Stabilization of Waste-to-Energy (WTE) fly ash for disposal in landfills or use as cement substitute.

This study investigated two approaches for managing Waste-to-Energy (WTE) fly ash (FA): (i) phosphoric acid stabilization of FA and disposal in non-hazardous landfills, so that it can pass the U.S. TCLP procedure and meet the U.S. Resource Conservation and Recovery Act (RCRA) standards; (ii) use of FA or phosphoric acid stabilized fly ash (PFA) as cement substitute in construction for avoiding disposal in landfills and reducing the consumption of Portland cement. The effect of stabilization was identified by TCLP tests and XRD quantification (QXRD), which showed that the economically optimal concentration for PFA to pass the RCRA was 1 mol/L H3PO4 (equivalent to 0.4 mol of H3PO4/kg of FA). Zn/Pb-phosphates were formed in treated ash by using high concentration H3PO4 (e.g., 3 mol/L). Thus, the hazardous FA was chemically stabilized to PFA, that were both discussed as cement substitute. QXRD and SEM results showed that both FA and PFA (1 mol/L H3PO4) chemically reacted with cement and water. Up to 25 vol% of the cement can be replaced by FA or PFA, with similar mechanical performance of cement mortars than that of reference. Testing by LEAF Method 1313-pH dependence showed that the FA and PFA cement mortars exhibited the same leachability of heavy metals; therefore, this study demonstrated the technical feasibility of utilizing either raw FA or stabilized PFA as supplementary cementitious material. The leachability of heavy metals in optimal FA or PFA 25 vol% cement mortar was under the U.K. WAC non-hazardous limits.

Materials and energy recovery at six European MBT plants.

Mechanical Biological Treatment (MBT; called "dirty" Materials Recovery Facilities in the U.S.) is a waste management method, developed mostly in Europe, which combines sorting of recyclable materials (metals, paper, plastics, glass) with composting/digestion of green/ food wastes and, in some cases production of a fuel material. In 2018-19, the authors visited six MBT facilities in Europe that use different approaches for the recovery of materials and energy from mixed MSW. These plants were studied with respect to feedstock composition, operating conditions, capital expenditure, financial viability and environmental impacts. The compost product of most facilities examined did not comply with agricultural standards and, therefore, it was classified as compost-like output (CLO) and used as daily cover in landfills. The best composting practice used source separated organic materials (yard and other green wastes) and yielded a marketable compost. MBT plants that did not include the recovery of fuel materials had lower landfill diversion rates and, also, lower capital and operating costs. It was concluded that an MBT plant must include a very efficient sorting and recyclables recovery line and charge a sufficient gate fee. Also, in addition to the recycled products, there should be a stream to recover fuel materials sent to a power plant or cement plant, thus increasing revenue, and landfill diversion, and maximizing greenhouse gas (GHG) savings.

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.

Major sources of mercury emissions to the atmosphere: The U.S. case.

In 1989, the two major sources of mercury emissions to the atmosphere in the U.S. were coal-fired power plants (80 tons Hg) and waste to energy power plants (82 tons Hg). This paper examines what has happened to these two major sources of mercury emissions since 1989. A comparison within the waste management industry is, also, provided. The 2014 total anthropogenic emissions of mercury in the U.S. were 51.8 t. The results of the analysis of emissions by industrial sector showed that the largest source of anthropogenic mercury were coal-fired power plants. Among industrial processes, the ferrous metals recycling and the cement industries were the largest emitters of mercury. With regard to waste-to-energy power plants, all of which, since the nineties, have installed advanced emission control systems, the results have been very satisfactory: The authors obtained mercury emission data from operators of most of the waste-to-energy (WTE) power plants in the US. The results showed that in 2014 the 77 U.S. WTE plants in total emitted 0.4 tons of mercury, corresponding to 0.77% of the U.S. total. This number was one half of that reported by the National Emissions Inventory (NEI) for "municipal waste combustion'' (0.64 t) due to the fact that the NEI survey included incinerators without energy recovery. A 2002 Earth Engineering Center study had shown that the mercury emissions of the U.S. WTE industry decreased from 81.8 t in 1989 to 2.2 t in 2001. The present study showed that between 2001 and 2014 the U.S. WTE industry mercury emissions were reduced further, by a factor of seven.

Review on fate of chlorine during thermal processing of solid wastes.

Chlorine (Cl) is extensively present in solid wastes, causing significant problems during the thermal conversion of waste to energy or fuels, by combustion, gasification or pyrolysis. This paper introduces the analytical methods for determining the Cl content in solid materials and presents the concentrations of Cl in various types of wastes, as reported in literature. Then, it provides a comprehensive analysis on the Cl emission behavior and Cl species formed during the thermal processing of the inorganic and organic Cl sources. The challenges resulted from the reactions between the formed Cl species and the ferrous metals, the heavy metals and the organic matters are summarized and discussed, e.g., high temperature corrosion, heavy metal evaporation and dioxin formation. The quality degradation of products (oil, char and syngas) by Cl is analyzed. Finally, the available controlling methods of Cl emission, including pre-treatment (water washing, sorting, microwave irradiation and stepwise pyrolysis) and in-furnace (absorbents, co-treatment and catalysts) methods are assessed.

