The CycleofWater: Clean WaterClarification – Dissolved Air Flotation (DAF)Potable water treatment plants process raw watersources through the treatment plants to produce aproduct that meets all ofthe regulatory requirementsfor consumption. Surface water treatment plantsusually will first remove solids in a clarification processprior to filtration. In this process, the treatment plantsgoal is to provide a consistent water quality to optimizethe filtration process and produce and collect solidsthat are easily dewatered and disposed. Those solidsconsist ofinorganic suspended or colloidal material,soluble material that has been precipitated by addingoxidant or changing pH range, and biological material(algae or pathogens) such as Cryptosporidium andGiardia.Traditionally, the clarification process consisted of somemethod to settle solids out ofthe raw water supply.With the new Dissolved Air Flotation technology, theraw water particles are flocculated and separated outofthe water by floating them to the surface, ratherthan settling them to the bottom ofthe basin. DAFis particularly effective in removing low-density solidssuch as turbidity, color, algae, Giardia/Cryptosporidium,and precipitated organics and metals. These are allcontaminants that do not settle well due to particlesize and/or density. These same smaller and/orlow-density flocculated particles can be removed inthe flotation process due to the millions of bubblesthat are released inthe reaction zone to capture theparticles and float them to the surface. DAF can alsobetter handle rapid changes in raw water temperatureand water quality provided that the coagulationchemistry is optimized.Due to short flocculation mixing times and loadingrates as high as 20 gpm/ft2 (48m/hr), the footprint forthe process is significantly smaller than conventionalsettling processes. In addition, the improved captureof solids results in more efficient operation ofthefiltration process, while delivering significantly highersludge solids to be sent for further processing than anysettling process.ITT’s Place In The CycleofWater: Everything But The Pipes
The CycleofWater: Clean WaterClarification – Low-Pressure Membrane PretreatmentMicrofiltration and Ultrafiltration (MF/UF) membranesuppliers are producing low-pressure membranes thatare applied in current treatment process schemes toenhance the water quality effluent required to meetadditional regulatory guidelines. The performanceofthese membranes can be improved when apretreatment system is utilized to reduce the potentialcontaminants such as algae, color, organics, anddissolved contaminants that can foul the membrane.Simple membrane filtration is inadequate to fullymeet the requirements ofthe Safe Drinking WaterAct because the water supply contains dissolvedcontaminants that exceed regulatory levels. Althoughthey offer many benefits, MF/UF systems alone do noteffectively control dissolved contaminants. In additionto expanding plant treatment capabilities, thesepretreatment processes have been found to optimizemembrane performance and reduce capital and wholelifecosts.CASE STORY:Greenville, South CarolinaReduces Raw Water TurbidityWith Dissolved Air FlotationThis ITT Leopold brand dissolved airflotation (DAF) system installation hasa total flow capacity of 75 MGD. It iscurrently the largest operating potablewater treatment dissolved air flotationsystem inthe United States, consistingof twelve trains at 6.25 MGD each. Thereduced turbidity from the raw waterinfluent to the Clari-DAF effluent is aconsistent 90%.A high rate dissolved air flotation clarification processprovides one ofthe best membrane pretreatmentalternatives. The process is designed with the conceptthat it is easier to float small diameter, low-densitysolids than to settle them. Typical of those floc solidsare ones created from color, organics, soluble metals,algae, or colloidal solids by adding inorganic chemicals.Flotation is preferable to sedimentation for these small,low-density hydroxide floc removals because solidswith hundreds of microns in size are required to settle,while particles of tens of microns in size can be floated.Removing the potential fouling material prior tomembrane treatment will result inthe ability toincrease the flux rate, which will reduce the numberof membranes required to treat the water, as well asreduce the frequency of backwashing and chemicallycleaning the membranes, prolonging the life ofthemembranes.17
GineersNow Water Leaders Magazine Issue 002
Water Leaders Magazine: Abengoa Water, Pedro Almagro, CEO. Innovative water solutions for sustainable development.
Exclusive: Latest water technologies, Water bath with wi-fi, bathing water quality standards, Soaring water demand in the Middle East, Toilet water reducer
Special Feature Stories: Chemicals, controls, desalination, EDR, filtration, nano filtration, ultra filtration, membranes, plumbing, MEP, mechanical, electrical, pumps, pipes, reverse osmosis, storage, valves
Country Focus: China, United States, Canada, United Arab Emirates, Saudi Arabia, Qatar, Bahrain, Kuwait, Oman, United Kingdom, Singapore, Hong Kong, Philippines, Malaysia, Indonesia, India, Australia
More engineering stories at https://www.gineersnow.com/topics/magazines