H2S adsorption by municipal solid waste incineration (MSWI) fly ash with heavy metals immobilization

Resource utilization of MSWI fly ash supporting TiO2/BiOCl nanocomposite for enhanced photocatalytic degradation of sodium isopropyl xanthate: Mechanism and performance evaluation

The removal of organic pollutants in water environments and the resource utilization of solid waste are two pressing issues around the world. Facing the increasing pollution induced by discharge of mining effluents containing sodium isopropyl xanthate (SIPX), in this work, municipal solid waste incineration fly ash (MSWI FA) was pretreated by hydrothermal method to produce stabilized FA, which was then innovatively used as support for the construction of FA/TiO2/BiOCl nanocomposite (FTB) with promoted photocatalytic activity under visible light and natural sunlight. When the content of FA was 20 wt% and the mass ratio of TiO2 to BiOCl was 4:6, a remarkable performance for the optimal FTB (20-FTB-2) was achieved. Characterizations demonstrated that TiO2 and BiOCl uniformly dispersed on FA contributing to high surface area and broad light adsorption of FTB, which exhibits excellent adsorption capacity and light response ability. Build in electric field formed in the interface of TiO2/BiOCl heterojunction revealed by density functional theory calculations accelerated the separation of photoinduced e- and h+, leading to high efficiency for SIPX degradation. The synergetic effect combined with adsorption and photocatalytic degradation endowed 20-FTB-2 superior SIPX removal efficiency over 99% within 30 min under visible light and natural sunlight irradiation. The photocatalytic degradation pathways of SIPX were determined through theoretical calculations and characterizations, and the toxic byproduct CS2 was effectively eliminated through oxidation of •O2-. For 20-FTB-2, reusability of photocatalyst was showed by cycle tests, also the concentrations of main heavy metals (Pb, Zn, Cu, Cr, and Cd) in the liquid phases released during photocatalyst preparation process (< 1 mg/L) and photodegradation process (< 8.5 μg/L) proved the satisfactory stability with low toxicity. This work proposed a novel strategy to develop efficient and stable support-based photocatalysts by utilizing MSWI FA and realize its resource utilization.

Effects of complex sulphur substrates on sludge bioleaching to improve heavy metal removal and microbial community diversity

In this study, H2S was used as a partial replacement nutrient substrate for sludge bioleaching. The effects of different combinations of H2S/sludge load and monomeric sulphur on heavy metal removal and microbial communities were investigated. Changes in pH, oxidation-reduction potential (ORP), SO42- concentration, heavy metal removal, and the content of heavy metal states during bioleaching were investigated, and community diversity analysis was performed. Daily introduction of H2S three times (at an interval of 8 h) at a gas flow rate of 2 ml/min and an H2S/sludge load of 15 ml/L with 5 g/L FeSO4·7H2O and 2 g/L monomeric sulphur as a nutrient substrate significantly accelerated both the bioleaching process and the pH drop in the sludge system, promoted the production of SO42-, and maintained a higher redox potential. The combination of H2S and monomeric sulphur had a significant effect on the leaching of heavy metals. Compared with the experimental group containing only H2S or monomeric sulphur, the removal rates of Zn, Ni, Pb, and Cr increased by 4.63%/13.8%, 8.5%/20.07%, 3.84%/9.5%, and 4.24%/8.02% respectively, while promoting the transformation of various heavy metal states to labile states, improving heavy metal stability, and reducing sludge ecotoxicity. High-throughput sequencing analysis showed that introducing the H2S gaseous matrix accelerated the decreasing trend of species number, bacterial abundance, and community diversity in the sludge system, promoting Proteobacteria as the dominant phylum, Acidithiobacillus, Metallibacterium, and Thiomonas as the dominant genera, and improving the bioleaching treatment effect.

Ecological treatment of El Kriymat boiler ash for recovering vanadium, nickel and zinc from sulfate leach liquor

The primary goal of this work is to develop a technology that allows for the recovery of metal values from waste products, thereby promoting the wise and efficient use of our nation's resources. To achieve this goal, an industrial waste of El Kriymat boiler fly Ash was used for recovering its content of vanadium, nickel and zinc. About 97, 95 and 99% respectively of these economic elements were first dissolved from boiler fly ash magnetic concentrate (after physical concentration). Leaching experiments using optimum conditions include: 180 g/L sulfuric acid concentration and 4% solid/solid proportion manganese dioxide acts as an oxidant at 80 °C. The recovery of vanadium (V) metal ions was carried out using 3% Alamine 336 in kerosene at an equilibrium pH value of 0.9. Subsequently, 15% sodium sulfide solution was used for co-precipitation of nickel and zinc metal ions in the raffinate solution at pH value of 3.5.

