This study unravels the intermolecular mechanistic degradation of palm oil mill effluent (POME) in sulfate removal, utilizing a distinctive coagulant derived from naturally abundant limestone (CaCO3), which was activated into calcium hydroxide [Ca(OH)2] through calcination and exothermic reactions. Sulfate was reduced from POME by 88.76% with the optimal conditions (pH 5, 200 g/L Ca(OH)2 dosage, and 135 min settling time) with strong correlation (r = 0.8237) and statistically significant (p = 0.0064) of Pearson's correlation. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) revealed an ideal morphology and elemental composition with reduction of 4.4753 m2/g surface area in Ca(OH)2 to slurry. Kinetic studies evaluated that sulfate removal at 4400 mg/L strongly followed the second-order model with a high coefficient of determination (R2 = 0.9883). Analysis using Fourier-transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) detected the formation of 2-isopropyl-5-methyl-1-heptanol (C11H24O). Overall, this study demonstrates the potential of Ca(OH)2 from CaCO3 as an efficient material for POME additional treatment, helping reduce VOCs and improve the value of industrial wastewater.

Biological methanation in ex situ biotrickling filter reactors (BTFRs) is a promising power-to-gas solution for converting renewable H₂ and CO₂-rich gas streams into biomethane under mild operating conditions. However, cross-study comparison remains difficult because reactor configurations, operating definitions, normalization bases, and performance metrics are reported inconsistently. This review critically synthesizes up-to-date evidence linking gas–liquid–biofilm mass transfer, hydrogenotrophic metabolism, reactor design, and operating conditions to CH₄ productivity, H₂ utilization, CO₂ conversion, product-gas quality, and long-term stability. Quantitative evidence reveals recurring process-intensification trade-offs: shorter gas residence time can increase productivity but reduce substrate utilization, while pressurization can improve conversion at the expense of compression and pressure-rated equipment. Packing architecture and liquid delivery enhance biofilm retention and effective contact but may also increase pressure drop, liquid hold-up, and diffusion resistance. Pilot and field-integrated studies demonstrate real-biogas utilization, recovery after H₂ interruptions, modular operation, and extended production of high-CH₄ gas. Although biological methanation has reached commercial application in other reactor configurations, publicly documented ex situ BTFR biomethanation remains predominantly at pilot scale. By consolidating the latest quantitative evidence and reporting needs, this review provides a knowledge base to guide scale-up and commercial development.

This study presents a novel hybrid membrane treatment train that integrates an anaerobic membrane bioreactor (AnMBR) with a fluidized bed membrane bioreactor enriched with partial nitritation and anammox (FMBRPN/A) for the treatment of industrial wastewater. The system was evaluated in terms of pollutant removal performance, microbial community structure, and energy efficiency, and benchmarked against a conventional full-scale aerobic/anoxic activated sludge system with an integrated constructed wetland (ASN/DN+Wetland). The AnMBR+FMBRPN/A achieved high removal efficiencies for COD (91.1 %) and total nitrogen (70.1 %), matching the performance of the conventional system while operating under low-carbon effluent conditions. Strategic aeration of FMBRPN/A enabled spatial separation of partial nitritation and anammox zones, promoting syntrophic coexistence of ammonium-oxidizing (AOB), nitrite-oxidizing (NOB), denitrifying (DN), and anammox (AMX) microbes in direct contact with the membrane surface, contrasted with microbial dynamics in traditional systems. The AnMBR+FMBRPN/A process had better energy performance, with 26.6 % reduction in electricity consumption (0.55 vs. 0.74 kWh/m3) and added benefits in biomethane recovery and reduced greenhouse gas emissions. These findings point to the potential of hybrid membrane bioreactors to transform industrial nitrogen management towards more efficient and sustainable solutions.

