The two (2) main technologies used to reduce suspended solids are clarification and media filtration. Clarifiers require a high level of monitoring and supervision to prevent the passing of large slugs of solids due to temperature and chemistry upsets. In addition, the organic polymers used in clarifiers (to promote flocculation), can also cause problems. An excess of these polymers will foul downstream filtration equipment such as RO membranes or nanofilters. Since these polymers are organic, they present a potential food source for bacteria which results in biological growth and biofouling of piping and downstream equipment. Reverse osmosis and nanofiltration systems require protection from particulates and in many cases there are particle dispersions in the low or submicron size range that are not adequately handled
by multimedia, cartridge or bag filtration. In the case of cartridge or bag filtration, frequent change outs can become cost prohibitive and labor intensive when trying to reduce the SDI (Silt Density Index) to an adequate level. Failure to reduce the level of the SDI will result in poor system performance, plugging and fouling of the RO membrane, increased cleaning frequency and therefore reducing the lifespan of the RO modules. These situations translate into higher operating costs. In most cases where these difficult pre-filtration conditions occur, the problem can be addressed with a microfiltration system using Porex Tubular Membrane Filter (TMF™) Modules.
Porex TMF systems are very similar to Reverse Osmosis systems, where a booster pump, piping, valves and TMF elements are mounted to a steel frame. The diagram above provides a typical example of a TMF system and process flow.
Typically, between 75 and 95% of the water passes through as permeate and is sent to the RO or Nanofilter system. The concentrate is recycled up stream of the TMF Modules at the Concentration Tank for re-dilution. Solids concentration is kept at 3-5% with the excess solids sent to a filter press for de-wetting or to disposal. The number of Tubular Membrane Filter Modules required is dependent upon the total flow rate requirement of the system. The modules are typically placed in series, or train, of up to 12 modules and systems is usually designed to allow at least one train of modules to be independently taken off line for routine maintenance cleaning. To support system design, a small pilot test system can be used to determine capacity and identify any issues, such as colloids, that might require further module cleaning.
Porex Filtration provides high quality membrane filter modules for use in water and wastewater treatment systems. We work with qualified distributors and OEM system builders who can provide complete systems.Click here for