The approach—known as a Chemically Enhanced Treatment Wetland—combines chemical treatment with natural wetland processes; researchers tested it on Twitchell Island, which features corn and rice crops, as well as wetlands. They dosed agricultural ditch water with dissolved organic material (DOM), then treated it with a coagulant to precipitate the DOM, forming flocculant. The resulting water then passed though treatment wetlands, where the flocculant settled and blended with plant detritus in the sediment. The study, reported in the September 2019 San Francisco Estuary and Watershed Science, found that the combined system removed drinking water contaminants including dissolved organic carbon, disinfection byproduct precursors, and methylmercury. Another possible benefit is subsidence reversal: the researchers found that sediment and carbon accreted about four times faster in the study wetlands with chemical pre-treatment than in those without (about 6 vs 1.5 centimeters per year). Other benefits include cost-effectiveness, minimal negative impacts, and a relatively small footprint.”This is a pretty easy solution for treatment on an island-by-island basis,” says lead author Philip Bachand. “There’s a lot of natural infrastructure that we can leverage to improve water quality.” This combined treatment system has yet to be scaled up, but that could change as new laws kick in. “Water quality regulations ultimately drive new technologies and strategies,” Bachand says.

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Photo courtesy of Philip Bachand
 

A new system for treating agricultural drainage water in the Delta could also help rebuild subsided islands.

The approach—known as a Chemically Enhanced Treatment Wetland—combines chemical treatment with natural wetland processes; researchers tested it on Twitchell Island, which features corn and rice crops, as well as wetlands. They dosed agricultural ditch water with dissolved organic material (DOM), then treated it with a coagulant to precipitate the DOM, forming flocculant. The resulting water then passed though treatment wetlands, where the flocculant settled and blended with plant detritus in the sediment. The study, reported in the September 2019 San Francisco Estuary and Watershed Science, found that the combined system removed drinking water contaminants including dissolved organic carbon, disinfection byproduct precursors, and methylmercury. Another possible benefit is subsidence reversal: the researchers found that sediment and carbon accreted about four times faster in the study wetlands with chemical pre-treatment than in those without (about 6 vs 1.5 centimeters per year). Other benefits include cost-effectiveness, minimal negative impacts, and a relatively small footprint."This is a pretty easy solution for treatment on an island-by-island basis," says lead author Philip Bachand. "There's a lot of natural infrastructure that we can leverage to improve water quality." This combined treatment system has yet to be scaled up, but that could change as new laws kick in. "Water quality regulations ultimately drive new technologies and strategies," Bachand says.