Adsorption on activated carbon is one of the three technological solutions dedicated to removing emerging pollutants from wastewater that are being tested in the PerFORM WATER 2030 project.
Activated carbon is a material with very high specific surface, distributed in microscopic pores, and capable of fixing certain types of chemical compounds on its surface by means of chemical and physical phenomena.
In detail, activated carbon adsorbs poorly polar organic compounds, a category that includes many emerging micropollutants.
Therefore, the use of this material as an additional process to conventional treatments allows to achieve high removal efficiencies for many conventional pollutants and emerging micropollutants.
In the view of making the process effective, or to prevent the activated carbon from adsorbing even those compounds present in much higher concentrations in water that could quickly exhaust its adsorbent power, it is good that it is applied downstream of the other treatments, when conventional pollutants and competing compounds have already been removed.
Finally, there are several ways in which activated carbon can be used, one of which consists in dosing it in the form of powder directly in the water flow, leaving it in contact for the time necessary for adsorption of pollutants and then removing it from the water as small separable particles.
In PerFORM WATER 2030 project an innovative technology based on powdered activated carbon (PAC) is being tested for the removal of emerging micropollutants.
This technology, developed by Veolia, is called Actiflo™ Carb and allows to remove non-flocculable organic matter, odors, flavors and some conventional contaminants from water, in addition to emerging micropollutants.
In detail, the technology is based on the dosage of powdered activated carbon together with other reagents in order to promote combined coagulation, flocculation and sedimentation on lamellar clarifier. Overall, the process is based on the idea of forming clots of activated carbon and other reagents that can hold the pollutants they come into contact with, and then be separated from the water flow, so as to transfer the pollutants from the liquid to the solid phase.
In the past, this technology has been successfully used for the production of high quality drinking water, since it resulted in the removal of 95% of many non-flocculable pollutant components, including disinfection by-products. Several experiences have shown its good performance also for wastewater in the removal of emerging micropollutants, even if the evidence is more limited in this latter case. In particular, it is still necessary to study the process in order to identify the ideal operating parameters to achieve appreciable removal rates of emerging micropollutants while guaranteeing the overall sustainability of the process.
The Actiflo™ Carb pilotfor the removal of emerging pollutants was positioned at the outlet of the secondary sedimentation tanks and upstream of the chemical disinfection process of the San Giuliano Est wastewater treatment plant, selected by CAP as a site of interest for the activity.
The system works with an inlet flow, Qin, which varies between 4 and 9 m3/h, which can be adjusted according to the configuration to be adopted. The recirculation flow rate is about 10% of the Qin. There are two diaphragm valves for recirculation and purge that open and close with variable timing depending on the solids that must be removed (usually the recirculation valve remains open for longer time, since the objective is to maintain activated carbon as long as possible in the system). The dosages of fresh PAC and two reagents are present: ferric chloride (FeCl3) and polyelectrolyte; these can change according to the operating conditions, but usually they have a range that varies between 5-20 ppm for fresh PAC, 2-7 mg/L for Fe and 0.5-1.5 mg/L for polyelectrolyte. The concentration of activated carbon in the system can range between 1 and 3 g/L. In addition, micro-sand is dosed in concentration between 5 and 10 g/L, acting as ballast for the clots to facilitate their sedimentation.
Actiflo™ Carb technology for the removal of emerging micropollutants is used worldwide.
Many installations are located in France and most of them are addressed to drinking water treatment; for the same purpose Actiflo™ Carb has also been successfully applied in China, Philippines, USA, UK, Saudi Arabia and Romania.
The same technology has also been applied to municipal wastewater (in China) and industrial wastewater (in China and France).
Back to Emerging micropollutants