|Author:||Fan, Chi Ho|
|Title:||Recyclable nanosorbents for water and wastewater treatment using vibratory shearing enhanced process (V-SEP) membrane filtration system|
|Subject:||Sewage -- Purification|
Sewage -- Purification -- Filtration
Water -- Purification
Water -- Purification -- Filtration
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Applied Biology and Chemical Technology|
|Pages:||xiv, 164 pages : illustrations ; 30 cm|
|Abstract:||Rapid industrialization inevitably leads to discharging various pollutants like heavy metals into drinking water sources such as lakes and rivers. Thus the shortage of clean water has become one of the biggest problems that we are facing. Several chemical processes based on chemical precipitation, adsorption with activated carbon, and ion exchange column have been developed to treat industrial wastewater prior to discharge. However, current processes suffer from some serious drawbacks such as high material, capital, regeneration costs and low efficiency. Membrane filtration like reverse osmosis (RG) is an advanced and commerizcd wastcwater treatment technology used in the past decades; however, it suffers from low effectiveness in treating a large volume of metal containing wastewater and high capital cost. To overcome these problems, polymer enhanced ultrafiltration technology was developed for wastewater treatment. Nevertheless, high shearing force created by the centrifuge pump during operation often causes degradation of the polymer, resulting in passage of fragmented molecules through the membrane and loss of polymer. Vibrating Shearing Enhanced Processing (V-SEP) membrane filtration technology is an advanced system which is able to solve inherent fouling problem in traditional membrane filtration technology. A new type of amphiphilic core-shell nanoparticle which is composed of well-defined poly(methyl methacrylate)(PMMA) hydropholic core and polyethylenimine (PEI) hydrophilic polymer shell is a promising nanosorbent for heavy metal removal. It is envisioned that the core-shell particles with spherical structure and hard PMMA core can withstand high shearing force during the filtration process, The PEI polymer which is covalently attached onto PMMA hard core can effectively adsorb heavy metal ions. On the basis of these two unique features of the V -SEP and core-shell nanosorbents, this thesis work aimed to develop a novel heavy metal treatment process using a combination of amphiphilic core-shell nanosorbent and V-SEP membrane filtration technology. The work included three major parts: 1) Scale-up synthesis of PMMA/PEI nanosorbent; 2) Purifying PMMA/PEI nanosorbent with V-SEP membrane filtration system; 3) Evaluation of heavy metal removal efficiency and nanosorbent regeneration using a combination of nanosorbent and V-SEP membrane filtration technology.|
Part I : Synthesis of PMMA/PEI Nanosorhents in a Pilot Scale Reactor: PMMA/PEI nanosorbent was synthesized in a pilot scale 20L reactor vta a surfactant-free emulsion polymerization by a semi-batch addition method. Particle sizes of three batches of PMMA/PEI nanosorbents were in range of 200 to 300 nm in diameter with narrow size distribution. Zeta-potential values of the three batches of the PMMA/PEI nanosorbents were around +40 mV and monomer conversions were up to 90%. Reaction temperature was continuously monitored during the synthesis and maintained below 85°C. These results showed that synthesis of PMMA/PEI nanosorbent could be scaled up from laboratory quantity to 20L pilot scale based on a similar polymerization mechanism. Part II: Purifying Nanosorbent by Membrane Filtration Process: PMMA/PEI nanosorbent can be easily purified by a high speed centrifuge in a laboratory scale, but it is not feasible to purify a large quantity of nanosorbent synthesized in Part I with the same technique. In fact, industrial scale centrifuge with such a high centrifugation speed is not available. V-SEP membrane filtration system was a suitable one for purifying PMMA/PEI nanosorbent in a pilot scale. Through systematic study of membrane types using a 6-inch membrane stirred cell. MF-03 PTFE microfiltration membrane with 0.1 um pore size was found to be the most appropriate one for purifying PMMA/PEI nanosorbent because of its low rejection percentage of unreacted PEI polymer through the membrane. Study of solid content of the nanosorbent on the flux performance suggested that appropriate solid contents for purifying nanosorbent with the V-SEP membrane filtration system were in the range of 8% to 10%. It was also found that around 240-378L of RO water was required to purify each batch of nanosorbent using diafiltration mode (continuous feeding). In order to reduce the volume of RO water used in the purifying nanosorbent, filtration of purification permeate in different types of ultrafiltration and nanofiltration membrane were conducted in a 6-inch membrane stirred cell. The result showed that NF-16 thin film composite nanofiltration membrane with 78% salt rejection gave the highest COD and conductivity rejection. Thus the NF-16 was the most appropriate membrane for recycling of purification permeate. Part III - Application of Nanosorbent in Wastewater Treatment using V-SEP Membrane Filtration System: Application of PMMA/PEI nanosorbent in wastewater treatment was studied in two stages: preliminary study in a 6-inch membrane stirred cells and pilot study in a V-SEP membrane filtration system. The preliminary study showed that Ag(I), Cu(II) and Cr(VI) ions could be effectively removed by the nanosorbents in the 6-inch membrane stirred cell. However, Ag(I) ions were difficult to be desorbed from the nanosorbent after washing with sulphuric and nitric acid solutions, respectively. Prior to the pilot study using nanosorbent with V-SEP membrane filtration system, the optimum operation pressure and concentration of the nanosorbent have been examined since these parameters could considerably affect the removal effectiveness of contaminant with membrane filtration system, Results indicated that the optimal nanosorbent concentrations were in the range of 10.5 to 15%, and the optimum operation pressure was at 30 psi with the use of an UF-19 membrane. These optimized parameters were used in subsequent studies with V-SEP membrane filtration system, The core-shell nanosorbent is also capable of adsorbing Cu(II) ions and to be regenerated with simple pH adjustment. Adsorption of Cu(II) ions and release of the metal ions could be repeated up to three cycles using the V-SEP membrane filtration system with UF-19 membrane.
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