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Page 1: Chap6 Water Remediation With Cover SEMMI
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Chapter 6

Water remediation by the electron beam treatment Salvatore S. EMMI and Erzsébet TAkÁCS

Introduction

Water shortage and security are becoming a major national and regional priority because of water-intensive lifestyles, rapid industrialization, urbanization, and agricultural intensification worldwide. Therefore the treatment of municipal and industrial wastewater as well as of drinking water is a prime task for environmental engineering. Let's consider, for example, the problems encountered with halogenated organic compounds. The ubiquitous nature of halogenated organics, from trichloroethylene to the wood preservative pentachlorophenol, has spawned considerable discussion about the impact of such halogenated organics in the environment. Chlorophenols are a serious health concern in drinking water treatment, as they can be present in the source water or be formed as by-products of chlorine-based disinfection methods. An ample literature reports on effective degradation of chlorophenols and other toxic pollutants such as dioxins, polychlorinated biphenyls (PCBs), and benzofuran derivatives [1-3]. Another class of compounds, emerged as a focus of attention because of their impact on the environment, is that of dyes and pigments, which are the single largest group of industrial chemicals. This chapter briefly surveys the electron beam (EB) Advanced oxidation Process, reporting some recent results on the decompositions of a dye (Apollofix-Red) and of a pesticide (carbofuran). Two successful applications of the technology on the industrial scale are also presented.

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Advanced Oxidation Processes (AOPs)

A large class of Advanced oxidation Processes (AoPs), such as UV-peroxide, ozonation, Fenton and Fenton-like processes, photocatalysis, electrokinetics and sonolysis have been effectively employed in order to decompose hazardous compounds in water [3-5]. All these methods are based on the generation and use of hydroxyl radicals as the primary oxidant for the degradation of organic pollutants (Fig. 1). Table 1 reports the reduction potentials of popular radical species relevant to wastewater remediation. From that it can be seen that •oH has the highest oxidative power. Being also a very fast reactant, •oH can attack and oxidize most of the hazardous compounds dissolved in water. Electron beams in the MeV range, and to a lesser extent γ-rays, are excellent tools to produce •oH radicals by operating the lysis of water induced by radiation (radiolysis).

Table 1. reduction potentials of radical species relevant to wastewater remediation* (ox + e– → red).

Species (alphabetic order) Couple pH Std Red Pot (1)

Chlorine (Cl2) Cl2/Cl2•– 0.42 .. 0.60

Chlorine dioxide (Clo2•) Clo2

•, H+/HClo2 ~ 1.30

Chlorine radical anion (Cl2•–) Cl2

•–/2Cl− 2.09(2)

Hydrogen peroxide (H2o2) H2o2, H+ / H2o, •oH 7 0.46 .. 0.87

Hydroxyl radical (1) (•oH) •oH / oH− 1.9

Hydroxyl radical (2) (•oH) •oH, H+/ H2o acid 2.7

Hypochlorous acid (1) (HClo) HClo, H+ / H2o, Cl• - 0.46

Hypochlorous acid (2) (HClo) HClo/ Cl−, •oH - 0.04

oxide radical ion (o•–) o•–, H2o/ 2 oH− 1.78

ozone (o3) o3 / o3•– 11-12 1.01

Perhydroxyl radical (1) (Ho2•) Ho2

•, H+ / H2o2 0 ~ 1.50

Perhydroxyl radical (2) (Ho2•) Ho2

• / Ho2− 0.79

Superoxide radical (o2•–) o2

•–, H+/ Ho2– 1.00

* A more positive reduction potential for the couple Ox/Red, means that Red is a more powerful oxidant. When protons are involved, the reduc-tion potential of the half-cell varies with pH. 1) Wardman P., J. Phys. Chem., Ref. Data, 1989, 18,1637-1755. 2) Atkins P.W., Physical Chemistry, Fifth Edition, Oxford University Press (1994).

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Figure 1 : hydroxyl radicals decompose pollutants. Typical •OH attack to an aromatic ring.

