Dyes and pigments are important industrial chemicals. The structures of dyes can be very diverse and complex, so the treatment of wastewater containing these chemicals can be very challenging. Fenton process is particularly attractive and effective to degrade a wide range of dyes. In order to reduce the expenses related to applying these processes, the use of waste materials in the heterogeneous Fenton process, as alternative sources of catalytic iron, is recently investigated in scientific literature. In this study effluent was obtained from dye house unit of carpet factory (Serbia) and it contained the mixture of six commercial dyes. Pyrite cinder, a residue from sulfuric acid production, was also used in this process as a source of catalytic iron. Effluent decolourization rate reached 75% under optimal condition. Additionally, the research included further characterization of obtained effluent in terms of mineralization and metal leaching. A significant degree of mineralization was achieved under the applied conditions. Although, dye degradation was satisfactory, the metal content of the solutions after the process suggests that an additional treatment step, by using lime, is necessary. Results indicated that the applied waste material is effective as iron source in modified Fenton processes for treatment of effluent containing mixture of dyes.

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Diclofenac (DCF) and metformin (MET) are pharmaceuticals often detected in influents and effluents of municipal sewage treatment plants and surface waters which may cause adverse effects to human health and the environment. In recent years, advanced oxidation processes (AOPs) have been demonstrated to be effective technology for the removal of many organic pollutants. The objective of this study was to evaluate the removal and toxicity of investigated pharmaceuticals by UV and UV/H2O2 processes. UV irradiation was provided by a Pen Ray lamp emission at 254 nm which was covered with a quartz tube and placed in the middle of the reactor. Experimental conditions of the process were: [DIC, MET] = 10 mg/L, [H2O2] = 2.5 mM, reaction time 3 h. Results obtained by only UV exposition of solution showed that diclofenac and metformin were degradated 30% and 50% during 3 h test. Addition of 2.5 mM H2O2 to photo reactor contributed to 90% and 100% removal of DCF and MET, respectively. Inhibition toxicity test of MET increased in the following range: 13% (C0) < 38% (UV) < 77% (UV/ H2O2), while toxicity measured for DCF solutions followed the range: 33% (UV) < 75% (C0) < 78% (UV/H2O2). The results confirmed that addition of hydrogen-peroxide accelerated the removal of investigated pharmaceuticals, but at the same time, lead to formation of the more toxic intermediates. The possible reason for better removal efficiency of metformin can be related to its simpler aliphatic structure in comparison to more aromatic diclofenac.

The most important component of coloured wastewaters is the synthetic dyes, which cause negative effects on aquatic ecosystems due to great solubility and persistence. Previous research points out that the heterogeneous Fenton process can be applied as an effective treatment of this type of wastewater. In this paper, the possibility of using waste red mud (RM), as a catalyst for the Fenton reaction, has been investigated. Sample of wastewater was obtained from the local textile industry, as follows: effluent before and after biological treatment. The optimization process was carried out using the response surface methodology, where the pH value, the concentration of H2O2 and the catalyst dose was varied. The following optimal reaction conditions were obtained for raw effluent: pH=3.26; [H2O2]=10 mM; [RM]=0.09 g, while for effluent after biological treatment: pH=3; [H2O2]=4.28 mM; [RM]=0.1 g. Under the given conditions, the efficiency of the Fenton process was 61.83 and 79.65%, respectively.

The use of clays as industrial catalysts requires optimization of modification methods during their preparation. The objective of this paper was to improve the traditional method of bentonite impregnation using ultrasound. For this purpose, three series of samples with Fe3+/clay molar ratios of 0.6–11 mmol/g were prepared, which differed in terms of preparation procedure. The first batch of samples was subjected to the conventional method of impregnation, where total synthesis of catalysts took 4 h. The other two series of samples were prepared with impregnation improved by ultrasound: preparation of Fe-polycation (5 min) and then its incorporation with a clay suspension for 5 and 10 min. The effect of clay preparation method on the catalyst stability and efficiency in a heterogeneous Fenton process was studied on aqueous solutions of synthetic Reactive Blue 4 dye. The catalysts prepared by the conventional method and the improved ultrasound method achieved high efficacy (91–97%, respectively), but their stability was different in the Fenton process. The catalysts prepared using ultrasound for 10 min exhibited greatest stability in the Fenton process. The catalysts synthesized with different Fe loadings displayed an increase in specific surface area and mesoporosity. Samples prepared by the improved impregnation method are comparable in terms of their characteristics with their counterparts prepared by the conventional method. It is thus possible to reduce the time taken by traditional catalyst synthesis by using optimized exposure time to ultrasonic waves.