TABLE OF CONTENTS In previous sections of this chapter, the principal categories of pollutants and their effects were identified. This section will discuss the various methods employed to treat the pollutants to produce cleaner wastewater discharges to surface waters.
Nearly 16,000 wastewater treatment plants are currently in operation in the United States. They range in size from the 1 billion gallon per day (GPD) Chicago main wastewater treatment plant to smaller package plants with flow rates in the vicinity of 5,000 GPD or less. For all facilities, whatever the size, wastewater is treated in a train of sequential treatment processes.
Primary treatment (or pre-treatment) involves unit operations such as screening, equalization, neutralization, sedimentation, air stripping, coagulation and precipitation, chelation, oxidation, oil removal, flotation, and temperature reduction. Primary treatment removes many of the gross contaminants such as grit, solids, and oil. Primary treatment may also include unit operations that condition or process wastewater (such as ammonia or sulfide stripping, or metals removal) so that it will be more suitable for secondary treatment and to protect downstream equipment.
Most of the types of primary treatment discussed below are employed to treat municipal wastewater or industrial process wastewater. Certain of these treatment processes can also apply to treating contaminated groundwater that has been extracted from the earth.
Secondary treatment (or biological treatment) involves biological oxidation of organic and inorganic pollutants. The bulk of pollutant removal occurs during secondary treatment.
Tertiary treatment is applied to secondary effluents to improve effluent...