Water radiolysis by electron beam

A beam of electrons, travelling through water, forms a swarm of highly reactive radicals: hydrated electron (eaq

−), hydroxyl radical (•oH) and hydrogen atom (•H) [6] (see G.V. Buxton, Chapter 1). To perform an AoP, eaq

– and H atoms should be neutralized to poorly reacting species or, better still, transformed into a further amount of •oH radicals. This is achieved by adding one or more scavengers to the system. Figure 2 outlines a variety of systems which characterize different EB operating systems. Among these, a straightforward oxidative degradation process is represented by the saturation of water with N2o above pH 3: N2o captures the strong reducing eaq

− and converts it stoichiometrically into •oH. As a result of this method, practically only •oH remains, except for a negligible quantity of H•. The plainness of this system is also suitable for mechanistic studies with pulse radiolysis, i.e. the chemical kinetics application of EB (see next page).

The rapidity with which the EB treatment initiates the decomposition of pollutants may be promptly checked by reasonably assuming that i ) •oH reacts with rate constants in the range 106-109 l mol−1 s−1 , and i i ) pseudo-first order conditions are maintained throughout the process (i.e. •oH reacts quantitatively with the pollutant). Therefore a pulse of electrons depositing 10 Gy of energy in N2o saturated water triggers the decomposition of ~ 5 x 10−6 mol/l of pollutant. In an ordinary accelerator facility, sweeping a flow of water with pulses of 1 microsecond duration at a repetition rate of 100 pulses per second, 0.5 millimol/l of compound per second are immediately modified. Certainly, the calculation of the production speed of the oxidizing species allows only a rough assessment of the efficiency of an AoP.

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In fact, the whole rehabilitation is affected by a wide range of factors, among which a primary role is played by the variety and nature of pollutants, and the required quality of water. As a matter of fact, industrial plants demonstrate the ability of EB to treat and recycle millions of litres of wastewater per day (see later), a goal well above the reach of the other technologies.

Figure 2 : homogeneous and heterogeneous aqueous systems used to produce •oh and other oxidizing radicals in typical E-beam aoP experiments. Any system can be employed separately or in association with the others. Oxidation chain carriers are red tagged.

To exemplify the destruction of a pollutant, the decomposition of a hydrocarbon is illustrated in Figure 3 : the right side represents the radical production systems, while on the left the most important reactions following •oH attack are given. In Figure 3, •oH operates its oxidizing action by abstracting a hydrogen atom from the hydrocarbon chain. Besides water, an alkyl radical is formed from the pollutant : this radical starts a series of reactions, such as peroxidation, fragmentation, further H abstraction, disproportionation, molecular growth etc. •oH may also initiate an oxidative pathway by accepting an electron (electron transfer), or by adding to a π electron system (bond breaking). The latter is the most common pathway in the presence of an aromatic ring, and it will be described later by means of two representative pollutants.

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Figure 3 : oxidative degradation of a hydrocarbon by E-beam aoP. Irradiated water produces •OH both directly and by the mediation of dissolved scavengers (right side). •OH oxidizes the hydrocarbon by H abstraction. The resulting alkyl radical starts a recursive chain degradation giving rise to new carbon- and oxygen-centered radicals, carbonyls, carbocations, hydroperoxides, polymers, etc. (left side).

Pulse radiolysis

The simultaneous presence of pollutants of different nature in wastewater gives rise to a very complex kinetic degradation scheme. The kinetic parameters of each reaction constitute the basic data needed to design an efficient degradation process. A suitable tool to make such kind of investigation is pulse radiolysis (Chapter 2) coupled with a kinetic spectrometry detection system [7]. Aiming to achieve meaningful results, reactions with water radicals are studied separately as outlined below (Chapter 1) :

– In N2 or Ar saturated solutions, between pH 3 and 11 the reactions take place with •oH, H• and eaq

−.

