This study investigates the potential of hydrochar derived from residual carbon sources (orange peel residues, sewage sludge, and refinery sludge) as sustainable precursors for bifunctional cathodes in electro-Fenton (EF) systems, addressing key operational limitations of conventional electro-Fenton systems, particularly the need for acidic pH and external iron dosing. The hydrochars were chemically activated with potassium hydroxide (KOH) in the presence of urea or melamine at temperatures of 700, 850, and 1000 ºC. KOH activation markedly enhanced porosity and surface area, while nitrogen doping introduced electroactive pyridinic and graphitic species that promote oxygen reduction reactions and hydroxyl radical generation. Electro-Fenton degradation of phenol, used as a model pollutant, demonstrated the superior performance of KOH-activated urea-derived hydrochars compared to melamine-derived and non-activated counterparts. Among all tested materials, the urea-derived hydrochar activated at 850 °C exhibited the highest activity, achieving 90% phenol removal and 80% mineralization within 30min under homogeneous EF conditions (pH 3, 2mM Fe2+). Remarkably, this material also exhibited outstanding performance under heterogeneous EF conditions (circumneutral pH, without external iron addition), achieving 80% phenol removal and 70% mineralization. This behaviour highlights the ability of the system to operate efficiently under circumneutral pH without external iron addition, significantly simplifying the process and reducing risks associated with chemical handling and secondary iron contamination. Overall, this study demonstrates a practical strategy to simplify electro-Fenton processes and enhance their applicability under safer and more sustainable operating conditions.

Graphitic carbon nitride (g-C3N4) has emerged as a promising metal-free semiconductor for solar-driven environmental applications. However, its performance in photoelectrochemical systems is often limited by rapid charge recombination and poorly understood interfacial charge transport processes. In particular, the occurrence of both anodic and cathodic photocurrents in g-C3N4-based photoelectrodes under different applied biases has been widely reported, revealing a dual photoresponse behavior that remains mechanistically unexplained. In this work, g-C3N4 thin films were fabricated on fluorine-doped tin oxide substrates by electrophoretic deposition using guanidinium chloride and urea as nitrogen-rich precursors. Structural and surface characterization confirmed the formation of a porous, defect-rich carbon nitride framework with compact in-plane packing and mesoporous features. Optical analysis revealed an average band gap of 2.82 eV with limited visible-light absorption. The photoelectrochemical performance of the films was systematically evaluated as a function of film thickness and illumination direction, either through the electrode–electrolyte or substrate–electrode interface. Open-circuit potential measurements and transient photocurrent analyses demonstrated a bias-dependent switching between anodic and cathodic photocurrent responses at approximately 0.18 V versus saturated calomel electrode. Back illumination consistently produced higher photocurrent densities, suggesting that charge transport limitations within the film significantly influence the dominant photoresponse mechanism. Kinetic analysis of photocurrent transients indicated that recombination processes, rather than carrier generation, govern the observed dual behavior. These findings provide new insight into the interfacial charge transport mechanisms in carbon nitride thin films and establish synthesis–performance relationships relevant for the design of systems for solar-driven water treatment and environmental remediation.

Accidental discharges of highly concentrated furfural can severely inhibit biological wastewater treatment in refineries. This study assesses an on-demand pretreatment based on heterogeneous Fenton oxidation assisted by zero-valent iron (ZVI) shavings to mitigate extreme shock loads in real refinery wastewater (ca. 75 g/L furfural). Experiments were conducted at 60-80 degrees C and at natural pH, evaluating the effects of temperature, H2O2 dosage, and ZVI loading, and quantifying furfural removal and improvements in biodegradability and toxicity by respirometry. At 80 degrees C, hydrogen peroxide alone achieved substantial furfural conversion (70%), confirming that thermal peroxide decomposition provides the primary oxidative driving force. The presence of ZVI further accelerated conversion (up to 97%) and shifted product selectivity toward short-chain carboxylic acids (mainly formic acid), while iron leaching remained negligible (< 0.1 mg/L). Although TOC removal was moderate (4-14%), the treated effluent showed a substantial increase in biodegradability and a marked reduction in toxicity, enabling safe downstream integration into activated sludge systems. A preliminary techno-economic assessment, framed within an event-based operating scenario, confirms the industrial feasibility of the approach when applied as an emergency mitigation measure, with an OPEX of 181 k & euro;/y. Overall, the findings demonstrate the feasibility of a rapid, simple and industrially relevant pretreatment strategy for emergency mitigation of extreme furfural releases prior to biological wastewater treatment.

