Pseudo-first Order Kinetic Constants Research Articles

Optimization and control of Electro-Fenton process by pH inflection points: A case of treating acrylic fiber manufacturing wastewater

The Electro-Fenton (EF) process has shown great potential in refractory wastewater treatment. However, its efficiency is highly pH-dependent and the high reagent costs for pH adjustment greatly limit its large-scale application. This study used a bench-scale EF reactor to study pH variation during the treatment of an acrylic fiber wastewater. The appearance of pH inflection points (pH IPs), i.e., sudden changes in pH, under different H2O2 dosages, current densities, and ratios of [Fe2+Theo]/[H2O2] (RFe:H2O2), were investigated. The pH IPs appeared on the time scale of 5–7.5min, and were favored at decreased H2O2 dosages (2.5–1.0mM), increased current densities (3–4.5mA/cm2), and elevated RFe:H2O2 (0.1:1–0.2:1). The appearance of pH IPs was indicative of the exhaustion of H2O2 and a significant decrease of COD degradation, as expressed by the pseudo-first order kinetic constant (k) of COD degradation. Besides this, the substitution of Fe(OH)3 by Fe(OH)2− and Fe(OH)2− occurred after pH IP appearance, and the dominant mechanism changed from electrochemical oxidation (EO) to electro-coagulation (EC) accordingly. In the presence of sufficient H2O2, the formation of Fe(OH)3 barely affected pH variation. After H2O2 exhaustion, i.e., the appearance of pH IPs, dissolved O2 rapidly oxidized Fe2+ to Fe3+, the hydrolysis of which contributed to immediate pH increase thereafter. The optimization of the EF process may be achieved by adjusting H2O2 doses and the control of pH IP appearance.

Characteristics of UV-MicroO3Reactor and Its Application to Microcystins Degradation during Surface Water Treatment

The UV-ozone (UV-O3) process is not widely applied in wastewater and potable water treatment partly for the relatively high cost since complicated UV radiation and ozone generating systems are utilized. The UV-microozone (UV-microO3), a new advanced process that can solve the abovementioned problems, was introduced in this study. The effects of air flux, air pressure, and air humidity on generation and concentration of O3in UV-microO3reactor were investigated. The utilization of this UV-microO3reactor in microcystins (MCs) degradation was also carried out. Experimental results indicated that the optimum air flux in the reactor equipped with 37 mm diameter quartz tube was determined to be 18∼25 L/h for efficient O3generation. The air pressure and humidity in UV-microO3reactor should be low enough in order to get optimum O3output. Moreover, microcystin-RR, YR, and LR (MC-RR, MC-YR, and MC-LR) could be degraded effectively by UV-microO3process. The degradation of different MCs was characterized by first-order reaction kinetics. The pseudofirst-order kinetic constants for MC-RR, MC-YR, and MC-LR degradation were 0.0093, 0.0215, and 0.0286 min−1, respectively. Glucose had no influence on MC degradation through UV-microO3. The UV-microO3process is hence recommended as a suitable advanced treatment method for dissolved MCs degradation.

Degradation of sulfamethazine in sewage sludge mixture by gamma irradiation

Abstract The gamma-irradiation-induced degradation of antibiotics sulfamethazine (SMT) in sludge mixture was investigated. The results showed that gamma irradiation was effective in removing SMT from contaminated sludge mixture. With an initial SMT concentration of 10 mg/L, the SMT removal efficiency reached 65% at 1.0 kGy and increased to 98% at 2.5 kGy. The SMT degradation rate was lower in the sludge mixture than that in pure water. The pseudo first-order kinetic constant of SMT degradation in pure water was 2.3 times higher than that in the sludge mixture. Analysis of the SMT concentrations in the supernatant and sludge residue revealed that 93–97% of SMT was observed in the supernatant and the detected SMT in the sludge residue was 168±29, 147±4, and 87±9 μg/g dry weight following irradiation at doses of 0, 1.0 and 2.5 kGy, respectively. The sludge solubilization slowly increased from 1.5% to 3.5% with increasing dose from 1.0 to 5.0 kGy, while the sludge activity decreased by 85–98%. Addition of H 2 O 2 exhibited a synergetic effect on the degradation of SMT, with the pseudo first-order kinetic constant k increasing by around 25%.

