Laboratory scale aerobic bioreactor conditioning of dairy processing wastewater as feedstock for Lemna minor production

Dairy processing wastewater is a nutrient-rich resource, containing chemical oxygen demand (COD) ranging from 1,150 – 68,814 mg/L, nitrogen (N) from 14 – 1,462 mg/L and phosphorus (P) from 7.2 – 650 mg/L, depending on the product stream. This resource has potential to be utilised for cultivation of Lemna minor as a value-added product, in line with EU circular economy principles. The purpose of this project was to condition dairy processing wastewater for downstream application as growth media for Lemna minor. Effluent from both systems were tested for nutrient removal, and IASBR effluent was more suitable for the coupled system, with removal efficiencies of >90% COD, 4 – 94% NH4+ and 30 – 80% P respectively. The coupled system yielded poor nutrient removal and little to no plant growth, with plants reaching senescence by day 28 of the trial. It can be concluded that Lemna minor cultivation failed as a result of both A/O and IASBR operational issues (including starting pH) and insufficient seeding of cultivation tanks. It is therefore recommended to focus future studies on the suitability of anaerobic treatment technologies for conditioning of dairy processing wastewater for Lemna minor cultivation. Future work with coupled wastewater treatment/duckweed cultivation systems should also involve investigation into plant-symbiont interactions, as well as profiling of wastewater microbial communities and their potential impacts on duckweed growth