6 research outputs found
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Chemically Enhanced Treatment Wetland to Improve Water Quality and Mitigate Land Subsidence in the Sacramento‒San Joaquin Delta: Cost and Design Considerations
Water quality impairment and land surface subsidence threaten the viability of the Sacramento–San Joaquin Delta (Delta), a critical component of California’s water conveyance system. Current-day irrigation drainage through Delta island peat soils affects drinking water treatment and is linked to mercury transport, potentially posing both ecological and public health concerns. To cost-effectively treat agricultural drainage water from subsided Delta islands to reduce the export of drinking Water Quality Constituents of Concern and mitigate land subsidence through accretion, we studied hybrid coagulation-treatment wetland systems, termed Chemically Enhanced Treatment Wetlands (CETWs). We provide cost estimates and design recommendations to aid broader implementation of this technology. Over a 20-year horizon using a Total Annualized Cost analysis, we estimate treatment costs of 747 per acre-foot (ac‑ft) water treated, and 70 per kg dissolved organic carbon (DOC) removed, depending upon source water DOC concentrations for a small 3-acre CETW system. For larger CETW systems scaled for island sizes of 3,500 to 14,000 acres, costs decrease to 239 per ac-ft water treated, and 14 per kg DOC removed. We estimated the footprints of CETW systems to be approximately 3% of the area being treated for 4-day hydraulic retention time (HRT) systems, but they would decrease to less than 1% for 1-day HRT systems. CETWs ultimately address several of the Delta’s key internal issues while keeping water treatment costs competitive with other currently available treatment technologies at similar scales on a per-carbon-removed basis. CETWs offer a reliable system to reduce out-going DOC and mercury loads, and they provide the additional benefit of sediment accretion. System costs and treatment efficacy depend significantly on inflow source water conditions, land availability, and other practical matters. To keep costs low and removal efficacy high, wetland design features will need site-specific evaluation
Recommended from our members
Chemically Enhanced Treatment Wetland to Improve Water Quality and Mitigate Land Subsidence in the Sacramento‒San Joaquin Delta: Cost and Design Considerations
Water quality impairment and land surface subsidence threaten the viability of the Sacramento–San Joaquin Delta (Delta), a critical component of California’s water conveyance system. Current-day irrigation drainage through Delta island peat soils affects drinking water treatment and is linked to mercury transport, potentially posing both ecological and public health concerns. To cost-effectively treat agricultural drainage water from subsided Delta islands to reduce the export of drinking Water Quality Constituents of Concern and mitigate land subsidence through accretion, we studied hybrid coagulation-treatment wetland systems, termed Chemically Enhanced Treatment Wetlands (CETWs). We provide cost estimates and design recommendations to aid broader implementation of this technology. Over a 20-year horizon using a Total Annualized Cost analysis, we estimate treatment costs of 747 per acre-foot (ac‑ft) water treated, and 70 per kg dissolved organic carbon (DOC) removed, depending upon source water DOC concentrations for a small 3-acre CETW system. For larger CETW systems scaled for island sizes of 3,500 to 14,000 acres, costs decrease to 239 per ac-ft water treated, and 14 per kg DOC removed. We estimated the footprints of CETW systems to be approximately 3% of the area being treated for 4-day hydraulic retention time (HRT) systems, but they would decrease to less than 1% for 1-day HRT systems. CETWs ultimately address several of the Delta’s key internal issues while keeping water treatment costs competitive with other currently available treatment technologies at similar scales on a per-carbon-removed basis. CETWs offer a reliable system to reduce out-going DOC and mercury loads, and they provide the additional benefit of sediment accretion. System costs and treatment efficacy depend significantly on inflow source water conditions, land availability, and other practical matters. To keep costs low and removal efficacy high, wetland design features will need site-specific evaluation
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Agricultural managed aquifer recharge — water quality factors to consider
The resilience and productivity of California's agriculture is threatened by groundwater overdraft, reduction in aquifer water quality, increased land subsidence damage to infrastructure and an irreversible reduction in groundwater storage capacity. Intentionally flooding agricultural fields during winter — a practice referred to as agricultural managed aquifer recharge (AgMAR) — can help counteract overdraft. However, the potential for AgMAR to exacerbate nitrate/salt leaching and contamination of at-risk aquifers remains a critical concern. To quantify the risk of groundwater contamination with AgMAR, we took 30-foot-long soil cores in 12 almond orchards, processing tomato fields and wine grape vineyards on low- and high-permeability soils, measured nitrate and total dissolved solids concentrations and calculated stored nitrate-N. Wine grape vineyards on permeable soils had the least nitrate leaching risk observed. However, almond orchards and tomato fields could be leveraged for AgMAR if dedicated recharge sites were established and clean surface water used for recharge. Historical land use, current nitrogen management and soil permeability class are the main factors to consider before implementing AgMAR
Experimental Dosing of Wetlands with Coagulants Removes Mercury from Surface Water and Decreases Mercury Bioaccumulation in Fish
Mercury
pollution is widespread globally, and strategies for managing
mercury contamination in aquatic environments are necessary. We tested
whether coagulation with metal-based salts could remove mercury from
wetland surface waters and decrease mercury bioaccumulation in fish.
In a complete randomized block design, we constructed nine experimental
wetlands in California’s Sacramento–San Joaquin Delta,
stocked them with mosquitofish (Gambusia affinis), and then continuously applied agricultural drainage water that
was either untreated (control), or treated with polyaluminum chloride
or ferric sulfate coagulants. Total mercury and methylmercury concentrations
in surface waters were decreased by 62% and 63% in polyaluminum chloride
treated wetlands and 50% and 76% in ferric sulfate treated wetlands
compared to control wetlands. Specifically, following coagulation,
mercury was transferred from the filtered fraction of water into the
particulate fraction of water which then settled within the wetland.
Mosquitofish mercury concentrations were decreased by 35% in ferric
sulfate treated wetlands compared to control wetlands. There was no
reduction in mosquitofish mercury concentrations within the polyaluminum
chloride treated wetlands, which may have been caused by production
of bioavailable methylmercury within those wetlands. Coagulation may
be an effective management strategy for reducing mercury contamination
within wetlands, but further studies should explore potential effects
on wetland ecosystems