Journal of Hazardous, Toxic, and Radioactive Waste

In order to solve the problem of unclear evolution paths after oil–gas storage and transportation accidents, which lead to a lack of targeted accident emergency, delayed disposal measures, and further deterioration of the accident, based on the existing accident scenario-response theory, this article summarizes 17 basic scenarios in oil–gas storage and transportation by analyzing 116 accident cases. Moreover, the accident scenario expressions are given in time and space dimensions, and general scenario evolution paths of fire accidents for oil–gas storage and transportation are constructed. On this basis, a dynamic scenario deduction network model is established by using a dynamic Bayesian network. In this model, key scenario nodes and their final scenario probabilities are determined in consideration of statistical probability obtained by the actual accident cases, empirical probability given by domain expert’s scoring, and state probability calculated by joint probability formula of a dynamic Bayesian network. As a case study, the scenario deduction process and result of a Dalian 7.16 accident are analyzed to verify the rationality and effectiveness of the proposed method. According to the proposed scenario deduction method, it can help decision-makers to make more targeted emergency disposal measures.

Lack of proper physical separation between the anodic and cathodic zones of a constructed wetland-microbial fuel cell (CW-MFC) causes higher oxygen diffusion into the anodic zone, which leads to nonproductive electron losses. In this investigation, performance of two upflow hydroponic CW-MFCs with a low-cost ceramic separator (R1) and without a separator (R2) was evaluated with Canna indica at the cathodic side. The chemical oxygen demand removal efficiencies of R1 and R2 were found to be 86.2 ± 8.1% and 91.5 ± 4.9%, respectively. However, from the polarization plots, internal resistance of R1 (240 Ω) was found to be 2.6 times lower than that of R2 (626 Ω). In addition, it was revealed that R1 (258.78 mW·m⁻³) exhibited almost three times higher power density than R2 (91.02 mW·m⁻³). The normalized energy recovery of the CW-MFC with a ceramic separator was also 2.7 times higher than that without a separator. The presence of a separator thus facilitated better anaerobicity to support substrate utilization by electrogenesis in the anodic zone of R1 and prevented oxygen diffusion, which resulted in higher energy recovery while only marginally compromising the efficiency of organic matter removal.

This study addresses the problem of disposal and effective reuse of waste material, fly ash, and construction concrete debris in order to find an optimized solution for their bulk disposal. Providing granular pile (stone column) in weak soils is a common practice which helps in improving the strength parameters and reducing the vertical deformation. Strengthening the fly ash fill with granular piles of construction-concrete debris of two different sizes under a footing of the same size was studied. Two nondimensional factors, bearing capacity ratio (BCR) and settlement ratio (SR), were compared for floating and end-bearing granular pile. Numerical analysis established the validity of experimental findings. Empirical expressions for scale effect (of model footing and tank dimensions) were derived with numerical modeling using PLAXIS 3D. Providing a geosynthetic-encased granular pile below a footing of the same size has shown remarkable improvement in BCR and SR values of weak fly ash bed.

Heavy metals in deposited dust at five urban districts in Cairo, Egypt, during 2015 were studied. Risk assessment modeling was applied to evaluate health risks of these metals for adults and children. The results show that contamination levels of metals were in the order of Ni > Cr > Ba > Cu > Zn > Cd > Pb > Co, suggesting a very high degree of contamination of deposited dust in Cairo.The daily doses exposure was ranked in the order D_ingestion > D_{dermal contact} > D_inhalation for children and adults (carcinogenic risk), while in the case of adult noncarcinogenic risk the ranking order was D_{dermal contact} > D_inhalation > D_ingestion at all sampling sites. The highest contribution to hazard indices in children was from hazard quotients (HQ_ing), compared with low or negligible contribution of HQ_ing in the case of adults. The carcinogenic risk was assessed for adults and children via three exposure routes with order of R_ingestion > R_{dermal contact} > R_inhalation. Finally, cancer risk values for heavy metals in Cairo are within the safe levels.

