In-situ regeneration of activated carbon with electric potential swing desorption (EPSD) for the H2S removal from biogas

Application of persulfate-based oxidation processes to address diverse sustainability challenges: A critical review

Over the past years, persulfate (PS) is widely applied due to their high versatility and efficacy in decontamination and sterilization. While treatment of organic chemicals, remediation of soil and groundwater, sludge treatment, disinfection on pathogen microorganisms have been covered by most published reviews, there are no comprehensive and specific reviews on its application to address diverse sustainability challenges, including solid waste treatment, resources recovery and regeneration of ecomaterials. PS applications mainly rely on direct oxidation by PS itself or the reactive sulfate radical (SO₄^•-) or hydroxyl radical (^•OH) from the activation of peroxodisulfate (PDS, S₂O₈^2-) or peroxymonosulfate (PMS, HSO₅^-) in SO₄^•--based advanced oxidation processes (SO₄^•--AOPs). From a broader perspective of environmental cleanup and sustainability, this review summarizes the various applications of PS except pollutant decontamination and elaborates the possible reaction mechanisms. Additionally, the differences between PS treatment and conventional technologies are highlighted. Challenges, research needs and future prospect are thus discussed to promote the development of the applications of PS-based oxidation processes in niche environmental fields. In all, this review is a call to pay more attention to the possibilities of PS application in practical resource reutilization and environmental protection except widely reported pollutant degradation.

Biochar for agronomy, animal farming, anaerobic digestion, composting, water treatment, soil remediation, construction, energy storage, and carbon sequestration: a review

In the context of climate change and the circular economy, biochar has recently found many applications in various sectors as a versatile and recycled material. Here, we review application of biochar-based for carbon sink, covering agronomy, animal farming, anaerobic digestion, composting, environmental remediation, construction, and energy storage. The ultimate storage reservoirs for biochar are soils, civil infrastructure, and landfills. Biochar-based fertilisers, which combine traditional fertilisers with biochar as a nutrient carrier, are promising in agronomy. The use of biochar as a feed additive for animals shows benefits in terms of animal growth, gut microbiota, reduced enteric methane production, egg yield, and endo-toxicant mitigation. Biochar enhances anaerobic digestion operations, primarily for biogas generation and upgrading, performance and sustainability, and the mitigation of inhibitory impurities. In composts, biochar controls the release of greenhouse gases and enhances microbial activity. Co-composted biochar improves soil properties and enhances crop productivity. Pristine and engineered biochar can also be employed for water and soil remediation to remove pollutants. In construction, biochar can be added to cement or asphalt, thus conferring structural and functional advantages. Incorporating biochar in biocomposites improves insulation, electromagnetic radiation protection and moisture control. Finally, synthesising biochar-based materials for energy storage applications requires additional functionalisation.

Thermal Analysis and Energy Efficiency Improvements in Tunnel Kiln for Sustainable Environment

Kiln is a prime need in the ceramics industry, where energy loss is a major part which consumes about 60% production cost through thermal energy for different applications. Higher density of fired and tunnel kiln refractory material lowers the thermal diffusivity and the proper selection of fired material minimizes the energy loss along the kiln. In particular, this research analysed the results of a heat recovery system comprised of a metallic recuperator which gives around 8% energy savings in natural gas consumption. In this work, detailed power quality analysis of low-power factor motors of a tunnel kiln was carried out and a power factor improvement solution was suggested to save electrical energy with payback period of 0.8 y. The motor operating at a low-power factor consumes more reactive power which does not produce beneficial work. A low-power factor around 0.4 causes network power loss, increases in transformer loss and voltage drops. The solution with accumulative capacitance power of 148.05 uF was installed to achieve the power factor to 0.9. Flu gas analyzer was installed to monitor the range of O2 in pre-heating, oxidation, and firing zones of the kiln which should be ≥8% and 3%, respectively. Regression analysis for thermal energy consumption of a tunnel kiln is done to find the forecast thermal energy consumption. This analysis can be used to find operational efficiency, supporting decisions regarding dependent variable of thermal energy consumption and independent variable of production. This research is very helpful for the ceramics industry to mitigate the energy loss at SMEs as well as in mass production level.

