Lemna, an aquatic plant to transform livestock farming residues into protein-rich biomass

  • Duckweed varieties able to absorb nutrients of animal manure wastewater and capable of producing high-quality biomass have been identified by CNB researchers
  • The duckweed Lemna is the basis for the first semi-industrial pilot plant in Europe recovering nutrients of porcine residues, enabling easy re-use in the area of origin
  • The project constitutes a perfect example of an application for a circular economy

Livestock farming and its impact

Livestock production is an economically important activity that significantly contributes to the diet of the population worldwide. However, particularly when it takes the form of intensive livestock farming, this activity has a significant impact on the environment, affecting water, air and soil quality, among other effects. As of the year 2015, livestock farming occupied close to 28 % of total European Landmass, or the equivalent to 65 % of the available agricultural land.

One of the main sources of environmental impact of livestock farming is the production of waste animal manure, which contains residues of organic origin such as animal urine and faeces, as well as other elements of animal origin, sometimes with a mixture of other organic residues including residual waters, vegetable harvest remnants, or others. Such mixtures, particularly in the case of pig livestock manure, can be very polluting. Research for the recycling and revalorisation of pig manure is ongoing.

Pig livestock farming has a strong impact in terms of residue generation, which need to be properly managed and disposed of
Pig livestock farming has a strong impact in terms of residue generation, which need to be properly managed and disposed of

On the challenges posed by high-scale livestock farming

A few years ago, Spain attained the first rank among the European countries by volume of porcine livestock, with over 28 million heads. Such a large population of pig livestock is hence linked to the generation of a high volume of residues in the form of porcine liquid manure. While a portion of these residues can be beneficial for agricultural use after appropriate treatment, amounts as large as those generated are well beyond what agriculture is capable of absorbing, hence they generate a large excess of such waste.

Large concentrations of livestock can have, on basis of the generated residues, a significant impact on the quality of water and the agricultural soil of a given area. The dumping of the excess liquid manure can give place to dire consequences for the soil and superficial waters, being cause to ecological and public health problems. The excess manure requires, as a result, of a suitable treatment according to the applicable law, a matter that can be economically taxing for livestock farmers.

The Lemna Life Project

To the possibility of treatment or use of pig liquid manure for the elaboration of compost adds now an alternative developed by the LIFE LEMNA Project, which is co-financed by the European programme LIFE. The initiative provides a new way to take advantage of these residues. A team of researchers of the National Centre for Biotechnology (CNB – CSIC) has identified a subaquatic plant capable of absorbing nutrients from livestock-derived residues. In what is an example of circular economy implementation, they found that the nutrients of those livestock-generated residues can be used efficiently to obtain, in turn, vegetable biomass by growing certain species of duckweeds, aquatic plants that can be used to feed livestock, closing the circle.

The plant is able to transform manure into a nutrient-rich biomass. The plant used, Lemna, is a small aquatic species with the capability of absorbing the nutrients directly from the water to grow at a very rapid rate. Lemna is the basis for the European project LIFE LEMNA, that spearheads the first semi-industrial pilot plant in Europe that allows to recover nutrients (nitrogen and phosphorus) from pig livestock residues, allowing to re-use them in the area of origin.

Close-up of Lemna growing on solid culture medium
Close-up of Lemna growing on solid culture medium

The industrial plant is located in Vila-sana (Lleida) and was launched together with the other project partners: the Valencian Agri-food Technological Institute AINIA (coordinator of the project), the company Ecobiogas and the livestock business Porgaporcs.

The benefits of Lemna for manure recycling

The duckweed is a floating small aquatic plant smaller than 1-cm with a circular shape and fast growth that has great capacity for absorbing nutrients from the water in which it develops. As explains Antonio Leyva, researcher at the CNB, “this plant is able, also, of producing biomass with a high nutritional value, which makes it a new source of high-quality protein”.

In the framework of this project, the CNB has created a collection of Lemna natural varieties from more than 40 different locations of the Iberian Peninsula, for which their capability for producing biomass and recovering nutrients has been tested. Carlos Alonso-Blanco, researcher of the CNB and participant in this project said: “the characterisation of more than 40 varieties does allow us to select the most adequate ones for their cultivation in various climatic regions”.

As explains Alfredo Rodrigo, engineer in environmental sciences from AINIA, in line with the Europa 2000 guidelines for environmental good practice and resource re-use, “this is a system that is a perfect example of circular economy, in which nutrients contained in pig liquid manure generated from farms are recovered by Lemna and later on, re-used either at the same farm or in nearby areas.”

Lemna growing in liquid medium. The protein richness of the produced biomass can climb as high as to 35-40%
Lemna growing in liquid medium. The protein richness of the produced biomass can climb as high as to 35-40%

In the framework of the project, the use of biofertilizers/biostimulants will be evaluated as a substitute to animal feed containing protein of other plant origins such as soya or rapeseed. Other applications that will be studied in further projects continuing on the steps of this one are the obtention of bioplastics, bio-based chemical products, among other new developments.

The results of the assays completed to date in the framework of the LIFE LEMNA project prove that, with an adequate selection of varieties of Lemna used, and with adequate plant growth management, biomass yields of over 17 tonnes of dry matter per hectare per year can be obtained, with a protein richness in the biomass of around 35-40 %. These data indicate a productivity of 7 tonnes of protein per hectare per year, which is a value 6-7 times higher than the productivity of soya, and almost three times higher than that of alfalfa.

Watch the LEMNA LIFE project video:

Lemna culture: technology to improve nutrient management and efficiency

Image credits:

Pig farm in Hungary picture by Imre Szodorai downloaded from Wikimedia Commons and licensed via a Creative Commons Attribution 3.0 Unported license (CC BY 3.0).

Pictures of Lemna in liquid and solid culture kindly provided by CNB and re-used with permission.