Denitrification and Biological Phosphorus Removal Using Focused, Pulse-Treated, Thickened Waste Activated Sludge as an Internal Carbon Source

Date of Award

Fall 2013

Document Type


Degree Name

Master of Science (MS)


Civil & Environmental Engineering


Environmental Engineering

Committee Director

Charles B. Bott

Committee Member

Mujde Erten-Unal

Committee Member

Gary Schafran

Call Number for Print

Special Collections LD4331.E542 H55 2013


Recent research shows that an internal carbon source, derived from the treatment of waste activated sludge (WAS), could be used as an alternative to external carbon sources for denitrification in biological wastewater treatment processes. In this study, a thickened waste activated sludge (TWAS) treatment technology, developed by the company OpenCEL, was used to treat TWAS with pulsed electric fields (PEF) to transform it into an organic substrate for heterotrophic denitrification in a biological nutrient removal (BNR) system. If effective, this technique could significantly reduce the external carbon source demand.

To determine the utility of OpenCEL-treated TWAS as an internal carbon source to aid in denitrification, this study employed three 22 L Sequencing Batch Reactors (SBRs) continuously-operating for five months and simulating a 4-stage Bardenpho configuration to determine if treated TWAS could reduce or replace an external carbon source. In the last three weeks of the study, the SB Rs' temperature was reduced from 20°C to 12°C to determine treatment efficiency under cold weather conditions.

Supplemental batch tests examining the biological activity of nitrifiers, heterotrophs, and PAOs in treated TWAS were also performed. This was done to quantify the extent bacterial inactivation due to the OpenCEL treatment. Simulation modeling of a full-scale wastewater treatment plant using Bio Win was performed to examine the effect of adding TWAS as a carbon source in a full-scale plant.

This study indicates that OpenCEL treated TWAS, without downstream separation of solids from soluble COD (sCOD), is not a viable supplement or alternative to external carbon addition. It was observed in the SBRs that both the untreated and treated TWAS were bioaugmenting the reactors, indicating incomplete PEF treatment of the TWAS. The incomplete treatment was verified by similar nitrifier, denitrifier, and PAO activity in treated and untreated TWAS batch tests. The simulation modeling showed that even if TWAS were completely inactivated through the PEF treatment, resulting in no bioaugmentation and substantial sCOD release, the additional solids added to the treatment train would demand a reduction in SRT to the point where nitrification is lost at cold temperatures. Thus, it was determined that OpenCEL treated TWAS, without downstream solids separation, is not a feasible technology for denitrification enhancement regardless of PEF treatment efficiency.


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