Cultivation of Duckweed on Anaerobically Digested Dairy Manure for Nitrogen and Phosphorus Removal

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The purpose of this research included identifying the optimum cultivation conditions of five different strains of duckweed while evaluating the nutrient uptake of nitrogen (N) and phosphorus (P) in anaerobically digested dairy manure to promote biomass production.

What did we do?

The growth of duckweed was assessed on the cultivation parameters of temperature, pH, dissolved oxygen, light intensity, nutrient concentrations, and biomass production. Three strains, namely Landoltia punctata, Lemna gibba and Lemna minuta, were identified as the promising candidates for their high levels of nutrient uptake and biomass production. The temperature and light intensity were maintained in an environmental chamber at 25°C and 10,000 lux, respectively. The nutrient uptake through duckweed cultivation, characterized by the changes of total nitrogen (TN), total Kjeldahl nitrogen (TKN), and total phosphorus (TP), was assessed on the anaerobically digested dairy manure in three dilution ratios i.e., 1:13, 1:18, and 1:27 by volume.

What have we learned?

In the dilution ratios 1:18 and 1:27 all duckweed strains grew successfully. However, in dilution ratio 1:13 all three duckweed species were inhibited by the high nutrient concentration. The batch system created an aerobic environment within the anaerobically digested dairy manure medium with a dissolved oxygen content of 2-6 mg/L. At the high light intensity of 10,000 (lux) a buffer was needed in order to keep the medium’s pH constant to promote duckweed growth. This research compared the nutrient reduction of the microbial growth within the anaerobically digested dairy manure and a standard solution of 1.6 g/L of Hoagland E-medium to the nutrient reduction from the three strains of duckweed at the dilution ratios of 1:13, 1:18, and 1:27. Experimental results revealed that the average duckweed productivities were 1.50, 1.30 and 0.50 grams per square foot per day for Landoltia punctata, Lemna gibba, and Lemna minuta, respectively. At the dilution ratio of 1:27 the highest significant reductions came from Landoltia punctata at 86.0% for TN, 87.5% for TKN, and a TP of 89.5%. At the dilution ratio of 1:18 Lemna gibba got the next highest at 83.8% for TN, 85.6% for TKN, and a TP of 76.2%. Lemna minuta came in last with the highest nutrient reductions in dilution ratio 1:18 with 83.1% for TN, 84.7% for TKN, and a TP of 76.5%. A light intensity of 10,000 lux, pH of 6.5, a temperature of 25°C and a dilution ratio of 1:27 promoted active duckweed growth on anaerobically digested dairy manure.

Future Plans

We will continue the duckweed cultivation work to optimize manure nutrient uptake and to convert duckweed biomass into bioethanol.

Corresponding author, title, and affiliation

Lide Chen, Assistant Professor/Waste Management Engineer, University of Idaho

Corresponding author email

Other authors

Kevin Kruger (University of Idaho)

Additional information

Kevin Kruger is a graduate student who conducted the duckweed cultivation tests.


This work is supported by the USDA NIFA and Idaho Agricultural Experiment Station.

How Can Algae Be Used to Manage Nutrients in Pig Manure?

green stylized pig logoUsually when people see the words “algae” and “manure” in the same paragraph, it is usually a negative take on the effects of manure nutrients on water. When excess nutrients are transported to water bodies (from lawn fertilizer, municipal waste treatment plants, manure and/or commercial crop fertilizer) algae use those nutrients and grow rapidly. When the nutrients are no longer sufficient for growth, the algae begins to die and decompose. This depletes oxygen in the water, which can lead to fish kills and other problems for aquatic life.

The same characteristics of algae that can make it a nuisance also make it an innovative way to treat wastewater when grown in an engineered system. The fact that the algae are able to utilize the nutrients within the water to multiply and grow rapidly can be exploited within a managed system to create a potential source of biomass, and serve as a biological mechanism to remove nutrients. The sustained biological activity of algae can also add dissolved oxygen to the water, potentially reducing the direct emissions of methane and nitrous oxide (greenhouse gases) from volatilization of stored manure. Current research is exploring the use of harvested algae as an animal feed, source of biofuel (algal oil production), or biomass in thermal energy production.

For more information:

Author: Rick Field, University of Arkansas and Jill Heemstra, University of Nebraska


This information is part of the program “Integrated Resource Management Tool to Mitigate the Carbon Footprint of Swine Produced In the U.S.,” and is supported by Agriculture and Food Research Initiative Competitive Grant no. 2011-68002-30208 from the USDA National Institute of Food and Agriculture. Project website.