This study investigates the preparation of porous photopolymer-derived carbons (PDCs) in powder and monolithic structures through oxidative stabilization, pyrolysis, steam activation (AC-PDD adsorbent), and acid functionalization. The effects of these treatments on the physicochemical properties of the materials were evaluated, coupled with their adsorption performance toward 2-nitrophenol (2-NP) and 4-nitrophenol (4 NP), selected as model adsorbates with strong and weak lipophilicity, respectively. In single-solute batch experiments, AC-PDD demonstrated the highest maximum adsorption capacities at equilibrium reaching 586.1 and 445.6 mg g-1 for 2-NP and 4-NP, respectively. Binary-solute adsorption allowed to remove both NPs (total maximum adsorption capacity of 453.8 mg g-1) and revealed antagonistic interaction between them, deeply studied at different NP initial concentrations (20-100 mg L-1). Adsorbents were reused over multiple cycles after regeneration with ethanol and AC-PDD exhibited the highest regeneration efficiency (> 70 %). For continuous-flow assays, monoliths with gyroid lattice structure were synthesized via digital light processing 3D-printing and subsequent carbonization and steam activation, resulting in G-AC-PDD sample. G-AC-PDD monoliths showed broad breakthrough curves with longer saturation times (more than one month) and preferential retention of 2-NP over 4-NP. Dynamic adsorption capacities (356.8 and 260.2 mg g-1 for 2-NP and 4-NP, respectively) exceeded the values obtained in batch mode for binary system at the same inlet concentration and a 0.2 mL min-1 of flowrate. These results demonstrate that carbon monoliths with high uptake capacities may be produced by additive manufacturing for the efficient removal of lipophilic compounds from aqueous solutions.

This study investigates the potential of hydrochar derived from residual carbon sources (orange peel residues, sewage sludge, and refinery sludge) as sustainable precursors for bifunctional cathodes in electro-Fenton (EF) systems. Hydrochars were chemically activated with potassium hydroxide (KOH) in the presence of urea or melamine at temperatures of 700, 850, and 1000 ºC. KOH activation markedly enhanced porosity and surface area, while nitrogen doping introduced electroactive pyridinic and graphitic species that promote oxygen reduction and hydroxyl radical generation. Electro-Fenton degradation of phenol, used as a model pollutant, demonstrated the superior performance of KOH-activated urea-derived hydrochars compared to melamine-derived and non-activated counterparts. Among all tested materials, the urea-derived hydrochar activated at 850 °C exhibited the highest activity, achieving 90% phenol removal and 80% mineralization within 30 min under homogeneous EF conditions (pH 3, 2 mM Fe2+). Remarkably, this material also exhibited outstanding performance under heterogeneous EF conditions (circumneutral pH, without external iron addition), achieving 80% phenol removal and 70% mineralization. These results confirm the intrinsic bifunctional activity of the derived electrodes, enabling efficient hydrogen peroxide generation and catalytic decomposition into hydroxyl radicals across a wider pH range.