Validation of a two-dimensional modeling of an externally irradiated slurry photoreactor

A two-dimensional model describing the behavior of a batch cylindrical photoreactor has been validated through a series of photocatalytic reactivity runs. The light intensity radiation field produced by 1–6 external UV fluorescent lamps was modeled together with Langmuir–Hinshelwood kinetics and 4-nitrophenol (NP) and Degussa P25 TiO2 were used as the probe molecule and the catalyst, respectively. The experiments were carried out under different conditions of light intensity, photocatalyst amount and substrate concentration. The model parameters were the kinetic constant of substrate adsorption, desorption and degradation and the exponent of the power law expressing the kinetics dependence on the light intensity. A least-squares best fitting procedure was used to fit the experimental data to the model and find the four required parameters. A satisfactory agreement was obtained between experimental and calculated values of the observed pseudo-first order kinetic constant, with a coefficient of determination R2=0.83. Notably, the present model is of general interest for cylindrical slurry photoreactors, where different molecules can be oxidized in the presence of several photocatalysts and it can be used, for instance, to accurately compare the performance of a set of catalysts.

One-step fabrication and high photocatalytic activity of porous graphitic carbon nitride/graphene oxide hybrid by direct polymerization of cyanamide without templates

Graphene oxide modified porous g-C3N4 (porous g-C3N4/GO) had been synthesized by means of one-step calcination of cyanamide for efficient photocatalysis under visible light irradiation (λ > 400 nm). We expect that the photocatalytic activity of this hybrid photocatalyst could be enhanced by the efficient visible light absorption due to the porous structure and efficient photo generated charge separation at the heterojunction formed between porous g-C3N4 and GO. Scanning electron microscopy (SEM) images demonstrated that the as prepared photocatalyst is composed of GO and porous g-C3N4. The UV-vis diffuse reflectance spectrum shows that optical absorption of porous g-C3N4/GO is more intensive than for pristine g-C3N4. The enhanced generation of photocurrent under visible light irradiation (λ > 400 nm) is observed for the porous g-C3N4/GO. The results of photocatalytic experiments reveal that the pseudofirst-order kinetic constant of photocatalytic degradation of methylene blue (MB) using the porous g-C3N4/GO is 6 times higher than that of pristine g-C3N4.

Enhancing electrocatalytic performance of Sb-doped SnO2 electrode by compositing nitrogen-doped graphene nanosheets

An efficient Ti/Sb-SnO2 electrode modified with nitrogen-doped graphene nanosheets (NGNS) was successfully fabricated by the sol–gel and dip coating method. Compared with Ti/Sb-SnO2 electrode, the NGNS-modified electrode possesses smaller unite crystalline volume (71.11Å3 vs. 71.32Å3), smaller electrical resistivity (13Ωm vs. 34Ωm), and lower charge transfer resistance (10.91Ω vs. 21.01Ω). The accelerated lifetime of Ti/Sb-SnO2-NGNS electrode is prolonged significantly, which is 4.45 times as long as that of Ti/Sb-SnO2 electrode. The results of X-ray photoelectron spectroscopy measurement and voltammetric charge analysis indicate that introducing NGNS into the active coating can increase more reaction active sites to enhance the electrocatalytic efficiency. The electrochemical dye decolorization analysis demonstrates that Ti/Sb-SnO2-NGNS presents efficient electrocatalytic performance for methylene blue and orange II decolorization. And its pseudo-first order kinetic rate constants for methylene blue and orange II decolorization are 36.6 and 44.0min−1, respectively, which are 6.0 and 7.1 times as efficient as those of Ti/Sb-SnO2, respectively. Considering the significant electrocatalytic activity and low resistivity of Ti/Sb-SnO2-NGNS electrode, the cost of wastewater treatment can be expected to be reduced obviously and the application prospect is broad.

Surface fluorination on TiO2 catalyst induced by photodegradation of perfluorooctanoic acid

The photoabatement of perfluorooctanoic acid in aqueous solution has been performed with a commercial nano-sized TiO2-based photocatalyst content of 0.66g/L under an UV irradiation of 95W/m2. PFOA degradation intermediates were investigated by HPLC–MS and 19F-NMR analysis. Evidences of a degradation mechanism based on two competitive pathways are discussed: photo-redox and β-scission pathways. Shorter perfluorinated carboxylic acids, CnF2n+1COOH (n=1–6), as expected degradation intermediates, were identified and their concentration trends over time were determined. The apparent pseudo-first order kinetic constant expressed as rate of PFOA disappearance was also measured: kapp 0.1296h−1. The influence of fluoride ions on TiO2 surface was analyzed by XPS technique, revealing a surface modification that affects the performances of the catalyst.

