Date on Master's Thesis/Doctoral Dissertation

5-2017

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Chemical Engineering

Degree Program

JB Speed School of Engineering

Committee Chair

Berson, Robert Eric

Committee Member

Watters, James

Committee Member

Rockaway, Thomas

Author's Keywords

anaerobic digestion; flocculant; polymer; wastewater; COD

Abstract

Anaerobic digestion (AD) of municipal sludge is a widely used stabilization process at municipal wastewater treatment plants. It is highly effective in reducing sludge volume and produces methane gas which is used as fuel in the wastewater plant. Following digestion sludge is sent to a centrifuge to separate the solids from the liquids. Louisville MSD adds flocculent to material in the centrifuge to better coagulate the solids, thereby aiding in separation of the solids from the liquids. The potential for further AD, COD reduction, and methane generation of the liquid effluent from the centrifuge was unknown, particularly in regards to whether the flocculant could impact AD. Previous studies on flocculent have been non-conclusive.

Respirometery tests for biogas production, theoretical biogas production based on COD content, and COD reduction measurements all indicate that trace amounts of polymer left in the wastewater after centrifugation, in the range of 2.5mg/L – 10 mg/L, can hinder anaerobic digestion of the wastewater. There was no effect on biogas quality (methane content in the biogas) due to trace amounts of polymer, in the 1mg/L – 10 mg/L range, in the wastewater. UV Vis can be used to indirectly measure anaerobic degradation of the polymer in the wastewater based on the clarity of the wastewater.

This study recommends that Louisville MSD should minimize the use of polymer to increase the anaerobic digestion potential ie. increase the amount of methane generated from the liquid stream after centrifugation.

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