Are iron chelates suitable to perform photo-Fenton at neutral pH for secondary effluent treatment?

There have been concerns about which iron chelate is most suitable for application in the photo-Fenton process as well as the fate of these chelates after application. In this study, five chelating agents, i.e. citric acid (CA), oxalic acid (OA), ethylenediamine disuccinic acid (EDDS), ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), representing the most used iron chelates were assessed for suitability of application in homogeneous photo-Fenton-like process at pH of 7. The efficiency of the iron chelates were assessed in the disinfection of secondary effluent. The results for the disinfection and bacteria regrowth followed the order EDTA>OA>NTA>CA>OA. All the iron chelates were observed to have increased the COD of the effluent with EDDS having the highest COD contribution. The ability of the chelates to remove aromaticity was measured by the UV254 measurement. The efficiency of the chelates to remove aromaticity decreased in the order CA>EDDS>NTA>CA>OA. To determine the fate of the chelates, toxicity tests were conducted on the chelates before and after irradiation and the results revealed a decrease in toxicity after photoirradiation, implying the chelates were degraded and the products/intermediates produced were of less toxicity as compared to the parent compounds.

Integration of ozone, UV/H2O2 and GAC in a multi-barrier treatment for secondary effluent polishing: Reuse parameters and micropollutants removal.

Current studies tend to combine different advanced treatment technologies to reduce costs and increase efficiency. The objective of this work was to assess the combination of ozonation and UV/H2O2 with activated carbon adsorption for the removal of effluent quality parameters and micropollutants from secondary effluent samples. The experiments were carried out using the following configurations: O3 + GAC + O3 (1); O3 + GAC + UV/H2O2 (2); UV/H2O2 + GAC + O3 (3); UV/H2O2 + GAC + UV/H2O2 (4). Configurations 1, 3 and 4 were the most efficient for organic matter removal, while configuration 1 had the lowest cost on laboratory scale. An additional ultra-filtration membrane unit (UF) was tested at the end of configuration 1, which was optimized in terms of ozone doses for the removal of three organophosphate micropollutants in ultrapure water (TNBP, TCIPP and TPHP at 10 µgL-1). The best cost-effective configuration of this treatment train was the one using 1 mg L-1 of ozone before and after GAC, which achieved around 100% of micropollutants abatement. The role of each treatment to the final micropollutant removal was also discussed, being the first ozone treatment responsible for about 15% removal of the mixture of contaminants, while GAC was responsible for an additional 80% removal. The complete treatment train reached almost 100% of contaminants removal (under detection limit of the method), as well as added security to the system. The achieved results were also compared to international reuse legislations, proving that the combination of O3 and GAC was an interesting option to achieve enough quality for some reuse purposes.

Optimization of UV/H2O2 and ozone wastewater treatment by the experimental design methodology.

The objective of this study was to optimize UV/H2O2 and ozonation systems by means of an experimental design using as a response the efficiency of the operational conditions to remove the methylene blue (MB) dye. Two classes of experimental planning were used: the Doehlert matrix (DM) and the central composite design (CCD). The most important variables for each process were hydrogen peroxide concentration, the ratio of illuminated volume/total volume of the reactor and recirculation flow rate for UV/H2O2, and ozone flow rate, consumed ozone and MB concentration for the ozonation. The DM was more efficient in optimizing the systems, since it used a smaller number of experiments and achieved similar results when compared to the CCD. After optimization, the disinfection efficiency of the systems was tested with secondary effluent evaluating the inactivation of microbiological indicators, Escherichia coli and total coliforms, using the optimized and the worst condition previously obtained with MB removal as response. The inactivation efficiencies in the optimum conditions were about 99%, allowing an efficient disinfection as well as the production of an effluent with quality to be reused according to specific legislations, while at the worse conditions, the inactivation did not reach standards for reuse.