Liquid-phase applications water contaminants, removal

Potable Water Treatment. Treatment of drinking water accounts for about 24% of the total activated carbon used in liquid-phase applications (74). Rivers, lakes, and groundwater from wells, the most common drinking water sources, are often contaminated with bacteria, viruses, natural vegetation decay products, halogenated materials, and volatile organic compounds. Normal water disinfection and filtration treatment steps remove or destroy the bulk of these materials (75). However, treatment by activated carbon is an important additional step in many plants to remove toxic and other organic materials (76—78) for safety and palatability. 

The removal of water contaminants by active carbon is the major market (55% in the USA) for liquid-phase applications, which in turn constitute 80% of total AC demand in the USA. AC is used both as a primary treatment, to render the effluent more amenable to other purification processes, and as the final tertiary stage in the purification of the effluent Of the total US water treatment market, about 50% is in drinking water, 40% in wastewater and the rest in ground water markets. Both powdered and GAC are used in water treatment. 

There are many types of reactors that can be used in the liquid-phase photocatalytic reactions. The selection usually depends on the experimental conditions and the application. Different water contaminants, ranging from hazardous contaminants of pesticides, herbicides, and detergents to pathogens, viruses, coliforms, etc., can be effectively removed in liquid-phase photoreactors. Table 7.3 summarizes various model compounds and microorganisms commonly used in the photocatalytic reactions. Examples of these various photocatalytic degradation processes and inactivation of the microorganisms will be considered in the following sections. 

Two-phase extraction uses a vacuum source to remove contaminated groundwater and soil vapor from the subsurface. The vacuum is applied to an extraction tube within a water well to increase groundwater removal rates and to volatilize and extract VOCs. According to the vendor, vacuum lift of water is not a limiting factor in the application of the technology. Since a mixed vapor/liquid column is extracted from the weU, the two-phase extraction technology allows a single piece of equipment (a vacuum source) to remove contaminants in both the liquid and vapor phases. 

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