A novel surface-interaction study using the raw limestone (adsorbent) and the sulfate present in Elaeis guineensis wastewater effluent (adsorbate), or what is well known as palm oil mill effluent (POME), has unveiled the physicochemical interactions underlying the removal process of sulfate via the adsorption method. The adsorption of sulfate from POME on limestone adsorbent was conducted in a batch technique in order to study the optimum percentage removal of sulfate. The experiment was performed with multiple conditions, namely the amount of the adsorbent (0.2-1.0 g), pH (2-13), contact time (60-300 min), and initial concentration (50%-90%). The best parameters for every condition were utilized after each experiment. The highest removal efficiency of each parameter for POME was found to be 0.6 g, pH 13, 240 min, and an initial concentration of 90% was 39.64%. The results were analyzed with a hypothesis t-test and paired t-test by comparing the t-calculated and t-critical values. The results showed that the t-calculated values were within the acceptance region, verifying the statistical significance and reliability of the results. The adsorption isotherm and kinetics study were determined by considering the parameter effects, initial concentrations, and contact time. The adsorption kinetics in the present study were best fitted to the Elovich kinetic model with a correlation coefficient (R 2 = 0.9834), signifying a good fit. The adsorption process also followed the Dubinin-Radushkevich isotherm model, as proved by an R 2 value of 0.9676, indicating physical adsorption was dominant on the heterogeneous limestone's surface.

A large volume of undesired chemical liquid generated by ethanol distillation is known as sugarcane vinasse. It is an acidic, dark brown distillery spent wash rich in organic compounds that can cause toxicity to living organisms, soil and water acidification, and groundwater contamination. This study introduces a hybrid chemical and biological treatment approach combining photocatalysis and a sequencing batch biofilm reactor (HP-SBBR). Chemical coagulation with alum was applied as a pretreatment due to its compatibility and low cost. Subsequently, the bio-photocatalytic reaction in HP-SBBR with zinc oxide (ZnO) photocatalyst achieved substantial degradation, evidenced by 93.1 % COD reduction and 99.7 % decolourisation at a low loading rate of 0.024 kg center dot COD/m3 center dot day. Kinetic studies and UV-vis spectra confirmed that the combination of light and microorganisms effectively reduce COD of sugarcane vinasse and improved the biodegradation index. Microbial analysis using 16S rDNA revealed predominant bacterial genera, including Pseudomonas sp. (28 %), Bacillus sp. (8 %), Tissierella sp. (7 %), and Azoarcus sp. (6 %). To assess toxicity, a phytotoxicity test using mung bean (Vigna radiata) showed an 85 % reduction in toxicity based on germination rate, indicating that treated vinasse is more suitable for reuse in agriculture. Although the integrated pre-coagulation and HP-SBBR system demonstrated strong technical feasibility and treatment performance, further studies on operating costs and technical constraints are necessary to evaluate its applicability and impact in full-scale vinasse management.

The palm oil industry is booming, with a projected market valuation of $100 billion by 2030, driven by its diverse applications in food, cosmetics, and biofuels. However, the industry's rapid growth is accompanied by a significant environmental concern: the presence of sulfate in palm oil mill effluent (POME). Sulfate in POME poses a calamity to the ecosystem, leading to eutrophication and toxicity to aquatic life, also contributing to acid rain formation and higher hydrogen sulfide biogas formation. This mini-review highlights the severity of sulfate pollution in POME, its environmental implications, and the challenges associated with its treatment. Various treatment approaches, including chemical, biological, and integrated methods, are discussed, focusing on their efficacy, feasibility, and scalability. On top of that, to guarantee total pollution removal, prevent treated effluents from contaminating the environment, and design more efficient treatment techniques, it is essential to analyze the intermolecular breakdown of compounds during wastewater treatment. Thus, this review intends to comprehend the significance of performing and analyzing intermolecular breakdown, as a promising validation for the end-product of wastewater treatment. The review underscores the need for sustainable and efficient treatment technologies to mitigate the environmental impacts by sulfate in POME, ensuring a systematic pretreatment of POME toward a safe final discharge from excessive sulfate.

In this reply, we address the concerns raised regarding the theoretical consistency of the modeling approaches used in our original study on hydrogen sulfide adsorption onto ZSM-5. Specifically, the issues relate to the application of the Temkin isotherm, the Weber-Morris intraparticle diffusion model, and the use of a dimensional distribution coefficient in the thermodynamic analysis. We acknowledge that the simplified Temkin model was misapplied and does not strictly conform to theoretical requirements; however, it was used to represent mid-range adsorption behavior consistent with our experimental conditions. The inclusion of an intercept in the Weber-Morris model is defended as a diagnostic feature that reveals the contribution of boundary layer resistance, which is relevant in fixed-bed gas-solid systems. The use of a dimensional coefficient Kd = qe/Ce in thermodynamic calculations is justified based on its practicality in real gas-phase systems where activity-based constants are not easily defined. Collectively, while theoretical refinements are acknowledged, the main findings of the original study remain robust and well-supported by the experimental evidence. In addition, the opportunities for further refinement in isotherm fitting and thermodynamic calculations are acknowledged, and directions for future work are outlined.

