Date of Award

5-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School

College of Science and Mathematics

Department/Program

Earth and Environmental Studies

Thesis Sponsor/Dissertation Chair/Project Chair

Yang Deng

Committee Member

Huan Feng

Committee Member

Jinshan Gao

Committee Member

Yueqiang Liu

Abstract

Phosphorus (P) is a major nutrient present in municipal wastewater. Without proper treatment and management, residual P in treated wastewater finally enters into natural receiving water bodies. Nutrient pollution resulting from excessive P, together with the other nutrient, i.e. nitrogen (N), is a leading cause of eutrophication, a ubiquitous U.S. water quality issue. An overgrowth of algae during eutrophication brings extremely adverse impacts on the water quality. The algal bloom can rapidly deplete dissolved oxygen, lead to the death of aquatic life, increase water turbidity, and cause taste and odor issues. Moreover, some harmful algal boom can produce toxins to give rise to various illnesses in human and animals. The aforementioned challenges are of particular concern when eutrophication occurs in drinking water sources. Although existing wastewater treatment technologies can remove P, to different extents, they are restricted by technical difficult to achieve a very low P concentration and/or poor removal capability for organic P in wastewater. On the other hand, the regulations on the P discharge from municipal wastewater treatment facilities are increasingly stringent, particularly for highly nutrient sensitive water bodies. Therefore, there is an urgent research demand to develop innovative, reliable, and efficient treatment technologies for elimination of phosphorus in municipal wastewater.

The primary objective of this dissertation is to evaluate the treatment performance of ferrate(VI) for removal of different phosphorus species at different wastewater treatment stages and elucidate the underlying reaction mechanisms. Two treatment scenarios were tested, i.e. chemically enhanced primary treatment (CEPT) and advanced wastewater treatment. The central hypothesis is that ferrate(VI) is capable of effectively removing inorganic phosphate through precipitation and/or adsorption due to the formation of iron (hdyr)oxides and alleviating organic phosphorus via chemical oxidation and precipitation/adsorption mechanisms. Laboratory sale tests were carried out to sequentially implement four tasks for achieving the objective.

In Task 1, ferrate(VI) treatment was applied to CEPT with a particular focus on the removal of phosphorus in wastewater. Results show that ferrate(VI) enabled CEPT could effectively remove total phosphorus by up to 87%. The most majority of phosphorus removed was particulate phosphorus. The removal was primarily ascribed by gravity-driven sedimentation. In contrast, ferrate(VI) CEPT poorly removed organic phosphorus present in municipal wastewater. Accompanied by the alleviation of phosphorus, ferrate(VI) addition improved the removal of particles and particulate organic matter in wastewater. In Task 2, ferrate(VI) removal of orthophosphate was investigated in a secondary effluent matrix at an advanced treatment scenario. Results show that ferrate(VI) could effectively alleviate phosphate (a majority of inorganic phosphorus) from secondary effluent primarily due to the adsorption mechanisms. Ferrate(VI) resultant particles comprised both amorphous and crystalline (hematite) iron (hydr)oxides. Effluent organic matter (EfOM) could inhibit the phosphate removal. Task 3 aimed to remove organic phosphorus for advanced wastewater treatment. Ferrate(VI) exhibited an excellent capability for abating of organic phosphorus in in secondary effluent. The presence of phosphate could suppress ferrate(VI) removal of organic phosphorus. In order to understand the underlying mechanisms, the reactions between ferrate(VI) and six organic phosphorus model compounds were separately investigated. Results show that ferrate(VI) degraded the model compounds into daughter P-containing molecules, followed by adsorption of the transformation compounds by the resultant iron (hdyr)oxide particles. Ferrate(VI) oxidation insufficiently decomposed the organic phosphorus into inorganic phosphorus. Of note, the treatment performance of ferrate(VI) for removal of phosphorus during the CEPT or advanced treatment relied heavily on ferrate(VI) dose and pH. In Task 4, a preliminary cost analysis was made. Although ferrate(VI) addition was more costly than traditional phosphorus removals with ferric slats, ferrate(VI) treatment brings many unmatched benefits such as the removal of organic phosphors. Finally, the impacts of ferrate(VI) technologies on urban water management, environment, and society were discussed, and future research directions were identified.

This dissertation research clearly demonstrates that ferrate(VI) treatment is a promising technology for elimination of different phosphorus species in municipal wastewater and abatement of other wastewater contaminants. Besides mitigation of phosphorus, organic matter, and particles in wastewater, ferrate(VI) has proven highly effective for degradation of micropollutants and inactivation of pathogens in water and wastewater. In this dissertation research, ferrate(VI) can be resiliently applied for CEPT or advanced treatment for improving wastewater quality. At the first scenario, the ferrate(VI) enabled technology can enhance the performance of traditional secondary wastewater treatment facilities. It can also be a standalone wastewater treatment process for many developing countries with the primary treatment only. At the second scenario, ferrate(VI) treatment as a post-treatment step is expected to dramatically improve water quality through the removal of persistent contaminants such as organic phosphorus and emerging contaminants. Implementation of ferrate(VI) technologies for wastewater treatment has profound impacts on the wastewater industry, environment, and society.

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