Sewage biogas efficient purification by means of lignocellulosic waste-based activated carbons

Agri-food waste biosorbents for volatile organic compounds removal from air and industrial gases - A review

Approximately 1.3 billion metric tons of agricultural and food waste is produced annually, highlighting the need for appropriate processing and management strategies. This paper provides an exhaustive overview of the utilization of agri-food waste as a biosorbents for the elimination of volatile organic compounds (VOCs) from gaseous streams. The review paper underscores the critical role of waste management in the context of a circular economy, wherein waste is not viewed as a final product, but rather as a valuable resource for innovative processes. This perspective is consistent with the principles of resource efficiency and sustainability. Various types of waste have been described as effective biosorbents, and methods for biosorbents preparation have been discussed, including thermal treatment, surface activation, and doping with nitrogen, phosphorus, and sulfur atoms. This review further investigates the applications of these biosorbents in adsorbing VOCs from gaseous streams and elucidates the primary mechanisms governing the adsorption process. Additionally, this study sheds light on methods of biosorbents regeneration, which is a key aspect of practical applications. The paper concludes with a critical commentary and discussion of future perspectives in this field, emphasizing the need for more research and innovation in waste management to fully realize the potential of a circular economy. This review serves as a valuable resource for researchers and practitioners interested in the potential use of agri-food waste biosorbents for VOCs removal, marking a significant first step toward considering these aspects together.

Enhanced benzene vapor adsorption through microwave-assisted fabrication of activated carbon from peanut shells using ZnCl2 as an activating agent

Herein, microwave-assisted activated carbon (MW-AC) was fabricated from peanut shells using a ZnCl2 activator and utilized for the first time to eliminate benzene vapor as a volatile organic compound (VOC). During the MW-AC production process, which involved two steps-microwave treatment and muffle furnace heating-we investigated the effects of various factors and achieved the highest iodine number of 1250 mg/g. This was achieved under optimal operating conditions, which included a 100% impregnation ratio, CO2 as the gas in the microwave environment, a microwave power set at 500 W, a microwave duration of 10 min, an activation temperature of 500 °C and an activation time of 45 min. The structural and morphological properties of the optimized MW-AC were assessed through SEM, FTIR, and BET analysis. The dynamic adsorption process of benzene on the optimized MW-AC adsorbent, which has a significant BET surface area of 1204.90 m2/g, was designed using the Box-Behnken approach within the response surface methodology. Under optimal experimental conditions, including a contact duration of 80 min, an inlet concentration of 18 ppm, and a temperature of 26 °C, the maximum adsorption capacity reached was 568.34 mg/g. The experimental data are better described by the pseudo-second-order kinetic model, while it is concluded that the equilibrium data are better described by the Langmuir isotherm model. MW-AC exhibited a reuse efficiency of 86.54% for benzene vapor after five consecutive recycling processes. The motivation of the study highlights the high adsorption capacity and superior reuse efficiency of MW-AC adsorbent with high BET surface area against benzene pollutant. According to our results, the developed MW-AC presents itself as a promising adsorbent candidate for the treatment of VOCs in various industrial applications.

Removal of Hexamethyldisiloxane via a Novel Hydrophobic (3-Aminopropyl)Trimethoxysilane-Modified Activated Porous Carbon

Volatile methyl siloxanes (VMS) must be removed because the formation of silica in the combustion process seriously affects the resource utilization of biogas. Herein, a series of APTMS ((3-aminopropyl)trimethoxysilane)-modified activated porous carbon (APC) adsorbents (named APTMS@APC) were prepared for VMS efficient removal. The as-prepared adsorbents were characterized using SEM, FTIR, Raman, X-ray diffraction analyses, and N2 adsorption/desorption. The results showed that the surface modification with APTMS enhanced the hydrophobicity of APC with the water contact angle increasing from 74.3° (hydrophilic) to 127.1° (hydrophobic), and meanwhile improved its texture properties with the SBET increasing from 981 to 1274 m2 g-1. The maximum breakthrough adsorption capacity of APTMS@APC for hexamethyldisiloxane (L2, model pollutant) was 360.1 mg g-1. Effects of an inlet L2 concentration (31.04-83.82 mg L-1) and a bed temperature (0-50 °C) on the removal of L2 were investigated. Meanwhile, after five adsorption-desorption cycles, the APTMS@APC demonstrated a superior cycling performance. This indicated that the hydrophobic APTMS@APC has a great significance to remove VMS.