Inventory of U.S. 2012 dioxin emissions to atmosphere.

In 2006, the U.S. EPA published an inventory of dioxin emissions for the U.S. covering the period from 1987-2000. This paper is an updated inventory of all U.S. dioxin emissions to the atmosphere in the year 2012. The sources of emissions of polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), collectively referred to in this paper as "dioxins", were separated into two classes: controlled industrial and open burning sources. Controlled source emissions decreased 95.5% from 14.0 kg TEQ in 1987 to 0.6 kg in 2012. Open burning source emissions increased from 2.3 kg TEQ in 1987 to 2.9 kg in 2012. The 2012 dioxin emissions from 53 U.S. waste-to-energy (WTE) power plants were compiled on the basis of detailed data obtained from the two major U.S. WTE companies, representing 84% of the total MSW combusted (27.4 million metric tons). The dioxin emissions of all U.S. WTE plants in 2012 were 3.4 g TEQ and represented 0.54% of the controlled industrial dioxin emissions, and 0.09% of all dioxin emissions from controlled and open burning sources.

Technical assessment of the CLEERGAS moving grate-based process for energy generation from municipal solid waste.

A technical analysis has been completed for a commercial-scale two-stage gasification-combustion system. The CLEERGAS (Covanta Low Emissions Energy Recovery GASification) process consists of partial combustion and gasification of as-received municipal solid waste (MSW) on a moving grate producing syngas followed by full combustion of the generated syngas in an adjoining chamber and boiler. This process has been in operation since 2009 on a modified 330-tonne day(-1) waste-to-energy (WTE) line in Tulsa, Oklahoma. Material balances determined that the syngas composition is 12.8% H2 and 11.4% CO, the heating value of the gas in the gasifier section is 4098 kJ Nm(-3), and an aggregate molecular formula for the waste is C6H14.5O5. The analysis of gas measurements sampled from the Tulsa unit showed that the gasification-combustion mode fully processed the MSW at an excess air input of only 20% as compared to the 80-100% typically found in conventional WTE moving grate plants. Other important attributes of the CLEERGAS gasification-combustion process are that it has operated on a commercial scale for a period of over two years with 93% availability and utilizes a moving grate technology that is currently used in hundreds of WTE plants around the world.

Dioxin emissions from municipal solid waste incinerators (MSWIs) in France.

The objective of this study was to determine whether the fear of dioxin/furan emissions from waste-to-energy plants was justified by the 2007 status of emissions of French municipal solid waste incinerators (MSWIs). All emissions were examined, plant by plant, but this paper focuses on the incinerator emission that is most frequently mentioned in the French media, toxic dioxins and furans. The study showed that there are 85 large MSWI that generate electricity or heat, i.e., waste-to-energy (WTE) plants, and 39 smaller MSW incinerators. The results showed that all French MSWI are operated well below the EU and French standard of 0.1 ng TEQ Nm(-3) (toxic equivalent nanograms per standard cubic meter) and that their total dioxin/furan emissions decreased from 435 g TEQ in 1997 to only 1.2g in 2008. All other industrial emissions of dioxins have also decreased and the major source is residential combustion of wood (320 g TEQ). It was extremely difficult to obtain MSWI emission data. This unwarranted lack of transparency has resulted in the public perception that MSWI plants are major contributors to dioxin emissions while in fact they have ceased to be so.

A screening life cycle metric to benchmark the environmental sustainability of waste management systems.

The disposal of municipal solid waste (MSW) can lead to significant environmental burdens. The implementation of effective waste management practices, however, requires the ability to benchmark alternative systems from an environmental sustainability perspective. Existing metrics--such as recycling and generation rates, or the emissions of individual pollutants--often are not goal-oriented, are not readily comparable, and may not provide insight into the most effective options for improvement. Life cycle assessment (LCA) is an effective approach to quantify and compare systems, but full LCA comparisons typically involve significant expenditure of resources and time. In this work we develop a metric called the Resource Conservation Efficiency (RCE) that is based on a screening-LCA approach, and that can be used to rapidly and effectively benchmark (on a screening level) the ecological sustainability of waste management practices across multiple locations. We first demonstrate that this measure is an effective proxy by comparing RCE results with existing LCA inventory and impact assessment methods. We then demonstrate the use of the RCE metric by benchmarking the sustainability of waste management practices in two U.S. cities: San Francisco and Honolulu. The results show that while San Francisco does an excellent job recovering recyclable materials, adding a waste to energy (WTE) facility to their infrastructure would most beneficially impact the environmental performance of their waste management system. Honolulu would achieve the greatest gains by increasing the capture of easily recycled materials not currently being recovered. Overall results also highlight how the RCE metric may be used to provide insight into effective actions cities can take to boost the environmental performance of their waste management practices.

