Search

In this study, calcium ferrites with different Ca : Fe atomic ratios (1 : 1, 1 : 2, 1 : 3 and 2 : 1) were prepared from Ca and Fe nitrates treated at 300, 700 and 900 °C and evaluated for phosphate adsorption and recovery from wastewater. TG, XRD, Mössbauer spectroscopy, SEM, VSM magnetic measurements, and BET analyses showed the formation of two different calcium ferrite phases, i.e. , CaFe 2 O 4 and Ca 2 Fe 2 O 5 at 700 and 900 °C. The adsorption results indicated that the formation of calcium ferrite structure is critical for phosphate adsorption/recovery. Evaluation of the pH, initial phosphate concentration, contact time, coexisting ions and desorption conditions showed remarkable adsorption capacities of 62-75 mg g -1 for CaFe1:2-700 and 28-43 mg g -1 for CaFe1:2-900. The phosphate adsorption on the Ca ferrite surfaces is so strong that the recovery/desorption showed limited efficiencies, e.g. , 15-39%., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The present work assessed some engineering approaches, such as the addition of the redox mediator anthraquinone-2,6-disulfonate (AQDS) (50 and 100 μM), microaeration (1 mL air min -1 ), and nitrate (100-400 mg L -1 ), for enhancing the biotransformation of the antibiotics sulfamethoxazole (SMX) and trimethoprim (TMP) (200 μg L -1 each) in anaerobic reactors operated at a short hydraulic retention time (7.4 h). Initially, very low removal efficiencies (REs) of SMX and TMP were obtained under anaerobic conditions (∼6%). After adding AQDS, the anaerobic biotransformation of these antibiotics significantly improved, with an increase of approximately 70% in the REs with 100 μM of AQDS. Microaeration also enhanced the biotransformation of SMX and TMP, especially when associated with AQDS, which provided REs above 70%, particularly for TMP (∼91% with 1 mL air min -1 and 50 μM of AQDS). Concerning nitrate, the higher the added concentration, the higher the REs of the antibiotics (∼86% with 400 mg L -1 ). Therefore, all the assessed approaches were demonstrated to be very effective in improving the limited biotransformation of SMX and TMP in anaerobic reactors, ensuring REs comparable to those found in higher-cost wastewater treatment technologies, such as conventional activated sludge, membrane bioreactors, and hybrid processes., (Copyright © 2020 Elsevier B.V. All rights reserved.)