Date of Award
Summer 2015
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Civil Engineering
First Advisor
Zitomer, Daniel H.
Second Advisor
Mayer, Brooke K.
Third Advisor
McNamara, Patrick
Abstract
As energy costs rise, water reclamation facilities (WRFs) desire lower cost, easily operated systems to remove BOD5 and suspended solids. WRFs typically utilize an aerobic process called activated sludge to remove biochemical oxygen demand (BOD). BOD, specifically 5 day BOD (BOD5), is used as an indicator of the organic strength of a solution. Anaerobic treatment provides an alternative to activated sludge by removing BOD5, generating biogas containing methane for energy and producing less biomass that requires disposal. Anaerobic treatment functions as an exceptional alternative to activated sludge when packaged as a system with a small footprint that operates at ambient temperature. These systems can produce effluent with organic constituent quality similar to activated sludge without requiring the energy inputs that conventional treatment demands. In this work, an anaerobic, fluidized bed reactor (FBR) treating both synthetic and real domestic primary effluent was utilized to remove BOD¬5 from wastewater. The reactor was operated at 10°C to determine operation under challenging, low-temperature conditions. An external, cross-flow tubular membrane, gravity settling, enhanced chemical coagulation, electrocoagulation and FBR treatment with no subsequent solids removal were all tested in an effort to increase effluent quality, targeting a final BOD5 of 10 mg/L or less. FBR treatment with no subsequent solids removal with an hydraulic residence time of 9 hours reduced BOD5 by 68%, from 199 ± 26 mg/L to 67 ± 15 mg/L (n=8). Clarification of anaerobic effluent by membrane filtration resulted in an average permeate BOD5 of 7 ± 4 mg/L. Gravity settling alone achieved an average BOD5 of 35 ± 5 mg/L (n=2). Chemical coagulation with 30 mg/L ferric chloride followed by gravity settling reduced the BOD5 to 14±5 mg/L (n=8). In comparison, full scale activated sludge with secondary settling achieved a final BOD5 of 9 ± 2 mg/L (n=9). Anaerobic treatment with enhanced sedimentation may lend itself to retrofitting existing plants by use of activated sludge tanks and existing secondary clarifiers, whereas membrane filtration requires large capital investment. Additionally, enhanced sedimentation is a robust and relatively simple process in comparison to membrane filter operation. Enhanced sedimentation is a viable option for clarification of anaerobic effluent from an anaerobic FBR treating primary effluent.