Graphical Abstract

Microporous Biocarbons Derived from Inonotus obliquus Mushroom and Their Application in the Removal of Liquid and Gaseous Impurities

Biocarbons were obtained by physical and chemical activation of the residue of the extraction of chaga fungi (Inonotus obliquus). The residue was subjected to heat treatment carried out in a microwave oven and in a quartz tubular reactor. The materials were characterized by elemental analysis, low-temperature nitrogen adsorption, determination of pH, and the contents of acidic and basic oxygen functional groups on the surface of biocarbons by the Boehm method. The final biocarbon adsorbents have surface areas varying from 521-1004 m²/g. The physical activation of the precursor led to a strongly basic character of the surface. Chemical activation of Inonotus obliquus promoted the generation of acid functional groups. All biocarbons were used for methyl red sodium salt adsorption from the liquid phase. The sorption capacities of biocarbons towards the organic dye studied varied from 77 to 158 mg/g. The Langmuir model was found to better describe the experimental results. The results of the kinetic analysis showed that the adsorption of methyl red sodium salt on the biocarbons followed the pseudo-second-order model. The acidic environment was conducive to the adsorption of the dye on the obtained biocarbons. Moreover, thermodynamic studies confirmed that the organic dye adsorption on the biocarbons was a spontaneous endothermic process. The biocarbons obtained were also tested as adsorbents of hydrogen sulfide in dry and wet conditions. The sorption capacities towards hydrogen sulfide varied in the range of 21.9-77.9 mg. The results have shown that the adsorption of hydrogen sulfide depends on the process conditions and the activation procedure of biocarbons (method of activation and thermochemical treatment of samples). It has been shown that the initial material used can be a new precursor for obtaining cheap and-more importantly-universal bioadsorbents characterized by high effectiveness in the removal of air and water pollutants.

Co-stabilization/solidification of heavy metals in municipal solid waste incineration fly ash and electrolytic manganese residue based on self-bonding characteristics

Municipal solid waste incineration (MSWI) fly ash and electrolytic manganese residue (EMR) were classified as hazardous waste, must be harmlessly processed prior to subsequent treatment or disposal. The competition between massive free manganese ions of raw EMR and other heavy metals was found, thus raw EMR was pretreated by calcining to eliminate competition of manganese with other heavy metals for stabilizer complexation. MSWI fly ash was successfully solidified with 6% NaH₂PO₄, 6% H₂NCSNH₂ and 20% sintered EMR (800 °C). The addition of sintered EMR enhanced solidification/stabilization of heavy metals in fly ash and the resulting product had a higher compressive strength for further reutilization like trench backfilling, structural fill and void filling. The stabilization/solidification mechanism of heavy metals was attributed to the combined interaction of heavy metal precipitation in stabilizers and ion exchange or physical encapsulation in silicate compounds like calcium silicate, which is a feasible and valuable approach to co-disposal of MSWI fly ash and EMR.

Improvement in the physicochemical characteristics of biochar derived from solid digestate of food waste with different moisture contents

The management of digestate from food waste (DFW) has become a worldwide challenge. Pyrolysis is a promising technology to generate biochar from the DFW. However, unlike other biomass, DFW usually has high salt and moisture content, which affects the properties of biochar generated from pyrolysis. The characteristics of biochar derived from DFW with different MCs (5%, 20%, 40%, and 60%) were investigated in the present study. It was found that more micropore and mesopore structures were generated in the biochar with the increase of MC from 5% to 60%, resulting in the Brunauer-Emmett-Teller surface area of the biochar increased from 89.23 m² g^-1 to 117.75 m² g^-1. The MC could also promote the variation of oxygen-containing functional groups and the generation of amorphous carbon structures, which are beneficial for the adsorption property of the biochar. Pyrolysis could stabilize the metals in the biochar, while MC has little effect on the metal speciations. These results provide fundamental information on the impact of MC on the properties of biochar derived from DFW and are important for the optimization of the pre-drying process.

