Aluminum- and iron-based coagulation for in-situ removal of dissolved organic carbon, disinfection byproducts, mercury and other constituents from agricultural drain water

• Published in: Ecological engineering 2019-09, Vol.134, p.26-38
• Main Authors: Bachand, Sandra M., Kraus, Tamara E.C., Stern, Dylan, Liang, Yan Ling, Horwath, William R., Bachand, Philip A.M.
• Format: Article
• Language: English
• Subjects: Agricultural pollution; Agricultural production; Aluminium; Aluminum; Aromatic compounds; By-products; Byproducts; Carbon sources; Coagulants; Coagulation; Disinfection; Dissolved organic carbon; Dissolved organic carbon surrogates; Dissolved organic matter; Dissolved organic nitrogen; Dosage; Ferric sulfate; Fluorescence; Haloacetic acids; Hybrid wetlands; Iron; Iron constituents; Iron sulfates; Isotherms; Land subsidence; Mercury; Mercury (metal); Metals; Mitigation; Monod equation; Nitrogen; Nutrients; Organic chemistry; Organic matter; Organic nitrogen; Phosphates; Pollutant removal; Pollutants; Pollution control; Quality control; Removal; Sacramento-San Joaquin Delta; Soil; Subsidence; Sulfates; Trihalomethanes; Water pollution; Water quality; Water quality constituents of concern; Wetland agriculture; Wetlands
• ISSN: 0925-8574; 1872-6992
• DOI: 10.1016/j.ecoleng.2019.02.015

[Display omitted] •In-situ coagulation system successfully employed for water quality improvement.•Al dosing resulted in higher removal efficiency than Fe dosing.•FDOM and UV254 suitable as source water DOC surrogate.•FDOM and UV254 as DOC surrogates after coagulant application presented challenges. Agricultural production on wetland soils can be significant sources of dissolved organic carbon (DOC), disinfection byproduct precursors, mercury and nutrients to downstream water bodies and accelerate land subsidence. Presented as a potential solution for in-situ water quality improvement and land subsidence mitigation, chemically enhanced treatment wetlands (CETWs) were used to leverage both coagulation and wetland processes. In this study, we evaluated the performance of coagulants ferric sulfate (Fe dosing) and polyaluminum chloride (Al dosing) to remove pollutants from agricultural drain water using the coagulation system designed for CETWs. Both coagulation treatments removed over 70% DOC from source waters, resulting in removal efficiencies (mg-DOC removed per mg-metal dosed) of 1 under Al dosing and 0.5 under Fe dosing. Coagulation by both treatments preferentially removed UV254 active compounds compared to the bulk DOC concentration, suggesting coagulation targeted aromatics more effectively. Phosphates and haloacetic acids were also removed more readily, whereas trihalomethanes, dissolved organic nitrogen and filtered mercury species were removed at similar or lower rates than DOC. Dissolved inorganic nitrogen was not amenable to coagulation and removal was not observed. Freundlich, Langmuir and Monod models explained 33% of the variance in DOC removal for Al dosing and 78–89% of the variance for Fe dosing. All three models indicated Al dosing had higher removal efficiency and affinity for DOC than Fe dosing under study conditions, but when used to predict maximum removal efficiency there was no cohesiveness between the three models due to different model assumptions. Consideration of fluorescence dissolved organic matter and UV254 as surrogates for DOC concentration showed both were equally suitable before coagulant application, but as surrogates after coagulant application, neither could be deemed more fit as a surrogate since both were shown suitable for different treatment scenarios.