Effluent Water Treatment
Industry today is coping with two water issues: quality and quantity. In many arid areas of the United States, the Middle East, Asia and Australia, water shortages due to drought and rising demand have put pressure on industry to conserve and use less process water.
Industry has two water quality issues. Intake water often has to be purer than the water used for drinking and bathing. In addition, discharges of process water in industrial treatment systems to streams, rivers, estuaries, and lakes require rigorous effluent treatment to reduce contamination of these water bodies. Some of the advanced industrial wastewater treatment strategies are discussed below.
Traditional Industrial Wastewater Treatment
Historically, water and wastewater treatment plants have used a a variety of strategies to remove contamination from their influent and effluent waters so that it can be either used as process water or discharged to the sanitary sewer. Among the technologies that can be used for water and waste water treatment are ion exchange, reverse osmosis, filtration, flocculation, oil-water separators or biological treatments. Most industrial plants that require high quality water have separate water and wastewater treatment systems with the influent water used in the plant and then sent as used process water to wastewater treatment plants. The plant must then make a significant investment in separate water and wastewater treatment systems.
The Changing Economics of Process Water Use and Disposal
Today, the economics for industrial wastewater treatment and water treatment are changing because of water shortages, rising commodity prices and a higher degree of water and waste water treatment. Current average national prices are increasing more than the rate of inflation for water purchase and wastewater disposal. Nationwide average wastewater disposal rates have increased by 12.1% from 2002-2004. Historically, wastewater rates had risen 2-4% above the CPI from 1986 to 2002. However, among industrial and commercial groups there are widely different wastewater discharge rates based on surcharges for carbon oxygen demand, solids content, flow of their wastewater and degree of effluent treatment. Among the industry groups with the highest wastewater discharge rates are specialty food manufacturing, drum and barrel manufacturing, inorganic chemicals manufacturing, and paint manufacturing and others that use metals or solvents in their process. Water purchase prices are also increasing faster than the CPI.
Rising costs for water, wastewater disposal and rising commodity prices have many corporations rethinking their water and waste water treatment strategies looking to reduce costs. Instead of only considering environmental regulations in their decision making, companies are now looking at other factors in their waste water treatment capital investment models including:
• Economic value of the commodities discharged in wastewater
• Permit costs
• Purchase costs for process water
• Disposal Costs for wastewater
• Waste Disposal costs
• Costs of wastewater treatment systems
By considering all of these factors, one question arises-why can’t we recover our process chemistry and our water from our effluent treatment and reuse these valuable resources in our plant to reduce our costs?
Advanced Industrial Wastewater Treatment
Recovery and reuse of process water in industrial treatment systems requires a new technological strategy based on the separation of process water from the process chemistry. These advanced industrial wastewater treatment system combine traditional off-the-shelf technologies such as membranes, reverse osmosis, micro- and ultra filtration with newer systems that allow recovery of water and process chemistries at a standard of quality that can be reused or recycled back into your process.
Resource and Recovery Technology
US based ThermoEnergy Corporation has introduced CASTTM and RCASTTM solution combined with off-the-shelf technologies such as ion exchange and carbon absorption to provide a unique, efficient and cost effective treatment system that can recover sufficient pure water, contaminates and feed stocks that they can be reused or recycled.
CAST® (Controlled Atmosphere Separation Technology) technology is highly adaptable technology, it adjusts temperature and pressure in a continuous flow system so that water or chemicals can be extracted based on their chemical and physical properties. The technology has two configurations: The CAST system extracts water from the waste materials (such as those found in a metal finishing plant); and the RCAST system, which separates volatile compounds from water (such as solvents from industrial wastewater). By using a vacuum, sensible heat, segregation of waste streams and the chemical properties of compounds; the CAST technology can be designed for a specific process and can separate water from a wide variety of materials from metals to volatile organic compounds.
The CAST technology has many competitive advantages over traditional wastewater evaporators. The systems use vacuum flash evaporation within a contained vessel and do not require a heat exchange surface and are not subject to scaling, salting and fouling that is typical of flash evaporation systems. The design allows to use external components like commercial heat exchangers that are cheaper and easier to maintain. It has high flow rates which in-turn create a high shear force within the vessel which maintains a clean heat transfer surface and allows the system to be operated with low temperature heat sources such as hot water, low pressure steam or waste heat. In addition, by spraying the wastewater into the CAST excellent distillate/condensate quality can be attained. Flash wastewater evaporators systems, like CAST, can be used on viscous liquids because of reduced carryover unlike other types of wastewater evaporators. Also the configuration of the system with the spraying of process solution just below the spray cone allows dissolved or entrained gasses to be dessicated from the feed and will collapse any foam allowing the CAST system to be used on liquids with foaming agents.
The design of the system allows the use of simple technologies, hot water heaters, cooling towers and pumps, as opposed to other wastewater evaporators that require refrigeration systems and/or high pressure steam boilers and other complicated/non-reliable components. The RCAST system separates high vapour contaminates. The unique technology is vital in wastewater recycling and can separate higher vapour pressure contaminates, including ammonia, solvents, ethylene and propylene glycol, for wastewater recycling or reuse for more efficient operations.
The diagram below illustrates the CAST technology.