– Below pH 2 in N2 or Ar saturated solutions, nearly equal amounts of the •oH radicals and H• atoms are present. This is because aqueous electrons are converted to H• by reacting with the hydroxonium ions:

eaq− + H3o+ → H• + H2o (1)

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– H• atoms reactions with solutes can be carried out alone below pH 2 in N2 or Ar saturated solutions containing 0.2 – 1 mol l–1 tert-butanol.

In this system, tert-butanol scavenges •oH and forms poorly reactive radicals : •OH + (CH3)3CoH → •CH2(CH3)2COH + H2o (2)

(The reaction between H• and tert-butanol is slow).

– Reductions by eaq− are performed in N2 or Ar saturated solutions above pH 3 and in

the presence of 0.2 – 1 mol l–1 tert-butanol (there is a small contribution from the H• atom reactions). Radicals formed from tert-butanol are also present.

– In air or oxygen saturated solutions, the reactive species are the •oH radical, and the couple o2

•−/Ho2• (superoxide radical anion/perhydroxyl radical). The couple is

originated by scavenging eaq− and H• with o2 :

eaq− + O2 → o2

•− (3) H• + O2 → Ho2

• (4)

and is in acid/base equilibrium with a pka value of 4.8

o2•− + H3o+ → Ho2

• + H2o (5)

– Solutions saturated with o2 and containing tert-butanol are used for studying the reactions of the o2

•−/Ho2• acid-base radical pair.

The degradation of pesticides : carbofuran

Carbofuran (C12H15No3), is a carbamic insecticide and nematocide vastly employed in North America and in some European countries to protect maize, rice, alfalfa, onion, garlic, potatoes, etc. However, it is toxic by contact and ingestion, and lethal over the level of 11 mg/kg (LD50, rats). The Maximum Contamination Level (MCL) for drinkable water, as established by EPA (USA), corresponds to 0.18 µmol/l.

Several AoPs have been proposed to operate carbofuran decomposition, and many of them have demonstrated their effectiveness. The choice of the more appropriate system will consider parameters like the rapidity of action and economical factors.

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Figure 4 : Gamma-radiolytic degradation of a pesticide carbofuran at 200 µmol l–1 and the synergistic effect of a metal oxide (tio2 ). Left) : carbofuran in deaerated atmosphere and in the absence of catalyst. Right) : carbofuran in oxygenated atmosphere and in the presence of TiO2. In the latter system the dose neces-sary to decompose 200 μmol l–1 carbofuran decreased by an order of magnitude.

The example below refers to a recent study by pulse and gamma radiolysis [8]. A pH ≈ 6 has been generally used. Hydroxylation mainly concerns the aromatic ring of carbofuran (Fig. 4 ) ; in fact, the first intermediate shows the absorption of a cyclohexadienylic type radical in the region 280-330 nm. The hydroxylation attack to carbofuran

•OH + carbofuran → •CF-oH (6)

proceeds with a rate constant kOH+CF = 6.6 x 109 l mol−1s−1. In the presence of oxygen, the carbofuran cyclohexadienylic radical adds oxygen (peroxidation) with a rate constant kperox ≈ 107 l mol−1s−1. As measured after gamma radiolysis, oxygen participation makes the global decomposition three times more efficient than in anaerobic solutions ; the efficiency is further enhanced by adding a 1% amount of Tio2. Typically, under these conditions a sample containing carbofuran 200 µ mol l–1 is completely decomposed by 1.25 kGy of γ-radiation dose, i.e. an order of magnitude more efficiently than without o2 and Tio2 (Fig. 4).

TiO2 catalysis

Tio2 catalysis proceeds through the production of •oH radicals at the solid-liquid interface. The mechanism of action lies on the separation of charge upon absorbing a radiation of energy higher than 3.2 eV, i.e. below 380 nm (UV photons, E-beam and γ-rays) : holes (h+) are left in the valence band (VB) and electrons (e −) are promoted to the conduction band (CB).

Carbofuran

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It appears that Tio2 particles in water are widely hydroxylated. Therefore holes escaping annihilation may migrate to the surface and oxidize adsorbed water molecules and hydroxyl ions. oxygen adsorbed at the surface captures electrons preventing their recombination with h+, and therefore favouring the yield of •oH radical (Fig. 5).

