Removal of micropollutants with the use of activated carbon and the HUBER Sandfilter CONTIFLOW®
The most frequently applied methods of advanced wastewater treatment with active carbon are added downstream treatment processes. The application methods can be divided into applications using powdered active carbon (PAC) and applications using granulated active carbon (GAC).
Powdered active carbon (PAC):
In most of the implemented projects the fourth (or "quaternary") treatment stage subsequent to the secondary clarifier consists of a contact reactor, sedimentation tank and downstream sandfilter. In the contact reactor the powdered active carbon is added into the effluent from the secondary clarification tank. After a defined adsorption time the trace substances adher to the large (inner) surface of the powdered active carbon particles and settle in the sedimentation tank. A portion of the fine fraction of powdered active carbon does not settle within the defined time. A filtration system is necessary to remove this rest of fine powdered active carbon after sedimentation. If powdered active carbon is used, it must be ensured that the 'contaminated' active carbon is separated to the greatest possible extent, irrespective of the amount of carbon added.
The HUBER Sandfilter CONTIFLOW® ensures that the powdered active carbon is retained and the effluent is virtually solids-free. An effluent quality of ≤ 1 FNU and AFS ≤ 5 mg/l can reliably be achieved and ensured.
Granulated active carbon (GAC):
The HUBER Sandfilter CONTIFLOW® can optionally be filled with granulated active carbon instead with sand and then operated as a GAC filter. The technical process of the machine remains the same as with sand and also the same retention of AFS can be guaranteed. Contrary to powdered active carbon, granulated active carbon can be regenerated. The current costs for regular carbon replacement can therefore be reduced compared to the use of new granulated active carbon.
Removal of micropollutants with the use of ozone and downstream HUBER Sandfilter CONTIFLOW®
The substances attacked by the ozone are normally not completely mineralized but only converted into unknown oxidation products. Particularly also poorly degradable carbon is oxidized with ozonisation and thus partly converted into a form in which it is available for microorganisms so that it can be removed from the wastewater in a downstream biological treatment system. Considering the fact that the transformation products can have negative ecotoxicological effects on the life in waters it is recommended to additionally treat the water downstream in a biological treatment stage prior to discharging it to the receiving water course.
As a biofilm forms on the sand grains a sandfilter can be called a biofilter. The biofilm consists of microorganisms which enable the sandfilter to biologically reduce the transformation products in the wastewater.
In combination with ozonisation the well-proven HUBER Sandfilter CONTIFLOW® can thus be operated with granulated active carbon instead of sand to remove the transformation products. In consideration of the fact that ozonisation and active carbon selectively remove micropollutants from the wastewater the most extensive removal of micropollutants would be achieved through the combination of both.