The rapid rise in consumption of surfactants day by day and the consequent increase in discharge from both industrial and residential areas into bodies of water has become a cause for concern. In this study, an industrial waste material (dolochar) was used for the removal of sodium dodecyl sulfate (SDS). Adsorption experiments were executed using batch and column mode. The experimental data were analyzed by various adsorption isotherm models, including: Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R). Out of these models, the Langmuir isotherm appeared to be the best fit (R² = 0.97) and produced a maximum adsorption capacity of 5.78 mg/g at optimized conditions. The effect of different parameters, such as adsorbent dose, contact time, pH, agitation speed, and particle size, on SDS removal efficiency was investigated. It was observed that all the variables play important roles in affecting the amount of SDS adsorbed and, therefore, the removal efficiency. Maximum adsorption capacity of 98% was attained at an adsorbent dose of 16 g/L, near neutral pH, 150 rpm as the agitation speed and particle size below 300 μm. A column study was performed with three different adsorbent doses (and hence different bed depths) of 10, 20, and 30 g. A bed depth service time (BDST) model was selected to check its validity and column performance, and to scale up the process parameters. The logit method was also applied to calculate various associated parameters. Characterization of dolochar before and after adsorption was performed using scanning electron microscopy (SEM).

A microbial fuel cell (MFC) is a bioelectrochemical system that can recover bioelectricity from wastewater, with simultaneous organic matter removal from the wastewater. However, due to the inferior power production of MFCs and the higher fabrication cost, successful field-scale demonstration of this novel technology is still to be accomplished. Power production of MFCs can be improved by employing a cathode catalyst to overcome the sluggish oxygen reduction reaction (ORR) on bare carbon-based electrodes. In this regard, to enhance the power generation in a MFC, three MFCs inoculated with marine algae Chaetoceros pretreated mixed bacterial culture were operated with different cathode catalysts. To examine the effect of cathode catalyst on power generation, Pd and MnO₂ were used as cathode catalysts in the MFC-Pd and MFC-Mn, respectively, while the third MFC (MFC-C) was devoid of any catalyst. The chemical oxygen demand (COD) removal efficiency was estimated to be 63.3% ± 1.83%, 62.8% ± 2.15%, and 61.3% ± 1.76% for MFC-C, MFC-Mn and MFC-Pd, respectively. The MFC-Pd exhibited highest coulombic efficiency of 25.82% ± 2.1%, followed by MFC-Mn (17.47 ± 1.6%) and MFC-C (10.68% ± 2.8%). The power density of MFC-Pd, MFC-Mn, and MFC-C was estimated to be 63.94, 27.12, and 10.46 mW/m², respectively. The results exhibited that the application of Pd as a cathode catalyst yields higher power in a MFC. Furthermore, the maximum power density of MFC-Mn, with MnO₂ as cathode catalyst, was 2.36 fold lesser than that obtained from the MFC-Pd and 2.59 times higher than MFC-C. In addition, the wastewater treatment efficiency measured in terms of COD removal efficiency was similar for all the MFCs given that similar operating conditions (Chaetoceros pretreatment on the anodic inoculum) were maintained in the anodic chamber of all these MFCs. However, as MnO₂ is a low-priced material, the energy recovered per dollar spent on the catalyst is six times higher for MnO₂ than for Pd. Thus, the combination of MnO₂ as cathode catalyst and Chaetoceros as a methanogenesis inhibitor demonstrated a low-cost, sustainable solution for power enhancement in MFCs.

