The invention provides methods and compositions for treating wash water from concrete production with carbon dioxide. The treated wash water can be reused as mix water in fresh batches of concrete.

A wastewater treatment apparatus is equipped with: a reaction tank that performs aerobic biological treatment on organic wastewater containing at least one of a sulfur compound and a nitrogen compound; a filter for removing the corrosive gas from the gas discharged from water in the reaction tank; a sensor for measuring carbon dioxide concentration contained in the gas after the corrosive gas has been removed; and a control device for controlling the aerobic biological treatment based on the carbon dioxide concentration measured by the measurement means.

A system and method for producing and purifying alkalinity for addition to a body of water for decreasing the CO.sub.2 burden of an atmosphere that is in contact with a body of water using an alkaline mass to increase dissolved alkalinity of the body of water without increasing the concentration of undesirable metals to undesirable levels in the body of water may include chemically characterizing the alkaline mass, contacting the alkaline mass with a volume of water, leaching the alkaline mass with the volume of water to form an alkaline leachate, maintaining in solid form or precipitating the undesirable metals from the alkaline leachate to form a purified alkaline leachate, and adding the purified alkaline leachate to the body of water.

The invention provides methods and compositions for treating wash water from concrete production with carbon dioxide. The treated wash water can be reused as mix water in fresh batches of concrete.

A wastewater treatment apparatus included: a reaction tank which performs biological treatment of raw water, which is organic wastewater; an adding device that adds a nutrient substance to the raw water; a meter that measures the concentration of at least a volatile organic compound in gas released from water in the reaction tank; and a control device for controlling an additive amount of the nutrient substance by the adding device based on a measured value of the concentration obtained by the meter.