Water treatment and reclamation by implementing electrochemical systems with constructed wetlands

Simultaneous pollutant removal and organic matter sequestration by coral sand-pyrite-based electroactive constructed wetlands

The development of integrated solutions for sewage treatment and soil restoration in remote regions remains a challenge. This study innovatively designed coral sand-pyrite-based electroactive constructed wetlands (E-CWs) to synchronize wastewater purification and organic matter (OM) enrichment. Metagenomic analyses revealed that the addition of pyrite increased the abundance of iron redox-related genes, whereas coral sand salinity promoted the enrichment of functional bacteria for OM decomposition. Furthermore, the combined substrate comprising coral sand and pyrite facilitated the adsorption and sequestration of OM, while providing a stable environment for microorganisms. This achieved dual objectives: efficient chemical oxygen demand removal (90.6 ± 2.4 %) from sewage and substantial OM sequestration in substrates (total organic carbon: 2.9-4.8 %). This study achieved sewage treatment through the combination of coral sand and pyrite as substrates of E-CWs and enhanced the OM content of the substrates, contributing to the improvement of local soil infertility.

Enhanced removal of chiral emerging contaminants by an electroactive biofilter

50% of pharmaceuticals and 25% of herbicides used worldwide are chiral. Each enantiomer has a unique toxicity and biodegradation profile, affecting differently to organisms. Chirality plays a key role in the behavior of these emerging contaminants (ECs) in terms of their pharmacological or herbicidal activity, but this peculiarity is often overlooked in environmental research. The complexity of chiral ECs is underestimated, as the varying sensitivity of biological systems to enantiomers is rarely considered. Biofilters can promote the activity of specific microbial communities, facilitating the degradation of ECs, due to the greater interaction between water and microorganisms and their compact design. Here, we show that an electroactive biofilter can alter the chirality of drugs and herbicides in wastewater treatment, impacting their removal and toxicity. The electrochemical biofilter (BioeF) removed 80% of pharmaceuticals and 50-75% of herbicides, outperforming the conventional filter (ConF). BioeF also showed greater chiral alterations and lower ecotoxicity. This work provides the first evidence of a relationship between changes in contaminant chirality and detoxification capacity, enhanced by electroactive systems. The increased microbial activity observed in the BioeF suggests that bioelectrochemical systems offer a valuable advance for ECs removal and ecotoxicity reduction, addressing the environmental challenge posed by ECs.

Microbial fuel cells to monitor natural attenuation around groundwater plumes

This research presents a straightforward and economically efficient design for a microbial fuel cell (MFC) that can be conveniently integrated into a borehole to monitor natural attenuation in groundwater. The design employs conventional, transparent, and reusable PVC bailers with graphite tape and granular activated carbon to create high surface area electrodes. These electrodes are connected across redox environments in nested boreholes through a wire and variable resistor setup. The amended electrodes were installed in pre-existing boreholes surrounding a groundwater plume near a former gasworks facility. Among all the MFC locations tested, the MFC at the plume fringe exhibited the highest electrical response and displayed significant variations in the differential abundance of key bacterial and archaeal taxa between the anode and cathode electrodes. The other MFC configurations in the plume center and uncontaminated groundwater showed little to no electrical response, suggesting minimal microbial activity. This straightforward approach enables informed decision-making regarding effectively monitoring, enhancing, or designing degradation strategies for groundwater plumes. It offers a valuable tool for understanding and managing contaminant degradation in such environments.

Comparing the performance of microbial electrochemical assisted and aerated treatment wetlands in pilot-scale: Removal of major pollutants and organic micropollutants

