In wastewater treatment, ultrafiltration (UF) devices are used to recycle and reuse water that contains virtually no physical solids.
Ultrafiltration definition, applications and industries using these process units are covered below.
Ultrafiltration (UF) is a variety of membrane filtration in which forces like pressure or concentration gradients lead to a separation through a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained in the so-called retentate, while water and low molecular weight solutes pass through the membrane in the permeate.
Applications of ultrafiltration
UF can be used for removal of particulates and macromolecules from raw water, to produce potable water. It has been used to either replace existing secondary (coagulation, flocculation, sedimentation) and tertiary filtration (sand filtration and chlorination) systems employed in water-treatment plants or as standalone systems in isolated regions with growing populations. When treating water with high suspended solids, UF is often integrated into the process, using primary (screening, flotation and filtration) and some secondary treatments as pre-treatment stages. Ultrafiltration processes are preferred over traditional treatment methods for the following reasons:
1. No chemicals required (aside from cleaning)
2. Constant product quality regardless of feed quality
3. Compact plant size
4. Capable of exceeding regulatory standards of water quality, achieving 90-100% pathogen removal.
When water recycling is simple, it often needs very little processing. However, when more intensive processing is required, the industry standard procedures include using UF, which is meant to remove physical solids from water by passing it through a semi-permeable membrane. Using ultrafiltration, solids are primarily captured by the filter and discarded.
Recycled water can also be used for a number of industrial purposes, including boiler or cooling tower feed water supplementation, pH adjustment, washing equipment, hardstands and vehicles, fire protection, process rinse water or processing water for production lines in manufacturing industries, toilet flushing, dust control, construction activities, and concrete mixing.
Recycling benefits
In addition to providing a dependable, locally controlled water supply, water recycling provides tremendous environmental benefits. By providing an additional source of water, water recycling offers ways to decrease the diversion of water from vital, sensitive ecosystems, thus ensuring that sufficient water flows to plant, wildlife, and fish habitats—allowing them to live and reproduce. A lack of adequate flow, as a result of diversion for agricultural, urban, and industrial purposes, can cause deterioration of both water quality and ecosystem health. Water users can fulfill their demands by using recycled water, which can free substantial amounts of water for the environment. Other environmental benefits include a reduction in wastewater discharges and reducing or preventing the potential for pollution.
Recycled water can save energy. As the demand for water increases, more water is extracted, treated, and transported, sometimes over great distances, which can require a lot of energy. Also, if the local source of water is groundwater, as more water is removed, the water level drops, which in turn increases energy needed to pump the water to the surface. Recycling water onsite or nearby reduces the energy needed to move water longer distances or to pump water from deep within an aquifer.
Tailoring water quality to a specific water use also reduces the energy needed to treat water. The water quality required to flush a toilet is less stringent than the water quality needed for drinking water and requires less energy to achieve. Using recycled water that is of lower quality for uses that do not require high-quality water saves energy and money by reducing water or wastewater treatment requirements.
Ultrafiltration is used in certain industries to accommodate reuse. Therefore, cost justification for ultrafiltration can include initial capital investment, membrane fouling and replacement costs and also additional pretreatment of feed water to prevent excessive damage to the membranes in the Ultrafiltration Units. Some of the benefits, however, remain more intangible.
Industries using ultrafiltration
Industries that consume large volumes of water or discharge highly toxic effluent are candidates to employ ultrafiltration for water reuse.
These include the chemicals, steel, plastics & resins, paper & pulp, pharmaceutical and the food & beverage industries, including soft drinks & canned foods, as well as power, water & wastewater treatment plants and others.
Ultrafiltration is used to recycle flow or add value to later products and more. In many cases ultrafiltration (UF) is used for prefiltration in reverse-osmosis plants to protect the reverse-osmosis process. Ultrafiltration is an effective means of reducing the silt density index of water and removing particulates that can foul reverse osmosis membranes.
Ultrafiltration is frequently used to pretreat surface water, seawater and biologically treated municipal water upstream of the reverse osmosis unit.
