Unravelling the impact of light, temperature and nutrient dynamics on duckweed growth

A meta-analysis study

Abstract

Nature-based solutions have been proven in recent decades as a reliable and cost-effective technology for the treatment of wastewater. They are widely used in several countries, mainly as secondary or tertiary biological treatment. Such systems rely on the ability of photosynthetic organisms to assimilate and remove, to a certain extent, nutrients valuable for their own growth. Different plant species have been studied for this purpose, but particular attention has been given to duckweeds, the smallest flowering plant in the world. These plants have been proven to be highly efficient for wastewater treatment given their rapid growth, natural abundance among macrophytes, and the quality of the biomass produced. However, despite being considered a seemingly simple technology, the performance of treatment systems based on duckweed is dependent on environmental and operational conditions not very well understood. While there have been many studies on growth of duckweed for wastewater treatment, the difference in species, systems, variables, scales and reporting units make it very difficult to draw comparisons across studies. This study employs a systematic review approach to conduct a meta-analysis of the effect of temperature, light, and nutrient availability on duckweed growth by means of standardized IQ-scores. The analysis of the results considered the duckweed species being used and the interaction between these parameters. The results suggest that daily light integral (DLI) is a useful parameter to assess the overall effect of light (photoperiod and intensity) on duckweed growth and that the effect of nitrogen and phosphorus supply should consider the nitrogen species available for plant growth and its ratio to phosphorus concentrations. By establishing the optimal range of culture conditions for duckweed, this study provides important insights for optimizing wastewater treatment systems that rely on duckweed for nutrient control and recovery, which is primarily mediated by duckweed growth.