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Toxicity assessment of wastewater after advanced oxidation processes for emerging contaminants' degradation∗
8 Toxicity assessment of wastewater after advanced oxidation processes for emerging contaminants’ degradation* Giovanni Libralato,1 Giusy Lofrano,2, 3 Antonietta Siciliano,1 Edvige Gambino,1 Giovanni Boccia,4 Carraturo Federica,1 Aliberti Francesco,1 Emilia Galdiero,1 Renato Gesuele,1 Marco Guida1 1
Department of Biology, University of Naples Federico II, Complesso Universitario di Monte Sant’Angelo, Naples, Italy; 2Centro Servizi Metrologici e Tecnologici Avanzati (CeSMA), University of Naples Federico II, Naples, Italy; 3 Department of Chemistry and Biology “A. Zambelli”, University of Salerno, Fisciano (Salerno), Italy; 4Department of Medicine, Surgery and Dentistry ‘Scuola Medica Salernitana’, University of Salerno, Fisciano (Salerno), Italy
Chapter outline 1. Introduction 196 2. Toxicity assessment 201 2.1 Biological indicators 204 3. Toxicity removal by photocatalytic processes treating CECs 206 4. Conclusions 208 References 208
*All authors equally contributed to this chapter. Visible Light Active Structured Photocatalysts for the Removal of Emerging Contaminants. https://doi.org/10.1016/B978-0-12-818334-2.00008-0 Copyright © 2020 Elsevier Inc. All rights reserved.
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1. Introduction At present, it is recognized that the dilution paradigm, “the solution to pollution is dilution,” failed as showed by some of the most famous case studies of boomerang environmental contamination such as the Minamata [1] and the Itai-Itai [2] diseases. The problem of wastewater treatment and monitoring is still currently present because of the occurrence of new wastewater contaminants, namely “contaminants of emerging concern (CECs),” the increased environmental consciousness of stakeholders, and the development of new and more efficient wastewater treatment technologies [3e5]. Firstly, the wastewater management was carried out by some European big cities such as Paris and London, at least two centuries ago, with a year-by-year more complex sewage system. At the beginning, wastewater was discharged into rivers with no treatment at all, and the pollutants’ load was naturally drifted to the sea. So that, rivers’ water quality started to decrease, showing the first signals of sufferance such as dire odors and fish death. Since the first wastewater treatment plants (WWTPs) based on activated sludge (AS) technologies were introduced, the quality of surface water started to get better, but, owing to the complex mixture of newly produced contaminants discharged to treatment plants, research has started developing new wastewater treatment technologies and (bio)monitoring tools to strengthen water resources protection. The aim is to defend water not only for human direct needs, but as in an ecological perspective, trying to provide and maintain the best life conditions for all organisms guaranteeing it for future generations as well. Currently, water scarcity, shortages, and levels of contamination are requiring an increasing level of sustainability in the management of water resources [6]. Deficient or nonexistent WWTPs are still causing water stresserelated phenomena limiting the access to potable water and general sanitation resulting in hygienic and health problems. To cope with this trouble, decentralized WWTPs have been documented as a potential solution to increase the access to clean and safe water, improving the efficiency of wastewater treatment and treated wastewater recovery and reuse, including the reduction/removal of CECs [6]. Currently, CECs can be discharged into fresh- and saltwater environments without any real restriction potentially increasing the sanitary and environmental risks. The presence of CECs was evidenced in natural and sewage water, and in both surface and groundwater [7,8]. CECs include a wide variety of pollutants
Chapter 8 Toxicity assessment of wastewater after advanced oxidation
such as pharmaceuticals [9e11], comprising antibiotics [12,13], personal care products (PCPs) [14,15], engineered nanomaterials [16e18], perfluorooctane sulfonate and perfluorooctanoic acid [10], endocrine-disrupting compounds [19e21], textile dyes [22,23], surfactants [24], and UV-B filters from sunscreen creams [25]. According to an author-by-author classification, PCPs are a group of compounds that may include soaps, lotions, toothpaste, and sunscreens but also disinfectants (e.g., triclosan), preservatives (e.g., parabens), fragrances (e.g., musks), insect repellents (e.g., N,N-diethyl-meta-toluamide), and Ultra-Violet (UV) filters (e.g., methylbenzylidene camphor) [26]. Although drugs are mainly for internal use, PCPs are intended mainly for an external use and thus they are not metabolized suggesting that they can enter also completely unchanged [14]. To cope with the potential risks posed by CECs, the European Union (EU) published in April 2018 an updated Watch List of potential water pollutants. EU Member States should carefully check their presence in the aquatic environment to investigate the ecological and sanitary risk they could pose. The updated Watch List included eight substances or groups of substances such as endocrine disruptors, antibiotics, and pesticides. But how to reduce/remove CECs? How to meet the goal of environmental sustainability reducing discharge’s dilution phenomena, maximizing treated wastewater reuse and the potential of by-products recovery or full removal? How to provide a “toxicity”-free treated wastewater to be discharged into surface waters or addressed to specific reuse activities? The problem of “residual” toxicity in treated wastewater could be a huge problem. Toxicity is detected via a biological tool potentially alerting about water quality characteristics [27,28]. The first toxicity tests are dated back to Aristotle, but their present use to control and assess the water pollution began in the United States just in the 1940s. For a long time, the use of toxicity bioassays for wastewater management encountered various stop and go in relation to their regulatory and management regime, and the ratio between economic growth and the protection of the environment. Now, wastewater toxicity assessment is considered as a current practice not only in United States, but also in Canada, Europe, and Japan (and many other countries worldwide) to increase water governance. Wastewater treatment by itself does not mean a complete removal of toxicity, even because disinfection’s products or by-products can contribute to it both directly and indirectly. Thus, we expect a significant reduction of toxicity down to threshold levels that can be deemed as safe considering
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technologies maximizing the following characteristics: efficiency and reliability, low costs for construction, management, and maintenance supporting self-sufficiency and acceptance by stakeholders and the general public [6]. In practice, this means that we are in search of the best available technologies (BATs) [29]. The term BAT was firstly defined in Article 2(11) of the 96/ 61/EC Directive (EC, 1996) as “the most effective and advanced stage in the development of activities and their methods of operation which indicate the practical suitability of particular techniques for providing in principle the basis for emission limit values designed to prevent and, where that is not practicable, generally to reduce emissions and the impact on the environment as a whole.” The best viable mix of technologies, processes, and management services reducing the pollution and increasing the efficiency contribute to the identification of BATs (or Best Available Technologies Not Entailing Excessive Costs, BATNEECs) [29]. Thus, the main aim of BATs is to make processes more cost-effective reducing costs, increasing competitiveness, reducing energy and primary raw material consumption, and waste/emission generation. Indeed, Chapter 34 of Agenda 21 [30] stated that “Environmentally sound technologies protect the environment, are less polluting, use all resources in a more sustainable manner, recycle more of their wastes and products, and handle residual wastes in a more acceptable manner than the technologies for which they were substitutes. Environmentally sound technologies in the context of pollution are process and product technologies that generate low or no waste, for the prevention of pollution. They also cover end of the pipe technologies for treatment of pollution after it has been generated. Environmentally sound technologies are not just individual technologies, but total systems which include know-how, procedures, goods and services, and equipment as well as organizational and managerial procedures.” According to Ref. [29], emission limit values, equivalent parameters, and technical measures must be based on BATs, without prescribing the use of any technique, but considering the technical characteristics of the installation, its geographical location, and the local environmental conditions. Under this point of view there is the need to strengthen the efforts to improve testing (e.g., toxicity bioassays), verify performances, and standardize environmental technologies, to establish a mechanism to validate objectively the performance of these products, increasing the purchasers’ confidence in new environmental technologies. Furthermore, standardization, preferably at the international level, can stimulate innovation and environmentally friendly practices.
