Process Wastewater Technologies LLC

- Model SAF - Submerged Aerated Filter

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This high-performance submerged aerated biological filter provides proven treatment of domestic and industrial wastes in hundreds of installations worldwide, the Submerged Aerated Filter (SAF) has few moving parts, requires very little maintenance and is easy to operate. The SAF could be described as a box of media. It utilizes a rigid, corrugated, structured polypropylene media to give a high surface area for biomass attachment (200 ft² per ft³). The media is arranged into cells-in-series where effluent is contacted with the fully submerged media in the presence of co-current aeration. Use of high-quality components means that a SAF will give many years of service.

  • Pre-assembled for rapid installation
  • Easily transported rental units are available
  • Compact, efficient design, less than
  • ¼ that of a comparable suspended-growth aeration tank
  • Minimal regular maintenance
  • Long life
  • Quiet operation with low odor and low visual impact
  • High quality effluent
  • Can be used in BNR flow schemes
  • Low sludge yield factor

The external walls of the SAF are manufactured of ¼' steel or ⅛' 304 Stainless Steel, with pressed ribs for stiffening. The surface is coated and may also be insulated for extreme environments. All plumbing is polished stainless steel and ABS or PVC plastic as standard. Air is supplied by two low-maintenance regenerative blowers (Duty-Standby). These are housed in a fiberglass kiosk along with the controls. A secondary clarifier tank follows the SAF for removal of any biomass that sloughs off the media during operation.

Utilizing a simple yet clever design, the SAF has few moving parts, requires very little maintenance, and is easy to operate. 10/15/5 (TSS/BOD/NH4-N) effluent is achieved after clarification. SAFs require no regular operator attendance, and are generally used for installations up to 3,000 P.E. There are hundreds of installations around the world. Coated steel or stainless steel construction and use of high-quality components mean that SAFs will give many years of service. They can be located above or below ground.

The SAF could be described as a “box of media”. It utilizes a rigid, corrugated, structured polypropylene media to give a high surface area for biomass attachment (200 ft2 per ft3). The media is arranged into cells-in-series where effluent is contacted with the fully submerged media in the presence of co-current aeration.

The external walls of the SAF are manufactured in 1/4 inch steel or 1/8 inch 304 stainless steel, with pressed ribs for stiffening. The surface is coated (choose a color!) and may also be insulated for extreme environments. All plumbing is polished stainless steel and ABS or PVC plastic as standard.

Air is supplied by two low-maintenance regenerative blowers (Duty-Standby). These are housed in a fiberglass kiosk along with the controls.The kiosk may be sound-proofed for sensitive urban environments. Air enters the process below the media via fine bubble membrane diffusers.

A secondary clarifier tank follows the SAF for removal of any biomass that sloughs off the media during operation.

Typically within 2 to 3 weeks of start-up a SAF will achieve a 10/20 effluent standard (takes less than 1 week on a re-start where a biofilm has been established before). Nitrification then ensues within 2 to 6 weeks, depending on the influent water temperature.

Biological phosphorus and nitrogen removal can be achieved with the SAF since the design incorporates sequential staged operations as required for BNR flow schemes.

Phosphorus removal utilizes the anaerobic, balance tank (septic tank) used prior to the SAF. Recycled sludge from the final clarifier is mixed with the influent in this stage. Nitrogen removal is then achieved via denitrification in the first cell of the SAF where, with no air injected, and the introduction of recycled nitrified effluent from the end of the process, the process becomes anoxic.

The latter SAF cells are fully aerated and BOD removal and nitrification are achieved in these. Full BNR requires a fourcell SAF, minimum.

Typically effluent from a full BNR scheme will be:

  • BOD less than 10 mg/l
  • Total nitrogen less than 5 mg/l
  • Ammonia nitrogen less than 1 mg/l
  • Total phosphorus less than 0.5 mg/l

Regular operation requirements include weekly inspection and de-sludging (less than an hour) and monthly inspection of aeration pattern. Maintenance is minimal as there are no moving parts in contact with the wastewater. Typically the air filter for the blowers needs to be replaced every six months (a five-minute job), and the diffusers need to be replaced every seven years (approximately 1/2-day operation).

Pre-assembled units are easily transported and rapidly installed.
  • Units are pre-assembled for rapid installation
  • Units are easily transported
  • Compact, efficient design, less than 1/4 that of a comparable suspended growth aeration tank
  • Minimal regular maintenance
  • Simple to maintain
  • Low sludge yield factor (common in fixed film processes)
  • Long life
  • Quiet operation with low odor and low visual impact–ideal for sensitive areas
  • High-quality effluent, exceeding secondary treatment requirements, can be used in BNR flow schemes

SAF units can be trailer-mounted for mobility, making them ideal for emergency, supplemental, or temporary use, or for pilot studies.
  • Automation packages including real-time monitoring from a remote location
  • Larger capacity designs, either in shop-fabricated tanks or assembled in precast or cast-in-place concrete tanks
  • Stainless steel walkway, handrail, and ladder/stairs for access
  • Pretreatment and matching final clarifier tanks

Rigid, corrugated structured polypropylene media provides substantial surface area for biomass attachment.

PWTech offers SAF units for rent in addition to sale. Because of their compact nature and clever design, SAFs are easily transported. This makes them ideal for a variety of applications, including:

  • Additional treatment where plants are failing to meet consent limits
  • Emergency use due to equipment failure
  • Use during plant upgrades
  • Temporary facilities (such as military operations or large construction operations)
  • Pilot studies

PWTech will arrange transport to site, installation, and periodic inspection of the units to ensure satisfactory operation. Rental units include the SAF, the clarifier, and an enclosed kiosk housing the blowers and controls.

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