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Duckweed Research and Applications for the Circular Bioeconomy in Ireland

In Ireland, interest in duckweed research and applications has steadily grown over the years. However, research and development efforts are somewhat scattered, with sometimes a lack of joined-up thinking. To bring key stakeholders together, as well as to bring in best international expertise, a one-day workshop on “Duckweed Research and Applications for the Circular Bioeconomy in Ireland” was organised in University College Cork (UCC) in the south of Ireland on the 9th of June 2023.

The interest in duckweed research and applications is in Ireland mostly driven by a strong focus on the transition to a more circular bioeconomy; an economy where waste is used as a resource. Consequently, the workshop had a strong emphasis on the use of duckweed (Lemnaceae spp.) as a tool for wastewater remediation and valorisation, the latter particularly in the form of protein. As detailed by Prof. Marcel Jansen of the ERI and School of BEES in his opening address, evolving laboratory-based duckweed research into real, commercial applications requires close and reciprocal interactions between different actors, such as entrepreneurs, policymakers, and researchers. In his welcome, Prof. Brian Ó Gallachóir, ERI Director and Associate Vice-President of sustainability at UCC, specifically focused on the importance of research impacting policy. The close link with policy was further emphasised by Patrick Barrett from the Department of Agriculture, Food and the Marine, who highlighted the development of, and strong support for, the Irish bioeconomy, with a focus on systemic thinking and innovation, development of skills, novel sources of biomass, novel processing of biological resources and zero waste. In his talk, duckweed research and applications were clearly indicated as a promising area that is closely aligned with the national bioeconomy agenda. Given the close link between Irish and European Union bioeconomy policies, this bodes well for duckweed research and applications throughout Europe.

A particular strength of duckweed research is the strong knowledge base that has been accrued over the last half century. Prof. Klaus Appenroth (Jena), in his plenary talk analysed the challenges of growing duckweed outdoors on sub-optimal media, outdoors outside the natural growing season, and indoors in an artificial climate. Prof. Appenroth flagged several key knowledge gaps, among others our relatively limited knowledge of duckweed pests and diseases. In a second plenary, Prof. Laura Morello (Milan) placed emphasis on duckweed biodiversity, taking the audience from Carl Linnaeus to Elias Landolt. Prof. Morello reported on the emerging awareness of “promiscuous duckweeds” with a range of hybrids occurring in the natural environment. This on the one hand complicates identification of strains, but on the other hand potentially results in new opportunities for applications as indicated by the high protein content of some polyploid strains. Dr Viktor Oláh (Debrecen) further explored the concept of biodiversity, reporting that some, but not all, mixed cultures of two species displayed substantially faster growth compared to corresponding monocultures.

Dr Vlastimil Stejskal (České Budějovice) reported on the use of duckweed in an Integrated MultiTrophic Aquaculture fish farm in Ireland. Dr Stejskal reported that one hectare of duckweed was able to remediate water fouled by 30 tonnes of rainbow trout and perch. Dr Niall O’Leary of the ERI and School of Microbiology reported on a cascading approach to remediate and valorise dairy processing waste. Microbial bioreactors were used to convert organic content of the wastewater into polyhydroxyalkanoates, after which duckweed could be used to valorise effluents rich in nitrogen and phosphorus. Dr Neil Coughlan of the ERI and the School of BEES reported how stacked (multi-layered) duckweed incubators can be used to remediate such effluents, although optimisation of remediation requires careful consideration of operational parameters such as flow rate. Dr Gruffydd Lloyd-Jones (Aberystwyth) reported on the valorisation of farm wastewater, emphasising the potential toxicity of ammonia, and the importance of pH management (i.e. lowering) to enable duckweed growth. Dr Lloyd-Jones presented the difficult dilemma of having to dilute wastewater in order to grow duckweed, whilst farmers are already struggling with large waste volumes. A lively discussion followed whereby the opportunity to add full strength farm wastewater into cascading ponds was flagged as a potential solution. Dr Reindert Devlamynck (Flanders) reported on the operation of a cascading duckweed system in Flanders, Belgium. Dr Devlamynck reported on the issue of the unequal removal of phosphorus and nitrogen, which may hinder release of “cleaned” wastewater to local surface waters. Dr Devlamynck also reported on the problem of gradual potassium accumulation, with the resulting increase in osmolarity impeding duckweed growth. Meritxell Abril Cuevas (Barcelona) reported on new trials involving culturing of duckweed, as well as halophytes (Salicornia sp.) to manage salinity issues when using swine wastewater.

Abril Cuevas also reported on plans to use duckweed biomass as a crop fertiliser. Following a lively debate, it was agreed that this is a very interesting idea since the duckweed is likely to act as a relatively slow-release fertiliser, while also adding organic matter to the soil. Prof. Brijesh Tiwari (Dublin) reported on a different approach to use duckweed biomass: the extraction of protein using a variety of clean technologies. Emphasis was on reduced negative impacts of the protein extraction process, for example by using different solvents and energy efficient processes. The ultimate aim of Prof. Tiwari’s group is to develop an innovative biorefinery process whereby consecutive extractions of valuable duckweed ingredients result in the complete use of the biomass. This contrasts with the approach taken by Priya Pollard who reported on how traditional ensiling processes can be used to preserve duckweed as, for example, an animal feed.

Several representatives of the business sector were involved in the workshop, and heavily engaged in discussions. Dr Paul Fourounjian (San Diego) gave a short overview of the United States duckweed industry, reporting GRAS (Generally Recognised as Safe) status of duckweed, as well as FDA (US Food and Drug Administration) approval for the use of duckweed protein in a range of food products. Dr Fourounjian reported on the exciting development of the company Plantible Foods, after which an interesting discussion arose about the (non-)compatibility of wastewater remediation and food applications.

The workshop was a substantial success, judging by the quality of the presentations, and especially the discussions and networking between delegates. In fact, when the idea for a workshop was initially conceived, the expectation was that some 20 delegates would register to attend. In reality almost 50 delegates registered, at which stage registration had to be stopped because of capacity issues. Attendees included a good mixture of local and international delegates, entrepreneurs, stakeholders and academics, as well as basic and applied researchers. It is clear that duckweed research and applications are widely perceived as being relevant for the development of a circular (bio-)economy. It is expected that the workshop on Duckweed Research and Applications has further boosted the field by highlighting opportunities, identifying knowledge gaps for further research, and above all by facilitating the creation of collaborative networks between participants.

The workshop was supported by the ERI Duck-Feed project (DAFM 2021R487), EPA Event Support (2023-ES-1181) and ERI Brainwaves project (funded by the ERDF through the IW Cooperation Programme).