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United States Department of Agriculture

Agricultural Research Service

Research Project: Aquatic and Riparian Weed Management to Protect U.S. Water Resources in the Far West United States

Location: Exotic and Invasive Weeds Research

Title: Wastewater polishing by a channelized macrophyte-dominated wetland and anaerobic digestion of the harvested phytomass

Authors
item Cohen, Michael -
item Hare, Caden -
item Kozlowski, John -
item Mccormick, Rachael -
item Chen, Lily -
item Parish, Meghan -
item Schneider, Linden -
item Knight, Zane -
item Nelson, Timothy -
item Grewell, Brenda

Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 18, 2012
Publication Date: December 17, 2012
Citation: Cohen, M.J., Hare, C., Kozlowski, J., Mccormick, R.S., Chen, L., Parish, M., Schneider, L., Knight, Z., Nelson, T.A., Grewell, B.J. 2012. Wastewater polishing by a channelized macrophyte-dominated wetland and anaerobic digestion of the harvested phytomass. Journal of Environmental Science and Health. 48(3):319-330.

Interpretive Summary: The Environmental Protection Agency lists the Laguna de Santa Rosa watershed as an impaired waterway due to eutrophic levels of nutrients. These nutrient levels, in part, fuel the explosive growth of invasive aquatic weeds in the watershed. This innovative research project explored the utility of constructed wetlands for wastewater treatment to improve water quality in the Laguna de Santa Rosa. Algae, duckweeds (Lemna, spp.), floating mosquito fern (Azolla filiculoides), and marsh pennywort (Hydrocotyle ranunculoides), aquatic plants that are invasive and abundant in the Laguna de Santa Rosa, were added to secondary-treated wastewater in three-tiered channelized modules. Cessation of harvesting in one module resulted in a significant increase in nitrate removal efficiency and decrease in phosphate removal efficiency. Compared to the influent, the effluent of the harvested module had significantly lower levels of estrogenic activity, as determined by a juvenile trout bioassay, and significantly lower densities of E. coli. Incorporation of constructed wetlands into an integrated treatment system can simultaneously enhance the economic and energetic feasibility of wastewater and organic waste treatment processes. Modules that were regularly harvested averaged a nitrate removal efficiency of 1.1 g N m-2 d-1; harvesting, sedimentation and gasification were responsible for 30.5%, 8.0% and 61.5% of the N losses, respectively. Although regular harvesting of the modules did not increase, and in fact slightly decreased, nitrate removal efficiency, the benefits of modest phosphate removal and production of methane and soil amendment from harvested phytomass can help to offset wetland management costs. Moreover, integrating anaerobic digestion into a broad waste management scheme can simultaneously enhance the energetic and economic feasibility of several processes that generate organic wastes, including wastewater treatment, biodiesel production and agriculture.

Technical Abstract: : Constructed wetlands (CW) offer a mechanism to meet regulatory standards for wastewater treatment while minimizing energy inputs. To optimize CW wastewater polishing activities and investigate integration of CW with energy production from anaerobic digestion we constructed a pair of three-tier channelized modules fed with secondary-treated municipal wastewater and stocked with floating aquatic vegetation. Modules that were regularly harvested averaged a nitrate removal efficiency of 1.1 g N m-2 d-1; harvesting, sedimentation and gasification were responsible for 30.5%, 8.0% and 61.5% of the N losses, respectively. Selective harvesting of a module to maintain dominance of filamentous algae had no effect on nitrate removal efficiency but lowered productivity by one-half. The average monthly productivity for unselectively harvested modules was 9.3 ± 1.7 g DW m-2 d-1 (± SE). Cessation of harvesting in one module resulted in a significant increase in nitrate removal efficiency and decrease in phosphate removal efficiency. Compared to the influent, the effluent of the harvested module had significantly lower levels of estrogenic activity, as determined by a juvenile trout bioassay, and significantly lower densities of E. coli. Aquatic vegetation from the constructed wetlands, and Azolla and Uruguyan water primrose (Ludwigia hexapetala) harvested from invaded reaches of the Laguna de Santa Rosa were harvested for anaerobic digestion trials. Anaerobic co-digestion of a mixture containing equal dry weight proportions of harvested aquatic vegetation, wine lees and dairy manure was greatly improved when the manure was replaced with the crude glycerol byproduct of biodiesel manufacture. Remaining solids were composted for use as a soil amendment. Thus, incorporation of constructed wetlands into an integrated treatment system can simultaneously enhance the economic and energetic feasibility of wastewater and organic waste treatment processes. Modules that were regularly harvested averaged a nitrate removal efficiency of 1.1 g N m-2 d-1; harvesting, sedimentation and gasification were responsible for 30.5%, 8.0% and 61.5% of the N losses, respectively.

Last Modified: 10/30/2014
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