Pilot scale evaluation of the BABIU process--upgrading of landfill gas or biogas with the use of MSWI bottom ash

Removal of CO2 from Biogas during Mineral Carbonation with Waste Materials

Biogas represents a source of renewable energy that could provide a replacement for fossil fuels to meet the increasing demand for energy. The upgrading of biogas through the removal of CO₂ to a content of 95-97% of CH₄ is necessary to increase its calorific value. This review focuses on biogas upgrading technologies using wastes or residues that enable the performing of mineral carbonation. In this research, we analyzed a natural biogas or synthetic one with a content of about (40-50%) of carbon dioxide. The chemical absorption is also briefly described in this study, due to its being the first step in innovative absorption and regeneration processes using mineral carbonization. Wastes with high calcium contents, i.e., ashes, steel-making slags, and stabilized wastewater anaerobic sludge, were considered for direct carbonization, taking into account the leaching of particles from carbonated wastes/residues. Moreover, the different types of reactors used for mineral carbonation have been described. The presented technological solutions are easy to use and economical, and some of them also take into account the regeneration of reagents. However, in the context of their direct use in biogas plants, it is necessary to consider the availability of wastes and residues.

A Review on Carbon Dioxide Minimization in Biogas Upgradation Technology by Chemical Absorption Processes

With an ever-increasing population and unpredictable climate changes, meeting energy demands and maintaining a sustainable environment on Earth are two of the greatest challenges of the future. Biogas can be a very significant renewable source of energy that can be used worldwide. However, to make it usable, upgrading the gas by removing the unwanted components is a very crucial step. CO₂ being one of the major unwanted components and also being a major greenhouse gas must be removed efficiently. Different methods such as physical adsorption, cryogenic separation, membrane separation, and chemical absorption have been discussed in detail in this review because of their availability, economic value, and lower environmental footprint. Three chemical absorption methods, including alkanolamines, alkali solvents, and amino acid salt solutions, are discussed. Their primary works with simple chemicals along with the latest works with more complex chemicals and different mechanical processes, such as the DECAB process, are discussed and compared. These discussions provide valuable insights into how different processes vary and how one is more advantageous or disadvantageous than the others. However, the best method is yet to be found with further research. Overall, this review emphasizes the need for biogas upgrading, and it discusses different methods of carbon capture while doing that. Methods discussed here can be a basic foundation for future research in carbon capture and green chemistry. This review will enlighten the readers about scientific and technological challenges regarding carbon dioxide minimization in biogas technology.

An innovative accelerated carbonation process for treatment of incineration bottom ash and biogas upgrading

Incineration is the main technology used for the management of municipal solid waste, in parallel to various recycling programs. However, incineration should not be considered as the final step for waste management as the ash still needs to be treated and disposed properly. In this work, an innovative accelerated carbonation of incineration bottom ash (IBA) using simulated biogas composition from anaerobic digestion processes (a mixture of CH₄ and CO₂) has been applied to lower the leaching of heavy metals from the carbonated IBA and its associated toxicity. Various temperatures and reaction times were explored for carbonation optimization and it was found that the carbonation at 25 °C for 8 h was the optimal reaction condition by taking into account the degree of carbonation and time constraint. The mineral content, functional groups, thermal stability, leaching patterns and ecotoxicity of both raw IBA and carbonated IBA were tested. It was found that carbonated IBA leached out less heavy metals than the raw IBA due to the locking of heavy metals in the calcite matrix. Cost-benefit analysis was also conducted on the industrial-scale process with a capacity of processing 10 tons of IBA per day. The results indicated that the proposed process had great economic potential.

