Graduation Year

2023

Document Type

Thesis

Degree

M.S.C.H.

Degree Name

MS in Chemical Engineering (M.S.C.H.)

Degree Granting Department

Chemical Engineering

Major Professor

John Kuhn, Ph.D.

Co-Major Professor

Sarina J. Ergas, Ph.D.

Committee Member

Ryan Toomey, Ph.D.

Keywords

Ammonia-oxidizing microorganisms, Ammonium removal, Bioregeneration, Ion exchange, Zeolite

Abstract

Nitrogen discharge from wastewater is a global issue and with increased urbanization as well as industrialization, it has become even more essential to develop more efficient wastewater treatment systems. The dominant form of nitrogen in wastewater is ammonium. Biological oxidation of ammonium to nitrite and nitrate is the first step in biological nitrogen removal processes. If left untreated, nitrogen can cause toxicity to aquatic life, unsafe changes in water quality, and eutrophication.

Biofilm carriers can help to improve the efficiency of traditional activated sludge wastewater treatment systems by reducing operating costs and reducing hydraulic retention time. Biofilm carriers also promote the growth of biomass by providing solid media that the microbes can adhere to and promote the production of extracellular polymeric substances.

Zeolites have been utilized in wastewater treatment in the past for ammonium removal due to their low cost and cation exchange properties. These ion exchange materials are also not toxic to microorganisms typically used in biological wastewater treatment and usually have high selectivity for ammonium compared to other competing cations present in wastewater. Chabazite is a low-cost zeolite with high selectivity for ammonium.

The overall objective of this thesis was to fabricate a biofilm carrier that incorporated chabazite and promoted biofilm growth to achieve a faster ammonium removal rate than raw chabazite. The ammonium removal rate was expected to be faster by creating concentrated areas of ammonium on the carrier, creating a more conducive environment for the microorganisms. The overall objective of this thesis was to fabricate a biofilm carrier that incorporated chabazite and promoted biofilm growth to achieve a faster ammonium removal rate than raw chabazite. The ammonium removal rate was expected to be faster by creating concentrated areas of ammonium on the carrier, creating a more conducive environment for the microorganisms.

Hydrogels were used in the past for bacteria immobilization and as carriers for wastewater treatment due to their swelling property, non-toxicity to the microorganisms as well as their porous nature. These properties allowed the organisms to be successfully immobilized reducing clogging within the system while still allowing diffusion of the wastewater to these organisms.

In this thesis, polyvinyl alcohol-sodium alginate (PVA-SA) hydrogel carriers with encapsulated chabazite were fabricated and implemented for the removal of ammonium in wastewater treatment plants. The reduction in particle size of the chabazite was also investigated and the results showed a higher ammonium removal rate when the smaller particle size was used. The smaller particle size also allowed for more homogenous distribution within the carrier.

This project also looked at changes in carrier performance when changing the geometry of the hydrogel carriers from disks to spheres and how the abiotic performance was affected. The results showed no significant differences even with smaller spheres due to the similar surface area to volume ratio. Kinetic and isotherm modelling of the PVA-SA hydrogel disk carriers were done, showing a best fit to the pseudo second order kinetic model with an R2 value of 0.978. The Freundlich isotherm model best fit the equilibrium isotherm data with an R2 value of 0.987.

Batch tests were done showing the effective removal of ammonium using these carriers with ammonia oxidizing microorganisms (AOM). This coupled approach of combining ion exchange with the bioregeneration by AOM has not been researched previously using chabazite and it was observed that this approach helped to promote ammonium removal as the batch test using the carrier with encapsulated chabazite and AOM on the outside of the carrier achieved the fastest ammonium removal rate (3 days) compared to the batch test using AOM and chabazite without a carrier (5 days). Both tests reduced the ammonium concentration in 8 days in the first cycle. This test was repeated with a batch test using the carrier with encapsulated chabazite and AOM but showed no bioregeneration due to the microbes possibly dying when placed in deionized water. The test was repeated at a smaller scale and showed bioregeneration of the zeolite based on the nitrite production. The small-scale test achieved a reduced cycle time from 8 days in the 1st cycle to 5 days in the 2nd cycle.

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