SAFF is “Submerged Activated Fixed Film Reactor” is a type of aerobic attached growth treatment process. It is principally designed to enhance the efficiency of conventional activated sludge process. The conventional process tanks occupy larger land area, involve constant monitoring of parameters like MLSS & SVI, require continuous power supply and are susceptible to shock loads. SAFF reactor, whereas , needs , less power , lower volume, no recycling of sludge , less footprint area, besides allowing higher loading to make it an acceptable product. With lower sludge generation plug flow design for positive treatment, SAFF reactors help the ETP users do away with a host of monitoring and running costs, making operations of ETPs easier. Besides this, parallel plate separators and tube settlers are products that are today replacing huge solid/sludge removal equipment.
The use of structured plastic media with the Activated sludge process helped to reduce the volume of the tanks with increased performance. The SAFF systems can easily fit in to underground basins because of small foot print area hence the system is most useful for Sewage Treatment Plants in crowded cities where space is a constraint.
The SAFF system can be designed with single stage or two-stage system depending on inlet BOD and COD and other parameters. The system involves attached growth and submerged growth treatment process. Media such as the COOLFill structures Media occupies around 50 to 70% tank volume depending on the type of effluent and rest of the portion is utilized for suspended growth as in the conventional aeration tank.
SAFF can be down flow or up flow system. The structured PVC media COOLFill is fully submerged in the influent wastewater. The oxygen requirement is met with the help of diffused aeration system, placed at the bottom below the packing media. The fine air bubbles passes through the packing assisting micro-organisms to degrade the organic constituents and reducing the pollution load of the effluent. The even distribution of air and water facilities a homogeneous flow across the entire biologically active plant surface area and enables homogeneous suspended solids retention and biomass growth throughout the media without short-circuiting or entrapment of gas bubbles. Additionally since the highest biological activity takes place in the lower half of the filter and treated water remains above the media , odours are eliminated.
The large biomass present in the reactor (as a result of the stable film of bacteria built on the media) stabilizes BOD/COD and NH4-N from influent wastewater flowing past the biofilm. The system includes advantages of both suspended and attached growth phase at same time in a single reactor.The various engineering design features of PVC COOLFill media like higher viodage ratio, spiral angle to flutes, fine corrugation on the fills, etc. are the heart of the efficient treatment making the system successful in wastewater treatment industry.
Media provides extra effective surface area available over the basin area for microorganisms to grow and remain in the reactor for longer time. This reduces the footprint area required for SAFF tank by 35 to 40 % compare to activated sludge process. The media can also be stacked up to 3.6m height, thus reducing the plan area further
Higher active surface area, fine corrugation helps in developing quantity of sludge inside the reactor, maintaining higher MLSS concentration in the tune of 6000 to 8000 mg/l in the reactor, which is normally not possible in the activated sludge system. Efficient BOD removal up to 95 to 97% can be achieved with single /two stage system.
Cross corrugation pattern of media ensures that diffused air bubble travels in zig zag fashion increasing the bubble travel path and thereby increasing the oxygen transfer rates (oxygen absorption efficiency). This ensures efficient use of aeration system. The increased contact time between the wastewater biomass-oxygen due to criss-cross stacking arrangement of media layers helps in achieving the desired results.
Attached growth treatment increases MCRT thus reducing the sludge generation. The sludge generated is also stable and denser and can be easily separated in the secondary settling.
Old conventional activated sludge / E.A. system can easily be upgraded with SAFF system. COOLFill Structured Media shall be installed easily on the support system. The system capacity increases the organic & hydraulic loadings. The media packing increases the MLSS in the reactor volume and there by deliver the desired results. Provision for diffused aeration shall be made at the tank bottom.
The crossflow media is made of sheets formed with flutes at 30 degrees to the horizontal. This structure gives the highest surface area configuration amongst all media configurations. CD –B19 with an available surface area of 250m2/m3 is suited for nitrification while CD-b27 with an available surface area of 108 m2/m3 is ideal for BOD removal of low strength effluents or with pre treatment.
The open flow media configurations are better suited for higher BOD systems for certain industrial effluent. This media structure is based upon alternating Crossflow and vertical flow sheets thereby reducing chances of plugging while giving high available surface area (90m2/m3 for CD-B27:33). The media offer will be completely non-clog type and shall be used successfully for high strength wastewater.
Primarily used for the BOD treatment of high strength effluent. Since the surface area with media is more than 140m2/m3, vertical flutes allow for large build of bio films without plugging / choking the media.