Ivana Grčić

Minimization of organic content in simulated industrial wastewater by Fenton type processes: A case study

Pre-treatment of simulated industrial wastewaters (SIM1, SIM2 and SIM3) containing organic and inorganic compounds (1,2-dichloroethane, sodium formate, sodium hydrogen carbonate, sodium carbonate and sodium chloride) by oxidative degradation using homogeneous Fenton type processes (Fe2+/H2O2 and Fe3+/H2O2) has been evaluated. The effects of initial Fe2+ and Fe3+ concentrations, [Fe2+/3+], type of iron salt (ferrous sulfate vs. ferric chloride), initial hydrogen peroxide concentration, [H2O2], on mineralization extent, i.e., total organic content (TOC) removal, were studied. Response surface methodology (RSM), particularly Box-Behnken design (BBD) was used as modelling tool, and obtained predictive function was used to optimize the overall process by the means of desirability function approach (DFA). Up to 94% of initial TOC was removed after 120 min. Ferrous sulfate was found to be the most appropriate reagent, and the optimal doses of Fe2+ and H2O2 for reducing the pollutant content, in terms of final TOC and sludge production were assessed.

Global parameter of ultrasound exploitation (GPUE) in the reactors for wastewater treatment by sono-Fenton oxidation

Modeling of the sonochemical reactors presents a great challenge due to issues related to the experimental investigation and description of the primary effects of the ultrasound. The main idea proposed in this work was to establish an algorithm consisting of the viable laboratory analyses and basic elements of chemical reaction engineering. In this paper, a novel modeling approach is presented. Proposed approach is characterized by the following; ultrasound was investigated as an auxiliary source of energy and the kinetic constants determined for the basic oxidation reactions, i.e. Fenton type oxidation were treated as independent of the ultrasound. Sonochemical effectiveness factor is expressed as a global parameter of the ultrasound exploitation (GPUE) that was introduced in the kinetic model as the e(US) factor. Factor e(US) is modeled as a function of employed frequency, actual power of the transducer, portion of the cavitationally active zone, i.e. dimensionless active volume and the average temperature in the reactor. Lumped system has been assumed. In order to obtain all the necessary data, the experimental study included different sets of experiments. The kinetics of the sonochemical processes, e.g. US/Fe(2+)/H(2)O(2), US/Fe(2+)/S(2)O(8)(2-), US/Fe(2+)/HSO(5)(-) was investigated in the term of mineralization of model wastewaters containing different types of organic pollutants. The Weissler dosimetry and peroxodisulfate decomposition upon sonication, were used to facilitate the determination of e(US). They follow zero order kinetics, thus can be used as a model reaction to reflect all the primary effects of ultrasound and to establish the empirical correlation for e(US) calculation. Finally, GPUE has been introduced in the adequate kinetic models and the overall model was validated.

Low frequency US and UV-A assisted Fenton oxidation of simulated dyehouse wastewater

The scope of the present study was to explore the treatment possibilities for the simulated dyehouse wastewater (WW) by the Fenton oxidation ultrasonic (US) or UV-A assisted. Composition of WW included reactive azo dye, C.I. Reactive Violet 2 (RV2), anionic surfactant (LAS) and auxiliary chemicals. An emphasis was put on the influence of the LAS on the treatment efficiency. To explore the pseudo-catalytic effect of LAS and reagent dosages on the extents of decolourization and mineralization, different experimental design techniques were utilized. Box-Behnken design was used as a base for optimization and determination of the influencing factors; numerical (Fe(2+/3+), H(2)O(2) and LAS concentration) and categorical factors (iron oxidation state and type of additional energy; US or UV-A). Furthermore, a mixture design methodology was applied. This two-step optimization approach lead to a single optimal point for two advanced oxidation processes studied in comparison. Models describing the dependency of the overall efficiency on influencing factors were obtained. Application of US/Fe(2+)/H(2)O(2) and UV-A/Fe(2+)/H(2)O(2) processes for the treatment of WW was assessed. Only 26% of mineralization was achieved by Fenton process alone applied for the treatment of the dyehouse effluent in 10-fold dilution, while 43% of mineralization was achieved by US or UV-A assisted Fenton after the 60 min.

Removal of Atrazine from Simulated Groundwater by AOTs

Abstract In this research degradation of atrazine from simulated groundwater by ozonation itself and the combination of ozone and UV photocatalysis using TiO2 have been investigated. It has been found that atrazine was degraded by photolysis alone but no reduction of TOC content has been noticed. However, with TiO2 photocatalyst involvement the rate of degradation has increased in comparison with photolysis itself. Reduction of TOC content was observed, too. Concerning preliminary results it has been found that ozonation itself was the most efficient in the pH range from 6 to 11. Ozonation process enhancement was achieved by introducing UV irradiation into the system. The use of TiO2 photocatalyst in the UV/O3 process slightly improved the overall performance. For all studied processes, the kinetics of atrazine degradation was monitored.

Monitoring of total metal concentration in sludge samples: case study for the mechanical-biological wastewater treatment plant in Velika Gorica, Croatia.