The degradation of phenol in water solution by TiO2 photocatalysis in a helical reactor

Heterogeneous photocatalysis is an advanced oxidation process (AOP) which has been widely studied by numerous researchers in the world and is used to degrade or remove a wide range of pollutants in water and air. The photocatalytic oxidation and mineralization of phenol in aqueous catalyst suspensions of titanium dioxide (TiO2) Degussa P25 (80% anatase, 20% rutile) has been carried out in a helical reactor. The photodegradation was investigated using two kinds of high pressure mercury irradiation lamps one emitting at 254 nm (15 Watts) and the other emitting at 365 nm (400 Watts). The effects of the recirculation flow, source of withdrawal, initial phenol concentration, amount of catalyst, suspension pH and light intensity on photodegradation of phenol were investigated. These parameters were studied to find the optimal conditions for a complete and fast oxidation of this organic compound. Kinetic experiments were performed at 32 oC over a range of phenol concentrations from 2.5 to 25 mg l-1, a range of TiO2 concentrations from 0.1 to 1 g l1, a range of suspensions pH from 3 to 9. The helical reactor was operated under a continuous flow-mode. Results showed that photodegradation is an effective method for the removal of phenol from wastewaters. The efficiency of the process depends strongly on the experimental conditions. The amount of catalyst, UV irradiation time, pH and light intensity were important parameters in the degradation process. The rate constants for the different parameters (TiO2, phenol concentration) were evaluated. Kinetic studies showed that titanium dioxide photocatalyst P25 was very active in phenol degradation; we observed that 99% of pollutant was degraded after 6 hours of UV irradiation; furthermore, we observed that phenol degradation was more effective under acidic conditions than alkaline. The kinetics were described by the Langmuir- Hinshelwood (L-H) kinetic model. An overall pseudo-first order kinetic constant has been calculated for phenol conversion and values obtained in acidic pH are higher than those calculated for basic pH media.

Influence of humic acids on the adsorption of Basic Yellow 28 dye onto an iron organo–inorgano pillared clay and two Hydrous Ferric Oxides

Effect of humic acids (HAs), macromolecules from natural organic matter, on the adsorption of Basic Yellow 28 is the aim of the present work. Three adsorbents were investigated in this study: an iron organo–inorgano pillared clay and two synthetic Hydrous Iron Oxide (Goethite and HFO). The surface charge was positive in the pH range of this study for the pillared clay; in contrast, it changes from positive to negative when the pH value increased (pH>9) for the two (oxy)hydroxides. Pseudo-first order kinetic rate constants and adsorption capacities increase from humic acid to BY 28. Adsorption isotherms of BY 28 and HA in single component were analysed using the Freundlich equation. Adsorption capacities increased sharply when the pH value of the dye solution was raised from 3 to 9. Increasing the pH medium from 3 to 9 reduces the HA adsorption capacities onto Fe-SMPM and iron oxyhydroxides, respectively. Fitting between measured and predicted sorption capacities of BY 28 and HA in a binary component system indicates that the Sheindorf–Rebuhn–Sheintuch (SRS) model, an extended Freundlich model, is able to describe the simultaneous adsorption of BY 28 and HA. Humic acids favourably affect the adsorption of BY 28, and a cooperative mechanism could be suggested. The synergetic effect existing between BY 28 and HA is shown by the interaction coefficients η12, which are generally high and increase with pH. Some phenomena have been advanced to explain this mechanism.

Solar light-induced photoelectrocatalytic degradation of bisphenol-A on TiO2/ITO film anode and BDD cathode

The degradation of bisphenol-A (BPA), an endocrine disrupting compound, by means of photoelectrocatalytic (PEC), photocatalytic (PC) and electrochemical oxidation (EO) was investigated. An immobilized TiO2/ITO film, prepared by a sol–gel method, served as the photocatalyst and the anode, while boron-doped diamond (BDD) as the cathode. Photochemical reactions were induced by simulated solar radiation, while anodic bias in the range 0.04–0.32mA/cm2 was applied to evaluate its effect on PC degradation, as well as the extent of direct EO. Experiments were conducted at initial BPA concentrations between 100 and 300μg/L, solution pH between 1 and 9 and two different electrolytes, i.e. HClO4 and NaCl.Current application always improved substantially the performance of photocatalytic degradation with the extent of enhancement (computed from the pseudo-first order kinetic constants of PEC and PC) reaching values as high as 90%. The interaction between PC and EO was found to be synergistic rather than additive; this is thought to be due to (i) a more efficient separation of the photogenerated electrons and holes, and (ii) the enhanced formation of peroxide and other reactive oxygen species favored on the BDD cathode.BPA degradation rates generally increased with increasing applied current, at strongly acidic conditions and in the presence of NaCl as the supporting electrolyte; at the conditions in question, complete BPA conversion could be achieved in no longer than 60–90min of reaction.

