Toxicity and Biodegradability Behavior of Xenobiotic Chemicals Before and After Ozonation: A Case Study with Commercial Textile Tannins

Ozonation of a natural tannin (NT; COD_o?=?1195 mg/L; TOC_o?=?342 mg/L; BOD_5,o?=?86 mg/L) and a synthetic tannin ST; COD_o?=?465 mg/L; TOC_o?=?55 mg/L; BOD_5,o?=?6 mg/L) being frequently applied in the polyamide dyeing process was investigated. Synthetic wastewater samples containing these tannins individually were prepared and subjected to ozonation at varying ozone doses (625– 1250 mgO₃/L wastewater), at pH?=?3.5 (the application pH of tannins) and pH?=?7.0 at an ozone dose of 1125 mgO₃/L wastewater. The collective environmental parameters COD, TOC, BOD₅, UV₂₅₄ and UV₂₈₀ (UV absorbance at 254 nm and 280 nm, representing aromatic and unsaturated moieties, respectively) were followed during ozonation. Changes in the biodegradability of the tannins were evaluated in terms of BOD₅ measurements conducted before and after ozonation. In addition, activated sludge inhibition tests employing heterotrophic biomass were run to elucidate the inhibitory effect of raw and ozonated textile tannins towards activated sludge biomass. Partial oxidation (45% COD removal at an ozone dose of 750 mg O₃/L wastewater and pH?=?3.5) of ST was sufficient to achieve elimination of its inhibitory effect towards heterotrophic biomass and acceptable biodegradability improvement, whereas the inhibitory effect and biodegradability of NT could not be reduced via ozonation under the same reaction conditions.     

Photo-Fenton-like treatment of BPA: Effect of UV light source and water matrix on toxicity and transformation products

UV-A (near-UV), UV-C (short-UV) and visible-light assisted Fenton-like treatment of Bisphenol A (BPA) was investigated in pure water and raw freshwater samples spiked with BPA. Treatment performances were evaluated in terms of BPA degradation, dissolved organic carbon (DOC) removal and H₂O₂ consumption rates. Complete BPA degradation accompanied with significant DOC removal was achieved for all studied processes. Increasing the initial solution pH only exhibited a negative effect on treatment efficiencies when bicarbonate alkalinity was used for pH adjustment, whereas the raw freshwater matrix and irradiation type also influenced oxidation rates appreciably. Acute toxicity analysis employing Vibrio fischeri revealed that the inhibitory effect of BPA decreased significantly during the course of Photo-Fenton-like treatment. Several transformation products could be identified via HPLC and GC–MS analyses including hydroxylated phenolic compounds (hydroquinone; 2-methoxy, 1-4-benzenediol; 4-isopropenylphenol; 4′-hydroxy-acetophenone; 1-(4-cyclohexylphenyl) ethanone; 4-isopropylenecatechol; 4-4′-dihydroxybenzophenone; 4-ethyl,1,3-benzenediol), as well as the ring opening products hexanoic acid methyl ester, fumaric, succinic and oxalic acids. A reaction pathway featuring hydroxylation, dimerization and ring opening steps is proposed.     

Ozonation of Spent Reactive Dye-Baths: Effect of HCO3?/CO32? Alkalinity

The effect of carbonate and bicarbonate alkalinity (soda ash buffer as 5,180 mg/L HCO3? alkalinity at pH 7 and as 5,100 mg/L CO32? alkalinity at pH 12) on the ozonation of reactive vinylsulphone dyestuffs in a simulated spent dye-bath has been studied at varying pHs. Adsorbable organic halogen (AOX) formation due to the high chloride content of the effluent and detoxification, which was evaluated in terms of the relative toxicity index Itox determined from the ED50 values for the marine photobacteria Vibrio fischeri, were also evaluated. Highest total organic carbon (56%), chemical oxygen demand (44%), and UV254 (77%) removals were achieved at pH 7 in the presence of HCO3? alkalinity. The fastest decolorization was observed for the case pH 2, the first order decolorization rate constant found as k620 = 0.16?min?1, closely followed by the pH 12 case with soda ash (k620 = 0.12?min?1) case. No positive correlation was evident between AOX, whose maximum value (=1.3 mg/L) appeared after 40 min ozonation at pH 7 and decreased to 0.54 mg/L after 120 min treatment, and Itox, which decreased to 0.16 at t = 50?min and increased rapidly thereafter. The Itox values were more related to color abatement kinetics. The maximum relative toxicity index of Itox = 0.83 occurred after 120 min. It was also established that the presence of alkalinity in the spent reactive dye-bath had no negative impact on the oxidation rates. In contrast, its absence seriously inhibited treatment efficiency. It is speculated that, with added soda ash, the carbonate radicals HCO3? and CO3??, which are more stable and selective than OH?, were produced and promoted the oxidation process.     

