Effect of chemical aging on phosphate adsorption and ecotoxicological properties of magnesium-modified biochar.

Using magnesium-biochar composites (Mg-BC) in adsorption allows for the efficient and economically relevant removal of phosphate (PO43-) from water and wastewater. Applying Mg-BC for pollutant removal requires evaluating the adsorption capacity of composites and their ecotoxicological properties. Investigating the composite aging during the application of these composites into the soil is also essential. In the present study, nonaged and aged (at 60 or 90 °C) Mg-BC composites were investigated in the context of pyrolysis temperature (500 or 700 °C). All analyzed biochars were examined by Fourier transform infrared spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and surface area. The content of polycyclic aromatic hydrocarbons (PAHs) (bioavailable Cfree and organic solvent-extractable Ctot), heavy metals (HMs), and environmentally persistent free radicals (EPFRs) were determined. Ecotoxicity was evaluated using tests with Folsomia candida and Allivibrio fischeri. The dependence of adsorption on pyrolysis temperature and composite aging time was observed. Changes in physicochemical properties occurring as a result of aging reduced the adsorption of PO43- on Mg-BC composites. It was found that nonaged Mg-BC700 was more effective (9.55 mg g -1) in the adsorption of PO43- than Mg-BC500 (5.75 mg g-1). The adsorption capacities of aged composites were from 21 to 61% lower than those of the nonaged composites. Due to aging, the content of Cfree PAHs increased by 3-5 times depending on the pyrolysis temperature. However, aging reduced the Ctot PAHs in all composites from 24 to 35% depending on the pyrolysis temperature. Ecotoxicological evaluation of Mg-BC composites showed increased toxicity after aging to both organisms. The use of aged BC potentially increases the contaminant content and toxicity of Mg-BC composites.

Removal of Acid Yellow 17 from Textile Wastewater by Adsorption and Heterogeneous Persulfate Oxidation.

Azo dyes commonly used in various industries have a stable and toxic structure. Wastewater containing AY17 dye as a model contaminant was investigated in terms of color and COD removal by both adsorption and persulfate oxidation activated with the PAC. In this study, the effects of temperature (25-50 °C), pH (3-10), persulfate concentration (1000-4000 mg/L), adsorbent dosage (0.1-0.5 g), reaction time (5-60 min), dye concentration (300-1000 mg/L) and NaCI concentration (0-1000 mg/L) on both color and COD removals from wastewater containing AY17 dye were examined. As a result of the study, it was seen that the dosage of adsorbent, pH and reaction time are important parameters in both systems. The use of the PAC as an adsorbent caused to shortening of the reaction time in the HPS system. It also showed that acidic and neutral pH values are more suitable for the removal of AY17 with both systems. Color and COD removal were determined as 100-88.4% and 100-96.6%, respectively, at optimum values obtained for the adsorption and HPS system. An experimental design was applied for various operating parameters in order to analyze experimental data. Models have been proposed for both color removal and COD removal estimates for both systems.