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Firstly, the Integrated Pollution Prevention and Control directive in 2003 provided the basic knowledge, now updated by Ref. [29], about the measures for the determination of BATs for wastewater (and waste gas) treatment supporting process-integrated methods for preventing and reducing the contamination. In most cases, they are production- or process-specific measures whose applicability requires a special assessment. The use of BATs in wastewater treatment is especially focused to the end-of-pipe approach, optimizing treatment procedures, preventing, or minimizing mixing of contaminated and uncontaminated wastewaters, considering the fact that it is the application (e.g., serial combination of some technologies) and the way of management that could make the difference. When wastewater is discharged into surface water (i.e., river, lake or sea, and all other kind of surface water bodies), BATs must (i) avoid a discharge situation such as excessive hydraulic load or toxic wastewater (i.e., potential damages to the river bed, the embankment, or the biosphere); choose the discharge point to optimize the dispersion; (ii) balance the wastewater not coming from central WWTP to reduce the impact on the receiving water body and to meet discharge requirement before discharging it; (iv) implement a monitoring system to check the water discharge with adequate monitoring frequency; (v) perform toxicity assessment as a complementary tool to obtain more information on the effectiveness of the control measures and on the hazard assessment for the receiving body. Generally, a case-by-case basis application is required. BATs listed by Ref. [29] included tenths of treatment technologies to provide the best existing treatment solution to solve specific problems. Chemical oxidation is defined as pollutants’ conversion by agents oxidizing recalcitrant substances into others that should be potentially less toxic, more (bio-)degradable, also due to their shorter-chained structure, degrading at the same time organic compounds causing color, odor, taste, and removing microorganisms too (i.e., disinfection) [29]. Among chemical oxidation, advanced oxidation processes treat wastewater via hydroxyl radicals generated by hydrogen peroxide in association to: (i) ferrous salts (Fenton’s agent) [31,32]; (ii) ozone; (iii) UV light; (iv) pressure; ultrasounds; (v) temperature [29]. Generally, AOPs are applied when contaminants are (not readily) biodegradable, thus potentially disturbing or overloading the treatment process in WWTP, or when they are too much toxic to be released into a traditional wastewater drainage system. Such contaminants might include (i) oil and grease; (ii) phenols,
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chlorophenols; (iii) monocyclic aromatic hydrocarbons (BTEX); (iv) polycyclic aromatic hydrocarbons (PAHs); (v) halogenated organic compounds; (vi) dyes, pesticides, cyanides; sulfides/ sulfites; and heavy metal complexes. Recently, several authors investigated AOPs for CECs reduction/removal such as in Refs. [13,24,33]. Generally, AOPs entail relatively high investment and operating costs requiring extensive wastewater pretreatment than irradiation-free processes, such as the traditional AS treatment. Thus, the overall costs for chemical oxidation are expected to be high with operating costs variable on the basis of the chemicals required and energy consumption [29]. Visible or solar driven photocatalytic processes (VSDPP) for the degradation of CECs can be included among the AOPs. They have recently emerged as very interesting alternatives for water treatment [34], including water detoxification and disinfection as well [35,36]. AOPs are physicalechemical processes enabling to produce deep changes in contaminants chemical structure due to free radicals generation such as hydroxyl radicals (HO)[37] with catalysts (e.g., metal supported catalysts, clays, carbon materials or semiconductors such as TiO2, ZnO, WO3, Cu2O, or composite material) [38]. Radical species can produce hydrogen abstraction or electrophilic addition to double bonds generating organic free radicals. Radicals can react with oxygen molecules forming peroxy radicals promoting a chain reaction of oxidative degradation potentially leading to the full mineralization of the targeted organics [39]. AOPs are generally classified according to the ways reactive species are generated. Besides traditional contaminants, VSDPP started to be applied to CECs for wastewater treatment including pharmaceuticals [12,13], endocrine disruptors [24], and textile dyes [22]. The main aim is to completely remove contamination from water supporting their reuse. Among CECs, antibiotics have been frequently treated with VSDPP such as for chloramphenicol [12] and spiramycin [13]. Antibiotics are quite widespread because of their use in both human and veterinary medicine. Improperly, antibiotics have been also used as growth promoters in animals and to increase feed nutritional efficiency [40]. Nevertheless, they are present in ng/L or mg/L, and their persistence and continuous discharge make them one of the most urgent environmental issues, also in relation to the development of antimicrobial resistance [41]. Anyhow, their treatment could be an expensive venture because of the (i) the high conversions needed (i.e., below detection limit) and (ii) the very low initial concentrations, making them quite expensive. The use of renewable energy sources to power the processes (i.e., solar
Chapter 8 Toxicity assessment of wastewater after advanced oxidation
photocatalysis) could decrease the general management costs [42]. Among AOPs, TiO2-assisted photocatalytic oxidation showed to degrade a range of organic compounds even at low temperatures presenting disinfectant abilities as well. It is scalable from liters to cubic meters per day operating both in continuous or in batch depending on the target material to be treated considering a suspended or immobilized catalyst [22] with an estimated investment cost of EUR 450,000e560,000 for a system that would treat about 2200 approximately 15 m3/week [29]. Such process is frequently used for the reduction of specific pollutant degradation such as pharmaceutical- or pesticide-contaminated waters including toxicity reduction.
2. Toxicity assessment According to European inventory of Commercial Chemical Substances, the existing commercial chemical substances in the European market are 106,211 (last update August 11, 2017) and wastewaters might potentially contain most of them as well as their by-products. Therefore, the whole characterization of a wastewater sample could be uneasy and costly just on a chemical basis. As a result of the precautionary principle, all substances should be analyzed, but the limited knowledge on wastewater constituents and their potential by-products, due to biotic and abiotic degradation, would start a never ending process [28]. Nevertheless, the chemical approach is still playing a leading role in wastewater quality monitoring; toxicity plays an important role [29]. The limited assessment abilities of chemical analyses with complex mixtures required the intervention of toxicity bioassay because (i) mixtures contain many substances that cannot be identified and/or detected; (ii) there is a lack of data about causeeeffect relationships for both pure substances and environmental samples; (iii) nano-(micro-)pollutants (e.g., endocrine disruptors, pharmaceuticals, nano-materials) are frequently unexplored or under explored; (iv) combined effects of mixture contaminants on bioavailability can be evidenced only using bioassays [27,28,43]; (v) spatial and temporal definition and comparability are not attainable in other ways; (vi) large areas to be monitored and hot spots to be identified [28]. Historically, most countries started with a chemical hazard and source-based approach, followed by the acute lethal bioassays to assess complex environmental mixtures and determine pollution bioavailability. Recently, subchronic and chronic effluent bioassays improved the ability of tracking the changes of effluent
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quality over time and predicting their potential long-term impacts on the receiving environment [28]. Historically, wastewaters have been assessed and regulated to a greater extent based on some background physical and chemical parameters (mainly chemical oxidation demand, biological oxygen demand, suspended solids, pH, and concentrations of specific hazardous substances) guaranteeing treated wastewater hygienic standard and thus the quick solution of short- and medium-term human health problems. However, it is very difficult to understand the potential environmental significance of complex wastewaters with just that sound basis knowledge. Besides the single substanceeoriented approach and checking the potential effects of whole wastewater samples to ecosystems, Whole Effluent Toxicity (WET) testing was started up and, now, it is fully applied in the US National Pollution Discharge Elimination System [44]. WET testing is an important component of USEPA-integrated approach for assessing the potential for water toxicity, even though not all point sources are regulated and monitored. The primary objective of WET testing is to ensure that the treated effluent released from industrial and municipal facilities into surface water does not produce adverse effects to aquatic life, compromising its general quality and health status. The WET approach aims to identify, characterize, and eliminate toxic effects on aquatic resources [28]. To determine if an effluent has the potential to be toxic, WET testing is performed on various aquatic organisms considering acute, subchronic, and chronic endpoints depending on the final goal to be achieved. WET can be performed on a variety of commonly used test species according to various exposure times and dilution regimes. It also defined speciesespecific threshold limit values for quality assessment, mainly based on Lowest Observed Effect Concentration/No Observed Effect Concentration data, but real final data integration are still missing (e.g., toxicity score and indices). Anyway, it must be kept in mind that the real toxicity of treated wastewater is a relative parameter, and not an absolute one depending on testing species sensitivities (e.g., life stage) and wastewater-specific composition, the methodological approach used, as well as the toxicity benchmark employed [45]. Several authors [28,46e48] reviewed pros and cons of the general application of WET testing to several wastewaters with various toxicity tests. WET testing is clearly a useful tool, but it is not a perfect one, having some imperfections: (i) variability, a range of values is normally provided; (ii) Species sensitivities, ecological relevance, sequestration of contaminants, depuration, acclimation, adaptation, and general lifestyle; (iii) laboratory-based experience avoiding all
