Reuse of municipal wastewater requires treatment so that the water meets the quality requirements for the intended use. Irrigation of vegetables consumed raw requires absence of pathogenic organisms. To achieve this, fecal coliform concentrations should be essentially zero and the water should be filtered. This requires intensive treatment. For developing countries, however, where adequate sewage treatment often is lacking, the World Health Organization allows up to 1000 fecal coliform bacteria per 100 ml, which can be obtained by lagooning. Potable reuse requires much more intensive treatment, including lime clarification, denitrification, carbon adsorption, reverse osmosis, and disinfection. Where hydrogeologic conditions permit groundwater recharge with surface infiltration facilities, considerable water quality improvement is obtained by the movement of the wastewater through the soil, vadose zone, and aquifer. The resulting soil-aquifer treatment costs are less than 40% of the costs of equivalent in-plant treatment. Soil-aquifer treatment systems also are simple and robust, offer storage of the water to absorb differences between supply and demand, and enhance the aesthetics of potable reuse of wastewater. Hence, they can play an important role in wastewater reuse.

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