Global industrialization has led to an alarming level of release of hazardous and toxic metals in water bodies. Disposal of wastewater containing heavy metals can have adverse impacts on human health, as well as on other components of the environment. The various conventional treatment processes used to date have many disadvantages, such as high amounts of sludge generation, chemical requirements, and cost. Bioelectrochemical systems can overcome these disadvantages and can generate renewable energy or valuable chemicals out of these wastes. Bioelectrochemical systems are processes that can convert the chemical energy derived from oxidation of waste into electrical energy. This chemical energy is derived by the microbial population present in activated sludge. This paper reviews the studies conducted on the three bioelectrochemical processes, namely a microbial fuel cell (MFC), a microbial electrolysis cell (MEC), and a microbial desalination cell (MDC), to treat industrial wastewater rich in heavy metals.

The release of untreated or partially treated pharmaceutical wastewater into water bodies has become a serious concern these days as the drugs and their intermediates present affect living forms heavily. Thus, the presented study evaluates the effect of a broad-spectrum antibiotic ampicillin drug on the performance of a technology called microbial fuel cell (MFC) which can generate electricity during wastewater treatment. In the current work, synthetic feed containing ampicillin was fed to two MFCs at different concentrations (10 and 25 mg/L). The MFC fed with 10 mg/L (MFC₁₀) showed 25% higher voltage than the control (MFC_C), whereas the reactor fed with 25 mg/L (MFC₂₅) of ampicillin showed 10.2% lower voltage generation than the control. In terms of chemical oxygen demand (COD) removal efficiency, MFC₁₀ performed better than MFC_C followed by MFC₂₅. MFC₁₀ and MFC₂₅ showed comparable ampicillin removal efficiencies of 86% and 84%, respectively. Hence, the ampicillin concentration of 10 mg/L was found to be optimum for enhancing the performance of the MFC. For a concentration close to 25 mg/L or higher, the performance of the MFC was found to be negatively affected.

This work presents the stabilization/solidification (S/S) process by substituting the portland mortar cement fractions by sludge. This sludge results from the wastewater treatment process of a cardboard plant by infiltration–percolation on different combinations of aggregate supports (matrix: sand/coal bottom ash). The prepared mortars incorporating concentrations 5, 10, 15, 20, and 30 wt% of sludge, have been the subject of mechanical studies (compressive and flexural strength), mineralogical study by XRD, and leaching tests. The mechanical strengths have two regimes: a slow decrease for substitutions up to 20%; and then a significant drop of 36% compared to the normal mortar for a sludge concentration of 30%. This decrease coincides with the inversion of the ratio of the CaCO₃/SiO₂ intensities deduced from the XRD patterns, and the appearance of a peak identifying a new well-crystallized phase may be hydrogarnet. The leaching of arsenic (As) and the heavy metals (Co, Mo, Ni, Pb, Zn, Cu, and Cr) released after 64 days is at concentrations well below the limit values. The released concentrations of Zn, Cu, and Cr increase significantly up to 16 days and then stabilize at 3.6, 19, and 19.1 mg/cm², respectively. However, As, Co, Mo, Ni, and Pb, which are initially present in sludge from wastewater filtration, have not been leached.

In the last couple of decades, microbial fuel cells (MFCs) have gained importance because of its ability to generate electricity from renewable and carbon-neutral energy sources, such as wastewater. The occurrence of simultaneous biological and electrochemical processes to facilitate the electron transfer mechanism increases the process complexity. Considerable experimental and modeling techniques have been carried out to identify the different processes involved and their relative effect on electricity generation to improve the performance of the MFCs for practical applications. Among the various statistical modeling approaches, the design of experiments (DoE) is used as a robust tool to determine the relationship between variables influencing the performance of the MFCs and to perform optimization of configuration and operation of the MFCs. It has several advantages over the one-factor-at-a-time (OFAT) methodology, in terms of time and resource management as well as obtaining relevant information. This review illustrates the most popular experimental designs used in MFC-related studies. It is expected that the paper will encourage researchers to incorporate this method into their experimental studies to ensure high-quality research output.