Cathodic Activation of Titania-Fly Ash Cenospheres for Efficient Electrochemical Hydrogen Production: A Proposed Solution to Treat Fly Ash Waste

Fly ash (FA) is a waste product generated in huge amounts by coal-fired electric and steam-generating plants. As a result, the use of FA alone or in conjunction with other materials is an intriguing study topic worth exploring. Herein, we used FA waste in conjunction with titanium oxide (TiO2) to create (FA-TiO2) nanocomposites. For the first time, a cathodic polarization pre-treatment regime was applied to such nanocomposites to efficiently produce hydrogen from an alkaline solution. The FA-TiO2 hybrid nanocomposites were prepared by a straightforward solvothermal approach in which the FA raw material was mixed with titanium precursor in dimethyl sulfoxide (DMSO) and refluxed during a given time. The obtained FA-TiO2 hybrid nanocomposites were fully characterized using various tools and displayed a cenosphere-like shape. The synthesized materials were tested as electrocatalysts for the hydrogen evolution reaction (HER) in 0.1 M KOH solution in the dark, employing various electrochemical techniques. The as-prepared (unactivated) FA-TiO2 exhibited a considerable HER electrocatalytic activity, with an onset potential (EHER) value of −144 mV vs. RHE, a Tafel slope (−bc) value of 124 mV dec−1 and an exchange current density (jo) of ~0.07 mA cm−2. The FA-TiO2′s HER catalytic performance was significantly enhanced upon cathodic activation (24 h of chronoamperometry measurements performed at a high cathodic potential of −1.0 V vs. RHE). The cathodically activated FA-TiO2 recorded HER electrochemical kinetic parameters of EHER = −28 mV, −bc = 115 mV dec−1, jo = 0.65 mA cm−2, and an overpotential η10 = 125 mV to yield a current density of 10 mA cm−2. Such parameters were comparable to those measured here for the commercial Pt/C under the same experimental conditions (EHER = −10 mV, −bc = 113 mV dec−1, jo = 0.88 mA cm−2, η10 = 110 mV), as well as to the most active electrocatalysts for H2 generation from aqueous alkaline electrolytes.

Sustainable Recovery of Valuable Nanoporous Materials from High-Chlorine MSWI Fly Ash by Ultrasound with Organic Acids

The new technology development for municipal solid waste incineration fly ash treatment and reuse is urgent due to landfill shortage and environmental effect of leached hazardous substances. Chlorine (Cl) is worth considering due to its high levels in fly ash. In this study, a treatment process of ultrasound combined with organic acid was used to eliminate Cl from fly ash to enhance its properties for reuse. Taguchi methodology was implemented to design the experiments by controlling four impact factors and the contribution of each factor was evaluated by the ANOVA analysis of variance. Following two treatment steps within 5 min with a solid/liquid ratio of 1:10 at 165 kHz, 98.8% of Cl was eliminated. Solid/liquid ratio was the most prominent factor that contributed to the Cl removal with more than 90%, according to the ANOVA analysis of variance. Tert-butyl alcohol (tBuOH), an •OH radical scavenger, was utilized to examine different effects of ultrasonic cavitation on Cl removal efficiency. A 20 kHz ultrasound was used to explore the influence of multi-frequency ultrasound with different mechanical and sonochemical effects on the fly ash dechlorination. This ultrasonic-assisted organic acid treatment was found to be a time and cost-effective pathway for fly ash Cl removal.

Co-digestion of primary sewage sludge with drinking water treatment sludge: A comprehensive evaluation of benefits

Anaerobic co-digestion of primary sludge with two types of drinking water treatment sludge (DWTS), namely iron- or aluminum-rich DWTS (Fe- or Al-DWTS) were systematically evaluated by biochemical methane potential tests, kinetic modelling, downstream process parameters and microbial community analysis. Specific methane yields decreased approximately 19% to 123 mL·g^-1 VS, while the hydrolysis constant k_h decreased from 0.21 d^-1 to 0.18 d^-1 for Fe-DWTS at 10% to 40% dosages. On the contrary, specific methane yields decreased 45-55% for Al-DWTS, and k_h decreased to 0.14 d^-1 at 40% dosage. Significant removals (>95%) of phosphate and hydrogen sulfide were observed for Fe- and Al-DWTS additions at 40% dosage. Microbial community analysis revealed that Al-DWTS increased the abundance of most hydrogenotrophic methanogens, while Fe-DWTS increased the abundance of acetoclastic methanogens. Kinetic modelling further revealed that Fe- and Al-DWTS additions affected the hydrolysis and methanogenesis process kinetics and the methane yield differently.