Ethyl lactate-Fenton treatment of soil highly contaminated with polycyclic aromatic hydrocarbons (PAHs)

This study reports on a novel ethyl lactate based Fenton treatment for soils contaminated with polycyclic aromatic hydrocarbons (PAHs). The degradation of four PAHs, i.e. phenanthrene, anthracene, fluoranthene and benzo[a]pyrene in soil using this novel treatment was compared to ethanol-Fenton and conventional Fenton treatments. Ethyl lactate/water system manifested a greater desorption capacity than ethanol/water system. A 6h ethyl lactate/water (fc=0.60) pretreatment followed by a 4h ethyl lactate/water (fc=0.20) based Fenton treatment effectively degraded all tested PAHs (>97% removal). Ethanol/water treatment was highly selective towards the degradation of anthracene and benzo[a]pyrene, with ∼30% of phenanthrene and fluoranthene remaining untreated, while conventional Fenton resulted in 31–57% of untreated PAHs after 24h. The pseudo-first order kinetic reaction rate constants of ethyl lactate/water based Fenton system were 12–42 times higher than conventional Fenton treatment in soil. The efficiency of treatment was mainly caused by enhanced solubility and desorption, and to a less extent, PAH reactivity, hydrogen peroxide stabilisation and enhanced OH radicals generation by the Fe3+/lactate complex formed.

Sorption of basic dyes onto granulated pillared clays: Thermodynamic and kinetic studies

Effect of the granulation process onto the thermodynamic and kinetic sorption parameters of two basic dyes (Basic Yellow 28-BY 28 and Basic Green 4-BG 4) was evaluated in the present work. The charge surface properties of the surfactant-modified aluminium-pillared clay (CTAB-Al-Mont-PILC) particles were not modified, and the isoelectric point remains constant after high shear wet granulation. The Gibbs free energy of both BY 28 and BG 4 sorption was negative and decreased with the granulation; the endothermic nature of the sorption process was confirmed by the positive values of ΔH°. Adsorption kinetics of the two dyes, studied at pH 6 and 150mgL−1, follow the pseudo-first order kinetic model with observed rate constants of 2.5–4.2×10−2min−1. The intraparticle diffusion model, proposed by Weber and Morris, was applied, and the intraparticle plots revealed three distinct sections representing external mass transfer, intraparticle diffusion and adsorption/desorption equilibrium. Diffusion coefficients, calculated from the Boyd kinetic equation, increased with the granulation and the particle size. Pseudo-first order kinetic constants, intraparticle diffusion rate constants and diffusion coefficients were determined for two other initial concentrations (50 and 100mgL−1) and include in a statistical study to evaluate the impact of granulation and initial concentration on the kinetic parameters. Kruskal–Wallis tests, Spearman’s rank order correlation and factor analysis revealed a correlation between (i) the diffusion coefficients and granulation, and between (ii) the intraparticle diffusion rate constants and initial concentration.

Degradation of perfluorinated compounds on a boron-doped diamond electrode

Perfluorinated compounds (PFCs) are persistent in environments due to the high energy of CF bond. Electrochemical oxidation of seven PFCs in aqueous solution on a boron doped diamond (BDD) anode was studied in this study. The kinetics results show that the pseudo-first order kinetic constants of perfluoroalkyl carboxyates and sulfonates increased with the increase of carbon chain length. PFCs decomposition began with a direct one electron transfer from carboxyl or sulfonate group to BDD, and the formed PFCs radicals were decarboxylated or desulfonated to yield the perfluoroalkyl radical which permitted a defluorination reaction between perfluoroalkyl radical and hydroxyl radical. The effects of potential, current density, initial pH, and perfluorooctanoate (PFOA) concentration on the removal of PFOA were investigated. The anodic potential played an important role in the decomposition, and the oxidation potential of PFOA was 2.76 vs. SCE/V (saturated calomel electrode). When the current density increased slightly from 0.12 to 0.59mAcm−2, PFOA removal was greatly enhanced from 0 to 97.48%. PFOA decomposition was higher in acidic solution compared to that in the alkaline solution. The pseudo-first order kinetic constants of PFOA decomposition increased with the increase of initial concentration.