Double chamber MFC with anaerobic bioanode and aerated cathode was developed for treatment of synthetic wastewater and azo dye, New Coccine (NC), including bioelectricity generation simultaneously in batch mode with 5 days. The organic matter removal affected by organic substrate loading and unaerated conditions was investigated. A maximum power density of 16.21 mW/m2 was attained in 1.500 g/L acetate while the internal resistance reduced from 800 to 400 Ω. However, the pollutants removal in COD (73.83%) for 0.750 g/L acetate was greater than with 0.375 and 1.500 g/L sodium acetate. The aeration in the cathode significantly enhanced the performance of MFC with 1.500 g/L acetate in the anodic chamber when compared to unaerated MFC. With low concentration of NC (10 mg/L) in the anodic chamber, an improve performance in COD removal (79.59%) and power density (22.60 mW/m2) was observed compared with that of without NC as the intermediates such as aromatic amines will operate as electron shuttles, stimulating electron transfer processes for reductive decolorization and the production of bioelectricity. When compared with 30 mg/L NC, the COD removal with 10 mg/L was slightly lower. Overall, the result successfully demonstrated the effective performance of MFC in wastewater degradation and bioelectricity generation under several operating conditions.

This study investigates the optimal operational parameters for biohythane production and dissolved sulfide removal during the two-stage anaerobic digestion across various hydraulic retention times. Biohythane, composed of hydrogen and methane, is a promising source of clean energy. However, the presence of dissolved sulfide, which can oxidize into toxic and corrosive hydrogen sulfide (H2S), poses a challenge to its quality and application in energy conversion equipment. A two-stage bioreactor was constructed, with the first stage, known as the acidogenesis phase, dedicated to biohydrogen production using mixed fruit waste (MFW) (initial glucose concentration 5 g/L, 60 degrees C, pH 6.0) and the second stage (methanogenesis phase) to biomethane production using acidogenic effluent (similar to 4.87 g/L initial VFA concentration, 37 degrees C, pH 8.5) with the addition of shredded tire (100 g) and an initial dissolved sulfide concentration of approximately 640 mg S2-/L (37 degrees C, pH 8.5). Experiments were conducted at various HRTs (2, 1.5, and 1 day) to optimize biomethane yield and dissolved sulfide removal. The results indicated that the modified Gompertz equation accurately fitted biohydrogen production, yielding 2.48 mol H2/mol glucose. The optimal HRT for biomethane production was 1.5 days, yielding 0.96 mol CH4/mol VFA, with butyric acid dominancy. The optimal HRT for dissolved sulfide removal was 24 h, achieving a removal efficiency of 78.13%, an adsorption capacity of 1.50 mg/g, and a final H2S concentration of 150 ppm. The present study demonstrated the efficacy of two-stage anaerobic digestion for the production of biohythane with removal of dissolved sulfide, thereby enhancing energy recovery from MFW.

This study assessed the effect of implementing multiple circuit connections and operating parameters (hydraulic retention time (HRT), organic loading rate (OLR), and external resistance) on the improvement of up-flow constructed wetland-microbial fuel cell (UFCW-MFC) in treating the mixed azo dyes wastewater and bioelectricity generation. The multiple-circuits UFCW-MFC facilitated the organic substrate degradation, which improved the removal efficiency of dyes by 8% and COD by 7%, as well as power production by 6.5 times, compared to single-circuit UFCW-MFC. The prolonged HRT from 1 to 3 d extended the interaction time between the pollutants and microbes, which further enhanced the removal efficiency of dyes by 9% and COD by 6%. The decrease in power generation by 1.3 times could be ascribed to the lower OLR at a higher HRT (0.864–0.288 g COD/d when HRT extended from 1 to 3 d) as the utilization of electrons was prioritized for decolorization compared to bioelectricity generation. The increase in OLR (0.288 to 0.754 g COD/d) with the same HRT (3 d) exhibited an improvement of 4% in decolorization and 2.4 times in power generation. This could be attributed to more electron production from the higher COD removal. The lower external resistance benefited the UFCW-MFC performance, where the best performance was obtained at 200 Ω as it approached the internal resistance (150 Ω).