Relationship between heavy metal consolidation and H2S removal by biochar from microwave pyrolysis of municipal sludge: effect and mechanism

The synergistic effects of pyrolysis byproduct, biochar (BC) on heavy metal consolidation, and H₂S removal during and after from microwave pyrolysis of municipal sludge were studied in this paper. The results showed that above 80% of heavy metals (Zn and Pb) were enriched in the biochar and the leaching toxicity of both heavy metals was lower than the national emission standards. The chemical specification analysis found the sum of acid-soluble/exchangeable fraction (F1) and reducible fraction (F2) for Pb and Zn metals decreased by 26 and 40%; however, the residual fraction (F4) increased 33 and 46%, which contributed to the good stabilization of heavy metals in biochar. Besides, biochar achieved high H₂S removal efficiency of 78.4% compared with the commercial activated carbon (AC). Furthermore, the biochar prepared by microwave pyrolysis had excellent adsorption performance, which was attributed to its larger specific surface area of 476.87m²/g under nitrogen atmosphere at 650^oC compared with traditional pyrolysis. The mechanism analysis showed that microwave pyrolysis resulted in the high alkaline condition and formation of a large number of microparticles containing large metal elements on the biochar surface, which mainly contributed to the stabilization of heavy metals. The metal oxides adsorbed on the surface of biochar can catalyze the oxidation of H₂S absorption, which will change the pH atmosphere of biochar reducing the leaching behavior of heavy metals. This study provided the good application potential of solid waste (biochar) for simultaneous heavy metal stabilization and H₂S capture.

Assessment of heavy metals mobility and correlative recovery and decontamination from MSWI fly ash: Mechanism and hydrometallurgical process evaluation

Fly ash from municipal solid waste incineration (MSWI) enriches many leachable toxic metals which readily migrate into the environment, posing serious risks to the ecosystem and human. In this study, the elements mobility, leaching availability as well as the potential maximum amounts of heavy metals in fly ash were thoroughly evaluated. To decontaminate the toxic elements from resulting fly ash leachates, The aqueous zinc (Zn) was recovered using Cyanex 572, cadmium (Cd) and copper (Cu) were effectively removed through adsorption process by a self-assembled hierarchical hydroxyapatite (HAP) nanostructure. The removal mechanism of Cd, Cu and Zn by leaching, extraction and adsorption was revealed with the results from XRD, ICP-MS and SEM. The results showed that fly ash has a high mobility under maximum availability leaching test (95% of fly ash was dissolved), a recovery rate of 91% for Zn can be obtained using Cyanex 572, and a high adsorption rate (> 95% for both Cu and Cd) was reached using HAP for the pristine fly ash leachate. The outcomes from isothermal and kinetic study revealed that Langmuir isotherm and pseudo-second order model can well describe the Cd and Cu adsorption behavior. Economic assessment suggested that the application of HAP for the removal of Cd and Cu is a technically sound and economically feasible approach. The findings of this study demonstrated that this comprehensive process integrated leaching, solvent extraction and consequential decontamination can be a practical strategy for MSWI fly ash treatment.

Application of Alum Sludge in Wastewater Treatment Processes: “Science” of Reuse and Reclamation Pathways

Alum sludge (AlS) refers to the inevitable by-product generated during the drinking water purification process, where Al-salt is used as a coagulant in the water industry. It has long been treated as “waste”, while landfill is its major final disposal destination. In fact, AlS is an underutilized material with huge potential for beneficial reuse as a raw material in various wastewater treatment processes. In the last two decades, intensive studies have been conducted worldwide to explore the “science” and practical application of AlS. This paper focuses on the recent developments in the use of AlS that show its strong potential for reuse in wastewater treatment processes. In particular, the review covers the key “science” of the nature and mechanisms of AlS, revealing why AlS has the potential to be a value-added material. In addition, the future focus of research towards the widespread application of AlS as a raw material/product in commercial markets is suggested, which expands the scope for AlS research and development.

