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326   Industrial Wastewater Treatment, Recycling, and Reuse


          radicals, especially hydroxyl radicals, are mostly utilized to destroy the pol-
          lutants in wastewater. The process can involve direct ozonization, wet air
          oxidation (WAO), hydrogen peroxide oxidation, and UV photolysis
          (Esplugas et al., 2002; Poznyak and Arazia, 2005; Salah et al., 2004). Ideally,
          the final products in advanced oxidation technology are simple products
          such as water and carbon dioxide, which means that there are no secondary
          pollution problems.

          8.1.1.4 Ozonation
          Ozonation is widely employed in water treatment or disinfection. Hoigne ´
          and co-workers have revealed that ozonation produces hydroxyl (OH) rad-
          icals through the decomposition of ozone (O 3 ) with OH and proposed the
          Staehelin, Buhler, and Hoigne ´ model for the complex reaction cascade dur-
          ing ozonation (Staehelin et al., 1984). The OH radical is one of the most
          reactive species in ozonation, and the amount of OH radical determines
          the efficiency of ozonation (Hoigne ´, 1988). Recently, some kinetic models
          were provided to explain the efficiency of OH radicals in AOPs using OH
          radical scavengers (Andreozzi et al., 1999). The ozonation method of waste-
          water treatment is applicable to wastewaters at very low phenol
                                   1
          concentrations of 1–5 mg L .
          8.1.1.5 Electrolysis
          The electrolytic method can also offer one tool for the treatment of waste-
          waters. The oxidation of organic matter may be classified into two types—
          direct oxidation, taking place at the surface of the anode, and indirect
          oxidation, which is distant from the anode surface. This technique can also
          remove 4-NP (Can ˜izares et al., 2004) but has limitations similar to those of
          chemical oxidation.


          8.1.1.6 Biodegradation
          Biological treatment of organic chemicals can be accomplished if proper
          microbial communities are established for degradation. Microbial strains
          such as Pseudomonas putida, Pseudomonas fluorescens, Acinetobacter, Trichosporon
          cutaneum, and Candida tropicalis are capable of degrading phenol at low con-
          centrations. At sufficiently high concentrations, phenol can become suffi-
          ciently toxic to inhibit the growth rate of these micro-organisms. Hence,
          for achieving satisfactory performance, the phenol concentration needs to
          be maintained well below toxic level, and the acclimatization of these organ-
          isms to the wastewater environment is also required. Biodegradation can also
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