Applications of agricultural residue biochars to removal of toxic gases emitted from chemical plants: A review

Crop residues are representative agricultural waste materials, massively generated in the world. However, a large fraction of them is currently being wasted, though they have a high potential to be used as a value-added carbon-rich material. Also, the applications of carbon-rich materials from agricultural waste to industries can have economic benefit because waste-derived carbon materials are considered inexpensive waste materials. In this review, valorization methods for crop residues as carbon-rich materials (i.e., biochars) and their applications to industrial toxic gas removals are discussed. Applications of crop residue biochars to toxic gas removal can have significant environmental benefits and economic feasibility. As such, this review discussed the technical advantages of the use of crop residue biochars as adsorbents for hazardous gaseous pollutants and greenhouse gases (GHGs) stemmed from combustion of fossil fuels and the different refinery processes. Also, the practical benefits from the activation methods in line with the biochar properties were comprehensively discussed. The relationships between the physico-chemical properties of biochars and the removal mechanisms of gaseous pollutants (H₂S, SO₂, Hg⁰, and CO₂) on biochars were also highlighted in this review study. Porosity controls using physical and chemical activations along with the addition of specific functional groups and metals on biochars have significantly contributed to the enhancement of flue gas adsorption. The adsorption capacity of biochar for each toxic chemical was in the range of 46-76 mg g^-1 for H₂S, 40-182 mg g^-1 for SO₂, 80-952 μg g^-1 for Hg⁰, and 82-308 mg g^-1 CO₂, respectively. This helps to find suitable activation methods for adsorption of the target pollutants. In the last part, the benefits from the use of biochars and the research directions were prospectively provided to make crop residue biochars more practical materials in adsorption of pollutant gases.

Using Waste Tire-Derived Particles to Remove Benzene and n-Hexane by Dynamic and Static Adsorption

Scrap tire rubber particles were used and evaluated to adsorb some gaseous volatile organic compounds (VOCs), such as benzene and n-hexane. The results present that the adsorption capacities were 0.18 and 0.072 mg/g for n-hexane and benzene, respectively, in the static adsorption mode; the effective adsorption may be attributed to the carbon black of the tire. The adsorption process is in accordance with the Freundlich isothermal model and Lagergren pseudo-first-order kinetic equation. Correspondingly, the adsorption process is multilayer adsorption analyzed by the intramolecular diffusion model. In the dynamic adsorption mode, the maximum adsorption efficiencies of n-hexane and benzene were 80.7 and 81%, respectively, at flow velocities of 0.1 L/min n-hexane and 0.2 L/min benzene.

The core microbiome is responsible for volatile silicon and organic compounds degradation during anoxic lab scale biotrickling filter performance

Volatile silicon compounds present in the biogas of anaerobic digesters can cause severe problems in the energy recovery systems, inducing costly damages. Herein, the microbial community of a lab-scale biotrickling filter (BTF) was studied while testing its biodegradation capacity on octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5), in the presence of toluene, limonene and hexane. The reactor performance was tested at different empty bed residence times (EBRT) and packing materials. Community structure was analysed by bar-coded amplicon sequencing of the 16S rRNA gene. Microbial diversity and richness were higher in the inoculum and progressively decreased during BTF operation (Simpson's diversity index changing from 0.98-0.90 and Richness from 900 to 200 OTUs). Minimum diversity was found when reactor was operated at relatively low EBRT (7.3 min) using a multicomponent feed. The core community was composed of 36 OTUs (accounting for 55% of total sequences). Packing material played a key role in the community structure. Betaproteobacteriales were dominant in the presence of lava rock and were partially substituted by Corynebacteriales and Rhizobiales when activated carbon was added to the BTF. Despite these changes, a stable and resilient core microbiome was selected defining a set of potentially degrading bacteria for siloxane bioremoval as a complementary alternative to non-regenerative adsorption onto activated carbon.

