Optimisation of Dairy Soiled Water as a Novel Duckweed Growth Medium

As a result of intensive agriculture, large quantities of liquid wastewaters are produced. Dairy soiled water (DSW) is produced in large volumes during the milking process of cattle. It comprises essential plant nutrients such as nitrogen, phosphorus, and potassium. The physicochemical properties of DSWs are highly variable as per individual farmer practices and seasonality. Currently, DSWs are disposed of primarily through land spreading, which frequently results in environmental pollution through land run-off. As a result of the large volumes produced coupled with the high variability, there are few alternative uses for DSWs, with presently little consideration of possible on-farm valorisation. Through a series of factorial experiments, the suitability of DSW as a novel duckweed (Lemna minor L.) cultivation medium is assessed. Different concentrations and pH values are assessed to determine the optimal conditions to support duckweed cultivation. Under the principles of circular economy, duckweed-based valorisation of DSWs can lead to the production of valuable, high-protein plant biomass that could be incorporated into animal feed to support livestock nutritional requirements. This study identifies the management of DSW’s pH as a key growth parameter in the successful cultivation of duckweed to underpin a circular economy approach for valorisation and improved environmental outcomes.