Characterizing the Drivers of Carbon Use in Post-Anoxic Denitrification

• Main Author: Bauhs, Kayla Terese
• Other Authors: Civil and Environmental Engineering
• Format: Others
• Published: Virginia Tech 2021
• Subjects: denitrification; post-anoxic; methanol; internal carbon; endogenous
• Online Access: http://hdl.handle.net/10919/104402

Three of Hampton Roads Sanitation District's (HRSD's) conventional activated sludge Water Resource Recovery Facilities (WRRFs) add methanol for post-anoxic denitrification: the Virginia Initiative Plant (VIP), Nansemond Plant (NP), and Army Base (AB). From 2017-2020, VIP averaged 0.49 ± 0.03 lb COD/lb N removed, while NP and AB averaged 1.48 ± 0.06 and 2.11 ± 0.15 lb COD/lb N, respectively. Significant methanol savings at VIP may result from post-anoxic denitrification using internal carbon that was stored in the anaerobic zone. An investigation into the factors affecting internal carbon-driven (internal C) denitrification was done via a series of batch tests. The capacity for internal C denitrification was demonstrated with sludge from all three WRRFs, despite not necessarily being used full-scale. For each WRRF, an increase in these rates correlated to higher phosphorus uptake rates, suggesting a dependence on the PAO population. Shorter aerobic times and more acetate in the anaerobic stage were shown to increase internal C denitrification rates to varying degrees, and this type of denitrification was only observed for bio-P biomass that was also nitrifying. Beyond internal carbon, other denitrification factors explored include moving the methanol dose point further into the anoxic zone, longer post-anoxic residence times, plug-flow conditions, solids residence time (SRT), and anoxic conditions prior to methanol dosing. Contributions from slowly biodegradable COD were minimal. Understanding the conditions that promote denitrification with internal carbon or other carbon sources would be required for effective strategies to achieve methanol savings at NP and AB that would rival those at VIP. === Master of Science === Three of Hampton Roads Sanitation District's (HRSD's) Water Resource Recovery Facilities (WRRFs) add methanol to facilitate denitrification in the post-anoxic zone: the Virginia Initiative Plant (VIP), Nansemond Plant (NP), and Army Base (AB). Significant methanol savings at VIP may result from denitrification using carbon that was stored in the biomass earlier in the treatment process. An investigation into the factors affecting this type of denitrification with internal carbon was done via a series of batch tests. All three WRRFs were able to use this internal carbon for denitrification in the batch tests, despite not necessarily using it full-scale. These denitrification rates were shown to relate to the performance of the biomass that is also responsible for phosphorus removal. Shorter aerobic times prior to the anoxic phase and more acetate in the stage where carbon is stored were shown to increase these denitrification rates, and this type of denitrification was only observed for biomass from WRRFs that implement nitrification. Beyond internal carbon, other denitrification factors explored include moving the methanol dose point further into the anoxic zone, longer post-anoxic residence times, plug-flow conditions, solids residence time (SRT), and anoxic conditions prior to methanol dosing. Contributions from carbon pushed downstream from overloading primary clarifiers was minimal. Understanding the conditions that promote denitrification with internal carbon or other carbon sources would be required for effective strategies to achieve methanol savings at NP and AB that would rival those at VIP.