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Comparison and predesign cost assessment of ozonation, electro-oxidation and heterogeneous photo-Fenton for the treatment of wastewaters from the chemical industry Helen Barndok, Daphne Hermosilla, Carlos Negro, and Angeles M Blanco ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b04234 • Publication Date (Web): 20 Mar 2018 Downloaded from http://pubs.acs.org on March 21, 2018
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ACS Sustainable Chemistry & Engineering
Comparison and predesign cost assessment of different advanced oxidation processes for the treatment of 1,4-dioxane-containing wastewater from the chemical industry
Helen Barndõk1, Daphne Hermosilla2*, Carlos Negro1 and Ángeles Blanco1
1 Department of Chemical Engineering, Universidad Complutense de Madrid, Avda. Complutense, s/n, 28040 Madrid. 2 Department of Agricultural and Forestry Engineering, Universidad de Valladolid, Campus Duques de Soria, 42004 Soria, Spain.
E-mail addresses (in order of appearance):
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[email protected],
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Corresponding author:
Tel.: 97512-9471 - Fax: 975129401 E-mail address:
[email protected] (Daphne Hermosilla)
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ABSTRACT The predesign cost analysis of the industrial implementation of several advanced oxidation processes (AOPs) as the pre-treatment of 1,4-dioxane-containing wastewater from the chemical manufacturing industry is herein assessed and discussed. Aiming to maximize biodegradability and minimize the generation of residues, ozonation (O3), conductive diamond electrochemical oxidation (CDEO), and zero-valent iron-based heterogeneous photo-Fenton process were tested. Sufficient biodegradability (≈60%) was reached by all the studied AOPs when the pre-treatment was performed until obtaining a 40% removal of the COD. The design criteria consisted on reaching this 40% COD reduction in a unit with a treatment capacity of 43800 m3·y-1. Considering the limitations inherent to this type of assessment, it resulted, from the analysis of capital investment and annual operational spending, that the cost of all the assessed AOPs was about 5 €·m-3.
Keywords: 1,4-dioxane, biodegradability, AOPs, pre-treatment, chemical industry, cost analysis.
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Introduction Water quality is turning into one of the most important issues of industrial development, especially taking into complementary consideration water scarcity effects affecting certain areas of the world, and the increasing global demand for water use. In particular, 1,4-dioxane is an emerging contaminant released in industrial effluents that is commonly and widely used as solvent; as well as it may be produced as a by-product in many chemical manufacturing processes [1,2]. This compound is frequently found present in the effluents outflowing conventional wastewater treatment plants (WWTPs), therefore indicating that traditional secondary treatments are not efficient to achieve the complete removal of this cyclic ether [1, 3-4]. 1,4-dioxane addresses multiple harmful effects [2, 6-7], including kidney failure, liver damage, and its role as tumour promoter, as reported in several animal studies. As a consequence, the treatment of 1,4-dioxanecontainng wastewater is critical to prevent the potential bio-accumulation of this persistent compound in the environment. Several advanced oxidation processes (AOPs) have already been implemented to treat wastewater streams contaminated with bio-refractory chemicals [8,9]. Specifically, the removal of 1,4-dioxane from synthetic water has been reported as successfully realized by diverse common AOPs [10,11]. In particular, the fastest removal of this compound has been addressed by photo-Fenton processes [12]. The conventional Fenton treatment, although it has been proved to be very efficient removing 1,4dioxane, it holds several key disadvantages, such as the need to acidify the medium, implying its subsequent neutralization, and the generation of iron sludge; to which it should eventually be added the cost of using UV radiation in the case of non-solar photo-Fenton alternatives [13,14]. Therefore, designing more cost-effective and less residues-generating treatments is of key importance; for example, applying solar light to
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assist the process, using solid iron sources to catalyse the treatment, and performing the reaction efficiently under pH conditions closer to neutral values in order to avoid iron leaching. Conductive diamond electrochemical oxidation (CDEO) alternatively likewise achieves very high reductions of refractory organics contents without generating secondary contamination [15]. Nevertheless, its efficiency looks like being restricted by mass transfer to available electrode surface, in addition to the need of using a costly material for the electrodes with little behaviour feedback in industrial applications up to date [16]. Ozonation, on the other hand, is a worldwide implemented full-scale treatment that does not produce any residue as well [17]; although the cost of ozone (O3) generation in long-lasting treatments may limit its viability to treat highlycontaminated industrial wastewater [18]. Considering all the above, the technical viability assessment of the degradation of 1,4-dioxane from real industrial effluents was carried out applying the following treatments: heterogeneous photo-Fenton method using zero-valent iron (Fe0) microspheres as the catalyst performed under neutral pH conditions [19]; CDEO on boron-doped diamond (BDD) electrodes [20]; and ozonation under basic conditions (O3/OH- [21]. Significant reductions of the content of 1,4-dioxane (>90%) were achieved by all these AOPs, but the economic analysis of these different treatment alternatives has not been addressed yet. The total cost of an AOP treatment, including capital investment and running process expenses [22], directly depends on the scale at which the process is performed, which is ultimately determined by the capacity of the treatment plant and the selection of the operative design point. Besides high removal percentages of chemical oxygen demand (COD) and total organic carbon (TOC) have been reported to be achieved by
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these three AOPs [19-21], the total mineralization of organic compounds is usually considered unfeasible to AOPs in highly-loaded industrial wastewater; with the exception of low-flow streams, for which the combination of AOPs with biological processes is the preferred option to increase biodegradability in the wastewater [23]. In these cases, the point at which sufficient biodegradability improvement is achieved by the AOP pre-treatment is going to determine the plant size and the oxidant requirements for the process, and, therefore, its total cost. The main scope of this essay was to technically and economically compare heterogeneous Fe0-photo-Fenton treatment (whether using UV or solar radiation), CDEO, and basic ozonation, as possible pre-treatments for 1,4-dioxane-containing industrial wastewater aiming to increase its biodegradability before further treating the effluent by conventional biological processes, ensuring the total removal of 1,4-dioxane from wastewater. A preliminary analysis of the capital investment and annual operational costs was performed for each treatment considering different design criteria in order to perform the appropriate financial comparison. The main novel contribution of this work is the study of the viability of 1,4-dioxane treatment taking into account economic features.
Material and methods The industrial wastewater polluted with 1,4-dioxane was collected from an chemical plant. The main characteristics of this wastewater were: COD = 475 ± 25 mg·L-1; pH0 = 8.8 ± 0.1; alkalinity = 950 ± 50 mg CaCO3·L-1; conductivity = 2.0 ± 0.1 mS·cm-1; and [1,4-dioxane] = 248 ± 12 mg·L-1. All wastewater analyses were performed according to the Standard Methods for the Examination of Water and Wastewaters [24]. Analytical grade chemicals were supplied by Merck KGaA (Darmstad, Germany), and Panreac
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S.A. (Barcelona, Spain). For the study of identification of reaction intermediates, a 7050 mg·L-1 1,4-dioxane solution was prepared using deionized water and adding 1000 mg·L1
of CaCO3 to emulate the conditions of the industrial effluent. Sodium hydroxide
(NaOH, 98.0%) was added when required to control the pH along ozonation trials. Sodium sulphate (Na2SO4, 99.0%) was used as supporting electrolyte in CDEO treatment experiments. Hydrogen peroxide (H2O2, 30% v/v) and Fe0 microspheres (>98.3% Fe;