The purpose of this article is to assess the feasibility analysis of microbial fuel cells (MFCs), particularly in the configuration of dual chamber salt bridge microbial fuel cell (DCSB-MFC), as a promising approach for simultaneous bioelectricity generation and wastewater remediation. The application of a salt bridge presents an economically viable alternative to the use of a proton exchange membrane, which is known for its high cost, in the construction of MFCs. This arrangement has been demonstrated to offer significant benefits in terms of enhancing the performance of new elements and evaluating operational parameters. However, it also encounters issues related to the total internal resistance (Rint) of the MFCs as well as power density (P). In addition, it has been found that traditional packing materials such activated carbon and gravel demonstrate poor permeability, internal resistance, and slow biofilm growth. Furthermore, there is a necessity to search for electrodes that possess high resistance to corrosion and are cost-effective to achieve optimal bioelectricity generation. Therefore, this article aims to emphasize the research areas that require attention. By addressing these areas, the actual implementation of this configuration can be brought closer to practical implementation.

The production and consumption of biohydrogen is growing because it is a "green," renewable energy that can be obtained in a relatively cost-effective manner through anaerobic digestion. Biohydrogen produced from biomass is a viable source of renewable energy; nevertheless, the presence of highly toxic and corrosive hydrogen sulfide (H2S) in the process can hinder the quality of biohydrogen production and limit its application in energy conversion equipment. Consequently, the goal of the research was to assess the feasibility of using ZSM-5 zeolite for H2S adsorption that function as activating agent to enhance biohydrogen quality under thermophilic conditions. The effect of ZMS-5 Zeolite loading (0.2-1.0 g) on biohydrogen production via dark fermentation from mixed fruit waste (MFW) was investigated using anaerobic sludge from a sewage treatment plant. The pH of the broth mixture was adjusted to 6.0, anaerobic conditions were created by purging it with nitrogen gas, and the temperature of the fermentative biohydrogen process was maintained at 60 degrees C. Meanwhile, the H2S adsorption test was run at ambient temperature with flow rates (100 ml/min) and an H2S inlet concentration of 10000 ppm. The results indicate that the Z + H2S exhibit spectral lines corresponding to the S-H asymmetric stretching vibration of H2S at 2345.97 cm-1. The ideal adsorption capacity is at 0.8 g with yet, increasing the dosage amount of adsorbents, increases the time required for the adsorbent to achieve 90% saturation. The non-linear curve fitting demonstrated that the adsorption kinetics of all dosages used followed those of the Avrami kinetic model. This approach of using ZSM-5 zeolite for H2S removal provides an advantage in terms of minimizing environmental pollution and having great potential uses in industrial processes. image

Research into the speciation of sulfur and hydrogen molecules produced through the complex process of thermophilic dark fermentation has been conducted. Detailed surface studies of solid-gas systems using real biogas (biohydrogen) streams have unveiled the mechanisms and specific interactions between these gases and the physicochemical properties of a zeolite as an adsorbent. These findings highlight the potential of zeolites to effectively capture and interact with these molecules. In this study, the hydrogen sulphide removal analysis was conducted using 0.8 g of the adsorbent and at various reaction temperatures (25-125 degrees C), a flow rate of 100 mL min-1, and an initial concentration of approximately 5000 ppm hydrogen sulphide. The reaction temperature has been observed to be an essential parameter of Zeolite Socony Mobil - 5 adsorption capacity. The optimum adsorption capacity attains a maximum value of 0.00890 mg g-1 at an optimal temperature of 25 degrees C. The formation of sulphur species resulting from the hydrogen sulphide adsorption on the zeolite determines the kinetics, thermodynamics, and mass transfer behaviours of Zeolite Socony Mobil - 5 in hydrogen sulphide removal and Zeolite Socony Mobil - 5 is found to improve the quality of biohydrogen produced in thermophilic environments. Biohydrogen (raw gas) yield was enhanced from 2.48 mol H2 mol-1 hexose consumed before adsorption to 2.59 mol H2 mol-1 hexose consumed after adsorption at a temperature of 25 degrees C. The Avrami kinetic model was fitted for hydrogen sulphide removal on Zeolite Socony Mobil - 5. The process is explained well and fitted using the Temkin isotherm model and the investigation into thermodynamics reveals that the adsorption behaviour is exothermic and non-spontaneous. Furthermore, the gas molecule's freedom of movement becomes random. The adsorption phase is restricted by intra-particle diffusion followed by film diffusion during the transfer of hydrogen sulphide into the pores of Zeolite Socony Mobil - 5 prior to adsorption on its active sites. The utilisation of Zeolite Socony Mobil - 5 for hydrogen sulphide removal offers the benefit of reducing environmental contamination and exhibiting significant applications in industrial operations. The speciation of sulphur and hydrogen molecules produced by thermophilic dark fermentation has been elucidated through surface studies of solid-gas systems utilising real biogas (biohydrogen) streams.

