Browsing by Author "Pishgar, Roya"

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    Nutrient (Ammonium and Phosphate) Removal Using Aerobic Granulation at Pilot scale
    (2019-07-22) Pishgar, Roya; Chu, Angus; Black, Kerry E.; Hettiaratchi, Joseph Patrick A.; Cuenca, Manuel Álvarez; Lu, Qingye
    This research investigated the causes of aerobic granulation inhibition and deterioration in nutrient removal performance of aerobic granular sludge (AGS) reactors at pilot scale. Identifying the underlying phenomena seems necessary to enhance predictability and reliability of this process under diverse circumstances. This can ultimately broaden the practicability of this technology for actual applications. Three pilot-scale (22-L) granular sequencing batch reactors (GBSRs) were operated to cultivate aerobic granules and to subsequently evaluate the treatment performance and AGS characteristics in the long run (up to ~500 days). While one reactor was operated under purely aerobic condition (O_SBR), the other two were run using alternating sequencing batch reactor (SBR) reaction phase arrangements (anaerobic/aerobic/anoxic/aerobic (AN/O/AX/O_SBR) and anaerobic/aerobic (AN/O_SBR) conditions). A series of ecophysiological experiments were conducted using an advanced molecular technique (16S rRNA phylogenetic gene sequencing analysis). Suspended-biomass batch experiments seeded with the inoculum of the GSBRs were chosen as the baseline, to reveal the functional diversity of the dominating bacteria in the AGS. Improper aeration pattern was identified as the main cause of preventing granulation at pilot scale. To maintain the aeration pattern and shearing activity regardless of the reactor scale, a scale-up factor (S) was developed which should be applied to the reactor dimensions, aeration rate, and surface area of the gas distributor simultaneously. Granulation time and size and effluent quality in terms of suspended solid concentrations and microbial washout pattern were regulated by the wastewater strength. Whereas, granule structure as well as AGS morphology and flocculent fraction were dictated by the SBR operation mode. Mineral-rich aerobic granules with hydroxyapatite (HAp) core were cultivated in the AGS reactors in this research regardless of the wastewater strength and SBR operation modes. Heterotrophic nitrification and biologically-induced phosphate precipitation (BIPP) were the dominant nutrient depletion pathways performed by the aerobic granules with lifeless cores. The contributions of these pathways to the overall ammonium nitrogen and phosphorus removal were 61 – 84% and 39 – 96%, respectively. Ecophysiological investigations characterized Thauera and Flavobacterium as the core heterotrophic nitrifiers. The species Flavobacterium, Acinetobacter, Pseudomonas, and Corynebacterium were identified as bio-calcifying species. Different types of denitrifiers and potential polyphosphate accumulating organisms (PAOs) were also identified. The long-term performance showed that the ammonium nitrogen (NH4-N) removal efficiencies established inverse relation with ammonium nitrogen loading rate (NLR). Phosphate (PO4-P) removal efficiency, on the contrary, showed a direct relation with chemical oxygen demand to phosphorus (COD:P) ratio. Heterotrophic nitrification and BIPP were the principal nutrient removal pathways during the long-term operation as well. The recovery of autotrophic ammonium oxidizing bacteria (AOBs) was feasible at low NLR (0.15 kg NH4-N m-3 d-1) and FA concentration (< 5 mg NH3 L-1). However, the recovery of autotrophic nitrite oxidizing bacteria (NOB) happened with delay and the PAO recovery was irreversible.
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    Removal of Dissolved Nitrogen Gas Using Mixed Liquor Vacuum Degassing in Biological Nutrient Removal Wastewater Treatment Facilities
    (2022-07-13) Hunter, Michael; Chu, Angus; He, Jianxun; Pishgar, Roya; Huang, Wendy
    The City of Calgary (The City) recently implemented a mixed liquor vacuum degassing (MLVD) system at Bonnybrook Wastewater Treatment Plant (WWTP) that uses rapid bubble desorption to lower the dissolved gas concentration in the mixed liquor, allowing for denitrification in the secondary clarifiers to occur while delaying microbubble formation. Total dissolved gas pressure (TDGP) sensors were constructed and deployed at site for a four-month test campaign to monitor TDGP in the wastewater before and after degasification. The MLVD system typically reduced the TDGP by 16 percent but the technology performance was inconsistent with the reduction in TDGP ranging from 10 to 26 percent. Vacuum pump off gas samples were analyzed to determine that nitrogen accounted for over 90 percent of the gas pressure reduction. As a result, the available capacity (in terms of concentration) for nitrogen to dissolve into solution prior to forming microbubbles in the secondary settling tanks (SSTs) (5 m deep tank with a 1 m deep sludge blanket) increased by 2 to 5 mg/L depending on MLVD performance (non-degassed mixed liquor available capacity of 7.4 mg/L increased to 9.5 to 12.5 mg/L after degasification). With inconsistent MLVD performance, an operational review was completed suggesting vacuum pump design improvements and operational optimization is required. Overall, the research provides an understanding and means to monitoring dissolved gas, specifically nitrogen, in biological nutrient removal facilities. Monitoring such parameters will become increasingly important as more stringent effluent requirements are enforced, wastewater becomes more concentrated through water conservation efforts, and processes are intensified within existing tankage.