Phenol derivatives containing substutient are used intensely in industry and their presence in surface and waste water is a problem requiring urgent solution due to their tendency for bioaccumulation, cancerogenic effects, high toxicity and weak biodegradability. In this study, the degradability and toxicity of chlorinated phenols 2-CP, 2,4-DCP and 4-CP and nitrated phenols 2-NP, 2,4-DNP and 4-NP were investigated. These phenols are included on the priority toxic pollutant list within the scope of clean water regulations according to both the US EPA-2014 and the European Union (2455/2001/CE) and form serious threats to public health and aqueous ecosystems.
The degradability of chloro and nitro phenols was researched by applying the Fenton/Fenton-like processes (under optimal conditions) and measuring the model pollutant concentrations, COD and TOC parameters. The effects of substituent type/position and number were determined with toxicity measurements using Vibrio fischeri bacteria (DIN/EN/ISO 11348-2). Statistical analysis was performed in detail for both Fenton/Fenton-like processes (T test) and toxicology measurement results (One-Way ANOVA) for the model pollutants (P<0.05).
In the first stage of the study, model pollutant removal of 95-100%, COD removal of 64-85% / 60-77% and TOC removal efficiency of 52-65% and 40-61% were achieved respectively with Fenton and Fenton-like processes.
In the second stage of the study, the results of toxicity measurements of the pollutants performed before processing found EC50(mg/L) and toxic unit values (TU) were 8.10-12.34 for 2-CP, 2.24-44.67 for 2,4-DCP, 1.20-83.33 for 4-CP, 13.43-7.44 for 2-NP, 8.92-11.21 for 2,4-DNP, and 4.77-20.9 for 4-NP, respectively. After processing, the EC50/EC20 and TU values were determined to fall to unobservable levels.
According to the order obtained with toxicity measurements of 4-CP > 2,4-DCP > 4-NP > 2-CP > 2,4-DNP > 2-NP, the chlor substituent had higher toxic effect compared to nitro. As the substituent numbers increase the toxicity increased; however, para position was identified to be more toxic compared to other positions. The reason for the 4 (para) position being more toxic than the 2,4 (ortho-para) position is thought to be due to the chlor or nitro linked to the 2 or ortho position binding to the OH group of phenol with a 5- and 6-member H-bridge in cis position forming a ring, which leads to inactivity.
Zeynep Ceylan and Şeyda Deniz Aydın