Figure 5 : Formation of oxidizing radicals at the solid-liquid interface of tio2 and water. Radia-tion promotes a separation of charge in the cata-lyst. H2O, OH–, and O2, adsorbed at the surface are converted to radicals by electrons and holes which migrate to the interface. Oxidative degradation is greatly enhanced (see also Fig. 4).

Decoloration of dyes : Apollofix-Red

In dilute dye solutions all the intermediates of water radiolysis, i.e. hydrated electron (eaq

−), hydroxyl radical (•oH) and hydrogen atom (•H) induce the decomposition of the solute.

The degradation of the dye can be easily followed by taking decoloration curves. This is usually done by preparing appropriate solutions, irradiating them by increasing the dose stepwise and by taking the UV-VIS absorption spectra after each irradiation [9]. The decoloration is due to the destruction of the color centers. The color fading with dose is illustrated in Figure 6.

The upper part shows the spectra of aqueous N2o saturated solutions of a reactive dye (Apollofix-Red), before and after EB irradiation with different doses (0-3 kGy), while the lower part shows the photographs of samples treated in the same way. The chromophore center of this dye is an azo group connecting a benzene ring with a naphthalene part. Decolored products are formed when the extensive conjugation is destroyed, for instance when the conjugation through the –C–N=N–C– bridge is lost. End-product analysis by High Performance Liquid Chromatograph (HPLC, diode array detection was used for this measurement) also showed a sharp decrease in the concentration of the starting compound (Fig. 7).

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Apollofix-Red

Figure 6 : Dye decoloration. aqueous n2o saturated solutions of a dye (apollofix-red 0.25 μmol l–1) are E-beam irradiated with increasing doses: the reaction with •oh destroys the color centers. This is shown both by a progressive weakening of the absorbance of samples (spectra) with dose (0-3 kGy) and also by a progressive increasing of their transparence (photographs below the spectra). The inset shows the decoloration-dose curve at 530 nm.

Figure 7 : three-dimensional hPLC chromatogram showing the separation of degradation products in n2o saturated dye (apollofix-red ar-28 at 0.25 mmol l–1) solution irradiated with 0.6 kGy dose. Destruction of AR-28 molecules and formation of degradation products in •OH radical reactions as measured by HPLC with diode array detection. AR I and AR II are used for AR-28 and for its hydrolysed form, respectively, PI and PII are products.

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The mechanism is not as straightforward as it may appear: in the first step, in fact, after •oH radical addition to any aromatic ring, a new colored product is formed, i.e. the cyclohexadienylic type radical may reform the conjugated system in disproportionation reactions [7,10]. The process is exemplified with a substituted benzene (Scheme 1). Using high doses, and especially in the presence of o2 or o3, aldehydes and organic acids are formed from the •oH-dye adducts and finally decomposed to Co2 and H2o (see upper part of Scheme 1).

Scheme 1 : Decomposition outline of the aromatic part of apollofix-red dye, modeled with a substituted benzene (lower part) and achieving its complete mineralization (upper part). A disproportionation reaction between two cyclohexadienylic radicals regenerates the aromatic ring structure in a phenol derivative. The R-group can be an alkyl group or a halogen atom.

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Electron accelerators and operative conditions

At present radiation technology is a popular method for sterilization, polymerization, polymers and semiconductors modification, but not for environmental remediation. Actually, while various new features of irradiated materials were worthy of industrial investments, the improvement given to the quality of water and air was not economically rewarding. In the past indeed, the requirement of high initial investments constituted a restraint to the E-beam implementation in the environmental field. Nowadays, however, accelerators are becoming cheaper while freshwater is more and more precious, such that radiation rehabilitation and recycling of wastewater can be profitably considered by both public authorities and investors.

