a novel osmotic membrane bioreactor (OMBR) was explored. Objective of this study was to investigate the effects of draw solution on membrane flux and air scouring at the feed side on fouling tendency in a pilot OMBR system composing the anoxic/aerobic and forward osmosis (FO) processes. Domestic sewage was the raw feed, FO membrane from HTI and NaCl/MgSO4 draw solutions were used in the experiments. Fluxes of 3 l/m2/h (LMH) and 7.2 LMH were achieved at osmotic pressure of 5 and 22.4 atm, respectively. No significant flux decline was observed at 3 LMH over 190 h and at 7.2 LMH over 150 h when air scouring was provided at the feed side of the membrane. However, without air scouring, the flux at 22.4 atm osmotic pressure declined by 30% after 195 h and then levelled off. The potential advantages of the fouling reversibility with air scouring under the operating conditions of the pilot OMBR and better water quality in OMBR over the conventional MBR were preliminarily demonstrated.

A dual membrane UF/RO process for reclamation of spent rinses from a nickel-plating operation—a case study

The objective of this work was to conduct treatability studies on rinse wastewater from process lines of a typical nickel-plating plant for reuse. The study comprised of three steps: (1) a plant process review and the treatability of different combinations of simulated spent rinses in the laboratory; (2) a variability monitoring of a combined rinse at the plant and a treatability study on a combined rinse in the laboratory; (3) a pilot study for reclamation of the combined rinse on site. The study established an optimum dual membrane ultrafiltration (UF)/reverse osmosis (RO) process for treating a combined liquor of spent alkaline, acidic and nickel-plating rinses which resulted in a treated water of a quality suitable for reuse as substitute for town water for the purpose of rinsing. The results of this study provided a good guide to the selection of a UF pretreatment combined with an RO membrane unit as the treatment system. The pilot plant had successfully operated for 6 months, consistently producing a high quality product water (< 95 microS cm-1) at an overall water recovery of 67.5%. The quality of reclaimed water was better than town water used at the factory. The product water from the pilot plant has been used as substitute of town water for in-process rinsing at the factory with no detrimental effects for 3 months.

Effect of feed pH on an integrated membrane process for the reclamation of a combined rinse water from electroless nickel plating

This study explored the effect of feed pH on an integrated membrane process of ultrafiltration/reverse osmosis (UF/RO) for the reclamation of spent rinse water from an electroless nickel-plating operation. Feed pH in the range of 2.54–6.64 was investigated. For UF pre-treatment, the experimental results showed that iron was not rejected by UF membrane when feed pH was below 3.68. However, when feed pH was raised to 3.68, iron rejection increased significantly and reached 98.7% at pH 6.64. For the RO process, it was found that for a particular wastewater containing weak acids and weak bases in this study, permeate pH was higher than the feed pH when the feed pH was low, but lower than the feed pH when the feed pH had reached 6.64. The critical point at which permeate pH would be equal to feed pH was about 6. This observation has not been reported previously. An attempt at explaining the observation was offered. The results showed that concentration of all measured contaminants in RO permeate decreased with an increase in feed pH. As a consequence, the permeate conductivity decreased with increasing feed pH. The membrane flux decreased with increasing feed pH. Total organic carbon (TOC) rejection increased with increasing feed pH due to the enhanced electrostatic repulsion between the negatively charged membrane surface and the negatively charged HOCH2CO2−. Moreover, the caustic soda consumption used for neutralization could be reduced by 39% in the integrated membrane process if the feed pH was set at 3.68 instead of 6.64. It was concluded that pH of the feed had a significant effect on the integrated membrane UF/RO process and the optimum pH of feed water for the treatment was in the range of 3.7–5.6.

A pilot study on a membrane process for the treatment and recycling of spent final rinse water from electroless plating

A hybrid process that includes microfiltration, UV irradiation, carbon adsorption, nanofiltration and ion exchange for treating and recycling spent final rinse water from an electroless plating operation has been developed. The process comprises four steps: (1) wastewater stream segregation, in which spent final rinses are segregated from other more heavily contaminated rinses and are combined to form a raw feed water stream for treatment; (2) pretreatment, in which the raw feed water stream is treated to remove particulates, microorganisms and free chlorine, and to reduce TOC; (3) heavy metal removal, in which the pretreated water is separated into a concentrate stream (containing salts) and a permeate stream (clean water) using a nanofiltration membrane; (4) polishing step, in which the permeate is further deionised using a mixed bed. The polished permeate stream is then recycled back to the plating operation rinsing system. The results of a pilot study showed that high quality product water (heavy metals free and <5 μS/cm in conductivity) is being consistently produced using a NF membrane system with an overall water recovery of 90%. The product water treated using this hybrid process is being recycled for use in the plant operation with no detrimental effects. The design data for a full scale NF plant with a treatment capacity of 25 m3/h has been obtained and the estimated payback period is between 13 and 18 months. The process is more applicable for reclaiming wastewater containing mainly heavy metals but low in monovalent ions.