In this paper, monitoring of total metal concentration in sludge samples from wastewater treatment process is elaborated. The presented results summarize the analyses of sludge samples in a period from 2008 to 2012. Possible sources of pollutions are given. Primarily, waste solid samples were collected from different pretreatment steps: (A) coarse grid, (B) fine grid and (C) aerated sand grease grid. Samples of A and B followed a repeatable pattern in 2008 and 2010. According to the results from 2008, samples of C contained measurable concentration of the following metals (mg/kg dry matter): Zn (21), Ni (1.05) and Ba (14.9). Several types of sludge samples were analyzed: fresh raw sludge (PS; 6-12 hour old), the sludge from the digester for anaerobic sludge treatment (DS; 48-72 hour old), samples from lagoons where the sludge is temporarily deposited (DOS and DOSold; 30-120 days) and sludge samples from agricultural areas (AA; aged over 180 days). Additionally, samples of dehydrated sludge (DEHS and DEHSold; 90-180 days) were collected upon construction of equipment for sludge dehydration in 2011. An analysis of total metal concentrations for Cu, Zn, Cr, Pb, Ni, Hg, Cd, Ba, As, Se, Sb, Co, Mo, Fe and Mn was performed by flame atomic absorption spectrometry (FAAS) and inductively coupled plasma-optical emission spectrometry (ICP-OES). The most recent results (year 2011) indicated a high concentration of heavy metals in PS samples, exceeding the MCLs (mg/kg dry matter): Cu (2122), Zn (5945), Hg (13.67) and Cd (6.29). In 2012 (until July), only a concentration of Cu exceeded MCL (928.75 and 1230.5 in DS and DEHS, respectively). A composition of sludge was variable through time, offering the limited possibility for future prediction. The sludge is being considered as a hazardous waste and a subject of discussion regarding disposal.

Sonochemical effectiveness factor (eUS) in the reactors for wastewater treatment by sono-Fenton oxidation: Novel considerations

A comprehensive algorithm was recently proposed for calculation of the sonochemical effectiveness factor and wastewater treatment modeling. The presented approach implies that ultrasound is an auxiliary source of free radicals in Fenton type reactions; introduction of ultrasound represents an enhancement of pollutant degradation rates. The sonochemical effectiveness factor was introduced in kinetic models as the eUS factor (Grčić et al., 2012 [1]). As a substantial follow-up, this study presents novel considerations. The eUS factor was modeled as a function of employed frequency, actual cavitation-related power intensity of ultrasound and a portion of the cavitationally active zone, i.e. dimensionless active volume. The effect of temperature was disregarded in the present model considerations. Cavitationally active zone in reactors was determined based on the erosion of aluminum foil, resulting in cone-shaped space arising from transducer. In the present study, sonochemical treatment of industrial wastewater containing HCOONa as organic pollutant was performed using different equipment: ultrasonic baths (UB1, UB2 and UB3), cylindrical reactor with homogenizer (HCR) and three-frequency hexagonal cell, i.e. ultrasonic pilot reactor prototype (PP). Explored frequency range was from 20 to 120 kHz. Homogeneous and heterogeneous Fenton-type sonochemical processes, US/Fe(II)(FeSO4,aq.)/H2O2 and US/Fe(II)(steel-plate)/H2O2, respectively, applied to industrial wastewater were investigated in terms of mineralization kinetics. Newly modeled eUS factor was introduced in corresponding kinetic models and the overall model was validated. Kinetic parameters of Fenton process were treated as independent of ultrasound, since eUS factor consists of cavitation-related phenomena responsible for the mineralization rate enhancement. In average, a 21% increase of mineralization efficiency was achieved using a single frequency, while more than 70% increase can be achieved by combining 20, 68 and 120 kHz in PP.

Mineralization of p-chlorophenol in water solution by AOPs based on UV irradiation

Protection of clean aquifers requires radical minimization of water consumption, overall reduction of wastewater and, furthermore, minimization of wastewater loading. Many organic pollutants in wastewater present a specific problem because of their toxicity, bioaccumulation and poor biodegradability. The scope of this paper is to investigate and identify the benefits offered by advanced oxidation processes (AOPs) as destructive methods for treatment of wastewater loaded with recalcitrant organic pollutants. The study was performed on model wastewater containing p-chlorophenol as a representative of organic chemical industry intermediates. Several UV based AOPs were studied: UV, UV/H 2O 2, UV/O3, UV/H 2O 2/O 3 and UV/Fenton. Optimal process conditions for the highest mineralization efficiency in the investigated range (pH, [H 2O 2] and [Fe 2+]) have been determined on the basis of HPLC measurements and the following ecological parameters: total organic carbon (TOC), adsorbable organic halides (AOX), chemical oxygen demand (COD) and biochemical oxygen demand (BOD 5). Toxicity is one of the most important ecological parameters in determining the level of water pollution. In this study, toxicity tests were performed on the zooplankton Daphnia magna in order to evaluate efficiency of the applied treatments. The UV/ Fenton and UV/H 2O 2/O 3 processes were found to be the most appropriate processes for degradation and mineralization of p-chlorophenol. Complete degradation was achieved after 15 minutes of UV/Fenton process treatment, while 92.1% TOC and 98.3% AOX removals were obtained after treatment of 60 minutes.