Escalating global water pollution exacerbated by textile-dyeing wastewater (TDW) poses significant environmental and health concerns due to the insufficient treatment methods being utilized. Thus, it is imperative to implement more effective treatment solutions to address such issues. In this research, different environmentally-friendly strategies involving effluent recirculation (ER) and Rubia cordifolia plant-derived purpurin electron mediator (EM) were introduced to enhance the treatment of real TDW and bioelectricity generation performance of an anti-gravity flow microbial fuel cell (AGF-MFC). The results revealed that optimum performance was achieved with a combination of hydraulic retention time (HRT) of 48 h with a recirculation ratio of 1, where the reduction efficiency of biochemical oxygen demand (BOD5), chemical oxygen demand (COD), ammonium (NH4+), nitrate (NO3-), sulphate (SO42-), ammonia nitrogen (NH3-N), colour and turbidity were 82.17 %, 82.15 %, 85.10 %, 80.52 %, 75.91 %, 59.52 %, 71.02 % and 93.10 %, respectively. In terms of bioelectricity generation performance, AGF-MFC showed a maximum output voltage and power density of 404.72 mV and 65.16 mW/m2, respectively. Moreover, the results also signified that higher treatment performance of TDW was obtained with natural purpurin from Rubia cordifolia plant than synthetic purpurin as EM. The reduced reactivity of highly stable synthetic purpurin EM for mediating the electron transfer was a contributing factor to the outperformance of plant-derived purpurin. Additionally, detailed electron-mediating mechanisms of purpurin were proposed to unravel the underlying electron transfer pathway involved in AGF-MFC. This research offers insight into the development of more sustainable solutions for managing TDW, and consequently reducing environmental pollution.

The ability of poly-ferric-silicate-sulphate (PFSS) synthesized via a co-polymerization process has been applied for the removal of diazo Congo red dye. A novel degradation pathway of diazo Congo red dye by using PFSS is proposed based on LC–MS analysis. Diazo Congo red dye was successfully removed using synthesized PFSS at lower coagulant dosages and a wider pH range, i.e., 9 mg/L from pH 5 to 7, 11 mg/L at pH 9, and 50 mg/L at pH 11. The azo bond cleavage was verified by the UV–Vis spectra of diazo Congo red-loaded PFSS and FTIR spectra which showed disappearance of the peak at 1584 cm−1 for –N=N– stretching vibrations. The synchronized results of UV–Vis spectra, FTIR, and the LC–MS analysis in this study confirmed the significance of the Si and Fe bond in PFSS towards the degradation of diazo Congo red dye. The successfully synthesized PFSS coagulant was characterized by FTIR, SEM, TEM, and HRTEM analysis. From this analysis, it was proven that PFSS is a polycrystalline material which is favorable for the coagulation–flocculation process. Based on all these findings, it was established that synthesized PFSS can be employed as a highly efficient polymeric coagulant for the removal of dye from wastewater.