The combination of treatment wetlands (TWs) with microbial electrochemical technologies (MET) is often studied in the lab to improve the performance and decrease the footprint of TWs. In this article we evaluated the long-term performance of four pilot-scale vertical sub-surface flow TWs for major pollutants' and organic micropollutants' removal from domestic wastewater. Three of them were filled with electroconductive material and operated under saturated (MET SAT), unsaturated (MET UNSAT) and unsaturated-saturated (MET HYBRID) conditions while the fourth one was a saturated intensified aerated system (AEW) filled with gravel. The MET-TWs achieved significant removals of COD (>78 %) with no clogging issues at the maximum applied OLR (249 g COD m-3 d-1) while under these loading conditions TSS removal exceeded 84 %. Among all electroactive TWs, UNSAT could remove 25 g NH4-N m-3 d-1 through nitrification when peak ammonium loading rate was applied; however this removal was significantly lower than AEW (35 g NH4-N m-3d-1). No important removal of P was observed in all systems with the exception of MET-SAT were precipitation reactions of P with iron occurred when anaerobic pretreated wastewater was used. The removal of the sum of studied organic micropollutants ranged between 70 ± 18 % (MET UNSAT) to 91 ± 4 % (AEW) and improved with feeding pulses increase. Moderate to high removal of specific microcontaminants was observed depending on the target compound, the studied system and the operational conditions. AEW and MET HYBRID systems complied with the limits set by EU for wastewater discharge to non-sensitive water bodies and for Class B water reuse. Scale-up calculations for a settlement of 500 PE showed that these systems require much less area per PE (0.51 m2 PE-1) comparing to conventional TWs while the operational cost was calculated to 0.07 € m-3 for the AEW and 0.02 € m-3 for the MET HYBRID.

Electroactive biofilters outperform inert biofilters for treating surfactant-polluted wastewater by means of selecting a low-growth yield microbial community

Electrobioremediation is one of the most innovative disciplines for treating organic pollutants and it is based on the ability of electroactive bacteria to exchange electrons with electroconductive materials. Electroactive biofilters have been demonstrated to be efficient for treating urban wastewater with a low footprint; however, their application can be expanded for treating industrial wastewater containing significant concentrations (2.4 %vol) of commercial surfactants (containing lauryl sulfate, lauryl ether sulfate, cocamydopropyl betaine, and dodecylbenzene sulfonate, among others). Our electroactive biofilter outperformed a conventional inert biofilter made of gravel for all tested conditions, reaching removal rates as high as 4.5 kg COD/m3bed·day and withstood Organic Loading Rates as high as 9 Kg COD/m3·d without significantly affecting removal efficiency. The biomass accumulation reduced available bed volume in the electroactive biofilter just by 39 %, while the gravel biofilter decreased by 80 %. Regarding microbial communities, anaerobic and electroactive bacteria represented a substantial proportion of the total population in the electroactive biofilter. Pseudomonas was the dominant genus, while Cupriavidus, Shewanella, Citrobacter, Desulfovibrio, and Arcobacter were potential electroactive strains found in relevant proportions. The microbial community's composition might be the key to understanding how high removal rates can coexist with limited biomass production, making electroactive biofilters a promising strategy to overcome classical biofilter limitations.

Nature-based solutions for antibiotics and antimicrobial resistance removal in tertiary wastewater treatment: Microbiological composition and risk assessment

This field-scale study evaluates the seasonal effectiveness of employing nature-based solutions (NBSs), particularly surface flow and horizontal subsurface flow constructed wetland configurations, as tertiary treatment technologies for the removal of antibiotics (ABs) and antibiotic resistance genes (ARGs) compared to a conventional treatment involving UV and chlorination. Out of the 21 monitored ABs, 13 were detected in the influent of three tertiary wastewater treatments, with concentrations ranging from 2 to 1218 ng·L-1. The ARGs sul1 and dfrA1 exhibited concentrations ranging from 1 × 105 to 9 × 106 copies/100 mL. NBSs were better at reducing ABs (average 69 to 88 %) and ARGs (2-3 log units) compared to the conventional tertiary system (average 36 to 39 % and no removal to 2 log units) in both seasons. Taxonomic compositions in influent water samples shifted from wastewater-impacted communities (Actinomycetota and Firmicutes) to a combination of plant rhizosphere-associated and river communities in NBS effluents (Alphaproteobacteria). In contrast, the conventional technology showed no substantial differences in community composition. Moreover, NBSs substantially reduced the ecotoxicological risk assessment (cumulative RQs). Furthermore, NBSs reduced the ecotoxicological risk (cumulative RQs) by an average of over 70 % across seasons, whereas the benchmark technology only achieved a 6 % reduction. In conclusion, NBSs present a robust alternative for minimizing the discharge of ABs and ARGs into surface water bodies.

