Abstract
Three organic fertilizers (EDTA (Ethylenedinitrilotetraacetic acid), EDDS (Ethylenediamine-N, N′-disuccinic acid) and DTPA (Diethylene triamine pentaacetic acid)) were tested as Fe-complexes in photo-Fenton process at natural pH for micropollutants (MPs) abatement and simultaneous E.coli inactivation. Less stable Fe-complexes show high iron precipitation, stopping MPs degradation. On the contrary, stable Fe-complexes imply low kinetic rates for MPs removal. To solve these inconveniences, three mixtures of organic fertilizers were also tested, trying to improve the kinetic rates of micropollutants oxidation and overcome iron precipitation. Three different pollutants (propranolol (PROP), acetamiprid (ACMP) and sulfamethoxazole (SMX)) were used as the target compounds. As the iron release is, in part, linked to the hardness of water, two water matrices from two different secondary wastewaters (Membrane Bioreactor (MBR) and Conventional Activated Sludge (CAS)) were tested. The best performance in micropollutant degradation and E.coli inactivation was achieved with the combination of EDDS + EDTA, accomplishing a good equilibrium between iron precipitation and rate of MPs removal. For instance, total removal of propranolol was achieved at 45 min in MBR, while it was only 85.7% in CAS, being an improvement of the process comparing with that obtained using single organic fertilizers. At the end of the treatment, 2.1 log-inactivation for E.coli was reached in CAS. The differences observed between both wastewaters were related to CAS’ higher DOC, turbidity, and hardness. Finally, from the physicochemical characterization conducted, including Biochemical Oxygen Demand at 5 days and phytotoxicity, it is possible to highlight the suitability of these treated effluents for its reuse in irrigation, as long as in CAS matrix the final values of E. coli are within the legal limit.
Highlights
Three organic fertilizers (EDTA (Ethylenedinitrilotetraacetic acid), EDDS (Ethylenediamine-N, N′-disuccinic acid) and DTPA (Diethylene triamine pentaacetic acid)) were tested as Fe-complexes in photo-Fenton process at natural pH for micropollutants (MPs) abatement and simultaneous E.coli inactivation
A low stability of iron chelates causes a fast abatement of MPs but, at the same time, quick iron precipitation causing a decrease in the process efficiency
The capability of three Fe-complexes (EDDS, EDTA and DTPA) as iron sources has been demonstrated in photo-Fenton process for micropollutants abatement in Membrane Bioreactor and Conventional Activated Sludge effluents
Summary
Three organic fertilizers (EDTA (Ethylenedinitrilotetraacetic acid), EDDS (Ethylenediamine-N, N′-disuccinic acid) and DTPA (Diethylene triamine pentaacetic acid)) were tested as Fe-complexes in photo-Fenton process at natural pH for micropollutants (MPs) abatement and simultaneous E.coli inactivation. Other chelating agents, like DTPA, which presents high stability with iron, shows low kinetic rates in MPs abatement In such case, continuous MPs degradation was observed, achieving good removals at the end of the treatment. The behavior of EDDS, EDTA and DTPA was studied in different wastewater effluents (López-Vinent et al, 2020b) and was discussed regarding the evolution of iron during the experiment These results displayed the necessity to search for chelating agents whose use could avoid high iron precipitation and lead to fast kinetic rates in MPs degradation. For this reason, mixtures of EDDS, EDTA and DTPA were used in this study. The turbidity, DOC and alkalinity can affect the photo-chemical reactions due to light scattering, competition for hydroxyl radicals due to the organic matter present in the matrix and hydroxyl radicals scavenging due to the presence of carbonate and bicarbonate
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