Multivariate analysis of anionic, cationic and nonionic textile surfactant degradation with the H(2)O(2)/UV-C process by using the capabilities of response surface methodology

Anionic, cationic and nonionic surfactants being frequently employed in the textile preparation process were subjected to H(2)O(2)/UV-C treatment. As a consequence of the considerable number of parameters affecting the H(2)O(2)/UV-C process, an experimental design methodology was used to mathematically describe and optimize the single and combined influences of the critical process variables treatment time, initial H(2)O(2)concentration and chemical oxygen demand (COD) on parent pollutant (surfactant) as well as organic carbon (COD and total organic carbon (TOC)) removal efficiencies. Multivariate analysis was based on two different photochemical treatment targets; (i) full oxidation/complete treatment of the surfactants or, alternatively, (ii) partial oxidation/pretreatment of the surfactants to comply with the legislative discharge requirements. According to the established polynomial regression models, the process independent variables "treatment time" (exerting a positive effect) and "initial COD content" (exerting a negative effect) played more significant roles in surfactant photodegradation than the process variable "initial H(2)O(2) concentration" under the studied experimental conditions.     

Effect of Fenton's treatment on the biodegradability of chromium-complex azo dyes.

Pretreatment of an acid dyebath effluent bearing a new generation chromium complex azo dyestuff (C0 = 350 mg/L) with Fenton's reagent was investigated. Preliminary optimisation (baseline) experiments were conducted to determine the Fe2+, H2O2 concentrations and pH required to the highest possible COD and colour removals. Kinetic studies were carried out at varying temperatures (20 degrees C < T < 70 degrees C) to establish a relationship between COD abatement and H2O2 consumption. The activation energy found for catalytic H2O2 decomposition (Ea = 9.8 kJ/mol) appeared to be significantly less than that of fermentative (Ea = 23 kJ/mol) and of thermal (Ea = 76 kJ/mol) H2O2 decomposition, implying that H2O2 decomposition during the Fenton's reaction occurs more spontaneously. The experimental studies indicated that approximately 30% COD and complete colour removal could be achieved under optimised Fenton pretreatment conditions (Fe2+ = 2 mM; H2O2 = 30 mM; pH = 3; at T = 60 degrees C). Long-term activated sludge experiments revealed that although the raw and pretreated acid dyebath effluent contained practically the same amount of "readily biodegradable" COD (inert COD fraction < or = 10%), biodegradation of the chemically pretreated acid dye effluent proceeded appreciably faster than that of the untreated acid dyebath effluent.     

Integrated photochemical and biological treatment of a commercial textile surfactant: Process optimization,process kinetics and COD fractionation

The biodegradability of surfactants is a frequent and complex issue arising both at domestic as well as industrial treatment facilities. In the present experimental study, the integrated photochemical (H₂O₂/UV-C) and biochemical (activated sludge) treatment of a commercial grade nonionic/anionic textile surfactant formulation was investigated. Photochemical baseline experiments have shown that once the initial pH and H₂O₂ dose were optimized, practically complete COD removal (COD_o = 500 ± 30 mg L⁻¹) could be achieved. Once the COD was elevated to values being typical for the textile fabric preparation stage, treatment efficiency was seriously retarded provided that the photochemical treatment conditions remained constant. Moreover, a definite relationship existed between H₂O₂ consumption and COD removal for H₂O₂/UV-C advanced oxidation of the textile surfactant. In the second part of the study, COD abatement was modeled for the biodegradation of untreated and photochemically pretreated textile surfactant formulation according to their COD fractions. Results have indicated that the readily biodegradable and rapidly hydrolysable COD fractions of the textile surfactant solution could be appreciably increased upon exposure to an optimum H₂O₂ concentration (60 mM; i.e. 2.1 g H₂O₂ (g COD_o)⁻¹) and extended UV-C irradiation times (i.e. 90 and 120 min).     

