Advanced Filtration Processes & Insights
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The document discusses advanced filtration processes in water treatment, highlighting techniques such as activated carbon filtration, microfiltration, ultrafiltration, and reverse osmosis. It explains their functions, advantages, and operational parameters, as well as their applications in water reclamation and reuse. Key considerations include filtration efficiency, potential drawbacks, and the importance of integrating various membrane systems for optimal water quality.
Advanced Filtration Processes & Insights
- 2. Introduction • Filtration: Water flows through a filter designed to remove particles from samples. The filters are made of layers of sand and gravel, and in some cases, crushed anthracite. • Filtration collects the suspended impurities in water, enhancing the effectiveness of disinfection. • Activated carbon filtration is most effective at removing or reducing impurities and contaminants such as chlorine, sediment, volatile organic compounds, bad taste and odour from water, etc. • The difference between carbon filtration and reverse osmosis is the presence of the high-quality reverse osmosis membrane. ( https://youtu.be/4RDA_B_dRQ0).
- 8. Cont.… • Filtration is a key unit operation in water reclamation, providing a separation of suspended and colloidal particles, including microorganisms, from water. • The three main purposes of filtration are to (1) allow more effective disinfection; (2) provide pretreatment for subsequent advanced treatment steps, such as carbon adsorption, membrane filtration, or chemical oxidation; and (3) remove chemically precipitated phosphorus. • At larger reuse facilities (>1,000 m3 /d), mono/dual-media filters are most commonly used for filtration with gravity or pressure as the driving force. • Both mono/dual-media filters using sand and anthracite have typical filtration rates between (4,900–14,600 L/m2 per hour) while achieving effluent turbidities between 0.3 and 4 nephelometric turbidity units (NTU).
- 9. Cont.… • Membrane filters, such as microfiltration (MF) and ultrafiltration (UF), are surface filtration devices, with pore sizes in the range from 0.1 and 10 µm for MF and 0.005 to 0.1 μm for UF. • In addition to removing suspended matter, MF and UF can remove large organic molecules, large colloidal particles, and many microorganisms. • The advantages of membrane filtration as compared with conventional filtration are the smaller space requirements, reduced labour requirements, ease of process automation, and more effective pathogen removal. • An additional advantage is the generation of a consistent effluent quality with respect to suspended matter and pathogens. • This treatment usually results in effluent turbidities well below 1 NTU.
- 10. • The drawbacks of this technology are potentially higher capital costs, the limited life span of membranes requiring replacement, the complexity of the operation, and the potential for irreversible membrane fouling that reduces productivity.
- 11. Advanced filtration techniques include the following: • Reverse osmosis (RO): In this process, water moves through a membrane with pores that block the passage of molecules larger than water. • RO is the most commonly used advanced filtration method, produces water of especially high purity, and is vital to desalination, water recycling, and wastewater treatment. • Nanofiltration, microfiltration, and ultrafiltration: These are all membrane processes similar to reverse osmosis. All three processes operate on roughly the same principle, though each is best suited for removing contaminant particles of different sizes. For example, microfiltration is best used with fresh water, because the contaminants found in it are of larger size than those found in saltwater, for which reverse osmosis is most often used.
- 12. Microfiltration and Ultrafiltration • MF and UF membrane processes can be configured using pressurized or submerged membrane modules. • In the pressurized configuration, a pump is used to pressurize the feedwater and circulate it through the membrane. • In a submerged system, membrane elements are immersed in the feedwater tank, and permeate is withdrawn through the membrane by applying a vacuum. • The key operational parameter that determines the efficiency of MF and UF membranes and operating costs is flux, which is the rate of water flow volume per membrane area. • Factors affecting the flux rate include the applied pressure, fouling potential, and reclaimed water characteristics. • Typically, MF and UF processes operate at flux rates ranging from 48 to 190 L/m2 per hour.
- 13. Cont.… • An ultrafiltration filter has a pore size of around 0.01 microns. A microfiltration filter has a pore size of around 0.1 microns, so when water undergoes microfiltration, many microorganisms are removed, but viruses remain in the water. Ultrafiltration would remove these larger particles and may remove some viruses • However, filtration efficiencies vary with the type of membrane and the physical and chemical characteristics of the wastewater, resulting in a wide range of removal efficiencies for pathogens. • MF and certain UF membranes should not be relied upon for the complete removal of viruses for several reasons. • Nevertheless, it is generally believed that the new filtration systems have significantly improved performance for microbial removal.
- 15. Cont.….. • Combining MF with chlorination is likely to improve the rate of virus removal. • MF and UF membranes sometimes in combination with coagulation can also physically retain large dissolved organic molecules and colloidal particles. • Effluent organic matter and hydrophobic trace organic chemicals can also adsorb to MF and UF membranes, but this initial adsorption capacity is quickly exhausted.
- 17. Nanofiltration and Reverse Osmosis • For reuse projects that require the removal of dissolved solids and trace organic chemicals and where consistent water quality is desired, the use of integrated membrane systems incorporating MF or UF followed by NF or RO can be required. • RO and NF are pressure-driven membrane processes that separate dissolved constituents from a feed stream into a concentrate and permeate stream. • Treating reclaimed water with RO and NF membranes usually results in product water recoveries of 70 to 85 %. • Thus, the use of NF or RO results in a net loss of water resources through the disposal of the brine concentrate. • RO applications in water reuse have been favored in coastal settings where the RO concentrate can be conveniently discharged to the ocean. • Thus, existing inland water reuse installations employing RO membranes are limited in capacity and commonly discharge brine to the sewer or a receiving stream provided that there is enough dilution capacity.
- 33. Cont.… • Most commonly used RO and NF membranes provide apparent molecular weight cutoffs of less than 150 and 300 Daltons, respectively, and are therefore highly efficient in the removal of organic matter and selective for trace organic chemicals. • Some of the organic constituents that are only partially removed by NF and RO membranes are low-molecular-weight organic acids as well as certain disinfection byproducts. • Recent advances in membrane development have resulted in low-pressure RO membranes and NF membranes that can be operated at significantly lower feed pressure while providing approximately the same product water quality. • However, certain monovalent ions (e.g., Cl– , Na+ , NO3 – ) are only partially rejected by NF, and NF membranes result in product water with higher TDS than RO. • Nowadays, most integrated membrane systems applied in reuse employ RO rather than NF. • However, certain low-pressure NF membranes offer opportunities for wider applications in water reclamation projects because they have lower energy requirements and can achieve selective rejection of salts and organic constituents that results in less concentrated brine streams.
- 34. Cont.. • For wastewater applications, RO and ultra-low-pressure RO membrane facilities typically operate at feed pressures between 1,000 and 2,100 kPa in order to produce between 13.5 and 20 L/m2 per hour of permeate.
- 35. Substances and contaminants are nominally removed by pressure- driven membrane processes
- 36. Cont.….
- 38. Video 1: What is reverse osmosis?
- 39. Video 2: How does RO work?
- 40. Tasks
- 41. Cont.… Question. Estimate the quantity and quality of the waste stream, and the total quantity of water that must be processed, from a reverse osmosis facility that is to produce 4000 m3 /d of water to be used for industrial cooling operations. Assume that both the recovery and rejection rates are equal to 90 % and that the concentration of the feed stream is 400 g/m3 .
- 42. Thanks