Removal of PCDD/F from incinerator flue gases by entrained-phase adsorption

The emission abatement of polychlorinated dioxins and furans (PCDD/F) Issued from municipal solid waste incineration is growing in importance because of more stringent emission standards and general concern about their toxic characteristics. These substances cannot be separated by conventional gas cleanup processes but are successfully removed through adsorption onto carbonaceous materials. The simplest technique is the entrained-phase injection of pulverized adsorbents in the flue gas, followed by fabric filter separation. The various related techniques are briefly reviewed here. Operating conditions and results obtained from Flemish MSWIs are given. The results illustrate the excellent overall removal efficiency. Furans are adsorbed to a slightly higher extent than dioxins. PCDD/F removal by carbonaceous adsorbents is thereafter modeled from first principles for the contribution of both entrained-phase (eta1) and cake filtration (eta2) to the overall efficiency (etaT). Application of the model equations and comparison of measured and predicted overall efficiencies for the Flemish municipal solid waste incinerators (MSWIs) demonstrate that the approach is meaningful and that the dominant parameters are the operating temperature, the dosage and activity of adsorbent, and the fraction of adsorbent in the filter cake. The model equations enable the MSWI operators to predict the adsorption efficiencies for any combination of operating parameters and to assess the sensitivity of the process to varying operating conditions.     

Removal of PCDD/F from Incinerator Flue Gases by Entrained-Phase Adsorption

Abstract

The emission abatement of polychlorinated dioxins and furans (PCDD/F) issued from municipal solid waste incineration is growing in importance because of more stringent emission standards and general concern about their toxic characteristics. These substances cannot be separated by conventional gas cleanup processes but are successfully removed through adsorption onto carbonaceous materials. The simplest technique is the entrained-phase injection of pulverized adsorbents in the flue gas, followed by fabric filter separation. The various related techniques are briefly reviewed here. Operating conditions and results obtained from Flemish MSWIs are given. The results illustrate the excellent overall removal efficiency. Furans are adsorbed to a slightly higher extent than dioxins.

PCDD/F removal by carbonaceous adsorbents is thereafter modeled from first principles for the contribution of both entrained-phase (η₁) and cake filtration (η₂) to the overall efficiency (η_T). Application of the model equations and comparison of measured and predicted overall efficiencies for the Flemish municipal solid waste incinerators (MSWIs) demonstrate that the approach is meaningful and that the dominant parameters are the operating temperature, the dosage and activity of adsorbent, and the fraction of adsorbent in the filter cake. The model equations enable the MSWI operators to predict the adsorption efficiencies for any combination of operating parameters and to assess the sensitivity of the process to varying operating conditions.     

Pollutant emissions from modern incinerators

Emissions of dioxins are mainly from incinerators, domestic and industrial coal combustion, and traffic. However, the major public concern and research effort are associated with the emissions of organic micropollutants from waste incinerators. This paper gives a brief overview of the more recent research and development for the removal of dioxins and heavy metals from flue-gas streams. Special attention is devoted to the origin and control of emissions from incinerators. It appears that flue-gas cleaning systems in modern incinerators are very reliable in removing almost all polluting emissions from flue-gas streams. However, the fly ash residues generated pose a significant disposal problem, as they are enriched with heavy metals and organic micropollutants.     

Consultant Guide/1989

The European Economic Community (EEC) has proposed strict limits on emissions of dioxins and furans from hazardous waste incinerators. The proposed limit is 0.1 ng/Nm³, expressed as the 2,3,7,8 TCDD toxic equivalent of 17 specific dioxin and furan congeners. These limits will potentially redefine technology selection and design for combustion, energy recovery, and air pollution control. The EPA has a different approach for controlling emissions of products of incomplete combustion (PICs) and reformation products such as dioxins and furans. Rather than limiting these contaminants individually and quantitatively, EPA proposes controlling them by assuring good combustion as measured by stack emissions of carbon monoxide (CO) and total hydrocarbons (THC).

Dioxins and furans are combustion by-products and emission control relies mainly on control of the combustion process. These compounds can also be reformed from certain precursor compounds and elements in lower temperature regions of the system downstream of the combustion process. Air pollution control technologies have demonstrated the ability to remove dioxins and furans as contaminants on fine particulate.

This paper will discuss the two regulatory approaches, the mechanisms for the formation and reformation of dioxins and furans, and the technologies available to control emissions.     

