Aerated Stabilization Basin Retention Time Studies

Retention Time StudiesEnvironmental Business Specialists (EBS) works with over forty aerated stabilization basins throughout the United States. EBS specializes in monitoring and troubleshooting aerated stabilization basins in the pulp and paper industry. There are several consulting services that EBS provides to help mills evaluate their systems in order to make the necessary changes to stay compliant.

Unlike activated sludge systems, aerated stabilization basins constantly change. ASBs accumulate solids which results in a lost of system capacity and a change in flow patterns. Two services that EBS provides that assist mills in evaluating these changes are tracer and depth studies. These two studies should be done in conjunction in order to get a clear picture of how well a basin is being utilized.

A depth study is conducted using Global Positioning System (GPS) and an electronic sonar. In a boat, several passes are made throughout the basin collecting thousands of depth measurements. The measurements are averaged in order to calculate the average depth of the basin. With the current basin depth and the original basin depth, the basin volume and total sludge accumulated can be calculated. The depth measurements are also used to plot a three dimensional graph of the basin.

While depth studies give the actual volume of a basin and the theoretical retention time of the basin, a tracer study tells how the basin is being utilized. EBS uses lithium chloride brine as a tracer. Lithium chloride is introduced into the system and samples are collected at the basin effluent over a period of time in order to measure how long the tracer takes to leave the system. The lithium concentration of the samples is analyzed and using that data, the retention time of a basin can be calculated.

In many cases the retention time calculated from the tracer study is less than the theoretical retention time of the system. This is due to non-ideal flow patterns in the system. These flow patterns can be a result of short circuiting or channeling which can be caused by a faulty baffle or sludge build up in the basin.

The information obtained from these studies can assist the mill in making decisions regarding baffle installation or repair, dredging, and basin capacity.

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