What is an EfloSAF? SAF stands for Submerged Aerated Filter meaning it is a Biological Filter as opposed to a physical filter. This Biozone is the heart of the plant where the fix...
The small volume of the media bed requires a small footprint, hence, the complete SAF plant itself requires a small land area. Biological treatment plants fall into two general groups; fixed biomass and suspended biomass. The SAF plant is the former and because the biomass is fixed on the media bed, it is just a case of gently moving the water to be treated through the media bed to ensure the biomass comes into full contact with the organic rich water. This is often done by hydraulic displacement using very little energy. Conversely, other designs require extensive energy inputs to keep the biomass is suspension and the ‘aeration tanks’ fully mixed. The next most important aspect of biological treatment is the air supply for the biomass. Once again, the SAF fixed film technology has a great advantage because only the air supply necessary for the biomass can be applied. Excessive air and energy is not needed for keeping biomass of moving bed media in suspension. It’s a win - win for SAF technology. Naturally, the quality of the final effluent is of utmost importance and here again the SAF leads with typically a 15:15 (BOD: Suspended Solids) quality before the application of tertiary treatment. Sand filtration after the SAF plant will see an effluent quality of 10:10 or better. The SAF process is aerobic and ideal for sewage and industrial waste waters. The latter particularly benefit from the high biomass concentration; equivalent to 9000 mg/l MLSS (volatile). This provides a long sludge age and low sludge production. This long sludge age, achieved by very gentle conditions in the biozone, creates an attached biomass that provides full nitrification and partial de-nitrification deep within the biomass layer. Apart for these benefits, the ‘sloughed’ waste sludge is very easy to settle in the downstream clarifier without carry over and also without any sludge bulking issues caused by filamentous bacteria. The SAF technology is ‘straight through’. This means no Return Activated Sludge systems are required, saving money and operator knowhow. The SAF technology is well proven in the MENA region efficiently treating the sewage and waste waters from numerous facilities including exclusive hotel resorts, municipal applications, labor camps and industrial applications. One unusual application of growing interest is for the de-nitrification of treated sewage effluent before it is re-used or discharged to the sea, lakes or for underground aquifer recharge. This is achieved by modifying the SAF to a SNAF standing for Submerged Non Aerated Filter. By eliminating the air diffusion system and relaxing it with a hydraulic flow control system, the aerobic SAF becomes and anaerobic/anoxic SNAF suitable for de-nitrification of treated sewage effluents.
SNAF: Biological nutrient removal
This is a non-aerated fixed film bioreator. SNAF - Submerged Non-Aerated Filter - specifically developed for the biological removal of nutrients from TSE before discharge to sensitive receiving waters. Nitrates in ground water, rivers & lakes and the sea are an increasing problem worldwide and are a result of agricultural and sewage discharges. Even arid regions such as the Middle East are suffering with increasingly high nitrate levels in ground water sources. Long term recharge of ground water aquifers requires nitrate removal to prevent a steady buildup of nitrates, particularly if the ground water is considered as a future source of potable water. Nitrate as nitrogen is typically in the region of 20 mg/l in well treated TSE but this concentration is still high and can lead to algae growth when discharged the sea, especially creeks, which then cause disruption to intakes of desalination plants. In landscape features such as lakes & rivers, the algae is aesthetically bad. In both the sea and lakes, the algae rapidly consume the available oxygen leading to fish deaths. The SNAF is a development of the successful SAF submerged aerated filter used extensively for aerobic biological treatment of sewage and industrial wastewaters. The SAF uses a series of air diffusers to deliver the necessary oxygen to the biomass as well as help provide the unique flow patterns within the media bed, ensuring high rates of biological oxidation with relatively low retention times and energy consumption. At the ‘heart’ of the SNAF process is a similar structured, fixed bed to that found in the SAF but instead of using air diffusion for the flow patterns in the media, hydraulic flow circulation is generated to ensue complete mixing and a very high concentration of attached, nutrient reducing biomass is maintained in the Biozone. The absence of an air supply allows the de-nitrification to take place. For the removal of nutrients in TSE, it is necessary to provide both an aerated oxidation step followed by a non-aerated reduction step. In this way, any ammonia in the TSE is oxidized to nitrate and the nitrate is reduced to nitrogen gas for release to the atmosphere. The SNAF technology will remediate these problems.
Case Study:
Project: Al Barari Villa Development, Dubai
Water Treatment Design: Eflo International Ltd, UK
Water Treatment Technology: EfloSAF and EfloSNAF
This high end development of private villas, mostly used for weekends and vacations, enjoys superb landscape design offering a jungle effect, including extensive use of rivers and lakes. The evaporation, especially due to the summer temperatures demanded a constant make up of lost water. In order to be green and to consider the environment, the client required the make up water to be re-used treated sewage effluent (TSE) from the municipal works. This supply of TSE served both the irrigation requirement for the landscaping and the river make up water. However, the TSE needed its nutrients to be removed before it was suitable to use in the rivers. The nutrients were principally nitrate and phosphate. If these entered the rivers, they would quickly produce algae blooms turing the rivers green. SAF technology had already been selected for the sewage treatment requirement of the development and it was only natural to select the SNAF for the treatment of the river make up water. An EfloSNAF plant for 1500 m3 per day was selected. The nitrogen reducing bacteria readily adhere to the support media. They are however, fairly delicate and so the gentle environment required is provided within the biozone which allows the bacteria to thrive. Eventually, when they reach a prescribed thickness, they “slough” away from the support media and are carried out with the hydraulic flow to be captured in the downstream settlement tank. The nitrates were treated to sufficiently low concentrations to not cause any algae problems. In this development, the other nutrient, Phosphate, was removed by coagulant dosing and sedimentation within the plant’s settlement tank. The Al Barari project was a successful partnership of the SAF and the SNAF technologies, deploying maximum biological treatment to reap the benefits of low operating costs and environmental gains.