Refinery oily sludge is typically managed via the API-DAF-biological treatment train, generating residual sludges rich in hydrocarbons and nutrients that are often disposed of with limited valorization. In this work, a photobiorefinery concept coupling wet air oxidation (WAO) with purple phototrophic bacteria (PPB) is evaluated using a realistic mixture of API, DAF and biological sludges at their production ratio. WAO effluents obtained at different severities were screened for biodegradability and further investigated under selected conditions. Effluent generated at 200 degrees C supported robust PPB growth, with WAO liquors at 33% (v/v) providing the best compromise between substrate availability and inhibition. In kinetic batch experiments, PPB exhibited similar maximum growth rates when treating WAO effluents obtained at 200 degrees C and 1-3 h, with soluble COD removals of 1453-1545 mg/L (45-48%) together with 26-37% of NH4+, but achieving higher biomass yields and faster carboxylic acid removal at 1 h. In contrast, ammonium and soluble COD reached partial plateaus, consistent with a persistent soluble fraction enriched in oxidized aromatic and N-heterocyclic compounds. Amplicon sequencing revealed a stable PPB core (Cereibacter, Rhodopseudomonas and Rhodocista), complemented by heterotrophic taxa associated with degradation of complex organics. Overall, these results delineate a WAO operating window that maximizes PPB-treatable carbon and support integrating WAO and PPB for valorization of real refinery sludge mixtures.

Electrochemical biosensors based on purple phototrophic bacteria (PPB) offer a low-cost, real-time alternative to conventional toxicant detection methods. This study explored a single-chamber PPB-based biosensor for early-range detection of glyphosate in aquatic environments (1–30 mg/L). The results show that the pure culture Rhodobacter capsulates (R. capsulatus) is highly sensitive to low-to-medium-high glyphosate concentrations, whereas the mixed PPB-enriched consortium system exhibits stronger responses at low concentrations and maintains stable signals at higher concentrations, displaying characteristic cross-over behavior that reflects functional differentiation within the microbial systems. Mechanistic analysis indicates that glyphosate suppresses substrate metabolism and photosynthetic pigment synthesis, thereby reducing electron donor generation while increasing resistance to extracellular electron transfer, ultimately leading to decreased electron flux. Principal component analysis further confirms that the current signal arises from the coupling of metabolic activity and electrochemical processes rather than a single concentration-dependent response. The system requires no electrode modification, achieves a detection limit of 0.121 mg/L, and exhibits good stability and adaptability in complex aquatic environments. This study provides a new bioelectrochemical strategy for rapid screening and tiered monitoring of high-load pollutants.

The management of pig slurry is associated with environmental concerns due to its high nitrogen content and greenhouse gas emissions. This work proposes a photobiorefinery concept integrating steam explosion pretreatment, ammonia recovery via gas-permeable membranes, anaerobic digestion, and microbial protein production using purple phototrophic bacteria (PPB). Pretreatment at 145 °C for 30 min led to 57% solubilization of organic matter and 29% reduction of total solids. More than 99% of ammoniacal nitrogen was recovered from the hydrolysate in less than 3 h. Methane production increased by up to 350% after pretreatment. The recovered nitrogen was used as a nutrient for PPB growth, enabling CO2 assimilation from biogas under photoautotrophic conditions and microbial protein production. The results demonstrate the feasibility of coupling thermal, biological, and phototrophic processes for the integrated valorization of pig slurry, with simultaneous recovery of energy and nutrients.

Purple Phototrophic Bacteria (PPB), owing to their unique metabolism and electron transfer capabilities, hold great promise for application in microbial electrochemical systems (MES). This study proposes a new strategy by incorporating solid waste-derived materials (HySludge, HyGreen, and HyOrange) produced by HydroThermal Carbonization (HTC), as functional electroactive carbonaceous materials in PPB-based MES. The study focuses on evaluating the impact of these materials on PPB growth, electrochemical reaction, and microbial community composition under both non-polarized and polarized conditions, with Graphite serving as a control. This study addresses 3 core issues: a) the potential of hydrochars to serve as a stable platform for attachment and electron exchange between PPB and electroactive bacteria (EAB); b) the feasibility of achieving effective extracellular electron transfer (EET) through surface functional groups, despite low electrical conductivity of materials; and c) the capacity of hydrochars to generate electron output under light-driven conditions. The results indicate that HySludge (sludge-derived hydrochar) supported efficient PPB growth and nutrient uptake under non-polarized conditions, achieving removal efficiencies of 95.2 % for acetate and 91.9 % for NH4+. Polarization further enhanced the synergistic coexistence of photoelectroactive and EAB communities such as Rhodopseudomonas, Cereibacter, and Pseudomonas in HySludge systems. It achieved complete removal of acetate and NH4+, generated current density of 1.6 A/m3 with a coulombic efficiency of 1.1 %. Although its conductivity is inferior to that of Graphite, HySludge still demonstrated electrochemical functionality and biological compatibility, indicating its potential as a viable alternative to conventional electrode material.