Nano zero valent iron (nZVI) composites were developed with iron loading ratios of 10% and 20% (w/w) using base materials, pumice, and zeolite. The four composites (PnZVI 10, PnZVI 20, ZnZVI 10, and ZnZVI 20) developed were then used to analyzing their efficiency for the removal of arsenite (III) [As(III)] from aqueous solution using a series of batch and column experiments. Scanning electron microscopy (SEM) images of the composites revealed that spherical iron nanoparticles were uniformly dispersed over the base materials. The removal efficiency was investigated for varying initial concentrations (25–200 mg/L) of As(III), pH (3–11), and adsorbent dose (0.5–5 g/L). All four composites showed a fairly high removal capability of As(III) over a wide pH range, in particular, between 5 and 9. The observed data were then evaluated against various adsorption kinetics equations, and the pseudo second order model fitted the data well, with the rate constants being in the range of 0.51–1.38 g/(mg·h). The Freundlich isotherm model emerged as the best to describe As(III) adsorption on the heterogeneous surface of composites, demonstrating the maximum adsorption capacity for PnZVI 20 = 24.96 mg/g. A plexiglass column setup with 20 cm height and 4.5 cm inner diameter was then used to study the in situ removal of As(III). A constant flux of 30 mL/h with 5 mg/L of As(III) concentration was applied at the bottom boundary of the column for 30 days. It was observed that approximately 99% of As(III) was removed during the process and 0.95 mg/g of As(III) was found to be adsorbed on the adsorbent at the end of the experiment. The high removal efficiency over a wide pH range in combination with its low cost and better hydraulic and mechanical properties demonstrated it to be a promising adsorbent for field application.

The current study explicates the feasibility of using dolochar, a solid waste generated from the sponge iron industry, for removal of color from synthetic textile dye solution containing equal amounts of the dyes Reactive Red 120 (RR 120) and Disperse Blue 3 (DB 3). The study investigated the significance of major experimental process parameters on adsorption. The experimental data were well fitted to the Langmuir isotherm model (R² = 0.99) with a maximum adsorption capacity of 39.71 mg g⁻¹. The adsorption kinetics were properly explained by a pseudo-second-order reaction (R² = 0.99). The values of the separation factor 0.109 (1 > R_L > 0), Freundlich exponent 3.108(n > 1), and thermodynamic parameters (ΔG, −4,371 kJ mol^−l at 303 °K and ΔH, 6,124 kJ mol⁻¹) pointed to favorable, spontaneous, and endothermic adsorption processes, respectively. Treatment of real dye-bath water with dolochar resulted in 94.4% dye removal efficiency. The viability of using dolochar as a potential adsorbent for dye removal from textile industry effluent is established in this study.

The transportation of hazardous materials (hazmat) is a complex process that continues to receive considerable attention from practitioners and researchers alike. A multimodal system that integrates road and railway networks is often argued as the optimal solution. Given the unique characteristics of each network, the integration of both networks generates an additional layer of complexity attributed to their interdependency. In this respect, the current study utilizes complex network theory to develop a network-of-networks (NoN) framework for multimodal hazmat transportation. Hazmat transportation routes are informed through various measures, including the shortest distance and least vulnerable routes. The case study considered herein applied the developed NoN framework to used nuclear fuel transportation. The analysis results indicate that optimal transportation routes are different for the shortest path and the least vulnerable analysis. These results are expected to inform future hazmat transportation route planning to incorporate more complex and dynamic network characteristics.

The objective of this study was to investigate the performance of the sequencing batch reactor (SBR) for the treatment of graywater using simultaneous nitrification, denitrification, and phosphorus removal (SDNPR). The SBR reaction phase includes anaerobic (1 h), aerobic (2 h), and anoxic (1 h) phases that demonstrated significant removal of chemical oxygen demand (COD) (96.62%), biochemical oxygen demand (BOD) (97.38%), phosphate (72%), ammonia (81.68%), and surfactant (92%). Further, a batch adsorption study was carried out using corncob for the removal of phosphate from graywater. The influence of activation temperature (250°C–700°C) and initial adsorbent dosage (100–500 mg L⁻¹) on phosphate adsorption was evaluated in the study. The highest phosphate adsorption was found at an adsorbent dosage of 500 mg L⁻¹ and an activation temperature of 550°C. The adsorption study describes a better fit model using the Langmuir isotherm for the equilibrium data, and the adsorption rate was controlled by pseudo-first-order kinetics.