A Promising Solution for Food Waste: Preparing Activated Carbons for Phenol Removal from Water Streams

Phenol and its derivatives are highly toxic chemicals and are widely used in various industrial applications. Therefore, the industrial wastewater streams must be treated to lower the concentration of phenol before discharge. At the same time, food waste has been a major environmental problem globally and the scientific community is eagerly seeking effective management solutions. The objective of this study was to understand the potential of utilizing food waste as a renewable and sustainable resource for the production of activated carbons for the removal of phenol from water streams. The food waste was pyrolyzed and physically activated by steam. The pyrolysis and activation conditions were optimized to obtain activated carbons with high surface area. The activated carbon with the highest surface area, 745 m2 g-1, was derived via activation at 950 °C for 1 h. A detailed characterization of the physicochemical and morphological properties of the activated carbons derived from food waste was performed and a comprehensive adsorption study was conducted to investigate the potential of using the activated carbons for phenol removal from water streams. The effects of pH, contact time, and initial concentration of phenol in water were studied and adsorption models were applied to experimental data to interpret the adsorption process. A remarkable phenol adsorption capacity of 568 mg g-1 was achieved. The results indicated that the pseudo-second-order kinetic model was better over the pseudo-second-order kinetic model to describe the kinetics of adsorption. The intraparticle diffusion model showed multiple regions, suggesting that the intraparticle diffusion was not the sole rate-controlling step of adsorption. The Langmuir isotherm model was the best model out of Freundlich, Temkin, and Dubinin-Radushkevich models to describe the phenol adsorption on activated carbons derived from food waste. This study demonstrated that food waste could be utilized to produce activated carbon and it showed promising capacity on phenol removal.

Nitrogen-doped porous biochar derived from marine algae for efficient solid-phase microextraction of chlorobenzenes from aqueous solution

Nitrogen-doped porous biochar (NPB) with a large specific surface area, wide pore size distribution, graphitized structure, nitrogen doping, and hydrophobicity was fabricated by high-temperature modification of algal biochar with potassium carbonate. This NPB was then uniformly coated on stainless steel wire as a novel solid-phase microextraction (SPME) fiber. The extraction efficiency of NPB-coated fiber for seven chlorobenzenes (CBs) was excellent; it was 1.0-112.2 times higher than that of commercial SPME fibers. A trace determination method was developed for seven CBs in water with the optimized extraction conditions by NPB-coated fiber and gas chromatography-electron capture detector, which showed wide linear ranges (1-1000 ng L^-1), low detection limits (0.007-0.079 ng L^-1), great repeatability (2.5-6.5% for intra-day, and 3.1-6.8% for inter-day), and excellent reproducibility (3.5-6.3%, n = 5). The practicality of the developed method was evaluated using real water samples and showed great recoveries (89.55-105.19%). This study showed that low-cost biomass wastes could be converted to advanced biochar materials by a facile method, and displayed excellent performance in SPME applications.

Microwave-assisted catalytic pyrolysis of waste printed circuit boards, and migration and distribution of bromine