Performance and mechanism of hydrogen sulfide removal by sludge-based activated carbons prepared by recommended modification methods

The sludge-based activated carbons (SACs) were prepared by sewage sludge and corn straw and modified by ferric nitrate. The H₂S removal performance and the desulfurization mechanism of the modified SAC were studied. Results showed that breakthrough sulfur capacity and saturation sulfur capacity of the SAC prepared by recommended modification were 27.209 mg/g and 48.098 mg/g, which were as 4.68 times and 7.02 times larger as those before modification, respectively. Additionally, results showed that the desulfurization products of unmodified SAC were mainly sulfur, while that of modified SAC were mainly sulfate. These results indicated that ferric nitrate modification changed the way of hydrogen sulfide removal by SAC: the desulfurization process of unmodified SAC can be expressed as S^2- → S⁰ → S⁴⁺ → S⁶⁺, and the oxidative active component was dominated by O*, while that of modified SAC can be expressed as S^2- → S⁰ → S⁶⁺, and the oxidative active components are both Fe³⁺ and O*.

Innovative operational strategies in photosynthetic biogas upgrading in an outdoors pilot scale algal-bacterial photobioreactor

Three innovative operational strategies were successfully evaluated to improve the quality of biomethane in an outdoors pilot scale photobioreactor interconnected to an external absorption unit: i) the use of a greenhouse during winter conditions, ii) a direct CO₂ stripping in the photobioreactor via air stripping during winter conditions and iii) the use of digestate as make-up water during summer conditions. CO₂ concentrations in the biomethane ranged from 0.4% to 6.1% using the greenhouse, from 0.3% to 2.6% when air was injected in the photobioreactor and from 0.4% to 0.9% using digestate as make up water. H₂S was completely removed under all strategies tested. On the other hand, CH₄ concentrations in biomethane ranged from 89.5% to 98.2%, from 93.0% to 98.2% and from 96.3% to 97.9%, when implementing strategies i), ii) and iii), respectively. The greenhouse was capable of maintaining microalgae productivities of 7.5 g m^-2 d^-1 during continental weather conditions, while mechanical CO₂ stripping increased the pH in order to support an effective CO₂ and H₂S removal. Finally, the high evaporation rates during summer conditions allowed maintaining high inorganic carbon concentrations in the cultivation broth using centrate, which provided a cost-effective biogas upgrading.

Optimization of a 660 MWe Supercritical Power Plant Performance—A Case of Industry 4.0 in the Data-Driven Operational Management Part 1. Thermal Efficiency

This paper presents a comprehensive step-wise methodology for implementing industry 4.0 in a functional coal power plant. The overall efficiency of a 660 MWe supercritical coal-fired plant using real operational data is considered in the study. Conventional and advanced AI-based techniques are used to present comprehensive data visualization. Monte-Carlo experimentation on artificial neural network (ANN) and least square support vector machine (LSSVM) process models and interval adjoint significance analysis (IASA) are performed to eliminate insignificant control variables. Effective and validated ANN and LSSVM process models are developed and comprehensively compared. The ANN process model proved to be significantly more effective; especially, in terms of the capacity to be deployed as a robust and reliable AI model for industrial data analysis and decision making. A detailed investigation of efficient power generation is presented under 50%, 75%, and 100% power plant unit load. Up to 7.20%, 6.85%, and 8.60% savings in heat input values are identified at 50%, 75%, and 100% unit load, respectively, without compromising the power plant’s overall thermal efficiency.

