The article attempts to assess the usefulness of the Taguchi method to optimise the purification process of synthetic textile wastewater (pH 6.7 - 7.2, Conductivity = 6.71 - 6.84 mS/cm, Salinity = 3581 - 3648 mg NaCl/l, Colour = 560 - 4710 mg Pt/l, COD = 2220 - 2290 mg O2/l, TOC = 394 - 551 mg/l) using K2FeO4. The research was conducted using 3 types of wastewater containing anionic detergent (sodium lauryl sulfate, 100 mg/l) and differing only in the concentration of azo dye Acid Green 16 (AG 16). Technical K2FeO4 was used as an oxidiser, which was subjected to physico-chemical analysis (purity, UV-VIS spectrum, surface characteristics and chemical composition using SEM and EDX methods). For planning and optimising the wastewater treatment process, the Taguchi method was used for four input parameters: pH (2, 7, 12), reaction time (10, 30, 50 min), AG 16 concentrations (20, 120, 220 mg/l) and K2FeO4 concentrations (25, 125, 225 mg/l), for which 9 experiments were performed in accordance with the plan adopted. Test result analysis allowed to indicate the optimal values for individual input parameters (pH 2, time = 50 min, AG 16 = 20 mg/l, K2FeO4 = 125 mg/l). Under these conditions, visual discoloration of wastewater was obtained (AG 16 = 0.4 mg/l, ↓98% ), colour removal (66 mg Pt/l, ↓88%) and DOC (249 mg/l, ↓37%).
The paper presents the application of potassium ferrate(VI) (K2FeO4 ) for the removal of selected pollutants from water and wastewater. The research results on the degradation of endocrine disrupting compounds (EDCs), decomposition of surfactants (SPCs), personal care products (PCPs), pharmaceuticals and their metabolites have been reviewed. Due to K2FeO4 strong oxidizing and coagulating properties, high stability, non–toxic by–products and non–selectivity it is sometimes called “environmentally friendly oxidant”. Due to this reasons K2FeO4 can be a multi–purpose water and wastewater treatment chemical and an alternative to advanced oxidation processes (AOPs).
The article compares the classic Fenton reagent (Fe2+/H2O2) with its modification with zero-valent iron (ZVI/H2O2) to remove azo dye Acid Red 27 from aqueous solutions at a concentration of 100 mg/L. For both methods, the most favorable parameter values were determined at which visual discoloration of the solutions tested was obtained (for Fe2+/H2O2:pH 3.5, H2O2=60 mg/L, Fe2+/H2O2=0.3, t=15 min, and for ZVI/H2O2: pH 3, H2O2=40 mg/L, ZVI=80 mg/L, t=15 min). Under these conditions, the COD value was reduced by 71.5% and 69.2% for the classic Fenton and its modification, respectively. A reduction in toxicity was also obtained for Vibrio fischeri bacteria to below 25% by using the Microtox test. ZVI digestion at acidic pH for 10 minutes allowed to shorten the reaction time by about four times - from 15 to 4 minutes. BET analysis showed that the specific surface area increases with the digestion time, which significantly accelerates the reaction. The visual discoloration of aqueous solutions was obtained, and the final COD values were very small, ranging from 49-53 mg O2/L. According to the Vibrio fischeri toxicity classification test for water samples, all solutions of dyes tested can be considered as non-toxic (toxicity value <25%). In the study presented, results of decreasing the COD value and concentration of the dye in the ZVI/H2O2 method obtained are slightly worse compared to the Fe2+/H2O2 method. However, taking the decolorisation time as a criterion, a four times faster decolorisation time was obtained in the ZVI/H2O2 method, compared to the Fe2+/H2O2 method.
The paper provides comprehensive information on the recent progress of the use of potassium ferrate(VI) (K2FeO4) for the removal of selected pollutants from water and wastewater. K2FeO4 provides great potential for diverse environmental applications without harm to the natural environment. Therefore K2FeO4 was used in removal of cyanides from gold ore purification processes, degradation of dyes and organic compounds in wastewater and algae removal in the water treatment process. The quoted research results indicate that K2FeO4 due to its strong oxidizing and coagulating properties, could be an alternative to the use of Advanced Oxidation Processes (AOPs) or be an additional option to conventional methods of water and wastewater treatment. As a result of using K2FeO4, the emerge intermediates of the impurities decomposition are nontoxic or show less toxicity than the initial substrates. The use of K2FeO4 is also associated with certain limitations of technical and technological nature, which requires further research in order to use its high efficiency in the degradation of various types of contamination on a technical scale.
The article presents the possibility of using potassium ferrate(VI) (K2FeO4) to remove dyes (Acid Red 27, Reactive Black 5, Acid Green 16) belonging to the single azo, double azo and triarylmethane classes from aqueous solutions with an initial concentration of 100 mg/l (Chemical Oxygen Demand (COD) values for AR27, RB5 and AG16 sulutions were 172, 156 and 198 mg O2/l, respectively). For the most favorable values of oxidation parameters of AR27 and RB5 (pH 7, K2FeO4 concentration, 180 and 240 mg/l, respectively, reaction time 10 min), visual discolouration of the aqueous solutions investigated and a decrease in COD values of 83.7% and 81.4%, respectively, were achieved. In the case of AG 16 dye, in the most favorable conditions of the oxidation process (pH 3, K2FeO4, concentration 300 mg/l, 15 min), visual discolouration and a decrease in the COD value of 83.8% were also obtained. The probable reasons for the higher resistance of AG16 to oxidation using K2FeO4 compared to AR27 and RB5 were also explained, based on the analysis of the structure and type of bonds present in the molecule AG 16.
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