Dissolved organic matter uptake kinetics during coagulation and water treatment implications

The kinetics of dissolved organic matter removal during coagulation were evaluated using sixteen waters, including two wastewater effluents, across a wide range of water quality (dissolved organic carbon (DOC): 2.10–8.00 mg/L; ultraviolet absorbance at 254 nm (UVA 254 ): 0.048–0.211 cm -1 ; specific ultraviolet absorbance (SUVA): 1.6–3.08 L/mg·m; fluorescence index: 1.40–1.88; turbidity: 1.6–36.5 NTU; pH: 6.5–8.6; alkalinity: 14–128 mg/L asCaCO3 ). Jar tests, completely mixed batch reactors (CMBR), assessed coagulation rapid-mixing, flocculation, and sedimentation, while pilot-scale reactors, plug flow reactor (PFR) and completely mixed flow reactor (CMFR), assessed coagulation rapid-mixing kinetics. Baseline CMBR testing included sampling at 1, 5, 10, 20, and 51 min post coagulant addition at 40 mg/L alum and 20 °C. Aluminum sulfate, ferric chloride, and ferric sulfate were tested at 10–107 mg/L. As isolated variables, pH (7–8.5), temperature (10–30 °C), rapid-mix speeds (55–250 RPM), turbidity (20–120 NTU), and molecular size fractions (<1 kDa and >1 kDa) were varied. Bench-scale CMBR tests ( n = 42) showed that 99.1%±8.0% of the DOC uptake occurred within the first minute for all waters and conditions, while the pilot-scale tests yielded 95% ( n = 3) DOC uptake within 0.25 min in PFR static mixers and >77% DOC uptake within two min in CMFRs. UVA 254 results yielded similar kinetic results. Additional tests combining powdered activated carbon (PAC) with coagulation showed that DOC removal was unaffected by PAC timing, while early PAC addition enhanced 2-methylisoborneol (MIB) removal. Delaying chlorine addition by 1 min after coagulant addition lowered haloacetic acid and haloacetonitrile formation by 22% and 17%, respectively, but only marginally, 4%, decreased trihalomethane formation.