To see that, let us focus on a couple of factors that mainly determine the economy of the EB remediation process: i.e. a high power (by which high volumes of water can be rehabilitated daily), and the efficiency (which establishes the transfer rate of the accelerator nominal power into useful energy). To this respect, it is instructive to learn from Table 2 that DC and UHF machines (Chapter 2) best match with these requirements. In the DC type machines, electrons are accelerated by a direct-current field, while in the UHF type, acceleration occurs across an electromagnetic field oscillating at few hundreds MHz. These accelerators achieve high powers coupled with moderately-high efficiencies, and therefore represent the best choice for wastewater treatment. At present, the linear accelerators, which are based on a microwave field, show efficiencies and power below the others, such that they are not suitable for environmental purposes.

Table 2. Features of accelerators for environmental processing.processing.

Type Accelerating field Efficiency range (%) Power (kW) (up to) Energy

range (MeV)

DC electrostatic 60-80 400 0.1-5

UHF 100-200 MHz 25-50 700 0.3-10

Linear 1.3-3 GHz 10-50 150 2-10

Considering some practical aspects, it has to be remarked that the EB is best used as a pre-treatment step to integrate a conventional bio-, and physico-chemical plant. Under such conditions a dose of 2 kGy allows the destruction of most organic pollutants with unmatched success even in case of bio-refractory compounds. Simultaneously, disinfection of wastewater is achieved. When only disinfection is required, the dose may be reduced to 0.2 kGy, resulting in more than 95% inactivation of the total coliform bacilli without any

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previous chlorination. An appropriate machine for these processes should produce 1-2 MeV electrons, while the output power can be within the 40 to 400 kW range, depending on the flow rate required. Studies showed that uniform dose distribution is achieved by transversally pumping a thin layer of effluent under the beam area, as illustrated in Figure 8.

Figure 8 : optimal flow system irradiator geometry. Penetration of 2 MeV electrons in water is 1 cm.

Industrial and municipal treatments

Data on the reactivity of various classes of toxic substances and of dyes with •oH and other radicals were made available by means of pulse radiolysis (see above). oxidative degradation in complex systems could then be simulated with numerical methods and tested on pilot plant scale. Finally, some fully operating industrial plants demonstrated the viability of EB processing both on the environmental and economical aspect.

Among these plants, the wastewater rehabilitation plant of the Voronezh synthetic rubber plant (Russia) is worth to mention [2]. Here, two electron accelerators (0.7-1 MeV energy and 50 kW power), can treat up to 2,000 m3 of wastewater per day with the specific goal to transform the non-biodegradable emulsifier Nekal into a biodegradable form. A further decomposition is achieved with biological methods.

Another industrial plant was put into operation in December 2005 for the EB treatment of dyeing wastewater (Fig. 9) in korea at Daegu Dyeing Industrial Complex (DDIC). DDIC includes about hundred factories, the majority of which has equipment for dip dyeing, printing, and yarn dyeing [11, 12]. The production requires high consumption of water and emits large amount of highly colored industrial wastewater. The whole facility treats up to

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80,000 m3 wastewater /day. From this volume, 10,000 m3/day are pre-treated presently by EB, using a 1 MeV - 400 kW - accelerator combined with bio-treatment facilities.

Figure 9 : Combined wastewater treatment at DDiC (from Bumsoo Han originals, EB-TECH Co., Ltd., Daegu, Korea, on permission of the author).

An instructive case study, illustrating different operational conditions in the Mediterranean area, was carried out by Lopes [13]. The author made a predictive modelling on the implementation of EB to the urban wastewaters of the city of Palermo (Sicily). At present the city of Palermo is served by two depurator plants. one of them, called “Corsairs water”, is under development to accomplish the treatment of 300,000 m3/day. Goal of Lopes's investigation aimed at assessing the disinfection line of the depurator by EB. The process was then modelled on a daily treatment of 33,000 m3 with 10 MeV electrons and a dose of 0.2 kGy, produced by one or two 190 kW accelerators of the UHF type, i.e. the Rhodotron TT300 (IBA).

