Abstract:

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 Aliivibrio 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.