Skip to main content
ARS Home » Research » Publications at this Location » Publication #238497
Title: Scrubbing the Bay: Nutrient Removal Using Small Algal Turf Scrubbers on Chesapeake Bay Tributaries

Author
item Mulbry, Walter
item KANGAS, PATRICK - University Of Maryland
item Kondrad Ingram, Shannon

Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2009
Publication Date: 1/12/2010
Citation: Mulbry III, W.W., Kangas, P., Ingram, S.K. 2010. Scrubbing the Bay: Nutrient Removal Using Small Algal Turf Scrubbers on Chesapeake Bay Tributaries. Ecological Engineering. 36:536-541.

Interpretive Summary: Restoration of the Chesapeake Bay poses significant challenges because of increasing population pressure, conversion of farmland to urban/suburban development, and the expense of infrastructure needed to achieve significant and sustained nutrient reductions from agricultural and urban sources. One approach for removing non-point source nutrients before they reach the bay is to deploy large scale nutrient removal facilities along its tributaries. As a first step toward testing the feasibility of such an approach, this study determined rates of nutrient removal and algal fatty acid production using small algae-based nutrient treatment units (termed algal turf scrubbers (ATS)) located along three Chesapeake Bay rivers. These ATS units (each containing only 1 square meter of growing area) were operated for 5 to 9 months from May 2007 to April 2008 on three western shore tributaries of the Chesapeake Bay in Maryland: the Bush River, the Patapsco River and the Patuxent River. In the best case (Patuxent River site from May to October 2007), daily removal rates corresponded to removal rates of 380 kg N and 70 kg P per hectare over a 150 day season. These values are considerably lower than those from similar studies on agricultural drainage water in Florida. It is likely that nutrient removal rates will be higher in longer raceways and can be further improved but optimizing water flow rates. One potential use for the algae byproduct from such a process is as a feedstock for biodiesel production. However, the fatty acid (FA) or “algal oil” content of the harvested material (0.3 to 0.6% of dry weight) was very low compared to reported literature values for green algae and varied little between sites. Mean algal FA production rates were equivalent to annual rates of 35 to 80 kg FA per hectare based on a 150 day operational season in Maryland.

Technical Abstract: Restoration of the Chesapeake Bay poses significant challenges because of increasing population pressure, conversion of farmland to urban/suburban development, and the expense of infrastructure needed to achieve significant and sustained nutrient reductions from agricultural and urban sources. One approach for removing non-point source nutrients before they reach the bay is to deploy large scale algal turf scrubbers along its tributaries. The objective of this study was to determine rates of nutrient removal and algal fatty acid production using small ATS units located along three Chesapeake Bay rivers. Small-scale ATS units (each containing 1 square meter of growing area) were operated for 5 to 9 months from May 2007 to April 2008 on three western shore tributaries of the Chesapeake Bay in Maryland: the Bush River, the Patapsco River and the Patuxent River. There were significant seasonal differences in N and P removal rates and differences in these values between the three sites. Average total nitrogen (TN) and total phosphorus (TP) removal rates at the Patuxent site fluctuated considerably but averaged 250 mg TN, 45 mg TP per square meter-day from May to October 2007, then decreased to 16 mg TN, 3 mg TP per square meter-day from December 2007 to February 2008. Average nutrient removal rates at the Bush river site also fluctuated but averaged only 85 mg TN, 10 mg TP per square meter-day from May to June 2007, before decreasing to <10 mg TN, <1 mg TP per square meter-day from July to September 2007. The Patapsco River unit began operation in August 2007 and reached its maximum removal values of 150 mg TN, 18 mg TP per square meter-day from mid-Oct to late-Nov 2007, then decreased to values of 45 mg TN, 4 mg TP per square meter-day from Nov 15 2007 to mid-April 2008. In the best case (Patuxent site from May to October 2007), daily removal rates of 250 mg N and 45 mg P per square meter are equivalent to removal rates of 380 kg N and 70 kg P per hectare over a 150 day season in Maryland. Fatty acid (FA) content of the harvested material (0.3 to 0.6% of dry weight) was very low and varied little between sites. Mean algal FA production rates (23 to 54 mg FA per square meter-day) are equivalent to annual rates of 35 to 80 kg FA per hectare based on a 150 day operational season in Maryland.