Chlorobenzenes removal from municipal solid waste incineration fly ash by surfactant-assisted column flotation

The organic contaminants in municipal solid waste incineration (MSWI) fly ash, including chlorinated aromatic compounds and polycyclic aromatic hydrocarbons, have high toxicity and a potential negative impact on the environment. An effective and low energy consumption technique to remove the organic contaminants from MSWI fly ash is required urgently. Organic contaminants, such as chlorobenzenes (CBzs), in MSWI fly ash are known to become enriched in the unburnt carbon (UC) fraction. It is proposed that removal of UC from fly ash will result in the effective removal of most organic micropollutants. In this research, we use a technique of surfactant-assisted column flotation to decontaminate MSWI fly ash by removal of the CBzs-enriched UC from MSWI fly ash. We find that 39.8% of CBzs can be removed from fresh MSWI fly ash with 61.7% UC removal efficiency, whereas only 33.2% of CBzs can be removed from weathered MSWI fly ash with a low UC removal efficiency of 33.7%. By adding a mixture of two kinds of surfactants: sorbitan mono-oleate and polyoxyethylene (20) sorbitan mono-oleate to the weathered fly ash, 47.0% of CBzs were removed at the hydrophile lipophile balance value of 13.5, while the UC removal efficiency increased to 49.0%. The results show that surfactants can enhance CBzs and UC removal efficiencies during the column flotation process. Higher CBzs and UC removal efficiencies can be expected by further optimizing the conditions of surfactant-assisted column flotation.     

Multifunctional metal-organic frameworks in oil spills and associated organic pollutant remediation

The release of toxic organic compounds into the environment in an event of oil spillage is a global menace due to the potential impacts on the ecosystem. Several approaches have been employed for oil spills clean-up, with adsorption technique proven to be more promising for the total reclamation of a polluted site. Of the several adsorbents so far reported, adsorbent-based porous materials have gained attention for the reduction/total removal of different compounds in environmental remediation applications. The superior potential of mesoporous materials based on metal–organic frameworks (MOFs) against conventional adsorbents is due to their intriguing and enhanced properties. Therefore, this review presents recent development in MOF composites; methods of preparation; and their practical applications towards remediating oil spill, organic pollutants, and toxic gases in different environmental media, as well as potential materials in the possible deployment in reclaiming the polluted Niger Delta due to unabated oil spillage and gas flaring.

     

吸附树脂组合工艺对微污染水的净化处理效果研究

利用江苏省盐城市串场河水作为源水,在常规处理工艺对源水进行前处理的基础上,结合树脂吸附处理工艺探讨了新型吸附树脂对水源水的处理效果和树脂吸附剂的再生效果.结果表明,新型吸附树脂按照ZH-02、ZH-03和ZH-00的顺序进行组合,对经沉淀砂滤预处理后的饮用水源水中微污染有机化合物具有较好的去除效果,处理2 000 BV后需对树脂进行再生,用2～2.5 BV的醇碱在常温下脱附,元素分析结果表明脱附效果较好,对水源水进行深度处理的原料成本大约为3.9元/t.     

Combined PCDD/F Destruction and Particulate Control in a Baghouse: Experience with a Catalytic Filter System at a Medical Waste Incineration Plant

ABSTRACT

Phoenix Services, Inc., owns and operates the Baltimore Regional Medical Waste Incinerator in Baltimore, MD. New regulations for dioxins and furans imposed a limit that was considerably below historical emission levels. To determine a method to comply with the new dioxin/furan regulations, Phoenix Services performed trials with powdered activated carbon (PAC). Although the results with carbon were acceptable, Phoenix Services decided to replace their woven fiberglass filter bags with catalytic filters that simultaneously destroy dioxins and furans and collect particulate matter (PM). The catalytic filter system offered several advantages to Phoenix Services, including destruction of dioxins and furans instead of adsorption on carbon. The catalytic filters also offered a passive solution that did not require new carbon injection equipment. In January 2000, a campaign to measure dioxins/furans and PM was undertaken.     

Landfill leachate effects on sorption of organic micropollutants onto aquifer materials

The effect of dissolved organic carbon as present in landfill leachate, on the sorption of organic micropollutants in aquifer materials was studied by laboratory batch and column experiments involving 15 non-polar organic chemicals, 5 landfill leachates and 4 aquifer materials of low organic carbon content. The experiments showed that hydrophobic organic micropollutants do partition into dissolved organic carbon found in landfill leachate potentially increasing their mobility. However, landfill leachate interacted with aquifer materials apparently increases the sorbent affinity for the hydrophobic micropollutants. The combination of these two mechanisms affected the observed distribution coefficients within a factor of two, in some cases increasing and in other cases decreasing the sorption of the chemicals. No means for prediction of the effect is currently available, but from a practical point of view, the effect of landfill leachate on retardation of organic micropollutants in aquifer material seems limited.     