Life cycle assessment applied to waste management in Italy: A mini-review of characteristics and methodological perspectives for local assessment

Life cycle assessment (LCA) and related tools are commonly used to evaluate the potential environmental impacts of waste treatment scenarios. This manuscript presents a mini-review of studies published over the last 10 years in Italy and aims to investigate how life cycle thinking tools are applied to assess the environmental sustainability of local-level waste policies. Results reveal that different waste flows, technologies and policies have been investigated independently and in varying detail. Review suggests that boundary selection significantly affects LCA results; integration of different waste systems is therefore crucial to avoid spatial or temporal shifts of environmental impacts. Moreover, the description of methodological characteristics, limitations and transversal aspects of Italian waste management studies allows various stakeholders to assess the reliability of past and future research for waste policy planning and rebound effects prevention. This review also highlights the need to define minimum requirements of transparency and ease of reporting of the studies to private and public stakeholders. Finally, the paper investigates whether using both the organisational LCA and the life cycle sustainability approach for the overall waste management process may be useful to develop a standard method to address multi-functionalities and multiple sites.

Performance of structural concrete using Waste-to-Energy (WTE) combined ash

In the U.S., about 27 million metric tons of municipal solid waste are used as fuel in Waste-to-Energy (WTE) power plants, generating about seven million tons of mixed bottom ash and fly ash (combined ash) annually, which are disposed of in landfills after metal separation. This study assessed the effect of using combined ash as a substitute of mined stone aggregates on the mechanical properties and leachability of cement mortar and concrete. The as-received combined ash was separated into three fractions: fine (<2 mm), medium (2-9.5 mm), and coarse (9.5-25 mm). The substitution of up to 100% of stone aggregate by the coarse and medium fractions of combined ash produced concrete with compressive strength exceeding 28 MPa after 28 days of curing. Similar results were obtained when the fine combined ash was used as a sand substitute, at 10 wt%, in mortar. The concrete specimens were subjected to several days of curing and mechanical testing. The results were comparable to the properties of commercial concrete products. The mechanical test results were supplemented by XRD and SEM analysis, and leachability tests by EPA Method 1313 showed that the optimal concrete products effectively immobilized the heavy metals in the combined ash.

Modalities for conversion of waste to energy - Challenges and perspectives

The United Nation is achieving its sustainable development objectives by focusing on the greener technologies for waste to energy (WTE) conversion. This necessitates the exploration of every conceivable sustainable route in different sectors. Among these, sustainable bio-economy, electricity, and waste management are the most dynamic areas. However, till now sustainability judgments for the generation of electricity from waste-to-energy supply chain (WTE-SC) technologies have been restricted in scale with respect to the three-dimensional sustainability structure (social, environmental, and economic). In most of the cases, the assessments were controlled by various environmental factors/indicators, via overlooking the economic and social indicators. In this review, we have tried to summarize a variety of state-of-the-art WTE technologies including biological and thermal treatment, landfill gas utilization and biorefineries technologies etc. These technologies can be implemented by various policy makers and agencies to deal with the communities fear before spreading and executing the relevant rules and regulations. The implementation of these rules and regulations for WTE-SC were scheduled to decide the barriers and challenges from the perspective of finance, institution, technology, and regulation.

Experimental Analysis and Model Validation on the Performance of Impregnated Activated Carbons for the Removal of Hydrogen Sulfide (H2S) from Sewage Biogas

Organic waste exploitation is crucial for waste emissions restraint in air, soil and water. This type of waste can be exploited to produce biogas, a valuable fuel exploitable for energy purposes. A circular approach for energy production is much cleaner and more sustainable than the traditional linear approach. In this work, organic waste was used for biogas production to feed a highly efficient solid oxide fuel cell power generator, which requires an ultra-purified fuel. Commercial sorbents were experimentally studied in conjunction with a dynamic adsorption model to predict the breakthrough time and organize the material change-over. In the presence of 0.1% oxygen in the gas mixture, AirDep® CKC showed a marked increase in the adsorption capacity (from 3.91 to 84.87 mg/g), overcoming SulfaTrap® R8G (49.91 mg/g). The effect of several operating parameters on adsorption capacity was evaluated: inlet H2S concentration, filter geometry and gas mixture velocity. Experimental data revealed that adsorption capacity increases with initial H2S concentration, following the typical trend of the Langmuir isotherm. Model simulations were in good agreement compared to experimental results, with an average relative error lower than 7%. A sensitivity analysis on the adsorption capacity was accomplished considering parameters from operational and empirical correlations.

