Cultivation of aquatic plants on cow manure digestate: A technical report

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Turning animal manure into energy generates a leftover product: digester bio slurry. Generally this bio slurry is separated in a solid and a liquid fraction. The use of the liquid fraction bio slurry (LFBS) in combination with residual heat and flu gas from the CHP unit could proof an interesting way to turning LFBS in to valuable biomass locally and thereby reducing the manure processing costs. The goal of the study described here is to assess the application opportunity of LFBS from a cattle manure co-digester in combination with aquatic biomass. In this study different aquatic plant types (submerged, floating and emerged) are used to observe there growth characteristics on different concentrations (1:50 an 1:100 dilutions) of LFBS. In addition to the aquatic plants soy plants are subjected to the same growth conditions to find out their response to a hydroponic culture using LFBS as sole fertilizer. The used plants (cattail, hornwort, water hyacinth and soy) generally grew well under the selected conditions. Unfortunately hornwort (submerged plant type) was overgrown by duckweed on the surface of the test setup, this might had led to lower biomass productions. Cattail, hornwort and soy were only tested in outside conditions. Water hyacinth was only tested in greenhouse conditions, first in a small scale setup (12 plastic boxes of 60x40 cm) followed by an upscaling step to a race way pond of 175 m2. While water hyacinth is notorious for its growth potential (potentially invasive in tropical and sub-tropical regions) in this study cattail showed higher specific biomass growth. Maximum projected dry matter biomass yields of 32.9 and 38.9 t/ha/year respectively. Soy beans were tested as an alternative to aquatic plants. Beans were directly sown in rockwool, which was used as rooting media floating in the bio slurry dilution. Remarkably the soy plants grew well and even developed beans, the projected yield was comparable to field yield. LFBS proofed to be a suitable nutrient source for the tested plants in an aquatic environment. Especially in countries, such as The Netherlands, where bio slurry and water is abundant, the cultivation of aquatic or terrestrial plants in a LFBS dilution could be an attractive alternative for soil bound agriculture.
Original languageEnglish
Place of PublicationLelystad
Number of pages26
Publication statusPublished - May 2017

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