Haldane-Andrews substrate inhibition kinetics for pilot scale thermophilic anaerobic degradation of sugarcane vinasse

An integrated review on the role of different biocatalysts, process parameters, bioreactor technologies and data-driven predictive models for upgrading biogas

As energy consumption and waste generation from human activities continue to rise, the technology of anaerobic digestion (AD), which converts waste into bioenergy, has gained popularity. Biogas produced from AD commonly contains 60 % CH4, 40 % CO2 and a minor fraction of impurities. Currently, several anaerobic reactors have been designed to upgrade the biogas with biomethane content above 90 %. This review summarizes the current trends in the biological upgradation of biogas from a bio-circular economy perspective to achieve sustainable energy goals. Examples of applications reporting the latest advancements in treating industrial effluents using high-rate anaerobic reactors have been mentioned. The integrated anaerobic-aerobic hybrid reactor offers a solution to the limitations of traditional methods in treating diverse effluents. A special focus on biological upgradation techniques such as in-situ, ex-situ, and hybrid mechanisms have been briefed. The key advantage of hybrid upgradation is its ability to address the pH rise during in-situ process. Additionally, the applications of artificial neural networks and optimization to upgrade biogas production have been discussed. The review concludes with future research directives with emphasis on the economic viability of the approaches.

Towards environmentally-friendly solutions for real textile-dyeing wastewater with energy recovery: Effluent recirculation and Rubia plant-derived purpurin electron mediator in microbial fuel cell

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.

Enrichment of biofertilizer-type hydrogen-oxidizing bacteria on urea containing Cu(II)

With the utilization of pesticides and fertilizers (e.g. urea), the presence of nitrogen and heavy metals (e.g. copper) can enter and pollute the environment. Biofertilizers can be used to replace chemical fertilizers to increase crop yields and reduce environmental stress. The utilization of hydrogen-oxidizing bacteria (HOB) to be biofertilizers has recently attracted more attention. However, the enrichment of HOB on urea and the effect of copper are undetermined. HOB were successfully enriched using urea in this investigation. The average urea conversion rate (AUCR) was 180.08 mgN/L/d with a hydraulic retention time of 10 h. Microbial community (R1) was dominated by Hydrogenophaga (83.92%), a biofertilizer-type HOB. After addition of 5.47 mg/L Cu2+, the AUCR was decreased by 16%-151.18 mgN/L/d, and the growth of HOB was inhibited by 48%. Meanwhile, inhibition was also reflected by the increase of polysaccharide content (20.27 ± 0.57 to 33.45 ± 2.53 mg/gVSS) and protein content (106.19 ± 19.39 to 125.14 ± 24.73 mg/gVSS) of extracellular polymeric substances in the HOB. The resulting microbial community (R2) was changed to Azospiralium-dominated flora (91.33%). Both enriched microbial communities (R1 and R2) exhibited the abilities of ACC degradation and phosphate solubilization. This study demonstrates that employing urea can directly enrich biofertilizer-type HOB and copper-tolerant HOB can be obtained in a 5.47 mg/L Cu2+ environment. The results provide potential methods to obtain biofertilizer from copper-containing urea wastewater via HOB.

Simulation of anaerobic co-digestion of steam explosion pulping wastewater with cattle manure: Focusing on degradation and inhibition of furfural

In this study, an extended Anaerobic Digestion Model No.1, which considered the degradation and inhibition properties of furfural, was established and implemented to simulate the anaerobic co-digestion of steam explosion pulping wastewater and cattle manure in batch and semi-continuous modes. Batch and semi-continuous experimental data helped calibrate the new model and recalibrate the parameters related to furfural degradation, respectively. The cross-validation results showed the batch-stage calibration model accurately predicted the methanogenic behavior of all experimental treatments (R² ≥ 0.959). Meanwhile, the recalibrated model satisfactorily matched the methane production results in the stable and high furfural loading stages in the semi-continuous experiment. In addition, recalibration results revealed the semi-continuous system tolerated furfural better than the batch system. These results provide insights into the anaerobic treatments and mathematical simulations of furfural-rich substrates.

Exploring the potential of thermophilic anaerobic co-digestion between agro-industrial waste and water hyacinth: operational performance, kinetic study and degradation pathway