Accelerated carbonation of wood combustion ash for CO2 removal from gaseous streams and storage in solid form

In this work, ash generated by the combustion of wood in a central heating plant was used to remove and permanently store by accelerated carbonation CO₂ contained in a gas mixture simulating biogas. The process was studied as an alternative treatment to the ones currently available on the market for biogas upgrading. The process was investigated at laboratory scale by setting up a facility for directly contacting the wood ash and the synthetic biogas in a fixed bed reactor. The process was able to completely remove CO₂ during its initial phase. After about 30 h, CO₂ started to appear again in the outlet stream and its concentration rapidly increased. The specific CO₂ uptake achieved in solid carbonate form was of about 200 g/kg of dry wood ash. This value is an order of magnitude higher than the ones found for waste incineration bottom ash carrying out similar experiments. The difference was ascribed to the physicochemical properties of the ash, characterized by a fine particle size (d₅₀ < 0.2 mm) and high content of reactive phases with CO₂ (e.g., Ca hydroxides). The leaching behavior of the wood ash was examined before and after the accelerated carbonation process showing that the release of several elements was lower after the treatment; Ba leaching in particular decreased by over two orders of magnitude. However, the release of the critical elements for the management of this type of residues (especially Cr and sulfates) appeared not to be significantly affected, while V leaching increased.

Biogas purification with biomass ash

The aim of the study was to investigate the option to purify biogas from small-scale biogas plants by entrapping CO₂ and H₂S with regionally available biomass ash. Connected to the existing biogas plant Neustift (Tyrol) wood ash placed in a 1 m³ container was used as a trap for CO₂ and H₂S in the biogas. With the process conditions chosen, for a period of a few hours CO₂ was trapped resulting in pure methane. The removal of H₂S was much longer-lasting (up to 34 d). The cumulative H₂S uptake by the biomass ash ranged from 0.56 to 1.25 kg H₂S per ton of ash. The pH of the ash and the leachability of Lead and Barium were reduced by the flushing with biogas, however toxicity towards plants was increased thus reducing the potential of ash use in agriculture. It can be concluded that biomass ash may be used for removal of hydrogen sulphide from biogas in small and medium biogas plants. The economic evaluation, however, indicated that the application of this system is limited by transport distances for the ash and its potential use afterwards.

The effect of the origin of MSWI bottom ash on the H2S elimination from landfill biogas

Municipal Solid Waste Incineration (MSWI) Bottom Ash (BA) is a potential alternative adsorbent for biogas treatment due to its reactivity with hydrogen sulfide (H₂S). The quality of BA depends however on the nature of the waste and the process technology of the waste incineration facility. To determine whether the origin of the BA could have an influence on its H₂S elimination efficiency, comparative experimental tests were conducted in a landfill site with six bottom ashes from different MSW incinerators. Results showed that one of the BAs (A) had a much higher adsorption capacity than the rest (B-F), with 37g H₂S/kg dry BA, compared to 11-16g H₂S/kg dry BA for the other bottom ashes. Detailed physico-chemical analyses of the six BA were performed and complemented by principal component analysis to understand the different behaviors. BA iron content and specific surface area provided by the quench product stood out as key factors that promote the elimination of H₂S.

Use of municipal solid waste incineration bottom ashes in alkali-activated materials, ceramics and granular applications: A review

This paper presents a literature review on the incorporation of municipal solid waste incinerated bottom ash as raw material in several markets, other than those where it is conventionally used, such as geotechnical applications and road pavement construction. The main findings of an ample selection of experimental investigations on the use of the bottom ash as precursor of alkali-activated materials, as an adsorbent material for the removal of hazardous elements from wastewater and landfill gases, as soil replacement in agricultural activities, as partial or complete substitute of raw materials for the manufacture of ceramic-based products, as landfill cover and as biogas production enhancer, were gathered, collated and analysed.

