Use of native microalgae grown in anaerobically digested sanitary sewage as a biofertilizer in Amaranthus cruentus L. plants

Abstract

Due to population growth, tons of wastewater are generated annually. Currently, most of the sanitation systems used do not take into account the cycle of nutrients, energy and water in a sustainable way, causing waste of substances and emissions of polluting residual loads in the environment. Therefore, new models and tools must be created and tested in order to reduce the waste of resources so precious and still useful. The wastewater is rich in mineral nutrients which could be recovered and used as fertilizers for crops. As an example of wasted minerals, we can mention the phosphorus and nitrogen that are present in the wastewater in large quantities. Microalgae appear as an important option to recover these nutrients lost in the current sewage treatment systems, contributing to the reduction of greenhouse gas emissions through photosynthesis, in addition to recovering mineral nutrients, converting them into algal biomass. In addition to being useful for the recovery of nutrients from sewage, microalgae have a biomass that contains high concentrations of proteins, lipids, vitamins, nitrogen and phosphorus, which are essential elements for plant development. Thus, the objective of this project is to evaluate the feasibility of using microalgae grown in wastewater as biofertilizers in the growth of Amaranthus cruentus L., a plant of economic interest. Specifically, gas exchange, photosynthetic pigments, biomass production in the aerial part and leaf mineral content will be analysed. In this way, it is expected to give a destination to the recovered nutrients, making it possible to close the nutrient cycle, contributing to a circular economy.