Applied Water Science. Группа авторов
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Название: Applied Water Science

Автор: Группа авторов

Издательство: John Wiley & Sons Limited

Жанр: Физика

Серия:

isbn: 9781119725268

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СКАЧАТЬ of organics (Wang et al., 2018).

      Traditionally, biological methods have been used in the management of pharmaceutical effluent. Pharmaceutical compounds and their metabolites undergo both aerobic and anaerobic decomposition in wastewater treatment processes (Hou et al., 2019; Patel et al., 2019). For instance, microbial cultures can be used to degrade pharmaceutical compounds. Environmental biodegradation is particularly important for the degradation of pharmaceutical compounds, especially when wastewater treatment plants are ineffective (Patel et al., 2019). Microorganisms can biotransform pharmaceutical compounds through metabolic biodegradation or via co-metabolic processes with other compounds. Because certain strains of algae, bacteria, and fungus biodegrade pharmaceutical compounds, biodegradation can be achieved using algal, bacterial, and fungal cultures.

       2.3.4.2 Advanced Removal Methods

      Except for some very polar hydrophilic pharmaceuticals such as iodinated contrast media and sulfamethoxazole, most pharmaceuticals can be removed by adsorption of activated carbon (Patel et al., 2019; Wu et al., 2019). Furthermore, pharmaceuticals can also be oxidized through advanced oxidation processes, of which ozonation is the most effective. Due to large pore sizes, low pressure membrane technologies such as ultrafiltration (UF) and microfiltration (MF) cannot effectively retain pharmaceutical compounds. Nonetheless, some hydrophobic pharmaceuticals can briefly adsorb onto the surfaces of MF and UF membranes providing a short-term decrease in concentration. The integration of MF or UF in membrane bioreactor systems does not result in additional removal of pharmaceuticals. On the other hand, high pressure membrane technologies such as RO and NF are effective in separating many pharmaceutical compounds from water (Motsa et al., 2014). The major drawback, however, is that brine with high concentrations of pharmaceutical compounds are difficult to manage post removal. RO, micro-, nano-, and UF have applied in the removal of pharmaceuticals. These are cross-flow filtration systems that use a selective semipermeable membrane. In RO, the pressure gradient between the permeate and feed sides of the membrane is the driving force, while ion repulsion is the major operational force in ultra- and nano-filtration since they use charged membranes (Motsa et al., 2014). To effectively remove pharmaceutical compounds, these physical techniques can be improved by integrating them with electrochemical advanced oxidation. While MF and UF can remove a significant level of pharmaceutical compounds, NF and RO exhibit higher removals (Colburn et al., 2019). Generally, NF has a lower energy demand since it uses lower operating pressures. Other methods like riverbank filtration and soil-aquifer treatment, which are natural processes with long retention times, can be included as extra treatment stages. The removal processes involved in riverbank filtration and soil-aquifer treatment are mainly biotransformation and adsorption.

      2.3.4.2.1 Advanced Oxidation Processes

      2.3.4.2.2 Photolysis

      There are two classes of photolytic treatments, namely, indirect and direct photolysis. Whereas direct photolysis involves the decomposition of pharmaceuticals following direct absorption of UV radiation, in indirect photolysis intermediate species such as reactive excited states and free radicals are generated through photosensitization or use of a photocatalyst (Patel et al., 2019). Subsequently, chemical reactions occur resulting in degradation. The efficiency of photolysis is influenced by the intensity and frequency of radiation, quantum yield, the chemistry of the pharmaceutical compounds, formation of the oxidant, and the composition of the aqueous system (Wu et al., 2019). Other photolysis processes are highly influenced by pH. A range of pharmaceutical compounds are degraded through indirect photolysis. Semiconductors such as TiO2 have been used as photocatalysts for the photodegradation of pharmaceuticals (Yahya et al., 2018; Cunha et al., 2019). The photocatalyst is activated by excitation of a valence band electron using light, to form an electron-hole pair. The holes thus generated exhibit high oxidation potentials, and can generate HO• from water on the surface of the photocatalyst. In general, TiO2-based photodegradation results in high removals and considerable mineralization of pharmaceutical compounds.

      2.3.4.2.3 Ozonation

      2.3.4.2.4 O3/UV/H2O2 as an Oxidant

      To enhance the performance of ozonation, photocatalysts, UV or visible radiation, and H2O2 can be integrated in advanced oxidation processes. On its own, UV radiation can photodegrade some pharmaceuticals, but will not effectively remove all xenobiotics. Under UV irradiation, H2O2 generates HO• radicals, which are broad-spectrum oxidants capable of photodegrading pharmaceuticals (Sharma et al., 2019). These advanced oxidation processes successfully remove a range of pharmaceuticals including refractory organics (Patel et al., 2019). In addition, H2O2 can be applied in enhancing ozonation through perozonation, via mechanisms similar to O3/UV, augmented with H2O2.

      2.3.4.2.5 Fenton Process

      With the capacity to work under both homogeneous and heterogeneous conditions, Fenton’s reagent is a strong oxidant made up of Fe2+ and H2O2 in solution (Meng et al., 2018). In heterogeneous processes, the catalyst is attached on a heterogeneous substrate, and the reactions are driven by the generation of HO• radicals (Tsoumachidou et al., 2017). The Fenton process can degrade pharmaceuticals such as sulfachlorpyridazine, trimethoprim, and tetracycline (Hou et al., 2019).

      2.3.4.2.6 Adsorption