Evaluation of sustainable development capacity of water sources: a case study of China

The issue of water scarcity has drawn attention from all over the world. The coordination of the interaction between ecological and environmental development of water sources and socio-economic development is currently an essential issue that needs to be solved in order to safeguard the water resources environment for human survival. In this essay, we suggest a paradigm for assessing the sustainable exploitation of water resources. First, three ecological, economic, and social factors are investigated. Twenty essential evaluation indexes are then constructed using the Delphi approach, along with an index system for assessing the potential of water sources for sustainable development. The weights of each evaluation index were then determined using the combination assignment approach, which was then suggested. The coupled degree evaluation model of the capability for sustainable development of water sources was then developed. In order to confirm the viability and validity of the suggested model, the model was used to assess the Liwu River water source's capacity for sustainable growth in the context of the South-North Water Transfer in Shandong, China. It is believed that the aforementioned study would serve as a helpful resource when evaluating the capacity of water sources for sustainable development.

A pilot-scale electrocoagulation-treatment wetland system for the treatment of landfill leachate

In the present study, the technical feasibility of an electrocoagulation-treatment wetland continuous flow system, for the removal of organic matter from landfill leachate (LL), was evaluated. The response surface methodology (MSR) was used to assess the individual and combined effects of the applied potential and distance between electrodes, on the removal efficiency and optimization of the electrocoagulation process. The hybrid treatment wetland system consisted of a vertical flow system coupled to a horizontal subsurface flow system, both planted with Canna indica. For a chemical oxygen demand (COD) concentration - without pretreatment of 5142.8 ± 2.5 mg L-1, the removal percentage for the electrocoagulation system was 79.4 ± 0.16%, under the optimal working conditions (Potential: 20 V; Distance: 2.0 cm). The COD removal efficiency in the treatment wetland with Canna indica showed a dependence with the hydraulic retention time, reaching 59.2 ± 0.2 % over 15 days. The overall efficiency of the system was about 91.5 ± 0.02 % removal of COD. In addition, a decrease in the biochemical oxygen demand (94.8 ± 0.14%) and total suspended solids (88.2 ± 0.22%), also related to the contamination levels of the LL, were obtained. This study, for the first time, shows that the coupling of electrocoagulation together with a treatment wetland system is a good alternative for the removal of organic contaminants present in LL.

Systematic analysis of the scientific-technological production on the use of the UV, H2O2, and/or Cl2 systems in the elimination of bacteria and associated antibiotic resistance genes

This study presents a systematic review of the scientific and technological production related to the use of systems based on UV, H2O2, and Cl2 for the elimination of antibiotic-resistant bacteria (ARB) and genes associated with antibiotic resistance (ARGs). Using the Pro Know-C (Knowledge Development Process-Constructivist) methodology, a portfolio was created and analyzed that includes 19 articles and 18 patents published between 2011 and 2022. The results show a greater scientific-technological production in UV irradiation systems (8 articles and 5 patents) and the binary combination UV/H2O2 (9 articles and 4 patents). It was emphasized that UV irradiation alone focuses mainly on the removal of ARB, while the addition of H2O2 or Cl2, either individually or in binary combinations with UV, enhances the removal of ARB and ARG. The need for further research on the UV/H2O2/Cl2 system is emphasized, as gaps in the scientific-technological production of this system (0 articles and 2 patents), especially in its electrochemically assisted implementation, have been identified. Despite the gaps identified, there are promising prospects for the use of combined electrochemically assisted UV/H2O2/Cl2 disinfection systems. This is demonstrated by the effective removal of a wide range of contaminants, including ARB, fungi, and viruses, as well as microorganisms resistant to conventional disinfectants, while reducing the formation of toxic by-products.

Influence of nitrogen sources on wastewater treatment performance by filamentous algae in constructed wetland system

Although filamentous algae have the characteristics of high nutrient assimilation ability, and adaptation to different conditions, studies on their role in water purification of constructed wetlands (CWs) are limited. In this study, the wastewater treatment capacity under different nitrogen sources was explored by constructing a filamentous algal CW (FACW) system. Results confirmed the fast and stable operation efficiency of the FACW system. Ammonia nitrogen was preferred in Cladophora sp. absorption and assimilation. The nutrient consumption rate (NCR) for total nitrogen (TN) of AG was 2.65 mg g-1 d-1, much higher than that of nitrate nitrogen (NG) (0.89 mg g-1 d-1). The symbiosis of bacteria and Cladophora sp. Contributed to pollutant removal. A stable and diverse community of microorganisms was found on Cladophora sp. Surface, which revealed different phylogenetic relationships and functional bacterial proportions with those attached on sediment surface. In addition, temperature and light intensity have great influence on the purification ability of plants, and low hydraulic retention time is beneficial to the cost-effective operation of the system. This study provides a method to expand the utilization of wetland plants and apply large filamentous algae to the purification of wetland water quality.