Aquatic plant treatment system (APTS) based on duckweed for cleaning the liquid fraction of digestate

Composting plants combine compost and energy production using the Anaerobic Digestion (AD). However, the AD process generates residue whose liquid fraction is polluting and therefore needs to be subjected to expensive waste treatments with the loss of the value of the mineral elements. Therefore, it is necessary to develop technologies allowing the treatment of liquid digestate fraction and the uptake of those minerals as plant nutrients. The purpose of the project DUCK-TECH has been to provide a solution through an integrated biological system, i.e., an aquatic plant treatment system (APTS). An APTS for the liquid digestate fraction treatment has been implemented using duckweed Lemnaceae aquatic plant species, taking advantage of their ability to recover nitrogen and phosphorous and to reduce COD. The aim of this study is to evaluate the phytoremediation and environmental performances of the APTS based on duckweed. The preliminary results highlight that the environmental impact of liquid fraction treatment with APTS deeply ranges, depending on the duckweed growing. A further increase of the performances could be achieved through the valorisation of the duckweed biomass as a starch source for new bio-products.