CO2 capture through electro-conductive adsorbent using physical adsorption system for sustainable development

The most critical energy and environmental challenge that our planet is facing today is to minimize the dependence on fossil fuels. Carbon dioxide may be of utmost significance as a solution of this issue through realization of carbon neutral energy cycle. Potentially, this could be achieved through the carbon dioxide capture as the urgent response to ongoing climate change. Activated carbon (AC) adsorption is one the most effective, environment friendly and techno-economic process for the carbon capture. In the current research, an electro-conductive-activated carbon was prepared by mixing powdered activated carbon (PAC) with an electro-conductive polymer (ECP). Different ratios of 0, 25, 50, 75 and 100 wt% of ECP with PAC were used for the different analyses of activated carbons in a gas mixture of CO₂/N₂ using a physical adsorption system. Adsorption and desorption analyses, capacities of the process and desorption effects were examined. Electro-conductive polymers (ECP) were mixed with AC samples, where breakthrough time was increased up to 400% when mixed with the PAC for CO₂ adsorption. Following adsorption analysis, desorption of activated carbons was conducted with different potentials. It was revealed that mixing could help the PAC sample to overcome the packing issue to increase the breakthrough capacity and the volumes before and after the breakthrough adsorption in the packed bed systems. The desorption rates of the PAC sample were also enhanced, and fast desorption was observed when mixed with ECP. It is envisioned that this method is very much promising carbon capture method for the techno-economic feasibility and sustainable development of the environment.

Use of Gasoline, LPG and LPG-HHO Blend in SI Engine: A Comparative Performance for Emission Control and Sustainable Environment

The rising global warming concerns and explosive degradation of the environment requires the mainstream utilization of alternative fuels, such as hydroxy gas (HHO) which presents itself as a viable substitute for extracting the benefits of hydrogen. Therefore, an experimental study of the performance and emission characteristics of alternative fuels in contrast to conventional gasoline was undertaken. For experimentation, a spark ignition engine was run on a multitude of fuels comprising of gasoline, Liquefied petroleum gas (LPG) and hybrid blend of HHO with LPG. The engine was operated at 60% open throttle with engine speed ranging from 1600 rpm to 3400 rpm. Simultaneously, the corresponding performance parameters including brake specific fuel consumption, brake power and brake thermal efficiency were investigated. Emission levels of CO, CO2, HC and NOx were quantified in the specified speed range. To check the suitability of the acquired experimental data, it was subjected to a Weibull distribution fit. Enhanced performance efficiency and reduced emissions were observed with the combustion of the hybrid mixture of LPG with HHO in comparison to LPG: on average, brake power increased by 7% while the brake specific fuel consumption reduced by 15%. On the other hand, emissions relative to LPG decreased by 21%, 9% and 21.8% in cases of CO, CO2, and unburned hydrocarbons respectively. Incorporating alternative fuels would not only imply reduced dependency on conventional fuels but would also contribute to their sustainability for future generations. Simultaneously, the decrease in harmful environmental pollutants would help to mitigate and combat the threats of climate change.

Modification of acidic and textural properties of a sulphated zirconia catalyst for efficient conversion of high-density polyethylene into liquid fuel

Consumption of plastic has a rapid increase of about 8% per annum and reached to 400 million per tonnes approximately, where about 50% of plastic was disposed after using only once. Different techniques for treating this increased waste faced a number of issues related to cost and environmental and sustainable development. Catalytic conversion has been found as one of the most viable solutions to solve this problem. Sulphated zirconia (SZ) catalyst modified with calcium carbide (CC) was found to improve high-density polyethylene (HDPE) conversion into liquid fuel. The liquid content was improved from 39.0wt% to 66.0wt% at 410 °C. HDPE was converted 100% by weight using, SZ/CC with 66wt% liquid yield as compared to the conversion of approximately 98wt% with about 40wt% only liquid yield for the pure SZ. The composition of hydrocarbon liquid product was significantly changed from paraffin (16%) and aromatic (58%) to olefin (74%) and naphthenic (23%) compounds. This significant increase in liquid was related to changes in the acidic and textural characteristics of the new hybrid catalyst, SZ/CC where the total ammonia desorption of 337.0 μm NH₃/g for the SZ was modified to 23.4 μm NH₃/g for the SZ/CC. Both SZ and SZ/CC catalysts showed characteristics of mesoporous material, where the internal pore volume of SZ had reduced from 0.21 mL/g for SZ to 0.04 mL/g for SZ/CC. Furthermore, XRD analysis indicated the presence of a new compound, CaZrO₃ in the SZ/CC, which confirmed a chemical interaction between the SZ and CC through sintering of ZrO₂ and CaO. Therefore, the SZ/CC catalyst improves the liquid yield significantly and the selectivity towards olefinic and naphthenic compounds.

