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Enhanced Primary Treatment during Wet Weather Flow by Metal-based Coagulants and Ferrate: Coagulation Optimization, Disinfection Kinetics Study, and Micropollutants Oxidation
- Author / Creator
- Al Umairi, Abdul Rahim
Wastewater during wet weather flow (WWF) is highly loaded with various pollutants including suspended solids, microorganisms, inorganics, organics, and micropollutants. My research compared different coagulant salts used in the enhanced primary treatment (EPT) during WWF. Then, my project explored ferrate as a coagulant/coagulant aid/disinfectant to be applied during the EPT and as an oxidant to degrade selected micropollutants.
Alum and poly-aluminum chloride surpassed ferric chloride and achieved higher removals of turbidity (90% to 93%) and ortho-phosphate (OP) (73% to 83%). All tested coagulants attained comparable removals of total suspended solids (TSS) (95% to 99%) and chemical oxygen demand (COD) (64% to 71%). The bench and full-scale data were in agreement. The turbidity and percent ultraviolet transmittance showed good correlations with TSS and OP which evokes their use for online process control and monitoring.
Ferrate as a coagulant was evaluated based on a two-level factorial design with an emphasis on the effects of rapid mixing, slow mixing, and polymer addition. At the optimized condition, ferrate (0.5 mg/L Fe) with a cationic polymer (1.25 mg/L) removed 83%, 87%, 70% and 23% of turbidity, TSS, COD, and OP respectively. General linear models were developed to adequately predict the responses. This study thoroughly examined ferrate, in a first application, as a coagulant aid with alum for the EPT. Ferrate (8 mg/L Fe) achieved 2.1 log removal of E.coli when used as a coagulant and more than 3 log removal when used as coagulant aid (with alum) or disinfectant (after coagulation/flocculation/settling). The target levels of turbidity (50%): diazinon (DZN), carbendazim (CDZ), perfluorooctanoic acid (PFOA), and highly reactive (removal > 85%): carbamazepine (CBZ), sulfamethoxazole (SMX), trimethoprim (TMP) and clindamycin (CLN). Most poorly and moderately reactive compounds as well as CLN showed less dependence on the pH. In contrast, PFOA was better removed at alkaline pH whereas CBZ, SMX and TMP were better removed at acidic pH. The oxidation kinetics of DZN and CLN were examined for the first-time using ferrate with pseudo-second order rate constants 0.7314 µM-1s-1 and 0.0418 µM-1s-1, respectively. Hydroxyl radicals showed no contribution to the oxidation process in the ferrate system, while superoxide radical did contribute. Interestingly, ferric iron (Fe(III)) (reduced form of ferrate) showed minor contribution (up to 25%) to the overall removal of the tested compounds. The combination of UV/ferrate improved the removal of CDZ by seven times while it hindered the degradation of MCPP with a minor contribution of hydroxyl radical.
- Graduation date
- Spring 2021
- Type of Item
- Doctor of Philosophy
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