Adsorption-Style Activated-Sludge Is It a Practical Treatment Process in North America?

Date of Award

Spring 2015

Document Type


Degree Name

Master of Science (MS)


Civil & Environmental Engineering


Environmental Engineering

Committee Director

Charles B. Bott

Committee Member

Peter Pommerenk

Committee Member

Gary Schafran

Call Number for Print

Special Collections LD4331.E542 D43 2015


Adsorption/Bio-Oxidation (A/B) processes occupy a small footprint and can be exceptionally energy efficient to the point of being energy positive in optimum conditions. They have the ability to handle industrially influenced municipal wastewater with high pH and BOD swings. The A/B plant configuration also appears to be a great platform for shortcut nitrogen removal processes because of the controlled carbon diversion capabilities of the adsorption stage (A-stage). In Europe, these plants have been successfully implemented at full scale since the early 1980s. However, in the U.S. there is a false conventional wisdom that plants operating at very low SRT's will not produce settleable sludge. European reports do not help dispel this myth because they include little to quantify their claims of excellent solids handling.

An A-stage HRAS portion of an A/B pilot plant was constructed at Hampton Roads Sanitation District's Chesapeake-Elizabeth (CE) wastewater treatment plant. This pilot plant was fed a continuous stream of CE plant raw water influent (RWI) and was operated to determine actual solids handling characteristics. Automated process control was used to ascertain the range of COD removal efficiency to analyze the practicality of operating a full-scale A/B plant in the United States. Having as versatile a COD removal range as possible ensures that the optimum level of carbon can always be sent to the downstream BNR process to allow for maximized BNR efficiency and recovery of the remaining carbon with minimal mineralization to CO2• The pilot A-stage was consistently able to provide the necessary C/N ratio necessary for the downstream B-stage BNR process to which it was directly connected. The solids handling performance displayed by this pilot plant indicates that the A-stage mixed liquor (ML) settles and dewaters reasonably well relative to sludges from HRSD's other full-scale plants. With basic automation equipment, which has become widely available in recent years, the A-stage can function with the reliability and performance which would be required of it as part of an A/B plant in the United States.


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