The development of analytical techniques and methods to characterise TE content and speciation in high microbial density environments (e.g. biological reactors, digestate, biological sludges) has been one of the main objectives of this program. One of the main challenges is the assessment of the bioavailable TE fraction. The diffusive gradient in thin-film (DGT) technique has been selected as the most promising one. The applicability and the robustness of the DGT technique have been investigated in complex matrices of digestates by ESR1. Deployment strategies were optimized for digestates samples from an anaerobic digestor. The relevance of DGT to assess the bioavailability of TE to anaerobic digestion biomass has been further investigated by ESR2, mainly through the evaluation of correlations between dissolved or labile fractions with biological responses. For this purpose, lab-sale bioreactors were used to follow simultaneously the DGT-labile fraction and the evolution of different microbial responses. ESR6 focused on the effect of TE on microbial community structure and activity in anaerobic sludge granules. ESR 8 focused on the effect of TM on the microbial community structure and activity of anaerobic digesters, working at the scale of complex communities and laboratory-scale bioreactors, predominantly. ESR9 explored the feasibility of integrating methane production with the selective recovery of Nickel (Ni) and Cobalt (Co) through anaerobic digestion (AD) technology. ESR11 developed a mathematical model to represent an appropriate tool to provide basic information on the mechanisms regulating biofilm growth and development. A further mathematical model was developed by ESR11 to describe the horizontal gene transfer through conjugation, focusing on the study of the influence of metal selective pressure on conjugative plasmid spread. ESR4 focused on the mathematical modelling of the role and dynamics of TEs in biofilm communities. A mathematical model was developed to investigate the influence of metals on biofilm attachment. Such model simulates the establishment and growth of a drinking water distribution system biofilm, focusing on the influence of ionic strength on bacterial adhesion and persistence of Legionella pneumophila. In addition, a new model was developed by ESR7 to simulate metal precipitation of trace metals within multispecies biofilms. The mathematical model accounts for the metal precipitation process and the effect of precipitates accumulation on the porosity of the multispecies biofilm system. A comprehensive multiscale mathematical model able to describe the biosorption of heavy/trace metals by multispecies biofilms in porous media was also developed by ESR7. The model was designed to accommodate the complex interplay of biological and hydrological processes across multiple scales. ESR10 proposed a complete trace metal speciation model for application in anaerobic digesters. The model presented has incorporated major trace metal speciation processes like complexation (with inorganic species, chelates, metabolites) and adsorption (on biomass, soluble inerts, precipitates) along with TM precipitation (with sulphides, carbonates, phosphates), biouptake, dose response and TM release during disintegration process. Data collected from anaerobic digestor in a full-scale wastewater treatment plant at EMASESA, one of the non-academic associated partners, was used for model application. ESR12 developed an integrated system for valorizing organic waste, focusing on metals recovery and the production of a safe digestate for agricultural reuse. The approach combined anaerobic bioleaching with microbial-induced carbonate precipitation (MICP) to efficiently recover valuable metals. Additionally, constructed wetlands (CWs) were employed to treat the resulting effluent, ensuring its suitability for irrigation and assessing its impact on microbial communities in soil and crops. ESR13 Investigated the soil physico-chemical characteristics effect, and organic micropollutants presence, on soil metal speciation after soil amendment with metal contaminated waste and impact on soil microbial communities. ESR14 evaluated the potential of constructed wetlands (CWs) to recover/remove metals from wastewater/digestate. ESR15 investigated the potential of phytoremediation to remove/recover metals from wastewater/ digestate, and to prevent metal toxicity in receiving soils.
