In this study, the treatment process of three cosmetic wastewater types has been investigated. Coagulation allowed to achieve chemical oxygen demand (COD) removal of 74.6%, 37.7% and 74.0% for samples A (Al₂(SO₄)₃), B (Brentafloc F3) and C (PAX 16), respectively. The Fenton process proved to be effective as well – COD removal was equal to 75.1%, 44.7% and 68.1%, respectively. Coagulation with FeCl₃ and the subsequent photo-Fenton process resulted in the best values of final COD removal equal to 92.4%, 62.8% and 90.2%. In case of the Fenton process, after coagulation these values were equal to 74.9%, 50.1% and 84.8%, while in case of the H₂O₂/UV process, the obtained COD removal was 83.8%, 36.2% and 80.9%. High value of COD removal in the Fenton process carried out for A and C wastewater samples was caused by a significant contribution of the final neutralization/coagulation. Very small effect of the oxidation reaction in the Fenton process in case of sample A resulting from the presence of antioxidants, ‘OH radical scavengers’ in the wastewater.

Rapid global industrialization constantly impacts the environment by discharging pollutants. Therefore, various materials are currently being investigated for environmental applications, including two-dimensional (2D) MXenes. Herein, we focus on MXene-enabled technologies for removing inorganic and organic contaminants present in gaseous and liquid forms, especially organic dyes, pharmaceuticals, and solid pollutants. We foresee a considerable potential for MXene-enabled technologies to remove heavy ions and radionuclides and recover precious elements. We show that MXenes could efficiently inactivate microorganisms without harming the environment. Finally, we discuss the associated opportunities and challenges in MXenes’ surface chemistry, semiconducting activity, interfacial effects, adsorption, and photocatalysis. Altogether, this article showcases outstanding opportunities for MXenes in the rapidly growing field of environmental applications. Graphical abstract

Fossil fuel combustion is a serious environmental problem. Significant quantities of flue gasses and wastewater, requiring further treatment, are produced. This article compares three wet flue gas desulfurization (FGD) wastewater treatment methods: coagulation with precipitation using iron(III) ions—recommended by the European Union as the best available technique (BAT)—and two alternative advanced oxidation processes (Fe²⁺/H₂O₂ and Fe⁰/H₂O₂). Both oxidation processes that were used met the technical FGD wastewater treatment requirements of the BAT. The best treatment effects, expressed as pollutants’ removal, were obtained for the Fe²⁺/H₂O₂ process for 150/300 mg/L reagent doses. It allows effective removal of boron up to 212 mg/L and heavy metals up to below the detection limit <0.010 mg/L for Pb and <0.005 mg/L for Cu. Therefore, the Fe²⁺/H₂O₂ process could be an option for FGD wastewater treatment as an alternative to the BAT recommended iron(III)-based coagulation with precipitation. Additionally, an analysis of variance was applied to check the significance of the two independent variables and their interactions. Statistical analysis confirmed high efficiency and applicability of treatment process.

Advanced oxidation processes (AOPs) such as H₂O₂/UV, O₃/H₂O₂, modified Fenton, and modified photo-Fenton processes have been investigated in terms of the treatment of landfill leachate with ratio of BOD₅/COD in the range of 0.22 to 0.24. The modification of Fenton and photo-Fenton processes consisted in the inclusion of precipitation and separation of humic substances at pH 3. Due to the precipitation, the value of COD decreased by 39% and BOD₅by 7.1%. The modification of the processes allowed us to improve the efficiency and to decrease the doses of reagents necessary to continue the process. Modified photo-Fenton process proved to be the most effective (92.7% COD removal) of all processes investigated. Additionally, modified-Fenton process was much more effective than the other two processes when compared up to 120 min, while after longer times it gave the least satisfactory results. After 30 min of modified-Fenton process BOD₅/COD ratio increased to 0.43. The parameter referred to as “efficiency of oxidants” was used to estimate the efficiency of all the processes—its value varied from 178 to 239%. Various substances including phthalates, hydrocarbons, silanes, and siloxanes were identified in raw and treated leachate.

Wastewater from a cosmetic factory, with an initial total organic carbon (TOC) of 146.4 mg/L, was treated with Fe₂O₃/Fe⁰/H₂O₂, Fe₃O₄/Fe⁰/H₂O₂, light/Fe₂O₃/Fe⁰/H₂O₂, and light/Fe₃O₄/Fe⁰/H₂O₂ processes. The light-supported processes were more effective than the lightless processes. The fastest TOC removal was observed during the first 15 min of the process. Out of the four tested kinetic models, the best fit was obtained for the modified second-order reaction with respect to the TOC value. The best treatment efficiency was obtained for the light/Fe₃O₄/Fe⁰/H₂O₂ process with 250/750 mg/L Fe₃O₄/Fe⁰ reagent doses, a 1:1 hydrogen peroxide to Chemical Oxygen Demand (H₂O₂/COD) mass ratio, and a 120 min process time. These conditions allowed 75.7% TOC removal to a final TOC of 35.52 mg/L and 90.5% total nitrogen removal to a final content of 4.9 mg/L. The five-day Biochemical Oxygen Demand to Chemical Oxygen Demand (BOD₅/COD) ratio was increased slightly from 0.124 to 0.161. Application of Head Space Solid-Phase Microextraction Gas Chromatography Mass Spectrometry (HS-SPME-GC-MS) analysis allows for the detection and identification of 23 compounds contained in the raw wastewater. The identified compounds were eliminated during the applied process. The HS-SPME-GC-MS results confirmed the high efficiency of the treatment processes.

Advanced Oxidation Processes (AOPs), such as the Fenton, photo-Fenton and H₂O₂/UV processes, have been investigated for the treatment of cosmetic wastewaters that were previously coagulated by FeCl₃. The Photo-Fenton process at pH 3.0 with 1000/100 mg L⁻¹ H₂O₂/Fe²⁺ was the most effective (74.0% Chemical Oxygen Demand (COD) removal). The Fenton process with 1200/500 mg L⁻¹ H₂O₂/Fe²⁺ achieved a COD removal of 72.0%, and the H₂O₂/UV process achieved a COD removal of 47.0%. Spreading the H₂O₂ doses over time to obtain optimal conditions did not improve COD removal. The kinetics of the Fenton and photo-Fenton processes may be described by the following equation: d[COD]/dt = -a[COD] t^m (t represents time and a and m are constants). The rate of COD removal by the H₂O₂/UV process may be described by a second-order reaction equation. Head Space, Solid-Phase MicroExtraction, Gas Chromatography and Mass Spectrometry (HS-SPME-GC-MS) were used to identify 48 substances in precoagulated wastewater. Among these substances, 26 were fragrances. Under optimal AOP conditions, over 99% of the identified substances were removed in 120 min.