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leading to decreased biodiversity and risks to human health (Mohr et al., 2008; Bollmann et al., 2014; Durak et al., 2020).

Table 1.1 Examples of biocides, activities where they are employed, and their types of products (BPD).

      Source: Adapted from Bollmann et al., 2014.

GroupCompound (abbreviation) CAS number	ActivityProduct types (BPD)
Triazines
Terbutryn (TB)886‐50‐0	AlgaecideBiocide: PT 7, 9, 10
Cybutryn, Irgarol 1051 (IRG)28159‐98‐0	AlgaecideBiocide: PT 21
Carbamates
Carbendazim (CD)10605‐21‐7	FungicideBiocide: PT 7, 9, 10
Iodocarb (IPBC)55406‐53‐6	FungicideBiocide. PT 6, 7, 8, 9, 10, 13Cosmetics
Isothiazolinones
Methylisothiazolinone (MI)2682‐20‐4	Bactericide/FungicideBiocide: PT 6, 11, 12, 13Cosmetics
Benzisothiazolinone (BIT)2634‐33‐5	Bactericide/FungicideBiocide: PT 2, 6, 9, 11, 12, 13
Octylisothiazolinone (OIT)26530‐20‐1	Bactericide/FungicideBiocide: PT 6, 7, 9, 10, 13
Dichlorooctylisothiazolinone (DCOIT)64359‐81‐5	Bactericide/FungicideBiocide: PT 7, 8, 9, 10, 11, 21
Phenylureas
Isoproturon (IP)34123‐59‐6	AlgaecideBiocide: PT 7, 10
Diuron (DR)330‐54‐1	AlgaecideBiocide: PT 7, 10
Triazoles
Tebuconazole (TBU)107534‐96‐3	FungicideBiocide: PT 7, 8, 9, 10
Propiconazole (PPZ)60207‐90‐1	FungicideBiocide: PT 7, 8, 9
Miscellaneous
Mecoprop (MCPP)93‐65‐2	AlgaecideRoof protection (not registered under BPD, since higher plants)

      BPD, Biocidal Products Directive; PT, product type.

      In response to these problems, environmental agencies have made an effort to restrict and/or regulate the use and disposal of biocides. At the same time, the scientific community aims to study efficient treatment processes to remove them from wastewaters, whether domestic or industrial.

      Different processes have been tested to evaluate an efficient treatment approach for industrial wastewaters. AOPs have been tried to oxidize organic compounds, which are difficult to convert into biologically less‐harmful final products (Pirilä et al., 2015). Pirilä et al. (2015) studied the photocatalysis process to treat four biocide compounds, including diuron, which is commonly used as a herbicide in agriculture, leading to contamination of the aquatic environment due to leaching from the soil. The elimination of this substance from wastewater is important due to its toxicity to photosynthetic organisms. This study revealed that diuron was removed more efficiently and with minimum energy consumption (Pirilä et al., 2015).

      AOPs can also be applied in combination with other processes to treat biocides, as in the study carried out by Vanraes et al. (2018), who developed and optimized a reactor that combines oxidative treatment by dielectric barrier discharge (DBD) with adsorption of micropollutants on activated carbon and with additional plasma gas. The objective was to minimize the formation of dangerous oxidation byproducts from the treatment of persistent pesticides, including diuron and isoproturon. The authors observed that activated carbon in DBD reactors causes a synergistic effect in removing pollutants and that DBD reactors allow the regeneration of activated carbon, increasing the life of the reactor (Vanraes et al., 2017; Vanraes et al., 2018).

Organic Compounds

      Industrial wastewater contains multiple polluting compounds, with the most toxic contaminants being organic compounds (Hashemi et al., 2018; Barak et al., 2020). Organic pollutants include phenols, chlorinated phenols, endocrine disrupting compounds (EDCs), azo dyes, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), hexachlorobenzene (HCB), pesticides, etc. (Das and Dash, 2019; Trojanowicz, 2020). Many of these compounds, such as some PAH, PCBs, EDCs, most phenols, DDT, etc., are recalcitrant: i.e. they can be more resistant to biological degradation (Knapp and Bromley‐Challoner, 2003). Among the pollutants of greatest concern are volatile organic compounds (VOCs) and persistent organic pollutants (POPs).

VOCs are generally defined as substances whose composition allows evaporation under normal internal temperature and pressure conditions. Thus, the lower the boiling point of a substance, the greater its volatility. Therefore, VOCs can be defined and classified in some cases according to their boiling point in indoor environments. The WHO classification is presented in Table 1.2 for illustration (WHO, 1989; EPA, 2017).

In outdoor environments, the emission of VOCs is regulated to prevent the formation of ozone (a constituent of photochemical pollution) and other pollutants. VOCs that are considered reactive can interact with nitrogen oxides (NO_x) and carbon monoxide (CO) in the presence of sunlight, producing ozone. However, compounds considered nonreactive can also cause damage to human health if emitted in indoor environments. For example, methylene chloride, used as a paint remover, is exempt from outdoor regulation according to the EPA but is considered a substance with carcinogenic potential by the International Agency for Research on Cancer (IARC) (EPA, 2017).

Table 1.2 Classification of organic pollutants by WHO.

      Source: Adapted from EPA, 2017.

Description	Abbreviation	Boiling Point Range (°C)	Example of compounds
Very volatile (gaseous) organic compounds	VVOC	<0 to 50–100	Propane, butane, methyl chloride
Volatile organic compounds	VOC	50–100 to 240–260	Formaldehyde, d‐Limonene, toluene, acetone, ethanol (ethyl alcohol), 2‐propanol (isopropyl alcohol), hexanal
Semi volatile organic compounds	SVOC	240–260 to 380–400	Pesticides (DDT, chlordane, plasticizers (phthalates), fire retardants (PCBs, PBB))

      In

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