Lightweight materials, characterized by low density, high specific surface area, and porous structures, have gained prominence in water and wastewater treatment due to their advantages over traditional materials, including ease of transportation and installation, enhanced adsorption and catalytic efficiency, strong mechanical performance, reduced energy consumption, recyclability, and adaptability to various treatment systems. This review categorizes these materials into natural and synthetic types, detailing the characteristics of these lightweight materials. The significant advancements in preparation techniques, including foaming processes, phase separation, sol-gel methods, and 3D printing technology are comprehensively reviewed and discussed. Furthermore, the applications of these materials in adsorption, filtration, catalysis, and environmentally friendly water treatment facilities are overviewed. The study underscores the essential role of lightweight materials in enhancing water treatment efficiency and provides theoretical guidance for their selection. It also identifies future research directions, emphasizing the development of multifunctional composite materials, cost-effective preparations and regeneration methods, as well as the evaluation of sustainability and environmental impact throughout the materials' lifecycle analysis. These insights aim to promote the commercial use of lightweight materials in conventional operation of water industry (adsorption, filtration, catalytic processes) and green nature-based solutions for water/wastewater purification.

In this study, a conceptual bioelectrochemical cell coupled with electroactive constructed wetland (ECW) and purple phototrophic bacteria (PPB) (termed as PPB-ECW) was constructed to systematically investigate its mechanisms and operational characteristics in wastewater treatment and electricity generation. A porous pottery pot was employed to replace the conventional proton exchange membrane, forming an open and electroactive environment. In the anode region, typical electroactive bacteria (EAB), represented by Hydrogenophaga and Ignavibacterium, were enriched and primarily facilitated efficient pollutant removal through the oxidation of organic substrates and electron release. In contrast, the cathode was dominated by Rhodopseudomonas palustris, a phototrophic and electroactive bacterium, which established an electrosyntrophic metabolic network characterized by electron transfer and light-driven energy utilization. The direct electron transfer (DET) of cathode PPB mainly depends on the outer membrane c-type cytochrome combined with light-driven cyclic electron flow. This coupling mechanism significantly enhanced pollutant degradation efficiency, with removal efficiencies of COD, TN, NH4+-N, and NO3--N reaching 98 %, 87 %, 88 %, and 100 %, respectively, among which NO3--N exhibited the most pronounced removal. The system achieved a maximum voltage output of 246 mV and a peak power density of 31 mW/m3. Compared with existing bioelectrochemical systems studies based on phototrophic microorganisms, this study systematically explained the synergistic mechanisms between anodic and cathodic microbial communities, and revealed the advantages of PPB in electron uptake and metabolism at the cathode. These findings provide both conceptual support and potential practical implications to further expand the scope of bioelectrochemical-based CW for wastewater treatment and energy recovery.

Reducing greenhouse gas emissions is critical for humanity nowadays, but it can be beneficial by developing engineered systems that valorize CO2 into commodities, thus mimicking nature's wisdom. Purple phototrophic bacteria (PPB) naturally accept CO2 into their metabolism as a primary redox sink system in photo-heterotrophy. Dedicated use of this feature for developing sustainable processes (e.g., through negative-emissions photo-bioelectrosynthesis) requires a deep knowledge of the inherent metabolic mechanisms. This work provides evidence of tuning the PPB metabolic mechanisms upon redox stressing through negative polarization (-0.4 and -0.8 V vs. Ag/AgCl) in photo-bioelectrochemical devices. A mixed PPB-culture upregulates its ability to capture CO2 from organics oxidation through the Calvin-Besson-Bassam cycle and anaplerotic pathways, and the redox imbalance is promoted to polyhydroxyalkanoates production. The ecological relationship of PPB with mutualist bacteria stabilizes the system and opens the door for future development of photo-bioelectrochemical devices focused on CO up-cycling.