The review discusses the transformation of waste to energy (WTE) through bioelectrochemical systems (BESs) treating organic waste, which makes up 47% of the total municipal solid waste generated. Emphasis is given to the intermediate step—use of a leach bed reactor—to successfully convert WTE by explaining the constructional elements and factors affecting the hydrolysis of organic waste. As hydrolysis is a rate-limiting step of anaerobic digestion (AD), operating parameters controlling solubilization of the readily degradable compounds are essential to obtain a volatile fatty acid and nutrient-rich leachate. The leachate treatment in BESs such as a microbial fuel cell, a microbial electrolysis cell, and a microbial desalination cell, along with factors that will affect the performance of these systems, is reviewed. Further, it describes the mechanisms involved to remove organics and nutrients, as well as the advantages, disadvantages, and challenges of individual systems. Finally, this review will aid future efforts to recover the energy present in organic waste with the help of BESs and to develop integrated solid waste management systems.

Coke oven wastewater from the iron and steel plant industry is composed of highly refractory and recalcitrant phenolic pollutants. To overcome the process instability, inhibition, and poor performance of coke oven wastewater treatment plants an efficient phenol degrading bacterial culture was isolated from the coke oven wastewater of a local steel plant industry in Odisha, India. In this study, the kinetics of phenol biodegradation by a newly isolated Pseudomonas citronellolis NS1 was carried out using batch shake flasks. The results revealed that the culture could degrade 1,500 mg/L⁻¹ of phenol almost completely within 90 h as the sole source of carbon and energy. In addition, under these conditions, approximately 95.5% of the chemical oxygen demand (COD) and 98.5% of toxicity removal were achieved by the indigenous P. citronellolis NS1. The growth and biodegradation kinetics of the isolated Pseudomonas species were evaluated at phenol concentrations pf 50–1,500 mg/L⁻¹. The specific growth rate of the culture followed the substrate inhibition kinetic pattern and the estimated biokinetic parameters were; μ = 0.246 h⁻¹, K_si = 890 mg/L⁻¹, and K_s = 14.85 mg/L⁻¹. Further, the effects of temperature on the biodegradation of phenol were carried out. The estimated values of maximum phenol biodegradation rate and the activation energy (E_a) of the enzyme-catalyzed reactions were 0.0152 h⁻¹ and 47.21 kJ · mol⁻¹ respectively at 36°C.

Ecological intervention is used for a diverse range of applications to provide sustainable solutions toward restoring natural capital. Eco-electrogenic engineered wetland systems (EEWSs), coupled with a microbial fuel cell (MFC), were designed and operated to utilize the natural ecological abilities by way of mimicking nutrient cycles to obtain the requisite treatment. An EEWS, designed with floating, emergent, and submerged aquatic macrophytes integrated with an electrode assembly, was studied for the treatment of fermented wastewater (generated from biohydrogen production using food waste). The experiment was carried out with 250 and 500 mg/L of organic carbon load, which accounted for combined chemical oxygen demand (COD) removal efficiencies of 87% and 85% and volatile fatty acid (VFA) removal efficiencies of 87% and 80%, respectively. The maximum in situ potential of 1.5 and 1.9 V at the current densities of 17 and 18 mA was recorded, respectively, at 250 and 500 mg/L. The hybrid system showed high efficiency in removing fermented acid-rich effluents and can, therefore, be utilized as a promising polishing/final treatment unit with sustainable footprints.

