Sequestration and Transformation in Chemically Enhanced Treatment Wetlands: DOC, DBPPs, and Nutrients

Abstract

This paper examines the effectiveness of chemically enhanced treatment wetlands (CETWs), wetlands that received water treated with coagulants, to remove dissolved organic carbon (DOC), disinfection byproduct precursors (DBPPs), nutrients, and metals from agricultural drain water. Wetlands consisted of controls with no coagulant addition, ferric sulfate dosed, and polyaluminum chloride dosed treatments. CETWs were more effective in removing DOC, DBPPs, phosphate, dissolved organic nitrogen, and metals than control wetlands. Coagulation-treated wetlands removed 245-349 g=m 2 =year DOC, whereas control wetlands produced 51 g=m 2 =year. Wetland passage released DOC in the controls and dosed treatments; this release was directly correlated to temperature, suggesting thermally dependent mechanism(s) were partly responsible. A first-order plug flow reactor kinetic model that considered hydraulic retention time (HRT), temperature, and DOC concentration was tested for wetland DOC processing. Models indicate that operating CETWs at high coagulant dosing and low temperature can result in the lowest DOC release. Operating at the lowest HRT to meet discharge targets helps overcome wetland processes that increase DOC release and provide the smallest footprint needed for treatment. individual papers. This paper is part of the Journal of Environmental Engineering, © ASCE, ISSN 0733-9372. © ASCE 04019044-1 J. Environ. Eng. J. Environ. Eng., 2019, 145(8): 04019044 Downloaded from ascelibrary.org by 44.224.250.200 on 07/05/20. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04019044-2 J. Environ. Eng. J. Environ. Eng., 2019, 145(8): 04019044 Downloaded from ascelibrary.org by 44.224.250.200 on 07/05/20. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04019044-3 J. Environ. Eng. J. Environ. Eng., 2019, 145(8): 04019044 Downloaded from ascelibrary.org by 44.224.250.200 on 07/05/20. Copyright ASCE. For personal use only; all rights reserved. Me for all wetlands. Constants were calculated using nonlinear multivariate regression and modeling was performed using STATISTICA version 8.0. Results DOC and DBPP Concentrations, Loads and Concentration RatiosAverage constituent concentrations, annual loads and concentration ratios for DOC and DBPPs are shown in Tables 1 and 2. Annually, Al and Fe coagulation removed 71%-72% of DOC loads entering the wetlands, 66%-69% of THM precursors, and 79%-81% of © ASCE 04019044-4 J. Environ. Eng. J. Environ. Eng., 2019, 145(8): 04019044 Downloaded from ascelibrary.org by 44.224.250.200 on 07/05/20. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04019044-8 J. Environ. Eng. J. Environ. Eng., 2019, 145(8): 04019044 Downloaded from ascelibrary.org by 44.224.250.200 on 07/05/20. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04019044-12 J. Environ. Eng. J. Environ. Eng., 2019, 145(8): 04019044 Downloaded from ascelibrary.org by 44.224.250.200 on 07/05/20. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04019044-16 J...

Chemically Enhanced Treatment Wetland to Improve Water Quality and Mitigate Land Subsidence in the Sacramento‒San Joaquin Delta: Cost and Design Considerations

“…During the coagulation step, coagulant dosing was operated to achieve 65% to 80% DOC removal. For both the Fe and Al treatments, the coagulation step, on average, achieved over 70% DOC removal (Hansen et al 2018;Bachand et al 2019aBachand et al , 2019c. However, passage of treated water through the wetlands reversed some of the removal by coagulation and increased DOC and DBPP levels (both concentration and annual loads) at the outflow relative to post-dose levels.…”

“…Overall, the Al CETWs removed 58% of source water DOC loads (~349 gDOC m -2 yr -1 ) and the Fe CETWs removed 41% (~245 gDOC m -2 yr -1 ), whereas the control wetlands produced 51 gDOC m -2 yr -1 (an 8% increase in DOC relative to the source water). DBPP load removals were an order of magnitude lower than DOC removal, with HAA precursors more effectively removed than THM precursors (Hansen et al 2018;Bachand et al 2019c). CETWs also consistently removed other WQCCs such as phosphate, DON, DFe, DAl, FTHg, and FMeHg at removal rates of 42% to 93% of source water loads (Stumpner et al 2015;Bachand et al 2019bBachand et al , 2019c.…”

“…Despite this, water exiting the coagulant treated wetlands had lower DOC and DBPP levels relative to untreated source water and control treatment outflow water. CETWs removed more DOC and DBPPs during winter months when inflow water DOC concentration was higher and wetland DOC production was lower (Hansen et al 2018;Bachand et al 2019c).…”

“…We based coagulant costs per alternative on the use of PAC (Al treatment), because of its better DOC and DBPP removal and floc stability (Liang 2016;Bachand et al 2019c), as well as lower Hg content, as compared to ferric sulfate (Fe treatment) (Bachand et al 2019b). We estimated coagulant costs for two different DOC levels; high DOC (24 mg L -1 ) and low DOC (10 mg L -1 ), based on observed source water DOC concentrations that entered study control wetlands during fall/winter and summer/spring, respectively (Appendix A, Figure A6).…”

“…We estimated coagulant costs for two different DOC levels; high DOC (24 mg L -1 ) and low DOC (10 mg L -1 ), based on observed source water DOC concentrations that entered study control wetlands during fall/winter and summer/spring, respectively (Appendix A, Figure A6). We assumed a DOC removal efficiency of 70%, based on study findings (Hansen et al 2018;Bachand et al 2019aBachand et al , 2019c. Using the aforementioned assumptions, and to treat low-DOC source waters, approximately 28K kg yr-1 of PAC are needed for Alternative 1 and 4M kg yr -1 of PAC for Alternative 4, with estimated annual costs of $40K and $4.6M, respectively (Table 4).…”