Cost evaluation

Cost evaluations for EB treatment may vary, mainly depending on accelerator voltage and power, on the cost of electricity, and on the reuse assigned to restored water (i.e., on the degree of pollutant decomposition or disinfection). Among other factors, the cost for generating a unity of power is of primary importance: 1 kW is cheaper for high power accelerators, i.e. it may cost 20 k$ for a 40 kW accelerator, but only 5 k$ for a 400 kW machine. Nonetheless, a realistic and updated evaluation is available from the experience at the Daegu plant above [12] and from the mentioned study at the University of Palermo [13]. Let us prospect two typical cases at Daegu, both using a 1 MeV-400 kW-accelerator (cost 2 – 2.5 million US$), running 365 days/year. Case A: 100,000 m3/day of wastewater from

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a municipal plant are rehabilitated for irrigation and industrial use with a dose of 0.2 kGy (disinfection only). Case B: 10,000 m3/day of textile wastewater are rehabilitated for self-recycling with a dose of 1-2 kGy (dyes decoloration and disinfection). In Case A, the capital investment per m3 of effluent would be around 0.11-0.12 US$, while the operating cost would be ca. 0.03 US$. In case B, costs increase 7-8 times, being respectively 0.82 US$/m3 and 0.24 US$/m3 (Tab. 2). These financial quotations include investments for the industrial plant (accelerator, shielded room, water reactor, design, and others), interest, depreciation, and electricity (80% efficiency at a cost ≈ 0.05 US$/kWh) and do agree with the actual costs after 12-15 months of operation. Costs for land, research and development, and for authority approval are not included. At the same site, EB treatment combined with bio-plant leads to ≈ 20% savings in operating costs, compared to bio-plant alone, reduces the residential time, and moreover yields water of better quality.

In the Palermo case [13], one accelerator (cost ≈ 4 million €) working almost at full capacity (180 kW), or two accelerators at half-power, are conceived. A comprehensive economical model reached conclusions matching with the Daegu budget plan: precisely, in Palermo, each m3 could cost 0.17 € employing one accelerator, or 0.28 € with two accelerators (Tab. 3). The latter system, although more expensive, is still acceptable as it could minimize risk of service interruption for possible failure. However, a pilot plant with only one accelerator should be a wise starting system, as has been done in Daegu.

Table 3. operational features and cost of EB treatment at DDiC (Daegu, Korea) and Corsairs Water (Palermo,

sicily).

Plant

Accelerator

Aim Status Dose, (kGy)

Water treated

(m3/day)

Total cost (/m3)

Model Type Energy, (MeV)

N. of Acc

Operating power (kW)

DDIC ELV-12 DC 1 1 400 disinfection tested in pilot plant 0.2 100 ,000 0.15 US$

1 1 400 industrial recycling operative 2.0 10,000 1.06 US$

Corsairs Water

Rhodotron TT300

UHF 10 1 180 disinfection study 0.2 33,000 0.17 E

10 2 90 each disinfection study 0.2 33,000 0.28 E

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Concluding remarks

In the preceding sections, the reader got acquainted with a few basic concepts on the remediation of water pollution by injecting energy in water and its latest developments. The Electron beam treatment is a physico-chemical method which pursues the rehabilitation of polluted waters by the oxidative action of the •oH radical, and we saw that the methods for •oH generation distinguishe various Advanced oxidation Processes.

The EB treatment is founded on the excitation and dissociation of water by high energy electrons. Energetic electrons are produced by devices which operate similarly to a TV set and, in the same way, are switchable on and off at the touch of a button. Exactly like in the TV operation, no radiation is stored in the environment. Wastewater can be rapidly and safety rehabilitated to be reused, for example, in industrial cooling and washing cycles, fire fighting, street washing, green park and horticultural irrigation. EB is particularly suitable for treating medium-large volumes of effluents from industries, hospitals, municipal plants, and animal-breeding. It does not give rise to concern for the environment, as it minimizes or rules out the addition and stock of chemicals. Furthermore, it works at room temperature and atmospheric pressure. Electrons penetrate in the depth of water even in case of turbidity (not possible by UV methods), and generate very high concentration of •oH in a fraction of a microsecond.