Environmental and human health risk evaluation of heavy metals in ceramsites from municipal solid waste incineration fly ash

Municipal solid waste incineration (MSWI) for power generation can reuse waste effectively, but it generates a large amount of fly ash enriched with heavy metals. If this fly ash cannot be treated properly, it can cause ecological damage and human health risk. According to the production of ceramsites from MSWI fly ash, an evaluation methodology is established, in which the influence of heavy metal stability on the environment is considered for the first time, and the health risks of heavy metals via different exposure pathways are distinguished. The results show that heavy metals in MSWI fly ash have moderate potential environmental risks to environment and have strong non-carcinogenic and carcinogenic risks both to children and adults. By contrast, heavy metals in ceramsites pose little risk to environment and human health. This paper explains some reasons of heavy metal content and leaching ratio change in ceramsite and also illustrates why stability is a concern through comparing the potential risk index method and the improved evaluation method. This evaluation system can be applied to different production processes of building materials using solid hazardous waste and provides a quantitative evaluation method for reducing environment and human health risks of heavy metals.

Electrospun PU nanofiber composites based on carbon nanotubes decorated with nickel-zinc ferrite particles as an adsorbent for removal of hydrogen sulfide from air

This study focuses on the synthesis of carbon nanotubes decorated with nickel-zinc ferrites and fabrication of polyurethane (PU) nanofiber containing CNT-ferrite composites as highly efficient adsorbents for removal of hydrogen sulfide. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformed infrared (FTIR) spectroscopy, and powder X-ray diffraction (PXRD) are used to perform microstructural and morphological characterization of the electrospun nanofibrous composites. To show the efficiency of the composite as an adsorbent, a breakthrough test is carried out. It is shown that the PU-CNT-ferrite composites are fabricated almost uniformly with an average fiber diameter of 320 nm and exhibit significant H₂S breakthrough capacity (498 mgH₂S/g) compared to both the pristine PU and PU-CNT nanofibers. These electrospun nanofibers based on CNT-ferrite composites, already studied for H₂S adsorption with promising results, open up new and interesting perspective into the design and fabrication of highly efficient membrane for practical application in the processes of air purification.

Selectivity of SO2 and H2S removal by ethanol-treated calcined eggshell at low temperature

Eggshell is a food waste produced worldwide in substantial amount with very limited recycling activity. In this study, the potential of ethanol-treated calcined eggshell was tested as sorbent for SO₂ and H₂S. Three variables were selected in the preparation of sorbents via response surface methodology (RSM), i.e., concentration of ethanol in water (50%, 70%, 90%), reaction temperature (20 °C, 40 °C, 60 °C), and contact time (30, 60, 90 min). Central composite design (CCD) was used to develop a quadratic model to correlate the operating variables with the adsorption capacity. Analysis of variance (ANOVA) was performed to identify the significant factors of the experimental design. It was found that the reaction temperature during the sorbent preparation was the most significant factor. The optimum preparation conditions using RSM were found at 20 °C of reaction temperature with 76.37% of ethanol concentration for 67 min of reaction time. The maximum adsorption capacity for the optimized sorbent was found to be 27.75 mg/g and 9.55 mg/g for SO₂ and H₂S, respectively. The prepared sorbent was more selective towards SO₂ compared with H₂S. Moreover, the presence of 40% of relative humidity in the inlet gas further enhanced the adsorption capacity of both gases. The ethanol-treated calcined eggshell was further substantiated by FESEM, BET, FTIR, XRD, and XRF. Results showed potential usage of eggshell as a sorbent for SO₂ and H₂S gases.

Alum sludge as an efficient sorbent for hydrogen sulfide removal: Experimental, mechanisms and modeling studies

This paper firstly reported a systematic study of using alum sludge (waterworks residue) for H₂S adsorption. Various trials were performed at ambient temperature in a fixed bed column to study the effects of H₂S flow rate, sorbent bed depth on the alum sludge adsorption efficiency of H₂S. The Breakthrough Curves were simulated by the Thomas model, Bed Depth Service Time model and Yoon-Nelson models. The mechanisms of H₂S adsorption onto alum sludge was examined by different physiochemical characterizations of exhausted and raw alum sludge. Moreover, the mass transfer coefficients were determined from mathematical descriptions of breakthrough curves. The alum sludge adsorption capacity was determined to be 374.2 mg of H₂S/g, slightly decreasing with the increasing flow rate and increasing with the increasing bed depth. All the three models successfully predict breakthrough curves which could be used for scaling-up purposes. The microporous structure, alkaline pH and the inherent metal species of the alum sludge promoted the formation of metal sulphate species. This study demonstrated that alum sludge could be used as cost-effective, largely available, and efficient sorbent for H₂S removal.