Chromium is found in different drinking water sources in many countries. Higher levels of chromium in drinking water are carcinogenic to consumers. Chromium removal can be achieved by employing various technologies, but not all are cost-effective to meet drinking water standards. In this work, Cr(VI) removal using three different industrial solid wastes, namely, fly ash, red mud, and dolochar, were explored and compared. Scanned electron microscopy was used to obtain the images of adsorbents both before and after adsorption. Adsorption experiments were executed using batch and column modes. The effect of pH (2–10), adsorbent dosage (5–35 g/L), contact time (5–180 min), agitation speed (90–210 rpm), and adsorbate concentration (5–150 mg/L) on the adsorption for all three adsorbents was studied in the batch experiments. At a pH value of 2 and an adsorbate dose of 25 g/L, chromium removal was found to be maximum for all three adsorbents. After a contact period of 120 min, it was found that the adsorption of chromium reached equilibrium for all three adsorbents. Dolochar was found to be the most effective one among the three adsorbents. Of the various adsorption isotherm models, the Langmuir isotherm appeared to be the best fit (R² > 0.99). From the fixed-bed column study at a bed depth of 10 cm, the breakthrough times were computed as 147, 193, and 219 min for fly ash, red mud, and dolochar, respectively. Similarly, the exhaust times were observed as 651, 780, and 631 min for fly ash, red mud, and dolochar, respectively. These results indicate that these industrial wastes can be utilized as low-cost alternatives to commercial adsorbents for the removal of Cr(VI).

The vulnerability of soil toward erosion might be reduced by having a good vegetative cover over the soil surface, slope improvement, and improving soil properties so that it is not easily detached and transported. However, the establishment of proper vegetative cover is a long process because it takes time for seeds to germinate and attain maturity. As an alternative approach, if soil resistance was increased by increasing the shear strength of soil against erosive forces offered by eroding agents, the soil system would become capable of withstanding the detachment of its particles on the application of shear stress. To achieve the desired strength, jute fiber and guar gum were added (0.3%, 0.5%, and 0.7%) to a test plot of 1 m² area which resulted in three different trays of three different strengths. The strength parameters were determined with the help of a triaxial test where unconsolidated undrained (UU) conditions were maintained throughout the experiment. The tray was maintained at different slopes (4%, 6%, 8%, 10%, and 12%) under a rainfall simulator of 1 m² area that was capable of producing rainfall intensity of 12.8 and 17.5 cm/h. The sediment outflow for a particular tray at different rainfall intensity and the slope were collected and measured. The recorded observations revealed that the value of the shear strength of soil increased as a result of the applied treatments and the soil loss rate/sediment outflow rate decreased for every combination of land slope and rainfall intensity. In addition, it was found that for a particular value of cohesion and angle of internal friction, the runoff rate increased with rainfall intensity for every land slope and the sediment concentration and sediment outflow rate increased with rainfall intensity as well as land slope. The results of this study will be useful for measuring soil loss, sediment runoff, and sediment discharged from farmland taking into account the properties of rainfall, soil, and flow.

Production of valuable chemicals and fuels using bioelectrochemical systems (BESs) from low-valued solids, liquid, and gaseous wastes has gained enormous attention among scientific communities. For example, a microbial fuel cell can produce bioelectricity using wastewater as substrate in anode and oxygen as oxidant in cathode. Partial desalination of sea water can be achieved in microbial desalination cells using the potential difference between the anode and cathode as a driving force. More interestingly, the microbial electrosynthesis cell is capable of producing organic acids, alcohols, methane, and bioplastics using CO₂ (a major greenhouse gas) as sole carbon feedstock. However, these technologies are still in the growing phase—mostly validated in lab-scale studies and, thus, yet to find position among field-scale prototypes. The fabrication details, main output, and various glitches during the bioconversion, where there is scope for further development, are outlined systematically. This manuscript provides a bird’s-eye view of all the different categories of BES, which will be helpful for the beginners of this field of research to understand the topic more clearly.