Influence of liquid-to-biogas ratio and alkalinity on the biogas upgrading performance in a demo scale algal-bacterial photobioreactor

The influence of the liquid-to-biogas ratio (L/G) and alkalinity on methane quality was evaluated in a 11.7 m³ outdoors horizontal semi-closed tubular photobioreactor interconnected to a 45-L absorption column (AC). CO₂ concentrations in the upgraded methane ranged from <0.1 to 9.6% at L/G of 2.0 and 0.5, respectively, with maximum CH₄ concentrations of 89.7% at a L/G of 1.0. Moreover, an enhanced CO₂ removal (mediating a decrease in CO₂ concentration from 9.6 to 1.2%) and therefore higher CH₄ contents (increasing from 88.0 to 93.2%) were observed when increasing the alkalinity of the AC cultivation broth from 42 ± 1 mg L^-1 to 996 ± 42 mg L^-1. H₂S was completely removed regardless of the L/G or the alkalinity in AC. The continuous operation of the photobioreactor with optimized operating parameters resulted in contents of CO₂ (<0.1%-1.4%), H₂S (<0.7 mg m^-3) and CH₄ (94.1%-98.8%) complying with international regulations for methane injection into natural gas grids.

Ignition sensitivity of different compositional wood pellets and particle size dependence

Partial or complete substitution of coal with renewable biomass like wood is a sustainable and effective solution to reduce the CO₂ emissions in the atmosphere. Utilization of these woods in the form of compact pellets facilitates in its handling and transportation with higher energy density. However, for electric power generation the pellets are broken up into their constituent milled finer particles for burning as a pulverised biomass flame. There is a dust fire/explosibility hazards in the process handling facilities such as in storage, conveying and milling. In the present work, four commercial pellets were investigated, and each pellet sample was split into three size ranges <63 μm, 63-500 μm and <500 μm. The flame propagation characteristics and their lean flammability limit for each pulverised pellet was determined using modified Hartmann dust explosion tube. It was found that the fine particles, with lower lean flammability limits of 0.3-0.7 equivalence ratio, intensify the explosibility risk (dP/dt of 10-15 bar/s for most reactive concentration) of the dust due to fast volatile release rate. Comparison was also made between particle size distribution (PSD) of the finer fractions (<63 μm) of wood samples in comparison to crop residue samples that showed 70-80% larger size distribution for wood samples due to elongated particles as showed by Scanning Electron Microscope (SEM). Results showed that the ash + moisture content had a stronger effect on wood samples than on agricultural residue's samples. The results showed that the explosibility characteristics of the pellets industry's feed-stocks was variable and dependent on the pellet composition and this needs to be taken into account in explosion protection and in utilising the pellets in the main pulverised biomass combustion.

Seasonal variation of biogas upgrading coupled with digestate treatment in an outdoors pilot scale algal-bacterial photobioreactor

The yearly variations of the quality of the upgraded biogas and the efficiency of digestate treatment were evaluated in an outdoors pilot scale high rate algal pond (HRAP) interconnected to an external absorption column (AC) via a conical settler. CO₂ concentrations in the upgraded biogas ranged from 0.7% in August to 11.9% in December, while a complete H₂S removal was achieved regardless of the operational month. CH₄ concentrations ranged from 85.2% in December to 97.9% in June, with a limited O₂ and N₂ stripping in the upgraded biogas mediated by the low recycling liquid/biogas ratio in the AC. Biomass productivity ranged from 0.0 g m^-2 d^-1 in winter to 22.5 g m^-2 d^-1 in summer. Finally, microalgae diversity was severely reduced throughout the year likely due to the increasing salinity in the cultivation broth of the HRAP induced by process operation in the absence of effluent.