Chapter 8 Toxicity assessment of wastewater after advanced oxidation
differences in diet, temperature, and water quality of in situ exposures; (iv) over- or under-protective; (v) uncertain level of protection; (vi) hazard assessment rather than receiving water risk assessment; (vii) holistic, but by themselves not diagnostic; (viii) potentially simple and cost-effective, but not necessarily environmentally realistic; (ix) effect-based, but not suitable for every wastewater specimen. Toxicity test protocols and method modifications could introduce further uncertainties affecting the potential performance and interpretation of results. Each parameter or method must be optimized, but, unfortunately, most of variables for the greater extent of toxicity bioassays have not yet been evaluated. Therefore, the selection of toxicity tests protocols is not so easy without codified conditions, being, generally, only intuitive or theoretical [49]. The conclusion is that WET testing cannot be used alone without consideration of site-specific conditions, even though a properly designed toxicity test can be not only reactive but also predictive [28]. Anyhow, the benefit in terms of environmental protection is limited if there is no clear understanding of how the ecotoxicity of effluents of concern can be reduced [50]. A Toxicity Reduction Evaluation (TRE) incorporating a Toxicity Identification Evaluation (TIE) could be undertaken to assess the nature of toxic components and their source [44]. TRE protocols were originally developed and designed on site-specific basis for a stepwise search for effective effluent toxicity control measures. The first TRE stage is to identify the test to be used for toxicity assessment to undertake toxicity tracking and TIE. Once a discharge has been selected for a TRE, the causative agents need to be found and the sources of ecotoxicity to be isolated. Chemical analysis of known toxicants may identify an obvious cause of toxicity, whereas TIE allows the characterization of toxic effluent components. Besides WET, the Whole Effluent Assessment (WEA) (Fig. 8.1) is a methodology to assess the possible hazardous character of effluents, which would be insufficiently controlled by chemical indications such as the sum of parameters or the limits set on individual substances [46]. WEA provides a range of information on effluents using PTB-criteria (Persistent, Toxic and liable to Bioaccumulate), considering at the same time chemical, physical, and biological (as WET) methods to check for biological effects, as the main tool of the Convention for the Protection of the Marine Environment of the North-East Atlantic strategy (OSPAR Convention). OSPAR’s objective about hazardous
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Figure 8.1 Whole Effluent Assessment (WEA) and best available technologies (BATs) in wastewater treatment. Modified from OSPAR, Whole effluent assessment, 2005. Publication number: 2005/219.
substances is “to prevent pollution of the maritime area by continuously reducing discharges, emissions and losses of hazardous substances, with the ultimate aim of achieving concentrations in the marine environment near background values of naturally occurring substances and close to zero for man-made synthetic substances. In achieving this objective OSPAR selects and prioritises substances on the basis of criteria for Persistence, Liability to Bioaccumulate and Toxicity (P, B and T); criteria that reflect the intrinsic hazardous properties of substances.” At what time the wastewater specimen is tested, WEA can increase the comprehension of the mixture effects within the discharge. WEA has an added value with respect to the single substancee oriented approach when it comes to the task of identifying effluents of concerns to the marine environment, to prioritize the actions, triggering further site specific inquiries, progressing in reducing the persistence of effluents as well as the potentiality for bioaccumulation and toxicity [28].
2.1 Biological indicators The first assumption to keep in mind is that there is no perfect effluent bioassay, no ideal endpoint or related statistics, but the
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best practice should be defined on a case-by-case basis by each jurisdiction according to a more general scientific and regulatory agreement. The main recommendation in the ecotoxicological literature is, generally, about the choice of good bioindicator species, taking into consideration that all of them are characterized by some advantages and disadvantages [28]. The use of a minimum of three test species to span a range of species sensitivities, instead of selecting the most sensitive one is recognized [4]. Some authors indicated that the use of a test battery approach should be preferred rather than a single species approach [51e53]. Generally, it is recommended to consider a vertebrate, an invertebrate, and a plant (algae), but because of practical reasons, lack of information, and ecological relevance, it is not always possible to satisfy this requirement. Recently, the reference document of the Joint Research Center about BATs [29] suggested a potential battery of toxicity tests to be used for wastewater quality monitoring and technology efficiency. Bioluminescent bacteria (EN ISO 11348e1, EN ISO 11348e2, or EN ISO 11348e3), microalgae (EN ISO 8692, EN ISO 10253, or EN ISO 10710), duckweed (ISO 20079:2005), daphnia (SO 6341:2012), and fish/fish egg (ISO 15088:2007) tests are widespread methods, including both acute and chronic endpoints, for complex wastewater toxicity assessment (Fig. 8.2). Such evaluation can provide an integrated insight of the potential mixture effects, such as synergistic ones, occurring in presence of a lot of different individual pollutants with the double aim of ecosystem/surface water protection and treatment plants efficiency optimization [29].
Figure 8.2 Wastewater toxicity assessment including commonly recognized biological models [29].
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3. Toxicity removal by photocatalytic processes treating CECs The conventional AS WWTPs in reducing/removing CECs showed the necessity to improve wastewater treatments introducing, for example, the AOPs [38]. Among several AOPs, heterogeneous photocatalysis has proven its potential in degrading antibiotics from aqueous matrices [12]. Anyway, it must be kept in mind that the elimination of mother compounds does not necessarily result in toxicity removal. It may be true that the targeted compound can be eliminated, but the photocatalytic degradation can produce intermediate by-products, which can still exert adverse biological effects as already evidenced by Refs. [12,13]. Therefore, the efficiency of the treatment process should be evaluated considering not only the reduction/removal of a targeted compound but also of the ecotoxicity on a WEA basis of the treated effluent [54,55]. So far, ecotoxicity data for AOPs treated solutions of CECs, and specifically of antibiotics [12,13], are scarce or missing, making their environmental risk assessment difficult. Klavarioti et al. [42] already reviewed in 2009 the removal of residual pharmaceuticals from aqueous systems by AOPs highlighting in several paper that the role of toxicity to assess the quality of treated effluent was scarce and frequently limited to just one or two acute toxicity tests (such as Vibrio fischeri bioluminescence inhibition test or Daphnia magna mortality test). Still from current literature, there is no general rule about how toxicity of CECs may behave after AOPs. Sometimes, toxicity decreased [42] after treatment suggesting that the targeted molecules and their by-products were efficiently eliminated pushing ahead the treatment up to their full mineralization. Sometimes, toxicity increased [42] highlighting that the coupled treatment-targeted compound(s) failed or mineralization occurred only in part, suggesting that by-products are potentially more toxic than the parent compound. In Table 8.1, the most recent results about CECs reduction/removal were summarized including the assessment of toxicity as well, when available. Several CECs are present, especially pharmaceuticals, with removal rates ranging from 66% up to >99%. Toxicity is not always considered and frequently only one toxicity test is provided, thus skipping the possibility of an integrated assessment of the final toxicity according to a battery of toxicity tests.
