Treatments for micropollutants in wastewater
The presence of micro-pollutants in wastewater is a gradually emerging problem, since traditionally adopted biological treatments are sometimes ineffective.
Many of the organic pollutants that can be found in the wastewater are made from synthetic chemicals, such as: pesticides, pharmaceutical products for human or veterinary use, components of cosmetics and personal care products, disinfectants, fungicides, etc.. These substances are very different from each other and did not exist in the past years.
If activated sludge is not effective, membrane bioreactors (MBR) can be used: they are suitable with high retention times of the mud. The addition of limestone in the treatment of primary sedimentation is also important for synthetic substances . Tertiary treatments with powdered activated carbon and ozonation ensure elimination of pollutants by 80% or more and must be applied downstream of the biological oxidation tank to minimize the consumption of reagents.
The exhausted activated carbon must be filtered and disposed of, usually by heat, together with sewage sludge. Downstream of the ozone treatment a sand filter must be installed, in order to remove the reaction products the ozone itself formed. The treatment with activated carbon accounts for less than 5% of the energy consumption of the plant, while the ozone accounts for 10 through 30%.
To avoid the use of ozone, hydrogen peroxide (H2O2) can be used instead, in combination with UV irradiation. However, due to the consumption of H2O2, management costs are high, what shows the need for a further investigation of photocatalytic systems (UV + TiO2), in which there is no consumptions of reagents as titanium dioxide is a catalyst that is not consumed in the reaction and can be recovered and reused many times.source: Hi-Tech Ambiente n. 8/2014