On global scale, eutrophication is one of the most prevalent environmental threats to water quality, primarily caused by elevated concentration of nutrients in wastewater. This study utilizes aluminum dross (AD), an industrial waste, to create a value-added material by improving its operational feasibility and application for removing phosphate and ammonium from water. The operational challenges of AD such as its powdered nature and effective operation under only extreme pH conditions were addressed by immobilizing in calcium alginate to form calcium alginate aluminium dross (Ca-Alg-Al dross) beads. These Ca-Alg-Al dross beads were further tested for phosphate and ammonium removal from natural wastewater in two different aqueous environment systems: (i) i ) vertical flow constructed wetlands (VF-CWs) followed by Ca-Alg-Al dross beads fixed bed system and (ii)Ca- ii )Ca- Alg-Al dross beads mounted floating constructed wetlands (FCW) for remediating polluted lentic ecosystems. Our results show maximum phosphate and ammonium removal of 85 +/- 0.41 % and 93.44%, respectively, in VF-CWs followed by Ca-Alg-Al dross beads fixed bed system. The Ca-Alg-Al dross beads mounted FCW system achieved maximum phosphate removal of 79.18 +/- 8.56 % and ammonium removal of 65.45 +/- 21.04 %. Furthermore, the treated water from the FCW system was assessed for its potential to inhibit algal growth by artificially inoculating treated water with natural algae to simulate eutrophic conditions. Interestingly, treated water from the FCW system was found capable of arresting the algal growth. Besides, scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and Fourier transform infrared (FTIR) spectroscopy confirmed the functional groups and surface properties and probable participation of multiple mechanisms including ion exchange, electrostatic attraction, and ligand complexation for phosphate and ammonium removal. Overall, these results offer a promising way to utilize AD for high-end applications in wastewater treatment.

Recovering these carboxylic acids from the fermentative streams in a sustainable, green, and economical way is a significant challenge. This work assessed hydrophobic eutectic solvents (HES) - water-immiscible - for the selective recovery of carboxylic acids via liquid-liquid extraction. Different trioctylphosphine oxide (TOPO) mixtures with menthol and thymol were studied and deeply characterized by H-1 and P-31 NMR to yield stable eutectic solvents, including a novel experiment of P-31 NMR at variable temperatures for the first time. Those stable eutectic solvents were tested in the liquid extraction of complex aqueous mixtures containing C-2-C-6 carboxylic acids and simple sugars (glucose and xylose). The back-extraction of the carboxylic acids for the recovery of the HES was optimized, being necessary in three stages for the complete cleaning of the eutectic solvent using NaOH 0.1 M. The eutectic mixture of TOPO and thymol in a molar ratio of 1:2 exhibited an overall recovery of C-5 and C-6 carboxylic acids over 70 %, allowing its selective extraction from the rest of the compounds in the complex mixture. Likewise, this HES (after back extraction) was successfully reused in a second extraction cycle, keeping the performance of the fresh one. Therefore, this study demonstrated that HES can have a high extraction selectivity for carboxylic acids of >= C-5. Moreover, these solvents were stable and allowed reusability, reducing the environmental impact and process costs.

