Circular Economy in the Biosolids Management by Nexus Approach: A View to Enhancing Safe Nutrient Recycling-Pathogens, Metals, and Emerging Organic Pollutants Concern

Biosolids are a byproduct of sewage treatment that can create synergies and opportunity costs for promoting a circular economy and the nexus approach (water, energy, and food). They enable a cleaner agricultural production, with food safety in local development. The biosolids contain nutrients that can be recycled by agricultural soils. However, they contain heavy metals and few studies report the micropollutants present and the legal requirements of different countries (policies). The present study aimed to contribute to the knowledge of the composition and characteristics of biosolids during four years of monitoring (2016-2019). We investigated the agronomic potential of biosolids in a sequencing batch reactor. The content of biosolids in the crops studied is a potential source of macronutrients, especially N, P, and S. Pathogens fell into class B for Conama 498 (Brazil), Norm 503 (USA), and Directive 86/278 (EU) relative to Escherichia coli and enteric viruses. Metals, also compared with the three previous standards, fulfilled threshold concentrations of the respective legislations. Emerging organic pollutants remained below the detection limit, except naphthalene, which a single time was found in the biosolids above the detection limit. Finally, PCA showed that the chemical elements of the biosolids do not vary significantly relative to changes in tropical climatic conditions (resilience to climate change). Our study confirms the safe biosolids' agronomic potential in promoting a circular economy in wastewater treatment plants. In line with a cleaner agricultural production in tropical soils, complying with the legislation on micropollutants and reducing the quantity of biosolids sent to landfill, or inadequately disposed of in the environment.