LCA comparison of windrow composting of yard wastes with use as alternative daily cover (ADC).

This study compared the environmental impacts of composting yard wastes in windrows with using them in place of soil as alternative daily cover (ADC) in landfills. The Life Cycle Assessment was made using the SimaPro LCA software and showed that the ADC scenario is more beneficial for the environment than windrow composting. ADC use is also a less costly means of disposal of yard wastes. This finding applies only in cases where there are sanitary landfills in the area that are equipped with gas collection systems and can use yard wastes as alternative daily cover. Otherwise, the environmentally preferable method for disposal of source-separated yard wastes is composting rather than landfilling.

Using a direct method to characterize and measure flows of municipal solid waste in the United States.

Although there are a myriad of sources of municipal solid waste (MSW) data in the United States, much of these data are not transparent and are also extremely difficult to find. In addition, the two major methods of quantifying national MSW flows-the BioCycle State of Garbage in America and the U.S. Environmental Protection Agency (EPA)/Franklin Associates' MSW "Facts and Figures" report-differ greatly in their reported results. This study, sponsored by EPA Region 9 and concentrating on the state of California, shows how an improved method of MSW measurement can be built upon the foundation provided by the State of Garbage in America (SOG) survey and complemented by an in-depth analysis of state data from various sources within a state. The primary goal of this methodology is to provide reliable, transparent, tonnage-based, and readily available MSW data for use by policy-makers, MSW managers, and the general public. California was used as the starting point because of the high volume of data available for that state, as well as the controversy surrounding its unusual method of collecting and reporting recycling rates. Also, because of California's size, its recycling tonnage has a large effect on overall U.S. national figures. It is therefore important to accurately quantify MSW management there. Results show that EPA underestimates U.S. MSW generation rates by a significant amount and that the methodology presented produces consistent and replicable results across different states.

Recycling in a megacity.

In the aftermath of the 9/11 disaster, Mayor Bloomberg of New York City unveiled an aggressive budget plan that included the temporary suspension of glass and plastics recycling. This was considered by many to be anti-environmental, but the results of this study show that for lack of markets, even at zero or negative prices, nearly 90% of the plastic and glass set aside by thoughtful New Yorkers was transported to materials recovery facilities (MRFs) and from there to landfills. Sending bales of plastics to landfills is not limited to New York City. It is an environmental paradox that the United States is digging up new oil fields in pristine areas and, at the same time, continues to convert greenfields to brownfields by burying nearly 20 million tons of plastic fuel annually. The study also determined that at the present rate of source separation, estimated to be less than 30% of the available recyclables in 1999, building large, modern MRFs may increase substantially the rate of New York City recycling and also allow single-stream collection of commingled recyclables, as is done in Phoenix, AZ. Single-stream collection simplifies separation at the source by citizens and increases the amount of collected recyclables. Also, because collection represents a large fraction of the costs of waste management, it may have a significant economic advantage.

Energy recovery from New York City municipal solid wastes.

This work was part of a major study that examined the policy and technology implications of alternatives for managing the municipal solid wastes (MSW) of New York City. At this time, of the 4.1 million metric tons of MSW collected by the City annually, 16.6% are recycled, 12.4% are combusted in Waste-to-Energy (WTE) plants, and the remaining 71% are landfilled. Despite the heterogeneity of organic materials in MSW, the composite molecular structure can be approximated by the organic compound C6H10O4. A formula was derived that allows the prediction of the heating value of MSW as a function of moisture and glass/metal content and compares well with experimentally derived values. The performance of a leading Waste-to-Energy plant that utilises suspension firing of shredded MSW, processes one million tons of MSW per year, and generates a net of 610 kWh/metric ton was examined. The results of this study showed that WTE processing of the MSW reduces fossil fuel consumption and is environmentally superior to landfilling.

Material and energy balances in a large-scale aerobic bioconversion cell.

On the basis of earlier experimental studies of the aerobic bioconversion of organic wastes, the preferred values of operating parameters and the biochemical rate constants of oxidation to CO2 and H2O were identified. Energy and material balances were then constructed for a large, 3 m deep aerobic cell holding 1,440 tons of the 'wet' component of organic wastes (major organic constituent: [C6H10O4]n). It was found that conduction/convection and radiation losses to the surroundings amount to a relatively small fraction of the chemical heat released by oxidation. Therefore, the surplus chemical heat must be removed by means of an upward water-saturated air flow that is several-fold the stoichiometric requirement for biodegradation. This study has quantified a basic process difference between anaerobic and aerobic bioconversion of organic matter: In the former, most of the chemical energy in the converted organic matter is stored chemically in the generated methane gas. In the latter, this energy is released in the cell and must be carried out in a relatively large air/water vapour flow through the cell.