Environmental radiological risk assessment of a coal ash and slag disposal site with the use of the ERICA Tool.

The aim of this study was to assess the environmental radiological risk of coal ash and slag to terrestrial wildlife. The research site used in this study was a disposal site of coal ash and slag with enhaced content of uranium decay chain radionuclides. With the use of the ERICA Tool, total dose rates to wildlife and risk of resultant radiobiological effects were estimated. As input data for the assessment, experimental activity concentrations of 238U, 226Ra and 210Pb in coal ash and slag and best estimates of activity concentrations for related daughter radionuclides and 235U decay chain were used. Where possible, the experimental data for activity concentrations of 238U, 226Ra and 210Pb in plants and related concentration ratios were used. Results were compared to background dose rates, also estimated by the Tool. The Tool's assessment data indicated internal exposure as the prevalent exposure pathway with 226Ra and 210Po as the main dose contributors. Also, the contribution of 235U decay chain to the total dose rate was not negligible since for some organisms it represented up to 11% of the total dose rate. The risk of an occurrence of radiobiological effects in plants on the coal ash and slag disposal site can be considered negligible since the estimated total dose rates were below the screening dose of 10 µGyh-1 and near the dose rates estimated for plants in the control area. However, the estimated dose rates for reference animals and Lichen & Bryophytes were above the screening dose rate for most organisms and on average 13 times higher than the estimated background dose rates. At the given dose rates, an occurrence of different radiobiological effects could not be excluded for animals in close contact with coal ash and slag such as earthworms and small burrowing mammals. A separate assessment performed on an example of reference plants showed that the use of activity concentrations in organisms as input data can result in an order of magnitude smaller estimates of dose rates in comparison to activity concentration in coal and ash as input data. Our study highlighted the need for experimental data in radiological risk assessments to mitigate the conservatism of the ERICA Tool and its tendency to overestimate dose rates.

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.

Sonochemical effectiveness factor (e(US)) 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 (Grcic 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.

Kinetic modeling and synergy quantification in sono and photooxidative treatment of simulated dyehouse effluent.

The aim of this work was to explore the application of sulfate radical based advanced oxidation processes: photooxidation (UV/PMS/PS), sonooxidation (US/PMS/PS) and combined sono-photooxidation (US/UV/PMS/PS) for the mineralization of simulated dyehouse effluent (WW); using peroxymonosulfate (PMS) and persulfate (PS) as oxidants. Experiments were performed in a reaction vessel of a defined geometry and axially positioned source of UV-C radiation, all placed in the ultrasonic bath (35 kHz). Mathematical model of the process was developed according to the proposed degradation scheme. Decomposition of dyestuff (C.I. Reactive Violet 2, RV2 and C.I. Reactive Blue 7, RB7), surfactant (linear alkylbenzene sulfonate; hereafter: LAS) and auxiliary organic components was explored in three types of model wastewater: WW, simulated effluent excluding inorganic species (WW-IS) and model solution that consists of a specific compound (hereafter: compound model solutions). The influence of inorganic matrix (Cl(-), CO(3)(2-)/HCO(3)(-)) was studied due to the corresponding quenching affinity toward HO and SO(4)(-) radicals. The efficiency of applied processes was evaluated and the response to combined phenomena (cavitation and irradiation) was quantified as synergy index, f(Syn). Sono-photooxidative treatment (US/UV/PMS/PS) of WW resulted in a partial mineralization and partial decolourization; approximately 40% of initial TOC and 30% of initial RB7 remained after 60 min of treatment, while RV2 and LAS molecule were completely decomposed. Circumstantially, the combined process increased the mineralization efficiency by a factor of 3 (f(Syn) = 3.026).

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.

Decolourization and mineralization of commercial reactive dyes by using homogeneous and heterogeneous Fenton and UV/Fenton processes.

The oxidative decolourization and mineralization of three reactive dyes in separately prepared aqueous solutions C.I. Reactive Yellow 3 (RY3), C.I. Reactive Blue 2 (RB2) and C.I. Reactive Violet 2 (RV2) by using homogeneous and heterogeneous Fenton and UV/Fenton processes have been investigated. The effects of H(2)O(2), Fe(2+) and Fe(0) concentrations, Fe(2+)/H(2)O(2) and Fe(0)/H(2)O(2) molar ratios at pH 3 and T=23+/-1 degrees C have been studied. Optimal operational conditions for the efficient degradation of all three dye solutions (100 mg L(-1)) were found to be Fe(2+)/H(2)O(2)=0.5mM/20mM and Fe(0)/H(2)O(2)=2mM/1mM. The experimental results showed that the homogeneous Fenton process employing UV irradiation was the most effective. By using this process, the high levels of mineralization (78-84%) and decolourization (95-100%) were achieved. Pseudo-first-order degradation rate constants were obtained from the batch experimental data.

Advanced oxidation processes in azo dye wastewater treatment.

The chemical degradation of synthetic azo dyes color index (C.I.) Acid Orange 7, C.I. Direct Orange 39, and C.I. Mordant Yellow 10 has been studied by the following advanced oxidation processes: Fenton, Fenton-like, ozonation, peroxone without or with addition of solid particles, zeolites HY, and NH4ZSM5. Spectrophotometric (UV/visible light spectrum) and total organic carbon measurements were used for determination of process efficiency and reaction kinetics. The degradation rates are evaluated by determining their rate constants. The different hydroxyl radical generation processes were comparatively studied, and the most efficient experimental conditions for the degradation of organic azo dyes solutions were determined.