Valorization of MSWI bottom ash for biogas desulfurization: Influence of biogas water content

In this study an alternative valorization of Municipal Solid Waste Incineration (MSWI) Bottom Ash (BA) for H₂S elimination from landfill biogas was evaluated. Emphasis was given to the influence of water content in biogas on H₂S removal efficiency by BA. A small-scale pilot was developed and implemented in a landfill site located in France. A new biogas analyzer was used and allowed real-time continuous measurement of CH₄, CO₂, O₂, H₂S and H₂O in raw and treated biogas. The H₂S removal efficiency of bottom ash was evaluated for different inlet biogas humidities: from 4 to 24g_water/m³. The biogas water content was found to greatly affect bottom ash efficiency regarding H₂S removal. With humid inlet biogas the H₂S removal was almost 3 times higher than with a dry inlet biogas. Best removal capacity obtained was 56gH₂S/kgdryBA. A humid inlet biogas allows to conserve the bottom ash moisture content for a maximum H₂S retention.

Experimental evaluation of two different types of reactors for CO2 removal from gaseous stream by bottom ash accelerated carbonation

Low methane content landfill gas may be enriched by removing carbon dioxide. An innovative process, based on carbon dioxide capture and storage by means of accelerated carbonation of bottom ash is proposed and studied for the above purpose. Within this research framework we devoted a preliminary research activity to investigate the possibility of improving the way the contact between bottom ash and landfill gas takes place: this is the scope of the work reported in this paper. Two different types of reactors - fixed bed and rotating drum - were designed and constructed for this purpose. The process was investigated at laboratory scale. As the aim of this phase was the comparison of the performances of the two different reactors, we used a pure stream of CO₂ to preliminarily evaluate the reactor behaviors in the most favorable condition for the process (i.e. maximum CO₂ partial pressure at ambient condition). With respect to the simple fixed bed reactor concept, some modifications were proposed, consisting of separating the ash bed in three layers. With the three layer configuration we would like to reduce the possibility for the gas to follow preferential paths through the ash bed. However, the results showed that the process performances are not significantly influenced by the multiple layer arrangement. As an alternative to the fixed bed reactor, the rotating drum concept was selected in order to provide continuous mixing of the solids. Two operating parameters were considered and varied during the tests: the filling ratio and the rotating speed. Better performances were observed for lower filling ratio while the rotating speed showed minor importance. Finally the performances of the two reactors were compared. The rotating drum reactor is able to provide improved carbon dioxide removal with respect to the fixed bed one, especially when the rotating reactor is operated at low filling ratio values and slow rotating speed values. Comparing the carbon dioxide specific removal obtained by using the rotating reactor (35-37g/kg_BA), in the best operating conditions, with that measured for the fixed bed reactor (21-23g/kg_BA), an increase of about 61-66% is observed.

Upgraded biogas from municipal solid waste for natural gas substitution and CO2 reduction--a case study of Austria, Italy, and Spain

Biogas is rich in methane and can be further purified through biogas upgrading technologies, presenting a viable alternative to natural gas. Landfills and anaerobic digestors treating municipal solid waste are a large source of such biogas. They therefore offer an attractive opportunity to tap into this potential source of natural gas while at the same time minimizing the global warming impact resulting from methane emissions in waste management schemes (WMS) and fossil fuel consumption reduction. This study looks at the current municipal solid waste flows of Spain, Italy, and Austria over one year (2009), in order to determine how much biogas is generated. Then it examines how much natural gas could be substituted by using four different biogas upgrading technologies. Based on current waste generation rates, exploratory but realistic WMS were created for each country in order to maximize biogas production and potential for natural gas substitution. It was found that the potential substitution of natural gas by biogas resulting from the current WMS seems rather insignificant: 0.2% for Austria, 0.6% for Italy and 0.3% for Spain. However, if the WMS is redesigned to maximize biogas production, these figures can increase to 0.7% for Austria, 1% for Italy and 2% for Spain. Furthermore, the potential CO2 reduction as a consequence of capturing the biogas and replacing fossil fuel can result in up to a 93% reduction of the annual national waste greenhouse gas emissions of Spain and Italy.