Mercury removal from incineration flue gas by organic and inorganic adsorbents

Experiments were performed to investigate various adsorbents for their mercury removal capabilities from incineration flue gases. Four different materials were tested; Zeolite, Bentonite, activated carbon (AC), and wood char. Real incineration off-gas and in-lab simulated combustion flue gases (N2 + Hg) were used. Three cylindrical-shaped sorbent columns with 5 cm in diameter and 20 cm in length were used. The gas flow rate was fixed at 660 l/h at all times. Concentrations of NO, CO, O2, CO2, SO2, H2O, HCl, and mercury were continuously monitored. Mercury removal efficiencies of natural Zeolite and Bentonite were found to be much lower than those of the referenced AC. Amount of Hg removed were 9.2 and 7.4 microg/g of Zeolite and Bentonite, respectively. Removal efficiencies of each layer consisted of inorganic adsorbents were no higher than 7%. No significant improvement was observed with sulfur impregnation onto the inorganic adsorbents. Organic adsorbents (wood char and AC) showed much higher mercury removal efficiencies than those of inorganic ones (Zeolite and Bentonite). Mercury removal efficiency of wood char reached over 95% in the first layer, showing almost same effectiveness as AC which currently may be the most effective adsorbents for mercury. Amount of mercury captured by wood char was approximately 0.6 mg/g of wood char, close to the amount captured by AC tested in this study. Hence, wood char, made from the waste woods through a gasification process, should be considered as a possible alternative to relatively expensive AC.     

An Assessment and Management Recommendations

Chlorinated plastics (PVC) accounted for 9.4 percent of the weight of “red bag”, supposedly infectious, waste from two community 150- and 98-bed hospitals. The hydrochloric acid, dioxins and furans generated during the burning of this red bag waste are important air pollutants. In this waste, PVC provides much of the organic chloride for the dioxins and furans generated. Their concentrations are least in flue gases from those plants with BACT design, flue gas clean up and management techniques—the most constrained incinerators. The many manually-fed, small categorical red bag incinerators associated with hospitals have no flue gas clean-up systems and represent minimally constrained incinerators. Their toxic stack emissions are considered a significant community health hazard. The evidence that the contents of red bag waste is infectious to such a degree that it cannot be disposed of as municipal solid waste without endangering the public with infectious diseases is not reflected in the relevant hospital accreditation guidelines, Centers for Disease Control recommendations, or related literature. Public health is compromised by the lack of accountability in the handling of some hospital and veterinary wastes, specifically body fluid contaminated equipment and containers as well as microbiological materials. Recommendations to protect public health are included. The most important of these is a manifest system of cradle-to-grave accountability for a limited portion of a hospital's waste.     

Combined PCDD/F destruction and particulate control in a baghouse: experience with a catalytic filter system at a medical waste incineration plant

Phoenix Services, Inc., owns and operates the Baltimore Regional Medical Waste Incinerator in Baltimore, MD. New regulations for dioxins and furans imposed a limit that was considerably below historical emission levels. To determine a method to comply with the new dioxin/furan regulations, Phoenix Services performed trials with powdered activated carbon (PAC). Although the results with carbon were acceptable, Phoenix Services decided to replace their woven fiberglass filter bags with catalytic filters that simultaneously destroy dioxins and furans and collect particulate matter (PM). The catalytic filter system offered several advantages to Phoenix Services, including destruction of dioxins and furans instead of adsorption on carbon. The catalytic filters also offered a passive solution that did not require new carbon injection equipment. In January 2000, a campaign to measure dioxins/furans and PM was undertaken. The measurements allowed the catalytic filter system to be evaluated. Some of the key findings of this investigation are The dioxin/furan emission was less than 0.1 ng toxicity equivalents (TEQ)/Nm3 at 11% O2. This concentration is approximately 2 orders of magnitude less than historical averages and it is well below the new regulatory limits, for both existing and new sources of this type; the amount of dioxin/furans destroyed by the catalytic filters was approximately 1.73 ng TEQ/Nm3 at 11% O2; and the particulate emission was 12-17 times less than the regulatory limit.     

