Wastewater Treatment Basics: What Is a Hollow Fiber Membrane?
What Is a Hollow Fiber Membrane?
Membrane products in common use include mixed cellulose ester microfiltration membranes, nitrocellulose filter membranes, polyvinylidene fluoride (PVDF) membranes, cellulose acetate membranes, regenerated cellulose membranes, polyamide membranes, PTFE membranes and PVC membranes. These membrane technologies are often used for the final polishing of high-purity water in the electronics industry, semiconductor manufacturing and large-scale integrated circuit production.
Ultrafiltration: Principle and Applications
Ultrafiltration (UF) is a pressure-driven membrane separation process based on sieving as its separation principle. With a filtration accuracy in the range of 0.005-0.01 μm, it can effectively remove particles, colloids, bacteria, pyrogens and macromolecular organic matter from water, and is widely used for the separation, concentration and purification of various substances.
Early industrial ultrafiltration was applied to wastewater and sewage treatment. Over the past three decades, as UF technology has matured, its applications have expanded greatly, covering the food industry, beverage industry, dairy industry, biological fermentation, biopharmaceuticals, pharmaceutical chemistry, biological preparations, traditional Chinese medicine preparations, clinical medicine, printing and dyeing wastewater, food-industry wastewater treatment, resource recovery and environmental engineering.
Raw water flows under pressure either outside the hollow fibers or through their inner lumen, forming outside-in and inside-out hollow fiber ultrafiltration membranes respectively. Ultrafiltration is a dynamic filtration process: retained substances are carried away with the concentrate, so the membrane surface is not blocked and the system can run continuously for long periods.
Membrane Structures and the Hollow Fiber Form
By structure, ultrafiltration membranes can be divided into plate-and-frame (sheet), hollow fiber, nanoscale-surface UF membranes, tubular and spiral-wound types. Among them, the hollow fiber ultrafiltration membrane is the most mature and advanced form of UF technology. Hollow fibers have an outer diameter of 0.4-2.0 mm and an inner diameter of 0.3-1.4 mm. The fiber wall is covered with micropores, and the pore size is expressed by the molecular weight of the substances retained (the molecular weight cut-off), which ranges from several thousand to several hundred thousand.
Membrane-based water treatment is applied to wastewater from pharmaceutical, brewing, catering and chemical production, municipal wastewater reuse, hospital effluent, residential wastewater reuse, papermaking and other production and domestic sewage. Membrane separation is a separation technology widely used for separating, concentrating and purifying substances in solutions or gases. The membrane wall is densely covered with micropores: under a certain pressure the feed liquid passes one side of the membrane, the solvent and small-molecule solutes permeate the wall as filtrate, while large-molecule solutes are retained by the membrane, achieving separation and concentration. Because the process is dynamic filtration, macromolecular solutes blocked by the membrane wall are flushed out with the concentrate, so the membrane is not easily fouled and can be used continuously for a long time. Filtration runs at ambient temperature and low pressure, with no phase change - a highly efficient and energy-saving process.
Hollow Fiber Membrane Product Forms
The hollow fiber membrane is an important form of separation membrane. Products include hollow fiber microfiltration (MF) membranes, hollow fiber ultrafiltration (UF) membranes, hollow fiber reverse osmosis (RO) membranes and hollow fiber curtain-type membranes (FPM), together with MBR technology applications. They are mainly used for mineral water purification, production and domestic water purification, pharmaceutical purification, juice concentration, water treatment and recovery in polluting industries such as papermaking, electroplating and chemicals, municipal wastewater reuse, and in the pharmaceutical, chemical, construction, textile, papermaking and petrochemical industries.
Related system configurations include two-way flow (TWF) hollow fiber membrane separation systems, continuous membrane filtration (CMF) systems, membrane bioreactors (MBR) and submerged curtain-type membrane modules, which can be flexibly customized to the size of the aeration tank.
Membrane technology has come into wide use in China and its promotion has entered a mature stage. Using membranes to separate pollutants from water molecules allows precious water resources to be reused, while valuable heavy-metal ions in the pollutants can also be filtered, concentrated and recovered, with considerable economic benefits. Well-known petrochemical, cashmere manufacturing, beverage, pharmaceutical and municipal wastewater treatment operators have already applied it on a large scale. It occupies no land and consumes little energy, with a clear return on investment and extremely broad prospects.
Typical Applications
Clarification filtration of brewed products such as soy sauce and vinegar
Clarification, filtration and turbidity removal of fruit wine, medicinal wine and low-alcohol liquor
Clarification, filtration and concentration of tea drinks and fruit beverages
Separation and refinement of traditional Chinese medicine extracts
Reclaimed water reuse in residential communities or buildings
Bacteria and turbidity removal for tap water and groundwater purification
Pretreatment upstream of reverse osmosis systems
Water supply purification for residential communities and housing units
Oil-water separation for machining cutting fluids and rolling coolants
Textile desizing wastewater and emulsion separation
Wastewater treatment in papermaking, electroplating and chemical industries
Food processing wastewater from milk purification and the processing of meat, fruits and vegetables, grain, soybeans, MSG, alcohol, brewing and beverages