The need to minimize eutrophication in water bodies and the shortage of phosphate rock reserves has stimulated the search for sequestration and recovery of phosphate from alternative sources, including wastewater. In this study, aluminium dross (AD), a smelting industry waste/by-product, was converted to high-value material by encapsulation in calcium alginate (Ca-Alg) beads, viz. Ca-Alg-AD and utilized for adsorptive/uptake removal and phosphate recovery from an aqueous environment. Encapsulation of AD in alginate beads solves serious operational difficulties of using raw AD material directly due to density difference constraining efficient contact of AD with pollutants present in water and post-treatment recovery of AD material. The phosphate removal was evaluated in both batch and continuous flow operation modes. The batch adsorption study revealed 96.86% phosphate removal from 10 mg L−1 of initial phosphate concentration in 70 min of optimal contact time. Further, the phosphate removal potential of Ca-Alg-AD beads turned out to be independent of solution pH, with an average of 95.93 ± 1.40 % phosphate removal in the 2–9 pH range. The result reflects phosphate adsorption on Ca-Alg-AD beads following a second-order pseudo-kinetic model. Ca-Alg-AD beads-based adsorption followed Freundlich and Langmuir isotherm models. Further, a continuous packed bed column study revealed a total phosphate adsorption capacity of 1.089 mg g−1. The chemical composition, physical stability, and surface properties of Ca-Alg-AD beads were analyzed by means of state-of-the-art analytical techniques, such as Scanning Electron Microscopy-Energy Dispersive X-ray spectroscopy (SEM-EDX), Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetry/Differential Thermal Analysis (TG/DTA). These characterization techniques comprehend the mechanism and influence of surface properties and morphology on the phosphate adsorption behaviour, which induce the involvement of multiple mechanisms such as ligand complexation, ion exchange, and electrostatic attraction for phosphate adsorption on Ca-Alg-AD beads.

This research presents an innovative approach for removing carbamazepine (CBZ), a persistent pharmaceutical contaminant, using a three-dimensional electro-Fenton (TDEF) system. The preliminary phase involved validating the configuration of the TDEF reactor. First, commercial electrodes, metal-mixed oxide as the anode, and stainless steel as the cathode were selected. After that, a third particulate electrode was introduced, working with two options: vineyard biochar and a lab-made conglomerate of perovskite and carbon black. Additionally, two collector systems were evaluated for easy recovery and reuse of this three-dimensional particulate electrode: a thermoplastic tube and a silicone bag. Among the tested configurations, the perovskite conglomerate retained within a silicone bag proved the most effective, achieving a 91 % CBZ removal efficiency at a natural pH (6.5) during a 5-hour batch operation. Considering excellent results, the system's efficacy was confirmed working on fortified tertiary wastewater (FTW) in continuous mode, emphasizing the adaptability to real-world conditions. Moreover, the reusability of microparticles was confirmed for three consecutive cycles, as well as through the characterization study using FTIR, without important modifications in the material after use. Results confirmed the technology's potential for removing CBZ operating with real conditions. Thus, the proposed process represents an alternative treatment to remove CBZ efficiently in a wide range of concentrations from real wastewater in a continuous treatment with a reasonable energy cost (ca. 27 kW/h & sdot; g CZP ). This novel system represents a costeffective, straightforward experimental setup suitable for future scaling and industrial applications.

The catalytic activity and stability of sulfonic-based UiO-66(Zr) materials were tested in the Friedel-Crafts acylation of anisole with acetic anhydride. The materials were prepared using microwave-assisted synthesis, producing microporous materials with remarkable crystallinity and physicochemical features as acid catalysts. Different ratios between both organic ligands, terephthalic acid (H2BDC) and monosodium 2-sulfoterephthalic acid (H2BDC-SO3Na), were used for the synthesis to modulate the sulfonic content. The sulfonic-based UiO-66(Zr) material synthesized with a H2BDC/H2BDC-SO3Na molar ratio of 40/60 exhibited the best catalytic performance in the acidic-catalyzed Friedel-Crafts acylation reaction. This ratio balanced the number of sulfonic acid sites and their accessibility within the UiO-66 microporous structure. The catalytic performance of this material increased remarkably at 200 °C, outperforming reference acids and commercial heterogeneous catalysts such as Nafion-SAC-13 and Amberlyst-70. Additionally, the best sulfonic-based UiO-66(Zr) material proved to be stable in four successive reaction cycles, maintaining both its catalytic activity and its structural integrity.