Submerged Aerobic Fixed Film reactor for domestic wastewater treatment

SAFF technology is based an attached growth type aerobic biological process which uses corrugated inert UV stabilized PVC media. The higher surface area of the Submerged Aerated Fixed Film technology allows for rapid digestion of biomass through attached microbes. Air is supplied through a diffused aeration system using a blower. The SAFF media is arranged on the bottom support system of a fixed reactor.

A typical treatment scheme consists of an initial screening followed by an oil and grease trap. The wastewater then flows into the SAFF process for biological treatment. In line with traditional sewage treatment, SAFF uses two stages of treatment - a reactor where BOD is oxidized by attached bacteria and a stage for secondary clarification for removing bio-sludge. In the process set-up presented in this factsheet, the secondary treated effluent passes through a multi-grade filter and then a disinfection unit (e.g. using chlorination) after which the treated effluent can be used for i.e. gardening and irrigation purposes.

The schematic diagram of a SAFF-based sewage treatment plant is presented in Fig. 1 below:

Figure 1. Schematic representation of SAFF technology. Source: POPHALI (n.d.)

Being a compact system, this technology is primarily used when the land is limited and there is a need for a compact system. The process helps reducing organic load and Suspended Solids (SS) compounds of the wastewater. This technology is mainly preferred in small to medium-sized treatment plants.

Due to a low F/M ratio (Food to Mass ratio) and long solid retention time (SRT) it tends to perform smoothly under reasonable variation in organic loading influent concentrations. Generally speaking, higher loading of BOD on the media enables to reduce the size of the reactor. A SAFF process requires 25-40% lesser tank volume as compared to activated sludge process. The sludge generation is normally lesser as compared to a suspended growth process.

However, major challenges which have been observed in SAFF technology is its inability to remove nutrients. Treated effluent of a SAFF unit has to be fed to another unit for nutrient removal (e.g.: a horizontal surface flow constructed wetland).  

For SAFF to become fully functional, a good biofilm growth needs to be formed on the media. This takes some initial time – a start-up period – which needs to be taken into account when planning to implement it.

The expectable service period for a SAFF system is 10-15 years due to the use of inert PVC media material.

Regular operation includes the following tasks:

• Proper monitoring of the inlets and outlets of STP units for free flow of wastewater
• Ensuring the sewage is being pumped at the constant designed rate
• Ensuring adequate DO supply
• Regular monitoring of biofilm growth and recycling of sludge as a decrease of biofilm in the reactor is observed.
• In case the SAFF is combined with a chlorination unit for disinfection control of chlorine dosing at the final outlet is necessary
• Regular desludging and/or recycling of the sludge
• Routine check-up of electro-mechanical equipment for efficient functioning
• Cleaning of the treatment units
• Monitoring of structural cracks and leakages
• Structural examination of steel frames etc, pipe connection fittings and check for signs of corrosion

SAFF technology is a commonly used technology in India to treat domestic sewage. It is popular due to its high degree of treatment with the added advantage of low footprint and comparably low operation and maintenance costs.  

SAFF has been used globally to treat domestic sewage. Satisfactory performance has been observed for removing biological load of sewage using SAFF.

The information presented in this factsheet is based on a document provided by the authors. It is important to note that the authors did not provide citations for the information presented herein. As a result, we are unable to verify the original sources of the data. This factsheet is intended to offer a summary of the available information, and readers are encouraged to independently verify the details for accuracy.