Microwave-assisted pyrolysis (MAP) of waste printed circuit boards (WPCB) was performed to investigate the characteristics of pyrolysis product and Br fixation. Pyrolysis conversion increased with increasing temperature, reaching 93.3 % at 650 °C. However, increasing heating time did not exhibit remarkable influence on pyrolysis conversion. At 350 °C, phenols were main compounds in the oil accounting for 91.15 %. As the temperature increased to 650 °C, polycyclic aromatic hydrocarbons and monocyclic aromatic hydrocarbons (except phenols) increased to 20.55 % and 19.03 %, respectively. Meanwhile, the total content of CO₂, CO, CH₄ and H₂ in the non-condensable gases increased significantly. Addition of ZSM-5 and kaolin promoted the recombination reaction of pyrolysis products, increased the relative percentage of monocyclic aromatic hydrocarbons (except phenols) and C₁₁-C₂₀ compounds in the oil, and reduced non-condensable gases. The oxygen bomb-ion chromatography was used to evaluate the Br content of pyrolysis residues. Higher pyrolysis temperature enhanced transfer of Br to pyrolysis gas. K₂CO₃, Na₂CO₃ and NaOH reacted with hydrogen bromide to generate KBr and NaBr, which significantly improved the Br fixation efficiency of pyrolysis residues (i.e. from 29.11%-99.80%, 96.39 % and 86.69 %, respectively) and reduced Br content in pyrolysis gas.

More Sustainable Chemical Activation Strategies for the Production of Porous Carbons

The preparation of porous carbons attracts a great deal of attention given the importance of these materials in many emerging applications, such as hydrogen storage, CO₂ capture, and energy storage in supercapacitors and batteries. In particular, porous carbons produced by applying chemical activation methods are preferred because of the high pore development achieved. However, given the environmental risks associated with conventional activating agents such as KOH, the development of greener chemical activation methodologies is an important objective. This Review summarizes recent progress in the production of porous carbons by using more sustainable strategies based on chemical activation. The use of less-corrosive chemical agents as an alternative to KOH is thoroughly reviewed. In addition, progress achieved to date by using emerging self-activation methodologies applied to organic salts and biomass products is also discussed.

Effects of temperature, oxygen and steam on pore structure characteristics of coconut husk activated carbon powders prepared by one-step rapid pyrolysis activation process

Activated carbon powders made from coconut husk (CHCs) were prepared by one-step rapid pyrolysis activation process. Effects of temperature, oxygen and steam on the pore structure of CHCs were investigated. Results showed that high temperature, oxygen and steam all motivated the development of the CHCs pore structure. High temperature accelerated the evaporation of volatiles and led to more micropore structures. Oxygen promoted the development of both micropores and mesopores. CHCs' porosity separately presented a linear and a logarithmic growth with the increase of the preparation temperature and oxygen content. CHCs prepared under 1000 ℃ with activation agents of 6% oxygen and 20% steam exhibited the largest specific surface area and total pore volume of 415.85 m²/g and 0.1748 cm³/g. Steam can diffuse into the CHC matrix and enhance the formation of more mesopores. Steam over 20% would over-burn the substance and lead to the collapse of some pore structures.

Potential use of Methylibium sp. as a biodegradation tool in organosilicon and volatile compounds removal for biogas upgrading

Organosilicon compounds are the most undesirable compounds for the energy recovery of biogas. These compounds are still resistant to biodegradation when biotechnologies are considered for biogas purification. Herein we isolated 52 bacterial species from anaerobic batch enrichment cultures (BEC) saturated with D4 and from an anaerobic lab-scale biotrickling filter (BTF) fed with a gas flow containing D4 as unique carbon source. Among those Methylibium sp. and Pseudomonas aeruginosa showed the highest capacity to remove D4 (53.04% ± 0.03 and 24.42% ± 0.02, respectively). Contrarily, co-culture evaluation treatment for the biodegradation of siloxanes together with volatile organic compounds removed a lower concentration of D4 compared to toluene and limonene, which were completely removed. Remarkably, the siloxane D5 proved to be more biodegradable than D4. Substrates removal values achieved by Methylibium sp. suggested that this bacterial isolate could be used in biological removal technologies of siloxanes.