The versatility of EB is further experienced by the ease with which radical kinetics is governed ; in fact, the concentration of •oH can be modulated on that of pollutants by easily tuning the beam current.

Conventional rehabilitation treatments are inadequate when wastewaters include bio-resistant chemicals, e.g. the carcinogenic polychlorobiphenyls (PCB’s) and aromatic compounds. In this case a pre-treatment with EB converts bio-refractory compounds to bio-degradable ones and increases their solubility in water, finally reducing cost and residential time. Therefore, the design of a cost effective rehabilitation plant conceives the usage of EB as a method for improving the biodegradability of hazardous compounds, rather than for achieving their complete mineralization (i.e. production of Co2 and water). Complete mineralization is, in fact, a rather costly objective and may not always prove to be necessary for remediation. on the other end, conversion of a pollutant into a useful non-toxic product (e.g., fuel or polymer) may be alternatively a desirable goal. However, if complete mineralization is the ultimate purpose of wastewater treatment, radio-catalysis may be associated with other radiolysis methods, granting a synergistic effect to the process. An environmental friendly metal oxide, such as Tio2 for instance, may be used in this case. Besides the benign chemical

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action, the EB kills viruses and bacteria and should be regarded as the method of choice for water security, i.e. a rapid rehabilitation of bio-contaminated waters, in the eventuality of environmental accidents, acts of terrorism or vandalism.

Recent industrial achievements and projects showed the EB method to be both economically rewarding and effective in protecting the environment, and as such was granted credit by the IAEA [14]. Finally the Electron Beam technology should be regarded both as a trustworthy and an innovative process to fulfil a sustainable chemistry.

References

[1] Getoff N., The Role of Peroxyl Radicals and Related Species in the Radiation-Induced Degradation

of Water Pollutants, in “Environmental Applications of Ionizing Radiation”, Cooper W.J., Curry R.D.,

o’Shea k.E. (eds), Wiley, New York, 1998, 231-246.

[2] Pikaev A.k., Electron Beam Purification of Water and Wastewater, in “Environmental Application

of Ionizing Radiation”, Cooper W.J., Curry R.D., o’Shea k.E., Wiley (eds), New York, 1998, 495-506.

[3] Pera-Titus M., Garcia-Molina V., Banos M.A., Gimenez J., Esplugas S., Degradation of chlorophenols

by means of advanced oxidation processes: a general review, Appl. Catal. B. Environment, 2004,

47, 219-256.

[4] Legrini o., oliveros E., Braun A.M., Photochemical process for water treatment., Chem. Rev., 1993,

93, 671-698.

[5] kamat P.V., Meisel D., Nanoparticles in advanced oxidation processes. Current opinion in Colloid

and Interface, Science, 2002, 7, 282-287.

[6] Buxton G.V., Greenstock C.L., Helman W.P., Ross A.B., Critical review of rate constants for reactions

of hydrated electrons, hydrogen atoms and hydroxyl radicals (•oH/•o–) in aqueous solution, J. Phys.

Chem. Ref. Data, 1988, 17, 513-886. Updated version : www.rcdc.nd.edu.

[7] Wojnárovits L., Takács E., Emmi S.S., Reactivity differences of hydroxyl radicals and hydrated

electrons in destructing azo-dyes, Radiat. Phys. Chem., 2005, 74, 239-246.

[8] Emmi S.S., De Paoli G., Takács E., Pálfi T., Electron beam remediation of wastewater. The

hydroxylation of carbofuran, 24th Miller Conference on Radiation Chemistry, Le Londe les Maures,

France, 10-15 September 2005, 64.

[9] Solpan D., Güven o., Takács E., Wojnárovits L., Dajka k., High-energy irradiation treatment of

aqueous solutions of azo dyes: steady-state gamma radiolysis experiments. Radiat. Phys. Chem.,

2003, 67, 531-534.

[10] Wojnárovits L., Takács E., Irradiation treatment of azo dye containing wastewater : An overview,

Rad. Phys. Chem., 2008, 77, 225-244.

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6 / Water remediat ion

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