Electrochemically assisted production of biogenic palladium nanoparticles for the catalytic removal of micropollutants in wastewater treatment plants effluent.

Biogenic palladium nanoparticles (bio-Pd NPs) are used for the reductive transformation and/or dehalogenation of persistent micropollutants. In this work, H2 (electron donor) was produced in situ by an electrochemical cell, permitting steered production of differently sized bio-Pd NPs. The catalytic activity was first assessed by the degradation of methyl orange. The NPs showing the highest catalytic activity were selected for the removal of micropollutants from secondary treated municipal wastewater. The synthesis at different H2 flow rates (0.310 L/hr or 0.646 L/hr) influenced the bio-Pd NPs size. The NPs produced over 6 hr at a low H2 flow rate had a larger size (D50 = 39.0 nm) than those produced in 3 hr at a high H2 flow rate (D50 = 23.2 nm). Removal of 92.1% and 44.3% of methyl orange was obtained after 30 min for the NPs with sizes of 39.0 nm and 23.2 nm, respectively. Bio-Pd NPs of 39.0 nm were used to treat micropollutants present in secondary treated municipal wastewater at concentrations ranging from µg/L to ng/L. Effective removal of 8 compounds was observed: ibuprofen (69.5%) < sulfamethoxazole (80.6%) < naproxen (81.4%) < furosemide (89.7%) < citalopram (91.7%) < diclofenac (91.9%) < atorvastatin (> 94.3%) < lorazepam (97.2%). Removal of fluorinated antibiotics occurred at > 90% efficiency. Overall, these data indicate that the size, and thus the catalytic activity of the NPs can be steered and that the removal of challenging micropollutants at environmentally relevant concentrations can be achieved through the use of bio-Pd NPs.

Microbial Electrochemically Assisted Treatment Wetlands: Current Flow Density as a Performance Indicator in Real-Scale Systems in Mediterranean and Northern European Locations.

A METland is an innovative treatment wetland (TW) that relies on the stimulation of electroactive bacteria (EAB) to enhance the degradation of pollutants. The METland is designed in a short-circuit mode (in the absence of an external circuit) using an electroconductive bed capable of accepting electrons from the microbial metabolism of pollutants. Although METlands are proven to be highly efficient in removing organic pollutants, the study of in situ EAB activity in full-scale systems is a challenge due to the absence of a two-electrode configuration. For the first time, four independent full-scale METland systems were tested for the removal of organic pollutants and nutrients, establishing a correlation with the electroactive response generated by the presence of EAB. The removal efficiency of the systems was enhanced by plants and mixed oxic-anoxic conditions, with an average removal of 56 g of chemical oxygen demand (COD) mbed material -3 day-1 and 2 g of total nitrogen (TN) mbed material -3 day-1 for Ørby 2 (partially saturated system). The estimated electron current density (J) provides evidence of the presence of EAB and its relationship with the removal of organic matter. The tested METland systems reached the max. values of 188.14 mA m-2 (planted system; IMDEA 1), 223.84 mA m-2 (non-planted system; IMDEA 2), 125.96 mA m-2 (full saturated system; Ørby 1), and 123.01 mA m-2 (partially saturated system; Ørby 2). These electron flow values were remarkable for systems that were not designed for energy harvesting and unequivocally show how electrons circulate even in the absence of a two-electrode system. The relation between organic load rate (OLR) at the inlet and coulombic efficiency (CE; %) showed a decreasing trend, with values ranging from 8.8 to 53% (OLR from 2.0 to 16.4 g COD m-2 day-1) for IMDEA systems and from 0.8 to 2.5% (OLR from 41.9 to 45.6 g COD m-2 day-1) for Ørby systems. This pattern denotes that the treatment of complex mixtures such as real wastewater with high and variable OLR should not necessarily result in high CE values. METland technology was validated as an innovative and efficient solution for treating wastewater for decentralized locations.

Assessing METland® Design and Performance Through LCA: Techno-Environmental Study With Multifunctional Unit Perspective.

Conventional wastewater treatment technologies are costly and energy demanding; such issues are especially remarkable when small communities have to clean up their pollutants. In response to these requirements, a new variety of nature-based solution, so-called METland®, has been recently develop by using concepts from Microbial Electrochemical Technologies (MET) to outperform classical constructed wetland regarding wastewater treatment. Thus, the current study evaluates two operation modes (aerobic and aerobic-anoxic) of a full-scale METland®, including a Life Cycle Assessment (LCA) conducted under a Net Environmental Balance perspective. Moreover, a combined technical and environmental analysis using a Net Eutrophication Balance (NEuB) focus concluded that the downflow (aerobic) mode achieved the highest removal rates for both organic pollutant and nitrogen, and it was revealed as the most environmentally friendly design. Actually, aerobic configuration outperformed anaero/aero-mixed mode in a fold-range from 9 to 30%. LCA was indeed recalculated under diverse Functional Units (FU) to determine the influence of each FU in the impacts. Furthermore, in comparison with constructed wetland, METland® showed a remarkable increase in wastewater treatment capacity per surface area (0.6 m2/pe) without using external energy. Specifically, these results suggest that aerobic-anoxic configuration could be more environmentally friendly under specific situations where high N removal is required. The removal rates achieved demonstrated a robust adaptation to influent variations, revealing a removal average of 92% of Biology Oxygen Demand (BOD), 90% of Total Suspended Solids (TSS), 40% of total nitrogen (TN), and 30% of total phosphorus (TP). Moreover, regarding the global warming category, the overall impact was 75% lower compared to other conventional treatments like activated sludge. In conclusion, the LCA revealed that METland® appears as ideal solution for rural areas, considering the low energy requirements and high efficiency to remove organic pollutants, nitrogen, and phosphates from urban wastewater.

Multi-Criteria Evaluation and Sensitivity Analysis for the Optimal Location of Constructed Wetlands (METland) at Oceanic and Mediterranean Areas.

METland is a new variety of Constructed Wetland (CW) for treating wastewater where gravel is replaced by a biocompatible electroconductive material to stimulate the metabolism of electroactive bacteria. The system requires a remarkably low land footprint (0.4 m2/pe) compared to conventional CW, due to the high pollutant removal rate exhibited by such microorganisms. In order to predict the optimal locations for METland, a methodology based on Multi-Criteria Evaluation (MCE) techniques applied to Geographical Information Systems (GIS) has been proposed. Seven criteria were evaluated and weighted in the context of Analytical Hierarchy Process (AHP). Finally, a Global Sensitivity Analysis (GSA) was performed using the Sobol method for resource optimization. The model was tested in two locations, oceanic and Mediterranean, to prove its feasibility in different geographical, demographic and climate conditions. The GSA revealed as conclusion the most influential factors in the model: (i) land use, (ii) distance to population centers, and (iii) distance to river beds. Interestingly, the model could predict best suitable locations by reducing the number of analyzed factors to just such three key factors (responsible for 78% of the output variance). The proposed methodology will help decision-making stakeholders in implementing nature-based solutions, including constructed wetlands, for treating wastewater in rural areas.