Impact of ultrasound application on oxidative desulphurization of diesel fuel and on treatment of resulting wastewater

The ultrasound-assisted oxidative desulphurization (UAOD) process of diesel fuel has gained growing attention due to the strict regulation of sulphur content in the fuel. The goal of the present study was to investigate the impact of ultrasound (US) application for oxidative desulphurization (ODS) of hydrocarbon fuels and for the subsequent treatment of produced wastewater, since sonochemical processes are a new and interesting area of research with wide application in the field of environmental engineering. For that purpose, the model diesel fuel with initial sulphur concentration of 1220–3976 mg l−1 was used for ODS and UAOD tests, and hydrogen peroxide/acetic acid was applied as the oxidant/catalyst system, respectively. The comparison of the process performance revealed that US significantly reduced the oxidation reaction time. The conversions of dibenzothiophene during 30 min of ODS and UAOD tests were 36% and 87%, respectively. Moreover, subsequent extraction with acetonitrile resulted in the final sulphur removal of 96.5%. The obtained results clearly indicated that UAOD process is beneficial for effective sulphur removal from the model diesel fuel. Furthermore, subsequent experiments included the application of the sono-Fenton process for resulting wastewater treatment. Monitoring of dibenzothiophene sulphone concentration and total organic carbon during the sono-Fenton treatment of wastewater revealed the decrease of 70–75% and 53–66%, respectively. The hypothesis on the possibility of degradation of dibenzothiophene sulphone by •OH radicals was confirmed by observed generation of benzoic acid and aliphatic carboxylic acids during experiments. Accordingly, the wastewater was purified to a satisfactory degree, enabling the reuse of treated water.

Photocatalytic Activity of TiO2 Thin Films: Kinetic and Efficiency Study

Abstract The aim of this work was to evaluate the photocatalytic activity of two distinct anatase thin films. Films were prepared following the sol-gel procedure from titanium (IV) isopropoxide (TF-1) and from commercial TiO2 P25 as a starting material (TF-2). The films were compared based on the salicylic acid (2-dihydroxybenzoic acid, 2-HBA) photocatalytic degradation in reactors of different geometry and under different irradiation conditions. Experiments were performed in (i) an annular photoreactors operated under turbulent flow (TAR1 and TAR2) and (ii) semi-annular reactor operated under laminar flow (LFR). The TF-1 and TF-2 were immobilized on the inner side of outer wall of TAR1 and TAR2 and on the bottom of LFR. Experimental study included sorption study and four consecutive photocatalytic runs (tirr= 8 h) using TF-1 and TF-2 in each reactor. Obtained results confirmed the stability and the similar photocatalytic activity of the both films. The 2,5-dihydroxybenzoic acid (2,5-DHBA) and 2,3-dihydroxybenzoic acid (2,3-DHBA) were identified as main 2-HBA degradation by-products. Kinetic models were developed accordingly. Incident photon flux was determined along the inner reactor wall in annular reactors and on the bottom of LFR, i. e. on the thin film surface (Itf, W m−2) using ESSDE radiation emission model. The irradiation factor, i. e. the product of absorption coefficient and incident photon flux at film surface (μItf(z))m was introduced into the kinetic models. Resulting reaction rate constants ki (min−1W−0.5 m1.5) were independent of reactor geometry, hydrodynamics, irradiation condition and the optical properties of thin films. Efficiencies of TF-1 and TF-2 in studied reactors were given on the basis of quantum yields (QY) for 2-HBA oxidation and overall mineralization toward CO2.

The sensitization effect of waste toner powder in the photocatalytic degradation of surfactant sodium dodecylbenzene sulfonate over immobilized TiO2–chitosan layer under UVC and solar irradiation

The application of dye sensitized photocatalysis for the degradation of surfactant in the model wastewater has been studied. The aim was to explore the possibility of the photocatalytic activity enhancement by introducing the waste toner powder in the photocatalytic films. The development and a partial characterization of the supported catalyst were described within this study. Waste toner and commercial TiO2 powder (AEROXIDE® P25) were integrated within the matrix of chitosan molecules as a thin layer films. The developed films contain the high amount of the TiO2 (approx. 90%) which structure appeared to be intact. The efficiency of the photocatalytic films for the oxidation of the anionic surfactant dodecylbenzene sulfonate (SDBS) has been evaluated. Preliminary experiments were performed in an annular batch reactor using UVC lamp. Photocatalytic films were supported on the glass, stainless steel and waste offset printing plates. Support was made in a form of plates or rings. Further experiments were performed under artificial and natural solar irradiation whereby photocatalytic films were fixed at the bottom of reaction cell (boat shaped flow reactor). In order to estimate the reaction rate constant for SDBS degradation over irradiated photocatalytic films and to evaluate the effects of photon absorption under different irradiation conditions, a detailed kinetic model was developed. The sensitization effect of the components in toner powder due to the visible light absorption for the photocatalytic oxidation of SDBS under solar irradiation was quantified.