Emerging trends in municipal solid waste incineration ashes research: a bibliometric analysis from 1994 to 2018

The rapidly increasing generation of municipal solid waste (MSW) threatens the environmental integrity and well-being of humans at a global level. Incineration is regarded as a technically sound technology for the management of MSW. However, the effective management of the municipal solid waste incineration (MSWI) ashes remains a challenge. This article presents the global dynamics of MSWI ashes research from 1994 to 2018 based on a bibliometric analysis of 1810 publications (research articles and conference proceedings) extracted from the Web of Science database, followed by a comprehensive summary on the research developments in the field. The results indicate the rapid growth of annual publications on MSWI ashes research, with China observed as the most productive country within the study period. Waste Management, Journal of Hazardous Materials, Chemosphere and Waste Management & Research, which accounted for 35.42% of documents on MSWI research, are the most prominent journals in the field. The most critical thematic areas on this topic are MSWI ashes characterisation, dioxin emissions from fly ash, valorisation of bottom ash and heavy metal removal. The evolution of MSWI ashes treatment technologies is also discussed, together with the challenges and future research directions. This is the first bibliometric analysis on global MSWI ashes research based on a sufficiently large dataset, which could provide new insights for researchers to initiate further research with leading institutions/authors and ultimately advance this research field.

H2S Removal with Sorbent Obtained from Sewage Sludges

Biochar obtained from sewage sludges are adopted for biogas cleaning. Sewage sludges are treated considering temperature, dwell time, activating agent, heating, and flow rate. The best performances achieved are registered considering the char produced at 400 °C using CO2 as an activating agent with a dwell time of 2 h. The adsorption capacity for the biogas cleaning CH4/CO2/H2S (20 ppm(v)) increased from 1.3 mg/g to 5.9 mg/g with the bed height. Future research with chemical activation processes will be made to improve the adsorption capacity achieved to produce cheaper sorbents than commercial ones.

Dose effects of calcium peroxide on harmful gases emissions in the anoxic/anaerobic landscape water system

Large-area hypoxia of urban landscape water often causes the emissions of harmful gases in summer, which not only reduces its sensory effects, but also brings a potential threat to aquatic ecosystem and human health. This study explored the dose effects of calcium peroxide (CaO₂) on inhibiting harmful gases emissions and restoring the scenic effect (including visual sense and olfactory sense) of anoxic/anaerobic landscape water system. The results indicated that the emissions of H₂S, CO₂ and CH₄ from the anoxic/anaerobic water system were obviously inhibited in the reactors with CaO₂ additions and the effect was positively correlated with the CaO₂ dose. Meanwhile, the concentrations of total chemical oxygen demand (TCOD) and soluble sulfide (S^2-), and turbidity in the overlying water (the water-layer above the sediment-water interface) were also decreased in the reactors dosed with CaO₂. The reason was ascribed to the improvement of the anoxic/anaerobic condition in the water system and the increase of the species richness, bacteria count and aerobic microorganism abundance in sediment. Furthermore, 0.12 kg-CaO₂ m^-2-sediment was selected as the optimal dose, which was based on considering the inhibiting effect of the harmful gases emissions, comprehensive influence and costs. Compared with control check (CK, the reactor without adding CaO₂), the optimal dose of CaO₂ could reduce 75.10% CH₄, 81.02% CO₂ and 100% H₂S in gases, and decrease 81.52% S^2-, 42.85% TCOD and 84.01% turbidity in the overlying water. In conclusion, all the dosages of CaO₂ could improve the anoxic condition of water system and 0.12 kg-CaO₂ m^-2-sediment was the optimal dose in inhibiting harmful gases emissions, which could keep an excellent water quality in this simulation experiment. Therefore, this study may provide a feasible method and the optimal dose for inhibiting the emissions of harmful gases and restoring the scenic effect in the similar anoxic/anaerobic landscape water.