Pre-treatment of penicillin formulation effluent by advanced oxidation processes

A variety of advanced oxidation processes (AOPs; O3/OH-, H2O2/UV, Fe2+/H2O2, Fe3+/H2O2, Fe2+/H2O2/UV and Fe3+/H2O2/UV) have been applied for the oxidative pre-treatment of real penicillin formulation effluent (average COD0 = 1395 mg/L; TOC0 = 920 mg/L; BOD(5,0) approximately 0 mg/L). For the ozonation process the primary involvement of free radical species such as OH* in the oxidative reaction could be demonstrated via inspection of ozone absorption rates. Alkaline ozonation and the photo-Fenton's reagents both appeared to be the most promising AOPs in terms of COD (49-66%) and TOC (42-52%) abatement rates, whereas the BOD5 of the originally non-biodegradable effluent could only be improved to a value of 100 mg/L with O3/pH = 3] treatment (BOD5/COD, f = 0.08). Evaluation on COD and TOC removal rates per applied active oxidant (AOx) and oxidant (Ox) on a molar basis revealed that alkaline ozonation and particularly the UV-light assisted Fenton processes enabling good oxidation yields (1-2 mol COD and TOC removal per AOx and Ox) by far outweighed the other studied AOPs. Separate experimental studies conducted with the penicillin active substance amoxicillin trihydrate indicated that the aqueous antibiotic substance can be completely eliminated after 40 min advanced oxidation applying photo-Fenton's reagent (pH = 3; Fe(2+):H2O2 molar ratio = 1:20) and alkaline ozonation (at pH = 11.5), respectively.     

H2O2∕UV-C and Fe2+∕H2O2∕UV-C versus TiO2∕UV-A Treatment for Reactive Dye Wastewater

This study investigated the advanced oxidation of commonly used reactive dyestuffs in exhausted dye-bath effluents in homogeneous (H2O2∕UV-C and photo-Fenton) and heterogeneous (TiO2∕UV-A) media. Photocatalytic treatment efficiencies of two different TiO2 powders (PC 500 and Mikroanatas) and the platinized Degussa P25 were compared with that of the more well-known Degussa P25 in varying pH media. Treatment performance was strongly affected by the initial H2O2 concentration for H2O2∕UV-C and photo-Fenton oxidation systems, whereas for the TiO2∕UV-A process only PC 500 TiO2 powder, an anatase crystal phase of the semiconductor, exhibited a significantly pH-dependent reaction efficiency. The decolorization rate followed the order of Fenton∕UV-C > Pt-P25∕UV-A > Mikroanatas∕UV-A > P25∕UV-A > PC 500∕UV-A > H2O2∕UV-C, whereas the decreasing order for total organic carbon reduction was Fenton∕UV-C > H2O2∕UV-C > Mikroanatas∕UV-A > Pt-P25∕UV-A > P25∕UV-A > PC 500∕UV-A for the studied reaction conditions. Removal of optical density at 254-nm wavelength ranged between 75 and 96%.     

Photodegradation of hydrophobic disperse dyes and dye-bath effluents by silicadodecatungstate (SiW12O40(4-/5-)) nanoparticles.

Polyoxometalate (POM) silicadodecatungstic acid has been applied as a photochemical catalyst for the degradation of SETAPERS Black WNSP, a disperse dyestuff preparation widely used to dye polyester and polyamide fabrics. It could be demonstrated that the disperse dyestuff was photo-reduced by SiW12O40(5-), the one-electron reduced form of POM, as evidenced by Heteropolyblue (HPB) formation. For completion of the photochemical redox cycle, isopropanol (IsOH) was required. Acetone (Ac) served solely as an effective solute and photosensitizer; however this effect was suppressed in the presence of POM. Threshold (0.087 mM) and optimum (0.375 mM) POM concentrations existed and decolorization kinetics were inhibited upon the addition of dye auxiliary chemicals. Increasing the dyestuff concentration from 50 mg/L to 150 mg/L did not affect initial decolorization kinetics revealing that not the formation of the excited [POM-Substrate]* complex, but its reduction to HPB was the rate limiting step. POM-mediated, IsOH-assisted UV-photodegradation of disperse dyes and dye-baths is by far more effective than applying other, more well known chemical oxidation methods (O3, H202/UV, Power Ultrasound). Key to the action of POM redox catalysts is the feature that particularly heteropoly tungstates undergo facile re-oxidation to their original state, thus allowing regeneration of the photocatalyst, a feature that may become critical for real-scale application.