Table 8.1 Overview of CECs removal considering the removal rate and toxicity. Treatment process Advanced oxidation Photocatalysis and solar photolysis UV/H2O2 integrated into an existing full-scale plant Ultraviolet photolysis Photocatalysis with 0.1 g/L TiO2 Photocatalysis with 1.6 g/L TiO2 UV/H2O2
CECs
Removal rate
Toxicity
References
Pharmaceuticals
>99%
e
[42]
Pharmaceuticals
66%e82%
e
[56]
Pharmaceuticals
67%e98%
e
[57]
Pharmaceuticals
80%
e
[58]
Spiramycin
91%
Chloramphenicol
90%
Residual toxicity >10%dresidual [13] by-productsdbattery of toxicity tests Residual toxicity of approximately [12] 10%dbattery of toxicity tests
Residual toxicity >10%dresidual [24] by-productsdbattery of toxicity tests Vibrio fischeriddegradation Mostly reduced Mild solar Acetaminophen, [59] of the compounds in real below the limit photo-Fenton Antipyrine, Atrazine, effluent wastewater led of detection Caffeine, to toxicity increase Carbamazepine, Diclofenac, Flumequine, Hydroxybiphenyl, Ibuprofen, Isoproturon, Ketorolac, Ofloxacin, Progesterone, Sulfamethoxazole, and Triclosan Ozonation Bezafibrate 60%e90% V. fischeridslight [60] decrease after treatment Ozonation Sulfamethoxazole >99% þ 10% V. fischeridtoxicity showed a [61] mineralization slight acute toxicity increment in the first stage of ozonation Nonylphenol deca-ethoxylate
e, toxicity not assessed.
92%
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4. Conclusions The occurrence and fate of CECs in the environment is gaining increasing attention. Especially pharmaceuticals are biologically active compounds (i.e., lipophilic and bio-recalcitrant) having the ability to bioaccumulate and be persistent in the environment. Nevertheless their environmental concentrations are very low (ng/L and mg/L), they can still exert adverse effects especially on aquatic organisms, but also on human health contributing to antibiotic resistant bacteria and genes selection. AOPs can offer interesting treatment solutions for CECs considering that the main problem that remained unexplored is not the removal of a targeted compound, but the generation of by-products and their related toxicity. Processes should push ahead the treatment process toward the full mineralization (>99%) also to remove toxicity from the effluent and ease its safe reuse. Currently, only few studies investigated AOPs treating CECs following not only the traditional parameters, but also toxicity. General results suggested that a case-by-case approach is necessary coupling specific AOPs technique to a targeted series of recalcitrant compounds.
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[10] B.O. Clarke, et al., Investigating landfill leachate as a source of trace organic pollutants, Chemosphere 127 (2015) 269e275. [11] A.J. Ebele, M.A.-E. Abdallah, S. Harrad, Pharmaceuticals and personal care products (PPCPs) in the freshwater aquatic environment, Emerg. Contam. 3 (1) (2017) 1e16. [12] G. Lofrano, et al., Photocatalytic degradation of the antibiotic chloramphenicol and effluent toxicity effects, Ecotoxicol. Environ. Saf. 123 (2016) 65e71. [13] G. Lofrano, et al., Municipal wastewater spiramycin removal by conventional treatments and heterogeneous photocatalysis, Sci. Total Environ. 624 (2018) 461e469. [14] J.M. Brausch, G.M. Rand, A review of personal care products in the aquatic environment: environmental concentrations and toxicity, Chemosphere 82 (11) (2011) 1518e1532. [15] D. Montes-Grajales, M. Fennix-Agudelo, W. Miranda-Castro, Occurrence of personal care products as emerging chemicals of concern in water resources: a review, Sci. Total Environ. 595 (2017) 601e614. [16] G. Vale, et al., Manufactured nanoparticles in the aquatic environmentbiochemical responses on freshwater organisms: a critical overview, Aquat. Toxicol. 170 (2016) 162e174. [17] K. Khosravi-Katuli, et al., Effects of nanoparticles in species of aquaculture interest, Environ. Sci. Pollut. Control Ser. 24 (21) (2017) 17326e17346. [18] G. Lofrano, G. Libralato, J. Brown, Nanotechnologies for environmental remediation: applications and implications, in: Nanotechnologies for Environmental Remediation: Applications and Implications, 2017, pp. 1e325. [19] A. Gogoi, et al., Occurrence and fate of emerging contaminants in water environment: a review, Groundw. Sustain. Dev. 6 (2018) 169e180. [20] J. Kapelewska, et al., Occurrence, removal, mass loading and environmental risk assessment of emerging organic contaminants in leachates, groundwaters and wastewaters, Microchem. J. 137 (2018) 292e301. [21] C. Qi, et al., Contaminants of emerging concern in landfill leachate in China: a review, Emerg. Contam. 4 (1) (2018) 1e10. [22] O. Sacco, et al., Crystal violet and toxicity removal by adsorption and simultaneous photocatalysis in a continuous flow micro-reactor, Sci. Total Environ. 644 (2018) 430e438. [23] G. Lofrano, et al., Emerging concern from short-term textile leaching: a preliminary ecotoxicological survey, Bull. Environ. Contam. Toxicol. 97 (5) (2016) 646e652. [24] M. Carotenuto, et al., Nonylphenol deca-ethoxylate removal from wastewater by UV/H2O2: degradation kinetics and toxicity effects, Process Saf. Environ. Protect. 124 (2019) 1e7. [25] M. Lorigo, M. Mariana, E. Cairrao, Photoprotection of ultraviolet-B filters: updated review of endocrine disrupting properties, Steroids 131 (2018) 46e58. [26] M.M. Tsui, et al., Occurrence, distribution and ecological risk assessment of multiple classes of UV filters in surface waters from different countries, Water Res. 67 (2014) 55e65. [27] G. Libralato, A. Volpi Ghirardini, F. Avezzù, Toxicity removal efficiency of decentralised sequencing batch reactor and ultra-filtration membrane bioreactors, Water Res. 44 (15) (2010) 4437e4450. [28] G. Libralato, V. Ghirardini Annamaria, A. Francesco, How toxic is toxic? A proposal for wastewater toxicity hazard assessment, Ecotoxicol. Environ. Saf. 73 (7) (2010) 1602e1611.