The enhancement of up-flow constructed wetland-microbial fuel cell (UFCW-MFC) performance in energy retrieval from caffeine containing wastewater has been explored via various operating conditions (hydraulic retention time (HRT), multianode (MA), multicathode current collector (MC), external resistance). The anaerobic decaffeination and COD removal improved by 37 and 12

In an aim to completely degrade refractory phenolic compounds for effective wastewater treatment, a sustainable strategy using anthraquinone-rich herbal plant contents as electron shuttles is presented. This study is the first attempt of treating four different chemical structures of monohydric phenols, while simultaneously generate lowcarbon electricity in a microbial fuel cell. An electron shuttle-mediated strategy was introduced to investigate the effect of electron shuttle against the degradation of phenolic pollutants and bioelectricity generation, by employing Rheum officinale extract as electron shuttle. Results revealed that there was a two-fold increase in chemical oxygen demand (COD) removal, degradation extent of phenol and cresol isomers, output voltage and power density of MFC, compared to the mediator-free MFC system. The degradation of phenol yielded higher COD removal, degradation efficiency, output voltage and power generation over cresol isomers, with and without the application of electron shuttle. A complete removal of COD and phenol, with output voltage of 620.06 mV and power density of 252.49 mW/m2 were obtained. Phenol outperformed cresol isomers with regard to its sole activating hydroxy (-OH) group, lower dipole moment and higher electronic conductivity (8.53 mS/ cm). Conversely, meta-cresol exhibited the lowest removal efficiency and power generation, ascribed to greater inductive influence of methyl group in meta position on the dissociation energy of the - OH group. Moreover, detection of the phenolic intermediates by gas chromatograph-mass spectrometer analysis was conducted, and detailed degradation pathways were presented.

This study aimed to compare the performance of biofiltration, constructed wetland, and constructed wetland microbial fuel cell (CW-MFC). The transformation from a biofiltration unit to a hybrid CW-MFC was demonstrated with the advantages of improvement of wastewater treatment while generating electricity simultaneously. The introduction of plants to the upper region of the bioreactor enhanced the DO level by 0.8 mg/L, ammonium removal by 5 %, and COD removal by 1 %. The integration of electrodes and external circuits stimulated the degradation rate of organic matter in the anodic region (1 % without aeration and 3 % with aeration) and produced 5.13 mW/m(3) of maximum power density. Artificial aeration improved the nitrification efficiency by 38 % and further removed the residual COD to an efficiency of 99 %. The maximum power density was also increased by 3.2 times (16.71 mW/m(3)) with the aid of aeration. In treating higher organic loading wastewater (3M), the maximum power density showed a significant increment to 78.01 mW/m(3) (4.6-fold) and the COD removal efficiency was 98 %. The ohmic overpotential dominated the proportion of total loss (67-91 %), which could be ascribed to the low ionic conductivity. The reduction in activation and concentration loss contributed to the lower internal resistance with the additional aeration and higher organic loading. Overall, the transformation from biofiltration to a hybrid CW-MFC system is worthwhile since the systems quite resemble while CW-MFC could improve the wastewater treatment as well as recover energy from the treated wastewater.

The treatment of single and binary azo dyes, as well as the effect of the circuit connection, aeration, and plant on the performance of UFCW-MFC, were explored in this study. The decolorization efficiency of Remazol Yellow FG (RY) (single dye: 98.2 %; binary dye: 92.3 %) was higher than Reactive Black 5 (RB5) (single: 92.3 %; binary: 86.7 %), which could be due to monoazo dye (RY) requiring fewer electrons to break the azo bond compared to the diazo dye (RB5). In contrast, the higher decolorization rate of RB5 in binary dye indicated the removal rate was affected by the electron-withdrawing groups in the dye structure. The closed circuit enhanced about 2% of color and 4% of COD removal. Aeration improved the COD removal by 6%, which could be contributed by the mineralization of intermediates. The toxicity of azo dyes was reduced by 11-26% and the degradation pathways were proposed. The dye removal by the plants was increased with a higher contact time. RB5 was more favorable to be uptook by the plant as RB5 holds a higher partial positive charge. 127.39 (RY), 125.82 (RB5), and 58.66 mW/m3 (binary) of maximum power density were generated. The lower power production in treating the binary dye could be due to more electrons being utilized for the degradation of higher dye concentration. Overall, the UFCW-MFC operated in a closed circuit, aerated, and planted conditions achieved the optimum performance in treating binary azo dyes containing wastewater (dye: 87-92%; COD: 91%) compared to the other conditions (dye: 83-92%; COD: 78-87%).