A review on the removal of hydrogen sulfide from biogas by adsorption using sorbents derived from waste

Biogas is a vital renewable energy source that could play an effective role in fulfilling the world’s energy demand, not only in heat and power generation but also as a vehicle fuel in the future. Unfortunately, due to impurities, biogas requires a series of upgrading steps, which affects its economics and sustainability. Hydrogen sulfide (H2S) is one of the impurities that economically and environmentally hinder the biogas utilization as a source of energy. H2S removal from biogas using different technologies was extensively studied and established. One of such technology is adsorption. Adsorption by solid sorbents is considered as a suitable removal technique for toxic gases such as H2S because of its simplicity, easy handling, and environmental friendly sorbents. In this review, the utilization of waste material-based sorbent for H2S removal was appraised. Other gaseous components of biogas such as siloxanes, CO2, etc., are out of the scope of this work. The potential and effectiveness of the waste-derived sorbents, either raw waste or modified waste, were summarized in terms of its characteristics, suitability, and sustainability. The review provides an insightful analysis of different types of wastes such as sewage sludge, food waste, forestry waste, fly ash, and industrial wastes as an alternative to commercial adsorbents to adsorb H2S gas. Based on the analysis, it was concluded that if these sorbents are to be successfully commercialized, its economic analysis, regeneration conditions, and potential utilization of the spent sorbents has to be further exploited. Nevertheless, there is a great prospectus in the future for these waste materials to be utilized as sorbents for H2S removal.

The Evaluation of the Heavy Metal Leaching Behavior of MSWI-FA Added Alkali-Activated Materials Bricks by Using Different Leaching Test Methods

Alkali-activated materials (AAMs) not only have the potential to replace cement applications in architecture and civil engineering, but also have an excellent effect on the stabilization solidification of hazardous industrial wastes. This study used two types of municipal solid waste incineration fly ash (MSWI-FA)-grate firing fly ash (GFFA) and fluidized bed fly ash (FBFA)-as AAMs brick raw materials. It is discovered from this study that AAMs bricks with different weight ratios of GFFA and FBFA can both meet the required standard of GB21144-2007 (Solid concrete brick). From the results obtained from the four leaching tests, the equilibrium pH of the leachate varies, resulting in significant differences in the leaching of heavy metals in Raw GFFA, Raw FBFA, and AAMs bricks with GFFA and FBFA. The AAMs brick with the addition of GFFA and FBFA has an alkali activation system to encapsulate heavy metals. By comparing the results obtained from the CEN/TS 14429 leaching behavior test and the four batch leaching tests, it was found that the most influential factors for the heavy metal leaching concentration are whether the heavy metal has been solidified/stabilized in the samples. GFFA and FBFA tend to have consistent characteristics after being activated by alkali to form AAMs bricks. This can be confirmed by the acid neutralization ability concentrated on a specific pH range. The results obtained from CEN/TS14429 verified that the AAMs bricks with the addition of GFFA and FBFA have excellent environmental compatibility and that it provides a comprehensive evaluation on the environmental compatibility of the test materials and products. This demonstrated that the MSWI-FA is suitable for used as alkali-activated materials and its products have the potential to be commercially used in the future.

Potential application of pre-treated municipal solid waste incineration fly ash as cement supplement

Pre-treatment process carried out on raw municipal solid waste incineration (MSWI) fly ash (FA) sample that did not comply initially with the USEPA method 1311 toxicity characteristic leaching procedure (TCLP) regulatory limits of 2011 reduced its chloride and heavy metal content appreciably, thereby making it compliant with the aforementioned regulatory requirement. More than 98% of each heavy metal was successfully removed. The process was excellent in removing cadmium (Cd) (99.99%) and very good at removing the rest. About 99.96% of Cu was eliminated, 99.96% of cobalt (Co), 99.95% of Zn, 98.61% of Cr, and 98.12% of nickel (Ni). Also, the leachate resulting from these pre-treatment steps met the China (GB 16889-2008) and USEPA method 1311 regulatory standards for safe discharge. The density and compressive strength of all the samples prepared increased as the FA content decreased. The compressive strength of all the samples passed the 1989 USEPA-recommended value of 0.34 MPa (50 psi), thereby making them suitable for industrial application. The sample that attained the highest compressive strength (2.08 MPa) after 28 days of curing incorporated 55% fly ash (FACS55), while the one with the least compressive strength (0.65 MPa) after the same period was made from only fly ash (FACS100). Moreover, the concentration of heavy metals in all the samples generally decreased with the FA content. Chromium was not detected in all the samples, thereby making this an excellent method for its immobilization. From the leachability test results, all the samples prepared met the USEPA method 1311 TCLP regulatory limits.