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[29] T. Brinkmann, et al., Best Available Techniques (BAT) Reference Document for Common Waste Water and Waste Gas Treatment/management Systems in the Chemical Sector, Publications Office of the European Union, 2016. [30] E.S. Agenda, 21: The United Nations Programme of Action from Rio, New York, 1992. [31] G. Lofrano, et al., Fenton’s oxidation of various-based tanning materials, Desalination 211 (1e3) (2007) 10e21. [32] G. Lofrano, et al., Fenton and photo-Fenton treatment of a synthetic tannin used in leather tannery: a multi-approach study, Water Sci. Technol. 55 (10) (2007) 53e61. [33] A. Bellino, et al., Antibiotic effects on seed germination and root development of tomato (Solanum lycopersicum L), Ecotoxicol. Environ. Saf. 148 (2018) 135e141. [34] E.R. Bandala, B.W. Raichle, Solar driven advanced oxidation processes for water decontamination and disinfection, in: Solar Energy Sciences and Engineering Applications, CRC Press, EH Leiden, The Netherlands, 2013, pp. 978e981. Print ISBN. [35] S.L. Orozco, et al., Effect of iron salt on the color removal of water containing the azo-dye reactive blue 69 using photo-assisted Fe (II)/H2O2 and Fe (III)/H2O2 systems, J. Photochem. Photobiol. A Chem. 198 (2e3) (2008) 144e149. [36] E.R. Bandala, Y. Velasco, L.G. Torres, Decontamination of soil washing wastewater using solar driven advanced oxidation processes, J. Hazard. Mater. 160 (2) (2008) 402e407. [37] G.P. Anipsitakis, D.D. Dionysiou, Radical generation by the interaction of transition metals with common oxidants, Environ. Sci. Technol. 38 (13) (2004) 3705e3712. [38] C. Teodosiu, et al., Emerging pollutants removal through advanced drinking water treatment: a review on processes and environmental performances assessment, J. Clean. Prod. 197 (1) (2018) 1210e1221. [39] M.A. Quiroz, E.R. Bandala, C.A. Martínez-Huitle, Advanced oxidation processes (AOPs) for removal of pesticides from aqueous media, in: Pesticides-Formulations, Effects, Fate, IntechOpen, 2011. [40] A.K. Sarmah, M.T. Meyer, A.B. Boxall, A global perspective on the use, sales, exposure pathways, occurrence, fate and effects of veterinary antibiotics (VAs) in the environment, Chemosphere 65 (5) (2006) 725e759. [41] W.H. Organization, Antimicrobial Resistance: Global Report on Surveillance, World Health Organization, 2014. [42] M. Klavarioti, D. Mantzavinos, D. Kassinos, Removal of residual pharmaceuticals from aqueous systems by advanced oxidation processes, Environ. Int. 35 (2) (2009) 402e417. [43] G. Libralato, A. Volpi Ghirardini, F. Avezzù, Seawater ecotoxicity of monoethanolamine, diethanolamine and triethanolamine, J. Hazard. Mater. 176 (1e3) (2010) 535e539. [44] U. EPA, NPDES Compliance Inspection Manual, US Environmental Protection Agency, Washington, DC. USA, 2004. [45] W.J. Warren-Hicks, et al., Assessment of whole effluent toxicity test variability: partitioning sources of variability, Environ. Toxicol. Chem. 19 (1) (2000) 94e104. [46] P.M. Chapman, Whole effluent toxicity testingdusefulness, level of protection, and risk assessment, Environ. Toxicol. Chem. 19 (1) (2000) 3e13.
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[47] G. Libralato, A. Volpi Ghirardini, F. Avezzù, Performance assessment of ASSBR and UF-MBR for hotel wastewater treatment, Water Sci. Technol. 60 (7) (2009) 1701e1709. [48] G. Libralato, The small-scale approach in wastewater treatment, in: Wastewater Reuse and Management, 2013, pp. 195e224. [49] P.J. Markle, et al., Effects of several variables on whole effluent toxicity test performance and interpretation, Environ. Toxicol. Chem. 19 (1) (2000) 123e132. [50] M. Hutchings, et al., Toxicity reduction evaluation, toxicity identification evaluation and toxicity tracking in direct toxicity assessment, Ecotoxicology 13 (5) (2004) 475e484. [51] M. Tonkes, P.J. De Graaf, J. Graansma, Assessment of complex industrial effluents in the Netherlands using a whole effluent toxicity (or WET) approach, Water Sci. Technol. 39 (10e11) (1999) 55e61. [52] G. Libralato, A.V. Ghirardini, F. Avezzù, Evaporation and air-stripping to assess and reduce ethanolamines toxicity in oily wastewater, J. Hazard. Mater. 153 (3) (2008) 928e936. [53] G. Libralato, E. Gentile, A. Volpi Ghirardini, Wastewater effects on Phaeodactylum tricornutum (Bohlin): setting up a classification system, Ecol. Indicat. 60 (2016) 31e37. [54] G. Lofrano, et al., An integrated chemical and ecotoxicological assessment for the photocatalytic degradation of vancomycin, Environ. Technol. 35 (10) (2014) 1234e1242. [55] G. Lofrano, et al., Advanced oxidation of catechol: a comparison among photocatalysis, Fenton and photo-Fenton processes, Desalination 249 (2) (2009) 878e883. [56] D. Kanakaraju, et al., Photolysis and TiO2-catalysed degradation of diclofenac in surface and drinking water using circulating batch photoreactors, Environ. Chem. 11 (1) (2014) 51e62. [57] J.C. Kruithof, P.C. Kamp, B.J. Martijn, UV/H2O2 treatment: a practical solution for organic contaminant control and primary disinfection, Ozone Sci. Eng. 29 (4) (2007) 273e280. [58] K. Lekkerkerker-Teunissen, et al., Pilot plant results with three different types of UV lamps for advanced oxidation, Ozone Sci. Eng. 35 (1) (2013) 38e48. [59] N. Klamerth, et al., Degradation of fifteen emerging contaminants at mg L1 initial concentrations by mild solar photo-Fenton in MWTP effluents, Water Res. 44 (2) (2010) 545e554. [60] R.F. Dantas, et al., Bezafibrate removal by means of ozonation: primary intermediates, kinetics, and toxicity assessment, Water Res. 41 (12) (2007) 2525e2532. [61] R.F. Dantas, et al., Sulfamethoxazole abatement by means of ozonation, J. Hazard. Mater. 150 (3) (2008) 790e794. [62] OSPAR, Whole effluent assessment, 2005. Publication number: 2005/219.
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Department of Biology, University of Naples Federico II, Complesso Universitario di Monte Sant’Angelo, Naples, Italy; 2Centro Servizi Metrologici e Tecnologici Avanzati (CeSMA), University of Naples Federico II, Naples, Italy; 3 Department of Chemistry and Biology “A. Zambelli”, University of Salerno, Fisciano (Salerno), Italy; 4Department of Medicine, Surgery and Dentistry ‘Scuola Medica Salernitana’, University of Salerno, Fisciano (Salerno), Italy
Chapter outline 1. Introduction 196 2. Toxicity assessment 201 2.1 Biological indicators 204 3. Toxicity removal by photocatalytic processes treating CECs 206 4. Conclusions 208 References 208
*All authors equally contributed to this chapter. Visible Light Active Structured Photocatalysts for the Removal of Emerging Contaminants. https://doi.org/10.1016/B978-0-12-818334-2.00008-0 Copyright © 2020 Elsevier Inc. All rights reserved.
