Duckweed from a Biorefinery System: Nutrient Recovery Efficiency and Forage Value

Abstract

This paper presents the results of an interdisciplinary study aimed at assessing the possibility of using duckweed to purify and recover nutrients from the effluent remaining after struvite precipitation and ammonia stripping from a liquid fraction of anaerobic digestate in a biorefinery located at a Dutch dairy cattle production farm. The nutritional value of duckweed obtained in a biorefinery was assessed as well. Duckweed (Lemna minuta) was cultured on a growth medium with various concentrations of effluent from a biorefinery (EFL) and digested slurry (DS) not subjected to the nutrient recovery process. The study’s results showed that duckweed culture on the media with high contents of DS or EFL was impossible because they both inhibited its growth. After 15 days of culture, the highest duckweed yield was obtained from the ponds with DS or EFL contents in the medium reaching 0.39% (37.8 g fresh matter (FM) and 16.8 g FM per 8500 mL of the growth medium, respectively). The recovery of N by duckweed was approximately 75% and 81%, whereas that of P was approximately 45% and 55% of the growth media with EFL0.39% and DS0.39%, respectively. Duckweed obtained from the biorefinery proved to be a valuable high-protein feedstuff with high contents of α-tocopherol and carotenoids. With a protein content in duckweed approximating 35.4–36.1%, it is possible to obtain 2–4 t of protein per 1 ha from EFL0.39% and DS0.39% ponds, respectively.

Quantitative and Qualitative Traits of Duckweed (Lemna minor) Produced on Growth Media with Pig Slurry

“…In the present study, the protein content of the duckweed produced was higher or comparable to the results reported by the aforementioned authors [49]. Our previous study [11] showed that biogas plant effluent could also serve as a good medium for the growth of duckweed (L. minuta) and allowed us to conclude that the installation used would enable the recovery of valuable fertilizing materials (struvite and ammonia) and the production of high-quality animal feed on the leachate. Compared to our previous study [11], the present research results indicate a comparable or higher content of protein, fat, fiber, and ash in the produced plant material-duckweed.…”

“…In the present study, the course of duckweed growth observed in Groups 2-5 was deemed appropriate. Our previous study [11] with effluent from a biorefinery demonstrated that its small addition (0.39%, 0.60%, and 0.78% concentration in the growth media) had a positive effect on the growth of duckweed (Lemna minuta). Stadtlander et al [39] drew a similar conclusion from their study with bovine slurry, wherein a decreasing concentration of the natural fertilizer promoted higher yields of duckweed (Spirodela polyrhiza and Lemna punctata) fresh mass.…”

“…As part of the recovery of fertilizing substrates from various growth media, aquatic plants can be used for the treatment of various types of wastewater [10][11][12]. Duckweed has been found to be important in sustainable production and has spurred social interest due to its unique morphological characteristics and phytoremediating potential.…”

Aquatic biomass as sustainable feedstock for biorefineries

“…78 The duckweed was subsequently used for the production of high-quality feedstuff for animals. 78 This approach not only uses resources in a circular approach but also allows for the effective recovery of minerals from these effluents. Duckweed was pre-treated by autoclaving at 121 °C for 20 min.…”

“…76 Another study demonstrated the use of duckweed to purify and recover nutrients from an effluent obtained after struvite precipitation and ammonia stripping from the liquid fraction of anaerobic digestate. 78 The duckweed was subsequently used for the production of high-quality feedstuff for animals. 78 This approach not only uses resources in a circular approach but also allows for the effective recovery of minerals from these effluents.…”