Continuous pretreatment, hydrolysis, and fermentation of organic residues for the production of biochemicals

Agricultural residues pose a valuable resource. Through microbial fermentations, a variety of products can be obtained, ranging from fuels to platform chemicals. Depending on the nature of the organic residue, pretreatment and hydrolysis are needed prior to fermentation in order to release fermentable sugars. Continuous set-ups are common for the production of methane or ethanol from lignocellulosic biomass, however, this does not apply for the fermentative generation of biochemicals, an approach that conserves chemical functionality present in biomass. Certainly, continuous set-ups could beneficially contribute to bioeconomy by providing techniques allowing the production of biochemicals in a sustainable and efficient way. This review summarizes research conducted on the continuous pretreatment, hydrolysis, and fermentation of lignocellulosic biomass, and particularly towards the production of the biobased molecules: Succinic and lactic acid.

Preparation of high-performance toluene adsorbents by sugarcane bagasse carbonization combined with surface modification

A series of activated carbons were prepared by carbonizing sugarcane bagasse combined with surface modification, which showed an excellent performance of adsorbing toluene (522 mg g⁻¹ at 30 °C).

Efficient removal of siloxanes and volatile organic compounds from sewage biogas by an anoxic biotrickling filter supplemented with activated carbon

The removal of siloxanes (D4 and D5) and volatile organic contaminants (hexane, toluene and limonene) typically found in sewage biogas was investigated in a lab-scale biotrickling filter (BTF) packed with lava rock under anoxic conditions. Complete removal efficiencies for toluene and limonene were recorded at all empty bed residence time (EBRT) tested. The influence of EBRT was remarkable on the abatement of D5, whose removal decreased from 37% at 14.5 min to 16% at 4 min, while the removal of D4 and hexane remained below 16%. The packing material was supplemented with 20% of activated carbon aiming at increasing the mass transfer of the most hydrophobic pollutants. This strategy supported high removal efficiencies of 43 and 45% for hexane and D5 at the lowest EBRT. CO₂ and silica were identified as mineralization products along with the presence of metabolites in the trickling solution such as dimethylsilanediol, 2-carene and α-terpinene.

Characterization the level of a new low-cost adsorbent material prepared from date palm kernel pits via DP-LIBS and ICP-OES spectroscopic techniques

We successfully developed a fast detection system based on orthogonal dual-pulsed laser-induced breakdown spectroscopy (DP-LIBS) to characterize the level of a new low-cost adsorbent material prepared from date palm kernel pits. The activated carbon (AC) was produced from different heated and chemically treated date palm kernel pit samples to be used as adsorbent material for the removal of some pollutants from wastewater. The quantitative, as well as qualitative analysis, was performed using the DP-LIBS analytical technique. Hence, the valuable elements like the carbon present in the date palm kernel pits was perfectly recognized. The registered spectra of the sample cover the spectral lines of carbon. The quantitative analysis of carbon, carried out in different samples of date palm kernel pits, using DP-LIBS revealed that the estimated limit of detection of carbon in these samples is about 225.19 mg/L. The precision of DP-LIBS data for determining the concentration of activated carbon element present in the date palm kernel pits was validated via the inductively coupled plasma-optical emission spectrometry (ICP-OES) as a standard technique.

Environmental Decision Support System for Biogas Upgrading to Feasible Fuel

Biogas production is a growing market and the existing conversion technologies require different biogas quality and characteristics. In pursuance of assisting decision-makers in biogas upgrading an environmental decision support system (EDSS) was developed. Since the field is rapidly progressing, this tool is easily updatable with new data from technical and scientific literature through the knowledge acquisition level. By a thorough technology review, the diagnosis level evaluates a wide spectrum of technologies for eliminating siloxanes, H2S, and CO2 from biogas, which are scored in a supervision level based upon environmental, economic, social and technical criteria. The sensitivity of the user towards those criteria is regarded by the EDSS giving a response based on its preferences. The EDSS was validated with data from a case-study for removing siloxanes from biogas in a sewage plant. The tool described the flow diagram of treatment alternatives and estimated the performance and effluent quality, which matched the treatment currently given in the facility. Adsorption onto activated carbon was the best-ranked technology due to its great efficiency and maturity as a commercial technology. On the other hand, biological technologies obtained high scores when economic and environmental criteria were preferred. The sensitivity analysis proved to be effective allowing the identification of the challenges and opportunities for the technologies considered.