Remoção de micropoluentes de esgoto real por um sistema bardenpho modificado com biomassa suspensa e fixa no reator aeróbio e por ozonização

Abstract

Several studies point to Wastewater Treatment Plants discharges as the main route for the dissemination of drugs, plastic additives and other micropollutants (MPs) in the aquatic environment, due to the limited efficiency of sewage treatments by conventional biological processes. It is possible to increase the efficiency of the biological degradation of micropollutants using treatment systems more advanced than conventional Activated Sludges, such as biological systems with membrane filtration (MBRs), attached (biofilm), in addition to suspended biomass (MBBR/IFAS), and systems with alternating redox conditions. Still, several micropollutants are recalcitrant even to the most advanced biological treatments, which makes it necessary to add tertiary treatments, such as Advanced Oxidative Processes (POAs), among others, ozonation. An attractive strategy to reduce the costs of ozonation is to increase the efficiency of the biological treatment that precedes it for removing micropollutants. The present study evaluated the removal of micropollutants from real wastewater in a pilot biological reactor that incorporates suspended and attached biomass (IFAS) with the modified BARDENPHO process (BARDENPHOmod-IFAS). The BARDENPHOmod-IFAS pilot system has a total volume of 400L in tanks or reactors with Anaerobic > Anoxic 1 > Aerobic > Anoxic 2 > Re-aeration processes, being the Aerobic tank the one incorporating MBBR technology. To guarantee fidelity to real conditions, the system was installed in a large municipal WWTP (2.5 m3.s-1) in the city of Rio de Janeiro, which receives a mixture of domestic sewage, septic tank waste, industrial effluents and leachate from a landfill. A period of operation and monitoring of 24 weeks included physicochemical parameters and nutrients; the removal of micropollutants by the pilot reactor was monitored during the last 7 weeks. As the content of adherent biomass in the support media - one of the main methods of controlling MBBR-type reactors - does not have an established quantification method, two extraction techniques and quantification of adherent biomass were compared, and the ultrasound technique promotes greater use of biomass than a mechanical stirring technique. The BARDENPHOmod-IFAS system showed low efficiency in removing COD and Phosphorus, but good efficiency in removing Nitrogen (63,77±9,7). However, the pilot system removed 98.7 ± 1.2% and 95 ± 8.7% of Bisphenol A and Bisphenol S respectively. The pilot system also reduced significantly the estrogenicity of the wastewater detected with the yeast estrogen screen (YES) test. The anaerobic tank, contrary to expectations can indeed contribute substantially to the removal of ibuprofen and 17α-ethinyl estradiol, being also essential for the removal of trimethoprim and the anoxic tank contributed to the estrone removal; however the pilot system was not able to remove carbamazepine. The efficiency of ozonation as a polishing step for both the municipal WWTP and the pilot system was evaluated for Bromazepam, Clonazepam and Diazepam. Treatability tests were carried out with ultrapure water, with the real effluents from the municipal WWTP and the pilot BARDENPHOmod-IFAS. The experimental apparatus included a cylindrical steel reactor equipped with a stainless-steel microbubble diffuser, with porosity of 20 µm. Regarding the specific dose of O3 applied, the ozonation was more efficient with the effluent from the pilot system, which was able to reach the satisfactory removal of all three compounds using doses close to those previously reported (1.74 mgO3 .mgCOD-1). The pseudo-first order degradation kinetics in both effluents were similar, despite the effluents containing different levels of DOC.