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 (<8 NTU), TSS (< 25 mg/L) and ferrate-induced iron particles (<0.6 mg/L Fe), as well as 5-log removal of E. coli, were achieved at 31 minutes with the optimum ferrate dose 10 mg/L Fe added as coagulant aid along with 6 mg/L Al of alum. To further investigate the inactivation of E. coli in the EPT effluent, different ferrate doses (5, 8 and 10 mg/L Fe) were tested at different temperatures (9 and 19 °C). By increasing the ferrate dose from 5 to 10 mg/L Fe, the E. coli inactivation level increased from 1.6 to 4 log removal within 3 minutes at 19 °C. The disinfection kinetics data fit properly into Chick-Watson, Hom and Collins-Selleck models with adjusted R2 ranging between 0.94 and 0.99. In particular, Chick-Watson’s model was the most suitable to model the ferrate disinfection kinetics in the EPT effluent. The inactivation rate constant was less dependent on temperature and more dependent on ferrate dose which was also confirmed by ANOVA. Flow cytometry analysis revealed that ferrate could cause a significant damage to E. coli cell membrane whereas a limited damage to DNA was observed. It was also confirmed that hydrogen peroxide was produced in-situ during the application of ferrate. Ferrate slightly increased the acute toxicity of the EPT effluent likely due to the formation of toxic by-products. This research also examined the effect of ferrate on the oxidation of selected micropollutants in a buffered solution. Ferrate exhibited high selectivity on the oxidation of the micropollutants that were classified into three groups: poorly reactive (removal <50%): atrazine (ATZ), fluconazole (FLC), mecoprop (MCPP), moderately reactive (removal>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.

  • Subjects / Keywords
  • Graduation date
    Spring 2021
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.