Daria Juretic

Photooxidation processes for an azo dye in aqueous media: modeling of degradation kinetic and ecological parameters evaluation.

Three photooxidation processes, UV/H(2)O(2), UV/S(2)O(8)(2-) and UV/O(3) were applied to the treatment of model wastewater containing non-biodegradable organic pollutant, azo dye Acid Orange 7 (AO7). Dye degradation was monitored using UV/VIS and total organic carbon (TOC) analysis, determining decolorization, the degradation/formation of naphthalene and benzene structured AO7 by-products, and the mineralization of model wastewater. The water quality during the treatment was evaluated on the bases of ecological parameters: chemical (COD) and biochemical (BOD(5)) oxygen demand and toxicity on Vibrio fischeri determining the EC(50) value. The main goals of the study were to develop an appropriate mathematic model (MM) predicting the behavior of the systems under investigation, and to evaluate the toxicity and biodegradability of the model wastewater during treatments. MM developed showed a high accuracy in predicting the degradation of AO7 when considering the following observed parameters: decolorization, formation/degradation of by-products and mineralization. Good agreement of the data predicted and the empirically obtained was confirmed by calculated standard deviations. The biodegradability of model wastewater was significantly improved by three processes after mineralizing a half of the initially present organic content. The toxicity AO7 model wastewater was decreased as well. The differences in monitored ecological parameters during the treatment indicated the formation of different by-products of dye degradation regarding the oxidant type applied.

Environmental aspects of photooxidative treatment of phenolic compounds

The study was aimed at evaluation of environmental aspects on photooxidative treatment of phenolic compounds by UV/H2O2 process. Hydroxy-, chloro-, nitro- and methyl-phenols substituted in ortho and para positions were used as model pollutants. The influence of pollutant chemical structure on variations of water quality during the photooxidative treatment was investigated. In that purpose, we monitored the changes of total organic carbon (TOC); chemical oxygen demand (COD); aromaticity, measured as absorbance at 280 (A280) and 254 nm (A254); biodegradability, estimated over ratio of biochemical and chemical oxygen demand (BOD5/COD); and toxicity, estimated on inhibition of Vibrio fischeri luminescence (TU). It was found that changes of monitored parameters are influenced by the type and position of substituent. Studied pollutants share sequence in degradation pathway and consequently some of the formed by-products are the same as well. However, their distribution and the formation of specific by-products with characteristic functional groups play significant role in observed variations of water quality, which was particularly reflected in biodegradability and toxicity. The cross-correlation between recorded sum-water parameters is assessed on the basis of calculated Spearman rank coefficients.

Photooxidation of benzene-structured compounds: influence of substituent type on degradation kinetic and sum water parameters.

The combined influence of substituent type and UV/H(2)O(2) process parameters on the degradation of four aromatic water pollutants was investigated using modified 3(3) full factorial design and response surface methodology. Degradation kinetics was described by the quadratic polynomial model. According to the applied ANOVA, besides pH and [H(2)O(2)], model terms related with the pollutant structure are found to be significant. Different optimal operating conditions and values of observed degradation rate constants were determined for each of the pollutants indicating that the type of substituent influences the overall process effectiveness over structurally defined degradation pathway. Biodegradability (BOD(5)/COD) and toxicity (TU) were evaluated prior to the treatment and at the reference time intervals t(1/2)(P), t(3/4)(P), t(1/4)(OC) and t(1/2)(OC) corresponding to the real time required to reduce the concentration of parent pollutant and organic content for 1/2, 3/4, 1/4 and 1/2 of initial amount. The observed differences are correlated to the structural differences of studied aromatics.

Structural Influence on Photooxidative Degradation of Halogenated Phenols

The influence of structure on degradation of five halogenated phenols (XPs) by UV/H2O2 process was investigated. The combined influence of type or number of substituents and UV/H2O2 process parameters (pH and [H2O2]) on the degradation kinetics of 2-fluorophenol (2-FP), 2-chlorophenol (2-CP), 2-bromophenol (2-BP), 2,4-dichlorophenol (2,4-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) was studied using modified miscellaneous 33 full factorial design and response surface modeling (RSM). Studied XPs obey first-order degradation kinetics within the investigated range of process parameters. Determined degradation rate constants (kobs) were correlated with process and structural parameters by the quadratic polynomial models. Analysis of variance (ANOVA) demonstrated RSM models’ accuracy and showed that, in addition to pH and [H2O2], model terms related with the pollutant structure are highly influential. kobs of mono-XPs follow the decreasing order 2-FP, 2-CP, and 2-BP, while CPs follow the decreasing order 2-CP, 2,4-DCP, and 2,4,6-TCP. Biodegradability (biochemical oxygen demand (BOD)5/chemical oxygen demand (COD)) and toxicity (TU) were evaluated prior to the treatment and at the reference time intervals. The observed differences are correlated with the structural characteristics of studied XPs.