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(2023)ThesisBiogenic taste and odour (T&O) events pose a series of challenges to drinking water treatment plants, increasing treatment costs and influencing customer perception of water quality. Granular activated carbon (GAC) is effective at removing these compounds from drinking water through adsorption; and the development of a biofilm on the surface of the granules turns the system into a biological activated carbon (BAC) and extends its lifetime. Selection of appropriate carbon types is fundamental to ensure high T&O removal throughout all phases of the GAC-BAC lifecycle, from adsorption-only to biofiltration. This study developed and applied a methodology to compare the adsorption capacity of nine different commercially available GACs; conducted bench-scale columns contactors and rapid biofilm growth experiments to assess carbon characteristics that affect biofilm development and biofiltration performance; and performed a metagenomic analysis to assess the effects of carbon characteristics, biofilm age and pre-exposure to T&O compounds on the microbiome, and how these impact biofiltration. The proposed adsorption methodology was successfully applied and revealed that the volume in pores smaller than 2 nm was the carbon characteristic with the most impact on adsorption of geosmin and MIB and should be the primary factor when selecting GACs for T&O. Results showed that different types of oxygen bonds showed opposite effects and total surface oxygen abundance showed little to no effect on adsorption; these results could be the answer to conflicting results reported by previous studies. The removability of dissolved organic carbon (DOC) by GAC rapidly declined over time, but removability of T&O compounds remained high throughout operation. Pre-exposure to T&O compounds had a small effect on their removability; it is hypothesized, however, that biological degradation may play a more important role on the removability of MIB than that of geosmin in BAC contactors. Intermittent exposure to T&O did not significantly affect T&O removability. Metagenomic results showed that BAC biofilms are extremely diverse and complex microbial communities, containing a multitude of different species of bacteria, viruses, archaea and eukaryotes. Carbon type, pre-exposure to T&O and carbon ‘age’ did not appear to significantly affect the microbial community composition. Two potential novel degraders of geosmin and MIB, Pseudomonas alcaligenes and Comamonas testosterone, were found.
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(2022)ThesisUrban stormwater runoff possesses the properties of intermittent occurrence, unexpectable volume and variable pollution which lead to different environmental issues, including flooding and waterlogging, pollution transportation, damage to downstream and contamination of the receiving waters. On the other hand, the low-level contamination (relative to sewerage) and large volume supply of stormwater makes it suitable as an alternative water resource to relieve the water shortage in the urban areas. Stormwater harvesting is under the concept of Water Sensitive Urban Design (WSUD) trying to treat stormwater properly for the different end-uses (like irrigation, toilet flushing and even for the uses close to human contact). Several treatment technologies (e.g., biofilters, constructed wetlands) have already been implemented to purify the stormwater with effective performance prior to reuse. However, the refractory organic micropollutants (especially herbicides) presented resistance to these nature-based solutions by showing variable treatment outcomes. In order to provide harvested stormwater for end-uses with high quality requirement (e.g., close to human contact recreational waters), a reliable treatment technology for organic micropollutants is desired as a post-treatment method in the stormwater harvesting system. This thesis aims to develop advanced oxidation processes (AOPs), in particular, photoelectrochemical oxidation (PECO), as the post-WSUD treatment approach for stormwater using its oxidation capacity towards the refractory organic micropollutants. Following the technology development procedure, three steps have been conducted: (1) testing the feasibility of AOPs for stormwater herbicides treatment; (2) investigating the intrinsic mechanism in the stormwater herbicides degradation process; and (3) assessing the operation conditions impact towards PECO stormwater treatment system. Boron-doped diamond (BDD) anode was used in the preliminary lab-scale tests for the feasibility study of AOPs towards stormwater organic micropollutants (two representative herbicides, diuron and atrazine - selected as the target pollutants in the study). The results showed that the effective herbicides degradation could be achieved by PECO process under 5 V operation (which was regarded as the optimal voltage in the system). The positive impact coming from voltage increase has been found in the study. BDD showed a remarkably durable property with stable removal performance under challenging voltage application (9 V) without observed deterioration. The catalysts loading showed negligible effect in removal performance. While the thermal effect was observed as a supporting factor for the process (higher temperature supported the oxidation process). Since BDD is not a perfect choice for scaled-up implementation due to its high manufacture cost, carbon fiber anode was chosen in the following studies and operated under low voltage (2 V) to avoid the possible anode deterioration under high voltage application. In the mechanism investigation, the superoxide radicals were found to be the major reactive species in PECO process. Meanwhile, hydroxyl radicals and free chlorine also demonstrated supporting impact for the oxidation process. With the identified intermediate products, degradation pathways of diuron and atrazine were proposed for the first time for three AOPs (PECO, electrochemical oxidation (ECO) and photocatalytic oxidation (PCO)) in stormwater herbicides degradation process. PECO was certified to be the preferrable stormwater treatment technology with the ability for further oxidation reactions towards herbicides degradation compared with ECO and PCO. In the third study, a flow reactor was designed and used to test the impacts of operational conditions (flow rate, light intensity, and initial pollutant concentration) for PECO process. An obvious improvement was observed for flow rate towards removal performance, while the light intensity was found to influence atrazine removal only. The initial pollutant concentration study demonstrated the robust performance of PECO flow reactor towards herbicides removal under challenging (240 μg L-1) pollutant concentration condition. The real stormwater experiments suggested the possible impacts coming from the stormwater chemistry towards PECO process. Further based on the energy consumption analysis, high flow rate (610 mL min-1) and normal light intensity (100 mW cm-2) were regarded as the optimal operational conditions for flow reactor system. Also, the effective PECO degradation performance of herbicides under the real stormwater environment has been verified by using the stormwater collected from field as supporting electrolyte in the experiments. Overall, this thesis confirms PECO as a promising stormwater herbicides treatment technology (potentially for all organic micropollutants) to provide further purification for stormwater high-quality targets. It also discusses the implications for the practical implementation and points out the future research directions for the system optimization.