Kinetic analysis and energy efficiency of phenol degradation in a plasma-photocatalysis system

Combination of two kinds of advanced oxidation processes (AOPs) is an effective approach to control wastewater pollution. In this research, a pulsed discharge plasma system with multi-point-to-plate electrode and an immobilized TiO2 photocatalysis system is coupled to oxidize target pollutant in aqueous solution. Kinetic analysis (pseudo-first order kinetic constant, k) and energy efficiency (energy yield value at 50% phenol conversion, G50) of phenol oxidation in different reaction systems (plasma alone and plasma-photocatalysis) are reviewed to account for the synergistic mechanism of plasma and photocatalysis. The experimental results show that higher k and G50 of phenol oxidation can be obtained in the plasma-photocatalysis system under the conditions of different gas bubbling varieties, initial solution pH and radical scavenger addition. Moreover, the investigation tested hydroxyl radical (OH) is the most important species for phenol removal in the synergistic system of plasma-photocatalysis as well as in the plasma alone system.

Photodegradation of crystal violet in TiO 2 suspensions using UV–vis irradiation from two microwave-powered electrodeless discharge lamps (EDL -2): Products, mechanism and feasibility

Aqueous crystal violet (CV) solutions containing P25–TiO 2 photocatalyst were irradiated with ultraviolet–visible (UV–vis) light from two microwave-powered electrodeless discharge lamps (EDL -2). The results demonstrated that approximately 94.4% of CV was effectively removed after 3 min of irradiation, with a pseudo-first order kinetic constant of 0.838 min −1. According to 32 kinds of products, a five-step degradation pathway of CV was proposed. Further investigations showed that (1) three kinds of N-demethylated products and 4-dimethylaminobenzophenone (DLBP) were the main intermediates; (2) malachite green (MG) and leuco-crystal violet could not be generated by N-demethylation and phototransformation reactions, respectively; (3) bis(4-(dimethylamino)phenyl)methanone preferentially generated via decomposition of the conjugated structure of CV could be further N-demethylated into DLBP. Moreover, the unique degradation pathways of CV and MG were ascribed to the different substituents on the conjugated structures. Additionally, the cost and kinetic constant of different processes was also evaluated, and the results indicated the feasibility of this method for treatment of CV in field situations.

Photonic Crystal Coupled TiO2/Polymer Hybrid for Efficient Photocatalysis under Visible Light Irradiation

Inverse TiO(2) opal photonic crystal coupled TiO(2)/poly(3-hexylthiophene) (bilayer TiO(2)/P3HT) was structured on FTO substrate for efficient photocatalysis under visible light irradiation (lambda > 400 nm). We expected that the photocatalytic capability of this hybrid photocatalyst could be enhanced by the efficient visible light absorption owing to the photonic crystal structure and effective charge separation owing to the unique heterojunction built between TiO(2) and P3HT. The bilayer TiO(2)/P3HT photocatalyst was prepared first by depositing inverse TiO(2) opal on FTO substrate via replicating polystyrene opal, followed by spin coating a layer of TiO(2) nanoparticles on the inverse TiO(2) opal. The as prepared bilayer TiO(2) was modified by P3HT via dipping method. Environmental scanning electron microscopy (ESEM) images demonstrated that the as prepared photocatalyst was composed of inverse TiO(2) opal layer and TiO(2) nanoparticles layer. The UV-vis diffuse reflectance spectra showed that the optical absorption for bilayer TiO(2)/P3HT was more intensive than for pristine TiO(2) nanoparticle/P3HT (NP-TiO(2)/P3HT) in the range of 400-650 nm. The enhanced generation of photocurrent under visible light irradiation (lambda > 400 nm) was observed using the bilayer TiO(2)/P3HT. The results of photocatalytic experiments under visible light irradiation revealed that the pseudofirst-order kinetic constant of photocatalytic degradation of methylene blue using the bilayer TiO(2)/P3HT was 2.08 times as great as that using NP-TiO(2)/P3HT, showing the advantage of the unique structure in the bilayer TiO(2)/P3HT for efficient photocatalysis.