Anaerobic co-digestion (co-AD) of agro-industrial waste, namely, palm oil mill effluent (POME) and sugarcane vinasse (Vn), with water hyacinth (WH) as co-substrate was carried out in two separate Anaerobic Suspended Growth Closed Bioreactors (ASGCBs) under thermophilic (55 °C) conditions. The highest chemical oxygen demand (COD) and soluble COD reduction in co-AD of POME-WH (78.61%, 78.86%) is slightly higher than co-AD of Vn-WH (75.75%, 78.24%). However, VFA reduction in co-AD of POME-WH (96.41%) is higher compared to co-AD of Vn-WH (85.94%). Subsequently, biogas production peaked at 13438 mL/day values and 16122 mL/day for co-AD of POME-WH and Vn-WH, respectively. However, the methane content was higher in the co-AD of POME-WH (72.04%) than in the co-AD of Vn-WH (69.86%). Growth yield (Y_G), maximum specific substrate utilization rate (r_x,max) and maximum specific biomass growth rate (μ_max) are higher in co-AD of POME-WH, as supported by the higher mixed liquor volatile suspended solids (MLVSS) and COD reduction efficiency compared to co-AD of Vn-WH. However, methane yield ([Formula: see text]) reported in the co-AD of POME-WH and Vn-WH are 0.2748 and 0.3112 L CH₄/g COD_reduction, respectively, which suggests that WH is a more suitable co-substrate for Vn compared to POME.

Transformation from biofiltration unit to hybrid constructed wetland-microbial fuel cell: Improvement of wastewater treatment performance and energy recovery

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/m³ 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/m³) with the aid of aeration. In treating higher organic loading wastewater (3M), the maximum power density showed a significant increment to 78.01 mW/m³ (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.

Chemical and biological combined treatment for sugarcane vinasse: selection of parameters and performance studies

Sugarcane vinasse has been reported as a high strength industrial wastewater that could cause severe environmental pollution due to its complex and bio-refractory compounds. Thus, the combined coagulation and sequencing batch biofilm reactor (SBBR) system was employed for the sugarcane vinasse treatment. This study aims to determine the recommended conditions of various parameters under coagulation and SBBR and investigate the effectiveness of combined processes. First, the approach of the coagulation process could achieve the maximum COD reduction and decolorization efficiencies of 79.0 ± 3.4% and 94.1 ± 1.9%, respectively, under the recommended conditions. Next, SBBR as an integrated biofilm reactor showed excellent synergistic biodegradability, removing 86.6 ± 4.3% COD concentration and 94.6 ± 3.8% color concentration at 3.0 g·COD/L of substrate loading concentration. The kinetic studies of SBBR revealed that the first-order kinetic model was the best fit for COD reduction efficiency. In contrast, the second-order kinetic model was the best fit for decolorization efficiency. The SBBR reaction was further investigated by ultraviolet-visible spectrophotometry (UV-Vis). In the combined processes, SBBR followed by the coagulation process (SBBR-CP) showed greater COD reduction and decolorization efficiencies (97.5 ± 0.3 and 99.4 ± 0.1%) when compared to the coagulation process followed by SBBR (CP-SBBR). This study demonstrated the removal performance and potential application of the combined sequential process to produce effluent that can be reused for bioethanol production and fertigation. This finding provides additional insight for developing effective vinasse treatment using combined chemical and biological processes.

Recent advances in biogas production using Agro-Industrial Waste: A comprehensive review outlook of Techno-Economic analysis

Agrowaste sources can be utilized to produce biogas by anaerobic digestion reaction. Fossil fuels have damaged the environment, while the biogas rectifies the issues related to the environment and climate change problems. Techno-economic analysis of biogas production is followed by nutrient recycling, reducing the greenhouse gas level, biorefinery purpose, and global warming effect. In addition, biogas production is mediated by different metabolic reactions, the usage of different microorganisms, purification process, upgrading process and removal of CO₂ from the gas mixture techniques. This review focuses on pre-treatment, usage of waste, production methods and application besides summarizing recent advancements in biogas production. Economical, technical, environmental properties and factors affecting biogas production as well as the future perspective of bioenergy are highlighted in the review. Among all agro-industrial wastes, sugarcane straw produced 94% of the biogas. In the future, to overcome all the problems related to biogas production and modify the production process.

Kinetic model discrimination on the biogas production in thermophilic co-digestion of sugarcane vinasse and water hyacinth

Co-digestion between sugarcane vinasse (Vn) and water hyacinth (WH) at various mixing ratios of 0:1, 1:0, 1:3, 3:1, and 1:1 was carried out under thermophilic conditions (55 °C) for 60 days. The effect of various mixing ratios on the pH changes, soluble chemical oxygen demand (sCOD) reduction, and cumulative biogas production was investigated. The first order, modified Gompertz, and logistic function kinetic models were selected to fit the experimental data. Model discrimination was conducted through the Akaike Information Criterion (AIC). The study revealed that co-digestion shows better performance compared to the mono-digestion of both substrates. Vn:WH mixing ratio 1:1 with inoculum to substrate ratio (ISR) of 0.38 g VS_inoculum/g VS_substrate is the most favorable ratio, achieving sCOD reduction efficiency and cumulative biogas production of 71.6% and 1229 mL, respectively. Model selection through AIC revealed that ratio 1:1 was best fitted to the logistic function kinetic model (R² = 0.9897) with Y_m and K values of 1232 mL and 31 mL/day, respectively.