The combined effect of polyaniline (PANI) coating on the carbon felt anode material and anodic inoculum pretreatment using Chaetoceros was evaluated in this study. The microbial fuel cell (MFC) with a PANI modified anode could generate a maximum power density of 216 mW/m² (20.52 W/m³). Similarly, MFC with a pretreated inoculum in the anodic chamber and an unmodified or PANI modified anode generated significantly higher coulombic efficiency (CE) compared with MFCs without any inoculum pretreatment and anode modification, owing to the effective inoculum pretreatment for the enrichment of electrogens. A 17% increase in CE was noted in MFC with a PANI modified anode (42.45%) compared with MFCs using a bare carbon felt anode (35.98%) due to the enhanced bioelectrochemical activity of the anode. The oxidative current was found to be higher in MFC with a PANI modified anode, which further supports the difference in power density. Reduction in charge transfer resistance was also observed in MFCs with a PANI modified anode during electrochemical impedance spectroscopy (EIS) analysis. The findings of this study reveal that electricity generation in MFCs can be enhanced by PANI modification of the anode and inoculum pretreatment using Chaetoceros marine algae.

Scaling up of a microbial fuel cell (MFC) is a challenging task and researchers are still struggling to achieve acceptable results when treating real wastewater at the field scale. In this study, a field-scale stacked MFC, consisting of six individual MFCs with a volume of 120 L each, was designed, constructed, and operated for on-site sanitary wastewater treatment. The first time the long term performance evaluation of such large-scale MFC with a total working volume of 720 L, treating actual sewage, is presented in this study. The stacked setup consisted of one hexagonal central chamber surrounded by six peripheral MFCs, MFC-1, MFC-2, MFC-3, MFC-4, MFC-5, and MFC-6. Cathode catalysts, Co_0.5Zn_0.5Fe₂O₄ and Sn₅Cu₈₄, were used in these stacked field-scale MFCs on carbon felt base material and a competitive performance was observed for both the catalysts. Goethite was used as an anode catalyst over a carbon felt anode for all MFCs. Chemical oxygen demand (COD) removal efficiency was observed to be directly related to hydraulic retention time (HRT) and 78.45% ± 19.12% of COD removal efficiency was observed at an HRT of 18 h. However, COD removal efficiency increased to 87.29% ± 7.28% with an increase in HRT to 36 h. Therefore, this stacked MFC system produced a final effluent with a COD of 303 ± 50 mg/L and produced a maximum power of 61 mW, which was used to illuminate the toilet premises at night.

Catalysts play an essential role in various electrochemical reactions followed during the synthesis of hydrogen peroxide (H₂O₂). Plenty of investigations on the role of catalysts in the synthesis of H₂O₂ have been made in recent times. In this regard, palladium (Pd) is the most favored catalyst used by the researchers for the production of H₂O₂; however, monometallic Pd catalysts hydrogenate H₂O₂ if no acids or halide stabilizers are used. Nowadays, direct synthesis of H₂O₂ is mainly furnished by active metal-based catalysts such as gold, palladium, nickel, platinum, iron, silver, or manganese. However, the alloys of Au-Pd/C, Ni-Pd/C, and Au-Pd/TiO₂ are also being encouraged because of their increased electrochemical activity. The efficacy of H₂O₂ production is highly dependent upon the type of cathode catalyst used and the pH of the solution. The electro-Fenton process, which uses Fenton reagents (dissolved Fe⁺² and H₂O₂) to produce hydroxyl ions, is also an effective method for the degradation of biorefractory organic pollutants present in wastewater. This novel process can be made feasible if H₂O₂ can be produced in situ. In situ H₂O₂ production can be particularly important and attractive for tertiary treatment of sewage and for the removal of emerging contaminants. Thus, this mini review focuses on the effectiveness of various metal-based catalysts and the application of bioelectrochemical systems for the synthesis of H₂O₂.