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Biological Aerated Filtration
Biological Aerated Filtration provides an excellent solution for effective removal of residual bio-degradable matter from an effluent treatment system thus meeting tight requirements and allowing re-use of treated water.
Biological filtration technology is well used for finishing the clarified water resulting from a secondary clarifier, even though it is particularly suitable when surfactants and nitrogen are present. Normally, the biological filtration assures reduction of biodegradable pollutants higher than 60-70% and 40-50% with respect to the surfactants.
The system is arranged on a vertical vessel in which water and oxygen are injected in the bottom of the filters and water is flowing from bottom to top across the media. Within the biological filter microorganisms do not float in the aerated water (mixed liquor) but they remain adhered, i.e. firmly attached to the filling media.
Granular Activated Carbon (GAC) is the media on which both bacteria and organic matter adhere, thus coupling the adsorption phenomena due to the high available surface to the biological degradation performed by the microbial growths. In order to purge the excess sludge the GAC media is regularly backwashed with a reverse flow.
ARTES Ingegneria in more than 30 years of experience has supplied several Biological aerated filters operating on industrial water effluents in the most severe conditions and able to meet extremely stringent requirements in terms of residual pollutants.
The stages of the purification process are quite similar to those of a gravity filter and can be summed up as follows: the waste water, without any coarse or fine suspended solids crosses the filtering layer constituted by active carbon backing, from bottom to top (reverse flow - in this way the biodegradable pollutants reduction can run slowly, uniformly and with high efficiency); the following phenomena occur in the filtering layer: the chemical adsorption of the carbon, contained in the organic substance, and the organic nitrogen bonded to it, which are present in the wastewater, is achieved by means of the active carbon. Also most of the pollutant present in the wastewater attaches itself to the active carbon on which the bacterial population (biofilm) grows up. The degradation process is an oxidation stage of the organic carbon achieved by means of the bacterial filaments (initially during the start-up stage they are in form of gel and subsequently as filaments), mainly in their external part, which bond the carbon to the oxygen present/injected in the water, creating carbon dioxide (CO2) which leaves the system in the form of a colourless and odourless gas. The organic nitrogen is initially transformed (oxidation) into nitrites (NO2-) and subsequently nitrates (NO3-): this process also occurs in the external part of the bacterial biofilm. The nitrates are degraded to nitrogen (N2) in the inner part of the biofilm. The nitrogen leaves the system as a colourless and odourless gas. The purified water that has crossed the bacterial bed reaches the discharge through a dedicated piping. When the biofilm layer becomes too thick the nitrogen gas inside it has trouble in freeing itself and tends to tear it (slough phenomena): in this case the slough is of course replaced by new biofilm and must be removed by counter washing with purified water in order to avoid blockages and decreased efficiency of the system.
Also, the flow rate of the incoming waste water and the oxygen injection may be regulated/controlled in order to assure the good condition for the entire process. In fact a flow rate higher than required can cause losses in the filling material with subsequent failure in the process and expenditures for replacing the activated carbon.
This innovative biological regeneration system of a chemical adsorbent (active carbon) has the advantage of being able to treat large flows of wastewater with a relatively small plant and without replacing the backing material as usually happens with pressure-operated activated carbon filter. Furthermore, the management of the purification process has minimal costs and the production of waste is extremely low. In short, the biological filtration plant represents the umpteenth confirmation of the fact that technological progress in general, and purification in particular, must constantly be sought in the prospective of low environmental impact in order to achieve a real and long-lasting ecological benefit.
BONO ARTES can offer biological filters as a compact plant with either metallic or concrete structures.
All electromechanical appliances are run by a Local Control Panel also available with PLC supervision and automatic control.
The system does not requires special maintenance operations and assures low management costs.
RUNNING CHARACTERISTICS AND ADVANTAGES
- High efficiency in COD/BOD5/Surfactants reduction
- Low operating costs
- No cost for chemicals
- No cost for the regeneration of the filling (activated carbon), with respect to a pressure operated activated carbon filter
- No cost for replacing the fine bubbles diffusors with respect to a biological activated sludge system
- Manual or automatic operation
Bono Artes Via Irno, 221 I-84135 Salerno (Sa) Italy Phone +39 089 271717 Fax +39 089 271259 VAT n. 03065820650
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