Kinetic approach for evaluation of total antioxidant activity

We propose a novel approach for assessment of total antioxidant activity by monitoring kinetics of hydrogen peroxide (H 2O 2) scavenging after its injection into liquid sample under study. H 2O 2 is known to be the strongest oxidant, really presented in human body in contrast to the majority of the model oxidative systems used for evaluation of antioxidant activity. In addition, kinetic approach, being more informative than the commonly used determination of the final product, obviously provides better discrimination of potential antioxidants. Prussian Blue based sensor due to its high sensitivity and operational stability allowed to monitor kinetics of hydrogen peroxide consumption in turbid and colored samples. The pseudo-first order kinetic constants of hydrogen peroxide scavenging in the presence of different food additives correlated with total antioxidant activity of these samples evaluated via standard procedure based on lipid peroxidation. However, in contrast to the standard method, the proposed kinetic approach is expressed and does not require fresh biological tissues.

Clotrimazole Inhibits Hemoperoxidase of Plasmodium falciparum and Induces Oxidative Stress: PROPOSED ANTIMALARIAL MECHANISM OF CLOTRIMAZOLE

The mechanism of antimalarial activity of clotrimazole was studied placing emphasis on its role in inhibiting hemoperoxidase for inducing oxidative stress in Plasmodium falciparum. Clotrimazole, in the presence of H2O2, causes irreversible inactivation of the enzyme, and the inactivation follows pseudo-first order kinetics, consistent with a mechanism-based (suicide) mode. The pseudo-first order kinetic constants are ki = 2.85 microM, k(inact) = 0.9 min(-1), and t(1/2) = 0.77 min. The one-electron oxidation product of clotrimazole has been identified by EPR spectroscopy as the 5,5'-dimethyl-1-pyrroline N-oxide (DMPO) adduct of the nitrogen-centered radical (aN = 15 G), and as DMPO protects against inactivation, this radical is involved in the inactivation process. Binding studies indicate that the clotrimazole oxidation product interacts at the heme moiety, and the heme-clotrimazole adduct has been dissociated from the inactivated enzyme and identified (m/z 1363) by mass analysis. We found that the inhibition of hemoperoxidase increases the accumulation of H2O2 in P. falciparum and causes oxidative stress. Furthermore, the inhibition of hemoperoxidase correlates well with the inhibition of parasite growth. The results described herein indicate that the antimalarial activity of clotrimazole might be due to the inhibition of hemoperoxidase and subsequent development of oxidative stress in P. falciparum.

Biodegradability Improvement of Aqueous 2,4-Dichlorophenol And Nitrobenzene Solutions By Means of Single Ozonation

The possibility of the integration of ozonation and biological processes as an economical way to treat biorecalcitrant organic compounds such as nitrobenzene and 2,4-dichlorophenol was investigated. In the pre-treatment step, stoichiometric coefficients and pseudo first-order kinetic constants were obtained. Biodegradability was monitored throughout the ozonation step, in order to evaluate the optimum ozone doses. The low TOC reduction after these ozone doses allowed much of the organic carbon to be removed in the biological stage. In the case of 2,4-dichlorophenol, the biodegradability improvement was checked in an aerobic bioreactor. By means of the combined ozonation-biological oxidation, up to 80% of the initial organic content was removed. Results presented in this study show the feasibility of using the combination of ozone and conventional biological treatments to treat wastewaters containing these pollutants.

Removal of drugs in aqueous systems by photoassisted degradation

Aqueous solutions of tetracycline, lincomycin and ranitidine were irradiated with UV light in homogeneous and heterogeneous systems. Two commercial polycrystalline TiO2 powders (Degussa P25 and Merck) were used as photocatalysts. After 5 h, an appreciable photolytic degradation of tetracycline and ranitidine was observed while the degradation of lincomycin was noticeably lower. As far as the mineralization is concerned, a small decrease of the TOC values was measured in the case of tetracycline whereas negligible variations were found for lincomycin or ranitidine. The presence of the photocatalysts greatly enhanced the degradation rates of the drugs with respect to those observed during the homogeneous experiments. The Langmuir–Hinshelwood kinetic model adequately describes the experimental results and both the pseudo-first order kinetic constants of the reactions and the adsorption constants were calculated. Merck TiO2 was more active than P25 Degussa for the photodegradation of tetracycline and ranitidine, whereas both photocatalysts showed similar performances for lincomycin. In the presence of TiO2 Degussa P25, tetracycline was almost completely mineralized, but the reduction of the initial TOC was ca. 60% in the case of lincomycin and ranitidine. A less significant mineralization was observed by using Merck TiO2.