Organic fertilizer as a chelating agent in photo-Fenton at neutral pH with LEDs for agricultural wastewater reuse: Micropollutant abatement and bacterial inactivation

Abstract

In a water scarcity scenario, the reused wastewater could be an essential source for agricultural irrigation considering that 60% of fresh water is destined to this area. In this study, an organic fertilizer (Diethylene triamine pentaacetic acid, DTPA) was used as a new chelating agent of iron for photo-Fenton's application at neutral pH using LEDs. Secondary effluents with different characteristics were tested for propranolol removal and bacterial inactivation. With DTPA, the best results were achieved with MBR matrix: 94.0% of propranolol removal and total bacterial inactivation after 120 min. IFAS matrix showed the worst results: 63.2% of propranolol removal and only 2-log reduction for Total Coliforms. The performance of DTPA as chelating agent was compared with EDTA and EDDS with two matrices. In MBR matrix, propranolol removal with EDTA was 100% in 15 minutes, while DTPA and EDDS reached similar results at 120 minutes (94.0 and 91.3%), respectively. The iron precipitation was evaluated, and DTPA showed high stability with Fe2+ (only 10.4% of iron reduction instead 97.3% for EDDS). In addition, it looks like that the stability of iron chelates plays an important role in bacterial inactivation. Thus, the experiments with DTPA showed the lowest bacterial growth-on-the-plate after 72 hours of the end of the experiment. Biodegradability and phytotoxicity were also evaluated and the experiments with DTPA had the lowest toxicity. The results of the experiments performed with DTPA were compared with the values in Proposal for agricultural water reuse suggesting that treated effluent accomplish the requirements for agriculture.