Natural biochemical reactions in the soil drive the soil pH to a neutral condition. A range of wastewater pH between 3 and 11 has been applied successfully to land treatment systems. Extended duration of low pH can change the soil fertility and lead to leaching of metals. When the acidity is comprised of mostly organic acids, the water will be neutralized as the organics are oxidized. The acidity of wastewater can be characterized with the total acidity with units of mg CaCO3 per L. The total acidity represents the equivalent mass as CaCO3 required to adjust the pH to a specific pH, commonly defined as 7.0. The soil buffer capacity is reported as mg CaCO3 per kg or tons CaCO3 per ac. The buffer capacity represents the soils ability to neutralize an equivalent amount of acidity. A balance between the total acidity applied in the wastewater and the buffer capacity of the soil can indicate the capacity of the soil to effectively neutralize the acid in the wastewater. The buffer capacity of the soil is restored after organic acids are broken. Most field crops grow well in soils with a pH range of 5.5 to 7.0. Some crops that have a high calcium requirement, such as asparagus or cantaloupes, prefer a soil pH greater than 7.0. If the pH of the soil begins to drop, liming is recommended to return the pH to the desirable range for crop production. Because of the ability of the soil to treat large amounts of organics acids, it is recommended that the pH of wastewater only be adjusted for extreme pH conditions (pH <5.0 or >9). If the mineral (nonorganic) cause of the high or low pH is a threat to crops or groundwater, adjustment may be necessary.
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