Master of Engineering Science
Chemical and Biochemical Engineering
George Nakhla & Jesse Zhu
Conventional wastewater treatment techniques - utilizing microorganisms to remove organics and nutrients (i.e. nitrogen and phosphorus) from a water stream and partially incorporate them into their cell structure - struggle to adapt with increased urbanization due to land and infrastructure requirements. The circulating fluidized-bed bioreactor (CFBBR) was developed as a way to provide biological treatment in an urbanized area by cultivating high-density bacteria on an inert media. The technology operates as a pre-anoxic nitrification/denitrification wastewater treatment process. The system is initially loaded with media, providing a platform for microbial growth. Internal recycle streams in the system provide the energy to fluidize the media – increasing mass transfer and accelerating microbial growth and pollutant removal rates. A pilot-scale CFBBR unit operated in Guangzhou, China, at an organic loading rate of 0.50 kg COD/day and a nitrogen loading rate of 0.075 kg N/day, was able to achieve a 93% reduction in carbon and an 88% reduction in nitrogen.
In addition, an innovative sensor network was constructed from open source hardware to monitor and adjust dissolved oxygen (DO) levels inside a 15 L lab-scale partial nitrification fluidized-bed. The treatment strategy for this biological process was to create reactor conditions that favour nitrifying bacteria that convert ammonia to nitrite, called ammonia oxidizing bacteria (AOB), over nitrifying bacteria that convert nitrite to nitrate, called nitrite oxidizing bacteria (NOB). The CFBBR, by virtue of its unique abilities to control biofilm thickness and accordingly biological solids retention time, offers significant advantages over other emerging nitrogen removal processes.
The control system was designed to automatically adjust the air flow to the bioreactor to maintain a DO level of approximately 1 mg/L, conditions that favour AOBs activity over NOBs. The unit operated continuously for 40 days as the bioreactor was fed with 200 mg/L of synthetic ammonia wastewater (devoid of carbon) to a maximum nitrogen loading rate of 6 g NH4-N/day. The control system was able to maintain an ambient DO level of 1.30 mg/L. At this loading rate, the effluent nitrate concentration was approximately 5% of the influent feed – indicating low NOB populations in the reactor.
Donohue, Joseph, "Process Control for Biological Nutrient Removal Processes in Fluidized Beds Treating Low Carbon to Nitrogen Municipal Wastewater" (2015). Electronic Thesis and Dissertation Repository. 3194.
Available for download on Saturday, June 30, 2018