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1. Introduction At present, it is recognized that the dilution paradigm, “the solution to pollution is dilution,” failed as showed by some of the most famous case studies of boomerang environmental contamination such as the Minamata [1] and the Itai-Itai [2] diseases. The problem of wastewater treatment and monitoring is still currently present because of the occurrence of new wastewater contaminants, namely “contaminants of emerging concern (CECs),” the increased environmental consciousness of stakeholders, and the development of new and more efficient wastewater treatment technologies [3e5]. Firstly, the wastewater management was carried out by some European big cities such as Paris and London, at least two centuries ago, with a year-by-year more complex sewage system. At the beginning, wastewater was discharged into rivers with no treatment at all, and the pollutants’ load was naturally drifted to the sea. So that, rivers’ water quality started to decrease, showing the first signals of sufferance such as dire odors and fish death. Since the first wastewater treatment plants (WWTPs) based on activated sludge (AS) technologies were introduced, the quality of surface water started to get better, but, owing to the complex mixture of newly produced contaminants discharged to treatment plants, research has started developing new wastewater treatment technologies and (bio)monitoring tools to strengthen water resources protection. The aim is to defend water not only for human direct needs, but as in an ecological perspective, trying to provide and maintain the best life conditions for all organisms guaranteeing it for future generations as well. Currently, water scarcity, shortages, and levels of contamination are requiring an increasing level of sustainability in the management of water resources [6]. Deficient or nonexistent WWTPs are still causing water stresserelated phenomena limiting the access to potable water and general sanitation resulting in hygienic and health problems. To cope with this trouble, decentralized WWTPs have been documented as a potential solution to increase the access to clean and safe water, improving the efficiency of wastewater treatment and treated wastewater recovery and reuse, including the reduction/removal of CECs [6]. Currently, CECs can be discharged into fresh- and saltwater environments without any real restriction potentially increasing the sanitary and environmental risks. The presence of CECs was evidenced in natural and sewage water, and in both surface and groundwater [7,8]. CECs include a wide variety of pollutants
Chapter 8 Toxicity assessment of wastewater after advanced oxidation
such as pharmaceuticals [9e11], comprising antibiotics [12,13], personal care products (PCPs) [14,15], engineered nanomaterials [16e18], perfluorooctane sulfonate and perfluorooctanoic acid [10], endocrine-disrupting compounds [19e21], textile dyes [22,23], surfactants [24], and UV-B filters from sunscreen creams [25]. According to an author-by-author classification, PCPs are a group of compounds that may include soaps, lotions, toothpaste, and sunscreens but also disinfectants (e.g., triclosan), preservatives (e.g., parabens), fragrances (e.g., musks), insect repellents (e.g., N,N-diethyl-meta-toluamide), and Ultra-Violet (UV) filters (e.g., methylbenzylidene camphor) [26]. Although drugs are mainly for internal use, PCPs are intended mainly for an external use and thus they are not metabolized suggesting that they can enter also completely unchanged [14]. To cope with the potential risks posed by CECs, the European Union (EU) published in April 2018 an updated Watch List of potential water pollutants. EU Member States should carefully check their presence in the aquatic environment to investigate the ecological and sanitary risk they could pose. The updated Watch List included eight substances or groups of substances such as endocrine disruptors, antibiotics, and pesticides. But how to reduce/remove CECs? How to meet the goal of environmental sustainability reducing discharge’s dilution phenomena, maximizing treated wastewater reuse and the potential of by-products recovery or full removal? How to provide a “toxicity”-free treated wastewater to be discharged into surface waters or addressed to specific reuse activities? The problem of “residual” toxicity in treated wastewater could be a huge problem. Toxicity is detected via a biological tool potentially alerting about water quality characteristics [27,28]. The first toxicity tests are dated back to Aristotle, but their present use to control and assess the water pollution began in the United States just in the 1940s. For a long time, the use of toxicity bioassays for wastewater management encountered various stop and go in relation to their regulatory and management regime, and the ratio between economic growth and the protection of the environment. Now, wastewater toxicity assessment is considered as a current practice not only in United States, but also in Canada, Europe, and Japan (and many other countries worldwide) to increase water governance. Wastewater treatment by itself does not mean a complete removal of toxicity, even because disinfection’s products or by-products can contribute to it both directly and indirectly. Thus, we expect a significant reduction of toxicity down to threshold levels that can be deemed as safe considering
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technologies maximizing the following characteristics: efficiency and reliability, low costs for construction, management, and maintenance supporting self-sufficiency and acceptance by stakeholders and the general public [6]. In practice, this means that we are in search of the best available technologies (BATs) [29]. The term BAT was firstly defined in Article 2(11) of the 96/ 61/EC Directive (EC, 1996) as “the most effective and advanced stage in the development of activities and their methods of operation which indicate the practical suitability of particular techniques for providing in principle the basis for emission limit values designed to prevent and, where that is not practicable, generally to reduce emissions and the impact on the environment as a whole.” The best viable mix of technologies, processes, and management services reducing the pollution and increasing the efficiency contribute to the identification of BATs (or Best Available Technologies Not Entailing Excessive Costs, BATNEECs) [29]. Thus, the main aim of BATs is to make processes more cost-effective reducing costs, increasing competitiveness, reducing energy and primary raw material consumption, and waste/emission generation. Indeed, Chapter 34 of Agenda 21 [30] stated that “Environmentally sound technologies protect the environment, are less polluting, use all resources in a more sustainable manner, recycle more of their wastes and products, and handle residual wastes in a more acceptable manner than the technologies for which they were substitutes. Environmentally sound technologies in the context of pollution are process and product technologies that generate low or no waste, for the prevention of pollution. They also cover end of the pipe technologies for treatment of pollution after it has been generated. Environmentally sound technologies are not just individual technologies, but total systems which include know-how, procedures, goods and services, and equipment as well as organizational and managerial procedures.” According to Ref. [29], emission limit values, equivalent parameters, and technical measures must be based on BATs, without prescribing the use of any technique, but considering the technical characteristics of the installation, its geographical location, and the local environmental conditions. Under this point of view there is the need to strengthen the efforts to improve testing (e.g., toxicity bioassays), verify performances, and standardize environmental technologies, to establish a mechanism to validate objectively the performance of these products, increasing the purchasers’ confidence in new environmental technologies. Furthermore, standardization, preferably at the international level, can stimulate innovation and environmentally friendly practices.
Chapter 8 Toxicity assessment of wastewater after advanced oxidation
Firstly, the Integrated Pollution Prevention and Control directive in 2003 provided the basic knowledge, now updated by Ref. [29], about the measures for the determination of BATs for wastewater (and waste gas) treatment supporting process-integrated methods for preventing and reducing the contamination. In most cases, they are production- or process-specific measures whose applicability requires a special assessment. The use of BATs in wastewater treatment is especially focused to the end-of-pipe approach, optimizing treatment procedures, preventing, or minimizing mixing of contaminated and uncontaminated wastewaters, considering the fact that it is the application (e.g., serial combination of some technologies) and the way of management that could make the difference. When wastewater is discharged into surface water (i.e., river, lake or sea, and all other kind of surface water bodies), BATs must (i) avoid a discharge situation such as excessive hydraulic load or toxic wastewater (i.e., potential damages to the river bed, the embankment, or the biosphere); choose the discharge point to optimize the dispersion; (ii) balance the wastewater not coming from central WWTP to reduce the impact on the receiving water body and to meet discharge requirement before discharging it; (iv) implement a monitoring system to check the water discharge with adequate monitoring frequency; (v) perform toxicity assessment as a complementary tool to obtain more information on the effectiveness of the control measures and on the hazard assessment for the receiving body. Generally, a case-by-case basis application is required. BATs listed by Ref. [29] included tenths of treatment technologies to provide the best existing treatment solution to solve specific problems. Chemical oxidation is defined as pollutants’ conversion by agents oxidizing recalcitrant substances into others that should be potentially less toxic, more (bio-)degradable, also due to their shorter-chained structure, degrading at the same time organic compounds causing color, odor, taste, and removing microorganisms too (i.e., disinfection) [29]. Among chemical oxidation, advanced oxidation processes treat wastewater via hydroxyl radicals generated by hydrogen peroxide in association to: (i) ferrous salts (Fenton’s agent) [31,32]; (ii) ozone; (iii) UV light; (iv) pressure; ultrasounds; (v) temperature [29]. Generally, AOPs are applied when contaminants are (not readily) biodegradable, thus potentially disturbing or overloading the treatment process in WWTP, or when they are too much toxic to be released into a traditional wastewater drainage system. Such contaminants might include (i) oil and grease; (ii) phenols,
