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In North America, there are predominantly two systems used to biologically treat industrial wastewater: the aerated stabilization basin (ASB or aerated lagoon) and the activated sludge system. These two systems have far more similarities than differences. Both pro ­cesses are based on the utilization of dissolved oxygen by microorganisms in converting organic and inorganic matter into a settleable form. The following provides information on the pros and cons of each system.

Aerated Stabilization Basin – Figure 1

The ASB, also known as a lagoon system, is a large body of water used for biological treatment. The placement and continuous operation aeration equipment is both the most important part of the system and the most expensive. Untreated effluent comes into the primary clari­fier and then into the ASB. As the effluent passes through the system, the BOD or “food” present is used as energy and a carbon source for bacteria. Once the treated water has gone through the ASB it typically enters a polishing pond for tertiary treatment where the remaining TSS (total suspended solids) settles out before being discharged as the final effluent.  These systems are particularly widely used in the pulp and paper industry in the southeastern United States, where mills are usually remote and have access to large tracts of land.