Direct Osmosis for Reverse Osmosis Fouling Control: Principles, Applications and Recent Developments

Reverse osmosis (RO) has been widely applied in various water and wastewater treatment processes as a prom- ising membrane technology. However, RO membrane fouling is a global issue, which limits it operating flux, decreases water production, increases power consumption and requires periodical membranes Cleaning-in-Place (CIP) procedure. This may result in low effectiveness, high cost and adds environmental issues related to the CIP solutions disposal. For- ward osmosis (FO) or direct osmosis (DO) is the transport of water across a semi-permeable membrane from higher water chemical potential side to lower water chemical potential side, which phenomenon was observed in 1748. The engineered applications of FO/DO in membrane separation processes have been developed in food processing, wastewater treatment and seawater/brackish water desalination. In recent years, DO has been increasingly attractive for RO fouling control as it is highly efficient and environmentally friendly technique which is a new backwash technique via interval DO by inter- mittent injection of the high salinity solution without stoppage of high pressure pump or interruption of the operational process and allows keeping RO membrane continuously clean even in heavy bio-fouling conditions and operating RO membranes at high flux. This paper provides the state-of-the-art of the physical principles and applications of DO for RO fouling control as well as its strengths and limitations.

A pilot study for reclamation of a combined rinse from a nickel-plating operation using a dual-membrane UF/RO process

Abstract A pilot study for reclamation of a combined rinse from a nickel-plating operation was conducted using a dual-membrane UF/RO process. The pilot plant has a product capacity of 1.5 m 3 /h. The OF unit, as a pre-treatment, was operated at 90% water recovery. The RO unit was operated with a 2:1 configuration in a feed-and-bleed mode with recirculation. Trial runs on various operating pressures and water recoveries were conducted and effect of feed pH on RO permeate quality was studied. Finding a critical pH value was explored to design the feed pH for RO process to treat this particular wastewater. A long-term run for the RO unit with an optimized 75% water recovery was later carried out to study the stability of the product and the fouling tendency of membranes. The cleaning-in-place methods were investigated for both OF and RO units. The pilot plant had successfully operated for 6 months at the time of reporting, consistently producing a high-quality product water ( 3 /h.

Optimization of Operating Conditions in Forward Osmosis for Osmotic Membrane Bioreactor

Objective of this study was to conduct a baseline study of osmotic membrane bioreactor (OMBR) - optimization of operating conditions in forward osmosis (FO). Experiments were conducted with an FO pilot system. Tap water was used as the feed and NaCl and MgSO4 solutions were used as draw solution. Effects of various operating conditions on flux have been investigated. In addition, pure water permeability of the FO membrane was tested. It was observed that the plant operation could be stablized within 1 h. When the membrane selective layer faced to the feed, a flux of 6.3 lm -2 h -1 (LMH) was achieved at 24 atm osmotic pressure and 25 oC and effects of feed velocity and air velocity on flux were not siganificant under the testing conditions due to low external concentration polarization (ECP). However, when the selective layer faced to the draw solution, the flux was enhanced by 64% due to much reduced internal concentration polarization (ICP), the flux sharply increased with an increase in velocity of the draw solution in the laminar flow pattern range due to a countable effect of dilutive external concentration polarization (DECP) and leveled off after the flow pattern became turbulent. NaCl performed much higher efficiency than MgSO4 as an osmotic agent due to a greater solute diffusion coefficient of NaCl.

Impact of anti-scalant on fouling of reverse osmosis membranes in reclamation of secondary effluent

The objective of the study was to evaluate the impact of anti-scalant on fouling of reverse osmosis (RO) membranes in reclamation of secondary effluent which was produced by a conventional activated sludge process at Kranji Water Reclamation Plant with the capacity of 151,000 m3/d. The study was carried out using a RO pilot plant with the capacity of 2.4 m3/h. The RO plant was in 2:1 configuration and was operated at 75% recovery and at membrane flux of 17 l m(-2) h(-1). Pilot trials were conducted with and without anti-scalant. Compositions of feed and concentrate streams were analyzed and the pilot data were normalized. The results of the study showed that the plant operation was stable during the first few days after stopping dosage of anti-scalant but after 3-6 days of operation the membranes were fouled. The time lag effect of anti-scalant without dosage was not reported previously and could be potentially beneficial to save chemicals. The membrane fouling was more serious at the second stage due to the formation of calcium phosphate scale when the pilot plant was operated without anti-scalant. The flux of fouled membranes could be completely recovered after clean-in-place (CIP) with citric acid, indicating that scaling dominated the fouling of the RO membranes. These findings in the study could be applied to select an appropriate anti-scalant for prevention from formation of calcium phosphate scale in the RO operation.