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chlorophenols; (iii) monocyclic aromatic hydrocarbons (BTEX); (iv) polycyclic aromatic hydrocarbons (PAHs); (v) halogenated organic compounds; (vi) dyes, pesticides, cyanides; sulfides/ sulfites; and heavy metal complexes. Recently, several authors investigated AOPs for CECs reduction/removal such as in Refs. [13,24,33]. Generally, AOPs entail relatively high investment and operating costs requiring extensive wastewater pretreatment than irradiation-free processes, such as the traditional AS treatment. Thus, the overall costs for chemical oxidation are expected to be high with operating costs variable on the basis of the chemicals required and energy consumption [29]. Visible or solar driven photocatalytic processes (VSDPP) for the degradation of CECs can be included among the AOPs. They have recently emerged as very interesting alternatives for water treatment [34], including water detoxification and disinfection as well [35,36]. AOPs are physicalechemical processes enabling to produce deep changes in contaminants chemical structure due to free radicals generation such as hydroxyl radicals (HO)[37] with catalysts (e.g., metal supported catalysts, clays, carbon materials or semiconductors such as TiO2, ZnO, WO3, Cu2O, or composite material) [38]. Radical species can produce hydrogen abstraction or electrophilic addition to double bonds generating organic free radicals. Radicals can react with oxygen molecules forming peroxy radicals promoting a chain reaction of oxidative degradation potentially leading to the full mineralization of the targeted organics [39]. AOPs are generally classified according to the ways reactive species are generated. Besides traditional contaminants, VSDPP started to be applied to CECs for wastewater treatment including pharmaceuticals [12,13], endocrine disruptors [24], and textile dyes [22]. The main aim is to completely remove contamination from water supporting their reuse. Among CECs, antibiotics have been frequently treated with VSDPP such as for chloramphenicol [12] and spiramycin [13]. Antibiotics are quite widespread because of their use in both human and veterinary medicine. Improperly, antibiotics have been also used as growth promoters in animals and to increase feed nutritional efficiency [40]. Nevertheless, they are present in ng/L or mg/L, and their persistence and continuous discharge make them one of the most urgent environmental issues, also in relation to the development of antimicrobial resistance [41]. Anyhow, their treatment could be an expensive venture because of the (i) the high conversions needed (i.e., below detection limit) and (ii) the very low initial concentrations, making them quite expensive. The use of renewable energy sources to power the processes (i.e., solar
Chapter 8 Toxicity assessment of wastewater after advanced oxidation
photocatalysis) could decrease the general management costs [42]. Among AOPs, TiO2-assisted photocatalytic oxidation showed to degrade a range of organic compounds even at low temperatures presenting disinfectant abilities as well. It is scalable from liters to cubic meters per day operating both in continuous or in batch depending on the target material to be treated considering a suspended or immobilized catalyst [22] with an estimated investment cost of EUR 450,000e560,000 for a system that would treat about 2200 approximately 15 m3/week [29]. Such process is frequently used for the reduction of specific pollutant degradation such as pharmaceutical- or pesticide-contaminated waters including toxicity reduction.
2. Toxicity assessment According to European inventory of Commercial Chemical Substances, the existing commercial chemical substances in the European market are 106,211 (last update August 11, 2017) and wastewaters might potentially contain most of them as well as their by-products. Therefore, the whole characterization of a wastewater sample could be uneasy and costly just on a chemical basis. As a result of the precautionary principle, all substances should be analyzed, but the limited knowledge on wastewater constituents and their potential by-products, due to biotic and abiotic degradation, would start a never ending process [28]. Nevertheless, the chemical approach is still playing a leading role in wastewater quality monitoring; toxicity plays an important role [29]. The limited assessment abilities of chemical analyses with complex mixtures required the intervention of toxicity bioassay because (i) mixtures contain many substances that cannot be identified and/or detected; (ii) there is a lack of data about causeeeffect relationships for both pure substances and environmental samples; (iii) nano-(micro-)pollutants (e.g., endocrine disruptors, pharmaceuticals, nano-materials) are frequently unexplored or under explored; (iv) combined effects of mixture contaminants on bioavailability can be evidenced only using bioassays [27,28,43]; (v) spatial and temporal definition and comparability are not attainable in other ways; (vi) large areas to be monitored and hot spots to be identified [28]. Historically, most countries started with a chemical hazard and source-based approach, followed by the acute lethal bioassays to assess complex environmental mixtures and determine pollution bioavailability. Recently, subchronic and chronic effluent bioassays improved the ability of tracking the changes of effluent
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quality over time and predicting their potential long-term impacts on the receiving environment [28]. Historically, wastewaters have been assessed and regulated to a greater extent based on some background physical and chemical parameters (mainly chemical oxidation demand, biological oxygen demand, suspended solids, pH, and concentrations of specific hazardous substances) guaranteeing treated wastewater hygienic standard and thus the quick solution of short- and medium-term human health problems. However, it is very difficult to understand the potential environmental significance of complex wastewaters with just that sound basis knowledge. Besides the single substanceeoriented approach and checking the potential effects of whole wastewater samples to ecosystems, Whole Effluent Toxicity (WET) testing was started up and, now, it is fully applied in the US National Pollution Discharge Elimination System [44]. WET testing is an important component of USEPA-integrated approach for assessing the potential for water toxicity, even though not all point sources are regulated and monitored. The primary objective of WET testing is to ensure that the treated effluent released from industrial and municipal facilities into surface water does not produce adverse effects to aquatic life, compromising its general quality and health status. The WET approach aims to identify, characterize, and eliminate toxic effects on aquatic resources [28]. To determine if an effluent has the potential to be toxic, WET testing is performed on various aquatic organisms considering acute, subchronic, and chronic endpoints depending on the final goal to be achieved. WET can be performed on a variety of commonly used test species according to various exposure times and dilution regimes. It also defined speciesespecific threshold limit values for quality assessment, mainly based on Lowest Observed Effect Concentration/No Observed Effect Concentration data, but real final data integration are still missing (e.g., toxicity score and indices). Anyway, it must be kept in mind that the real toxicity of treated wastewater is a relative parameter, and not an absolute one depending on testing species sensitivities (e.g., life stage) and wastewater-specific composition, the methodological approach used, as well as the toxicity benchmark employed [45]. Several authors [28,46e48] reviewed pros and cons of the general application of WET testing to several wastewaters with various toxicity tests. WET testing is clearly a useful tool, but it is not a perfect one, having some imperfections: (i) variability, a range of values is normally provided; (ii) Species sensitivities, ecological relevance, sequestration of contaminants, depuration, acclimation, adaptation, and general lifestyle; (iii) laboratory-based experience avoiding all
Chapter 8 Toxicity assessment of wastewater after advanced oxidation
differences in diet, temperature, and water quality of in situ exposures; (iv) over- or under-protective; (v) uncertain level of protection; (vi) hazard assessment rather than receiving water risk assessment; (vii) holistic, but by themselves not diagnostic; (viii) potentially simple and cost-effective, but not necessarily environmentally realistic; (ix) effect-based, but not suitable for every wastewater specimen. Toxicity test protocols and method modifications could introduce further uncertainties affecting the potential performance and interpretation of results. Each parameter or method must be optimized, but, unfortunately, most of variables for the greater extent of toxicity bioassays have not yet been evaluated. Therefore, the selection of toxicity tests protocols is not so easy without codified conditions, being, generally, only intuitive or theoretical [49]. The conclusion is that WET testing cannot be used alone without consideration of site-specific conditions, even though a properly designed toxicity test can be not only reactive but also predictive [28]. Anyhow, the benefit in terms of environmental protection is limited if there is no clear understanding of how the ecotoxicity of effluents of concern can be reduced [50]. A Toxicity Reduction Evaluation (TRE) incorporating a Toxicity Identification Evaluation (TIE) could be undertaken to assess the nature of toxic components and their source [44]. TRE protocols were originally developed and designed on site-specific basis for a stepwise search for effective effluent toxicity control measures. The first TRE stage is to identify the test to be used for toxicity assessment to undertake toxicity tracking and TIE. Once a discharge has been selected for a TRE, the causative agents need to be found and the sources of ecotoxicity to be isolated. Chemical analysis of known toxicants may identify an obvious cause of toxicity, whereas TIE allows the characterization of toxic effluent components. Besides WET, the Whole Effluent Assessment (WEA) (Fig. 8.1) is a methodology to assess the possible hazardous character of effluents, which would be insufficiently controlled by chemical indications such as the sum of parameters or the limits set on individual substances [46]. WEA provides a range of information on effluents using PTB-criteria (Persistent, Toxic and liable to Bioaccumulate), considering at the same time chemical, physical, and biological (as WET) methods to check for biological effects, as the main tool of the Convention for the Protection of the Marine Environment of the North-East Atlantic strategy (OSPAR Convention). OSPAR’s objective about hazardous
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Figure 8.1 Whole Effluent Assessment (WEA) and best available technologies (BATs) in wastewater treatment. Modified from OSPAR, Whole effluent assessment, 2005. Publication number: 2005/219.
