Investigation of the Effect of Substituent Species/Positions and Numbers on Removal of Toxicity from Chloro and Nitro Phenol Compounds with Fenton and Fenton-like Processes

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.