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Many chemicals function as both oxidizing agents (i.e., oxidants) and disinfecting agents (i.e., disinfectants); therefore, both oxidizing and disinfecting properties must be considered when selecting a chemical. The important characteristics of chlorine, chlorine dioxide, monochloramine, ozone, and UV radiation are described in many chapters of this handbook series(1-3). This chapter places emphasis on chlorination and chlo-ramination of potable water.Chlorination and chloramination of wastewater,sludge, and septage are also important (1-10),but will be introduced in separated chapters of this handbook series.

Chlorine is an efficient disinfectant as well as an oxidizing agent, and perhaps is the most frequently used chemical by environmental engineers and scientists since 1800s. The oldest water treatment facilities used only chlorine for water disinfection, which became the foundation of our industrial development. Today chlorine has been used in various forms for sanitary, commercial, industrial, and military applications. This chapter is a sister chapter to the following book chapters in the series:

Chlorine has been used as a disinfectant in potable water systems for over 100 yr. Free chlorine and combined chlorine (chloramines) are the two forms of chlorine widely used for the disinfection. Free chlorine is added as chlorine gas or sodium/calcium hypochlorite to the water. The reaction of chlorine in water produces hypochlor-ous acid and hydrochloric acid: Cl2 + H2O ↔ HOC1 + HC1 Chlorine Hypochlorous acid Hyddrochloric acid:

Since the early 1970s, advanced oxidation processes (AOPs) have been used considerably to remove both low and high concentrations of organic compounds from diverse sources such as groundwater, municipal and industrial wastewater, sludge destruction, and volatile organic compound (VOC) control. These processes, although often having high capital and operating costs, are the only viable treatment methods for effluents containing refractory, toxic, and non-biodegradable materials. In the AOP, the organic compounds can be completely mineralized to carbon dioxide and water mostly by hydroxyl radicals, the second most powerful oxidizing agent generated in in the reaction environment. The rate constant values of oxidation of the organics with hydroxyl radicals range from 10 to 10 M1s

In any chemical reactor, if there are chemical reduction reactions, there must be chemical oxidation reactions occurring at the same time

Oil and grease (O&G) is a common pollutant frequently found in the effluent of a wide range of industries. Oil and grease concentrations in wastewater, as recommended by the US Environmental Protection Agency, are not determine as the presence of specific compounds but are measured by their extractability using a particular solvent. Hexane and Freon are primary solvents used to extract oily compounds from wastewaters. Therefore, the term “oil and grease” contains a wide range of contaminants, which may include but are not limited to fatty acids, surfactants, petroleum hydrocarbons, phenolic compounds, animal and vegetable oils, etc. Many industries such as steel, aluminum, food, textile, leather, petrochemical, and metal finishing were reported as sources of high concentrations of oil and grease in their wastewaters as shown in Table 1.

Water removal from municipal and industrial effluent streams constitutes an important step in wastewater and sludge treatment. The purpose is to concentrate, separate, dispose, or utilize wastes and pollutants and to regenerate and return clean water to the environment. In this context, the discussion here will be limited only to industrial and municipal sludge dewatering, evaporation, and drying (–).

Solvent extraction, or liquid-liquid extraction, is the separation of impurities (solutes) from a liquid solution by contacting it with another immiscible liquid (solvent) in which the impurities have a high affinity. The high affinity driving the separation can be either physical solubility differences or a chemical reaction. The solvent may be a single component liquid (toluene) or a mixture (isopropyl ether/octanol).