substances is “to prevent pollution of the maritime area by continuously reducing discharges, emissions and losses of hazardous substances, with the ultimate aim of achieving concentrations in the marine environment near background values of naturally occurring substances and close to zero for man-made synthetic substances. In achieving this objective OSPAR selects and prioritises substances on the basis of criteria for Persistence, Liability to Bioaccumulate and Toxicity (P, B and T); criteria that reflect the intrinsic hazardous properties of substances.” At what time the wastewater specimen is tested, WEA can increase the comprehension of the mixture effects within the discharge. WEA has an added value with respect to the single substancee oriented approach when it comes to the task of identifying effluents of concerns to the marine environment, to prioritize the actions, triggering further site specific inquiries, progressing in reducing the persistence of effluents as well as the potentiality for bioaccumulation and toxicity [28].
2.1 Biological indicators The first assumption to keep in mind is that there is no perfect effluent bioassay, no ideal endpoint or related statistics, but the
Chapter 8 Toxicity assessment of wastewater after advanced oxidation
best practice should be defined on a case-by-case basis by each jurisdiction according to a more general scientific and regulatory agreement. The main recommendation in the ecotoxicological literature is, generally, about the choice of good bioindicator species, taking into consideration that all of them are characterized by some advantages and disadvantages [28]. The use of a minimum of three test species to span a range of species sensitivities, instead of selecting the most sensitive one is recognized [4]. Some authors indicated that the use of a test battery approach should be preferred rather than a single species approach [51e53]. Generally, it is recommended to consider a vertebrate, an invertebrate, and a plant (algae), but because of practical reasons, lack of information, and ecological relevance, it is not always possible to satisfy this requirement. Recently, the reference document of the Joint Research Center about BATs [29] suggested a potential battery of toxicity tests to be used for wastewater quality monitoring and technology efficiency. Bioluminescent bacteria (EN ISO 11348e1, EN ISO 11348e2, or EN ISO 11348e3), microalgae (EN ISO 8692, EN ISO 10253, or EN ISO 10710), duckweed (ISO 20079:2005), daphnia (SO 6341:2012), and fish/fish egg (ISO 15088:2007) tests are widespread methods, including both acute and chronic endpoints, for complex wastewater toxicity assessment (Fig. 8.2). Such evaluation can provide an integrated insight of the potential mixture effects, such as synergistic ones, occurring in presence of a lot of different individual pollutants with the double aim of ecosystem/surface water protection and treatment plants efficiency optimization [29].
Figure 8.2 Wastewater toxicity assessment including commonly recognized biological models [29].
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3. Toxicity removal by photocatalytic processes treating CECs The conventional AS WWTPs in reducing/removing CECs showed the necessity to improve wastewater treatments introducing, for example, the AOPs [38]. Among several AOPs, heterogeneous photocatalysis has proven its potential in degrading antibiotics from aqueous matrices [12]. Anyway, it must be kept in mind that the elimination of mother compounds does not necessarily result in toxicity removal. It may be true that the targeted compound can be eliminated, but the photocatalytic degradation can produce intermediate by-products, which can still exert adverse biological effects as already evidenced by Refs. [12,13]. Therefore, the efficiency of the treatment process should be evaluated considering not only the reduction/removal of a targeted compound but also of the ecotoxicity on a WEA basis of the treated effluent [54,55]. So far, ecotoxicity data for AOPs treated solutions of CECs, and specifically of antibiotics [12,13], are scarce or missing, making their environmental risk assessment difficult. Klavarioti et al. [42] already reviewed in 2009 the removal of residual pharmaceuticals from aqueous systems by AOPs highlighting in several paper that the role of toxicity to assess the quality of treated effluent was scarce and frequently limited to just one or two acute toxicity tests (such as Vibrio fischeri bioluminescence inhibition test or Daphnia magna mortality test). Still from current literature, there is no general rule about how toxicity of CECs may behave after AOPs. Sometimes, toxicity decreased [42] after treatment suggesting that the targeted molecules and their by-products were efficiently eliminated pushing ahead the treatment up to their full mineralization. Sometimes, toxicity increased [42] highlighting that the coupled treatment-targeted compound(s) failed or mineralization occurred only in part, suggesting that by-products are potentially more toxic than the parent compound. In Table 8.1, the most recent results about CECs reduction/removal were summarized including the assessment of toxicity as well, when available. Several CECs are present, especially pharmaceuticals, with removal rates ranging from 66% up to >99%. Toxicity is not always considered and frequently only one toxicity test is provided, thus skipping the possibility of an integrated assessment of the final toxicity according to a battery of toxicity tests.
Table 8.1 Overview of CECs removal considering the removal rate and toxicity. Treatment process Advanced oxidation Photocatalysis and solar photolysis UV/H2O2 integrated into an existing full-scale plant Ultraviolet photolysis Photocatalysis with 0.1 g/L TiO2 Photocatalysis with 1.6 g/L TiO2 UV/H2O2
CECs
Removal rate
Toxicity
References
Pharmaceuticals
>99%
e
[42]
Pharmaceuticals
66%e82%
e
[56]
Pharmaceuticals
67%e98%
e
[57]
Pharmaceuticals
80%
e
[58]
Spiramycin
91%
Chloramphenicol
90%
Residual toxicity >10%dresidual [13] by-productsdbattery of toxicity tests Residual toxicity of approximately [12] 10%dbattery of toxicity tests
Residual toxicity >10%dresidual [24] by-productsdbattery of toxicity tests Vibrio fischeriddegradation Mostly reduced Mild solar Acetaminophen, [59] of the compounds in real below the limit photo-Fenton Antipyrine, Atrazine, effluent wastewater led of detection Caffeine, to toxicity increase Carbamazepine, Diclofenac, Flumequine, Hydroxybiphenyl, Ibuprofen, Isoproturon, Ketorolac, Ofloxacin, Progesterone, Sulfamethoxazole, and Triclosan Ozonation Bezafibrate 60%e90% V. fischeridslight [60] decrease after treatment Ozonation Sulfamethoxazole >99% þ 10% V. fischeridtoxicity showed a [61] mineralization slight acute toxicity increment in the first stage of ozonation Nonylphenol deca-ethoxylate
e, toxicity not assessed.
92%
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4. Conclusions The occurrence and fate of CECs in the environment is gaining increasing attention. Especially pharmaceuticals are biologically active compounds (i.e., lipophilic and bio-recalcitrant) having the ability to bioaccumulate and be persistent in the environment. Nevertheless their environmental concentrations are very low (ng/L and mg/L), they can still exert adverse effects especially on aquatic organisms, but also on human health contributing to antibiotic resistant bacteria and genes selection. AOPs can offer interesting treatment solutions for CECs considering that the main problem that remained unexplored is not the removal of a targeted compound, but the generation of by-products and their related toxicity. Processes should push ahead the treatment process toward the full mineralization (>99%) also to remove toxicity from the effluent and ease its safe reuse. Currently, only few studies investigated AOPs treating CECs following not only the traditional parameters, but also toxicity. General results suggested that a case-by-case approach is necessary coupling specific AOPs technique to a targeted series of recalcitrant compounds.
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