The Farm Manure to Energy Initiative: Using Excess Manure to Generate Farm Income in the Chesapeake’s Phosphorus Hotspots

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Currently, all the Bay states are working to achieve nutrient reduction goals from various pollution sources.  Significant reductions in phosphorus pollution from agriculture, particularly with respect to phosphorus losses from land application of manure are needed to support a healthy aquatic ecosystem.  Producers in high-density animal agricultural production areas such as Lancaster County region of Pennsylvania, the Delmarva Peninsula, and the Shenandoah Valley region of Virginia, need viable alternatives to local land application in order to meet nutrient reduction goals.

Field demonstrations will be monitored to determine whether the technologies are environmental beneficial, and economically and technically feasible. Specific measures of performance include: reliability and heat distribution, in-house air quality, avoided propane or electricity use, costs to install and maintain, fertilizer and economic value of ash or biochar produced, air emissions, and fate of poultry litter nutrients. Technology evaluation results will be shared on a clearinghouse website developed in partnership with eXtension.

The Farm Manure to Energy Initiative is also supporting efforts to develop markets for nutrient rich ash and biochar co-products. Field trials using nutrient rich ash and biochar from poultry litter thermochemical processes for fresh market vegetable production are currently underway at Virginia Tech’s Eastern Shore Agricultural Research and Experiment Station.


The Farm Manure to Energy Initiative is a collaborative effort to evaluate the technical, environmental, and economic feasibility of farm-scale manure to energy technologies in an effort to expand management and revenue-generating opportunities for excess manure nutrients in concentrated animal production regions of the Chesapeake Bay watershed.

What Did We Do?

The project team went through a comprehensive review process and identified three farm-scale, manure to energy technologies that we think have the potential to generate new revenue streams and provide alternatives to local land application of excess manure nutrients.  Installation and performance evaluation of two of these technologies on four host farms in the Chesapeake Bay region are underway. Partners have also completed a survey of financing options for farm-scale technology deployment and published a comprehensive financing resources guide for farmers in the Chesapeake Bay region.

What Have We Learned?

To date, we have not identified any manure to energy technologies that also provide alternatives to local land application of excess manure nutrients for liquid manures.  Thermochemical manure to energy technologies using poultry litter as a fuel source seem to show the most promise for offering opportunities to export excess nutrients from phosphorus hotspots in the Chesapeake Bay region. Producing heat for poultry houses is the most readily available energy capture option.  We did not identify any vendors with a proven approach to producing electricity via farm-scale, thermochemical manure to energy technologies. With respect to the fate of poultry litter nutrients, preliminary air emissions data indicates that most poultry litter nitrogen (greater than 98%) is converted to non-reactive nitrogen in the thermochemical process. Phosphorus and potash are preserved in the ash or biochar coproducts. Preliminary field trial results indicate that phosphorus in ash and biochar is bioavailable and can be used as a replacement for commercial phosphorus fertilizer, but bioavailability varied according to the thermochemical process.

Future Plans

We are currenty in the process of installing and measuring the performance of farm-scale demonstrations in the Chesapeake Bay region.  We are collaborating with the Livestock and Poultry Environmental Learning Center to develop a clearinghouse website for thermochemical farm-scale manure to energy technologies that will be hosted on the eXtension website.  Performance data from our projects will be shared on this website, which can also be used as a platform to share information about the performance of other farm-scale, thermochemical technology installations around the U.S. Technical training events using farm demonstrations as an educational platform will be hosted during the later half of the project. Additional field and row crop trials to demonstrate the fertilizer value of the concentrated nutrient coproducts are also planned using ash from farm demonstrations.


Jane Corson-Lassiter, USDA NRCS,; Kristen Hughes Evans, Executive Director, Sustainable Chesapeake

Additional partners in the Farm Manure to Energy Initiative include: Farm Pilot Project Coordination, Inc., University of Maryland Center for Environmental Studies, University of Maryland Environmental Finance Center, Virginia Cooperative Extension, Lancaster County Conservation District, the Virginia Tech Eastern Shore Agricultural Research and Extension Center, National Fish and Wildlife Foundation, Chesapeake Bay Funders Network, Chesapeake Bay Commission, and International Biochar Institute.

Additional Information


Funding for this project is provided by a grant from the USDA Conservation Innovation Grant program, the National Fish and Wildlife Foundation via the U.S. EPA Innovative Nutrient and Sediment Reduction Program, the Chesapeake Bay Funders Network, as well as technology vendors and host farmers participating in the technology demonstrations.


The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2013. Title of presentation. Waste to Worth: Spreading Science and Solutions. Denver, CO. April 1-5, 2013. URL of this page. Accessed on: today’s date.