Fate of PBDEs during food processing: Assessment of formation of mixed chlorinated/brominated diphenyl ethers and brominated dioxins/furans

The aim of this study was to evaluate effects of food processing on PBDE levels, in particular influence of heat treatment on degradation of PBDEs, including possible formation of chlorinated diphenyl ethers or brominated dioxins/furans as degradation products. It was shown that PBDEs heated in the presence of chlorine (from either organic or inorganic sources) formed mixed chlorinated/brominated diphenyl ethers. However, no PCDEs were formed in the presence of lipids. Lipid medium increased stability of PBDEs exposed to UV irradiation. Profile of congeners formed in result of the debromination reaction was significantly different than profiles observed by some other authors in aliphatic organic solvents. Grilling processes increased concentrations (calculated on the fresh product basis) of the studied compounds by 4–8/22–34% for electric/coal grill, respectively. Depending on the congener and on the applied heat treatment, PBDE mass in pork meat after grilling dropped by 26–53%. No detectable quantities of either brominated dioxins or furans were formed during thermal processing of food containing typical levels of PBDEs.     

Toxic chlorinated and polyaromatic hydrocarbons in simulated house fires

Toxic chlorinated hydrocarbons (polychlorinated biphenyls, benzenes and dioxins and furans) and polyaromatic hydrocarbons were examined in combustion gas and deposited soot wipe samples from simulated house fires. Concentrations of these substances were high during the fires, the amounts of polychlorinated dioxins and furans (PCDD/Fs) in the combustion gas varying from 1.0 to >7.2 ng/m3 (I-TEQ) and those of polyaromatic hydrocarbons from 6.4 to 470 mg/m3. Thus large amounts of organic compounds may be released in house fires. As a result, there is a need for careful personal protection of fire-fighters and remediation workers against combustion gases during a fire and on contaminated surfaces after it.     

Impact assessment of waste management options in Singapore

This paper describes the application of life cycle assessment for evaluating various waste management options in Singapore, a small-island city state. The impact assessment method by SimaPro is carried out for comparing the potential environmental impacts of waste treatment options including landfilling, incineration, recycling, and composting. The inventory data include gases and leachate from landfills, air emissions and energy recovery from incinerators, energy (and emission) savings from recycling, composting gases, and transport pollution. The impact assessment results for climate change, acidification, and ecotoxicity show that the incineration of materials imposes considerable harm to both human health and the environment, especially for the burning of plastics, paper/cardboard, and ferrous metals. The results also show that, although some amount of energy can be derived from the incineration of wastes, these benefits are outweighed by the air pollution (heavy metals and dioxins/furans) that incinerators produce. For Singapore, landfill gases and leachate generate minimal environmental damage because of the nation's policy to landfill only 10% of the total disposed wastes. Land transportation and separation of waste materials also pose minimal environmental damage. However, sea transportation to the landfill could contribute significantly to acidification because of the emissions of sulfur oxides and nitrogen oxides from barges. The composting of horticultural wastes hardly imposes any environmental damage. Out of all the waste strategies, the recycling of wastes offers the best solution for environmental protection and improved human health for the nation. Significant emission savings can be realized through recycling.     

Removal of arsenic(V) from aqueous solutions using iron-oxide-coated modified activated carbon.

Removal of arsenic(V) from aqueous solutions was evaluated with the following three different sorption materials: coal-based activated carbon 12 x 40 (activated carbon), iron(II) oxide (FeO)/activated carbon-H, and iron oxide. The apparent characteristics and physical chemistry performances of these adsorbents were investigated by X-ray diffraction, nitrogen adsorption, and scanning electronic microscope. Also, batch experiments for arsenic removal were performed, and the effects of pH value on arsenic(V) removal were studied. The results suggest that the main phases of the iron oxide surface are magnetite, maghemite, hematite, and goethite; fine and uniform iron oxide particles can cover activated carbon surfaces and affect the surface area or pore structures of activated carbon; adsorption kinetics obey a pseudo-first-order rate equation; and adsorption capacities of adsorbents are affected by the values of pH. The optimum value of pH for iron oxide lies in a narrow range between 4.0 and 5.5, and arsenic(V) removal by FeO/activated carbon-H is ideal and stable in the pH range 3 to 7, while activated carbon has the lowest adsorption capacity in the entire pH range. Also, the adsorption characteristics of FeO/activated carbon-H composites and virgin activated carbon match well the Langmuir adsorption model, while those of iron oxide fit well the Freundlich adsorption model.     

Control of mercury emissions from a municipal solid waste incinerator in Japan

The control of Hg emissions from a municipal solid waste incinerator (MSWI) is very important, because more than 78% of municipal solid waste (MSW) is incinerated. The Hg content of coal used in utility boilers is relatively low in Japan. In this study, recent trends in the Hg content of MSW in Japan and activated carbon (AC) injection as a control technology of Hg emission from an MSWI are discussed. The effect of AC injection on Hg removal from flue gas in an MSWI was investigated by pilot-scale experiments using a bag filter (BF). The injection of AC increases the Hg reduction ratio by 20-30% compared with cases without AC injection. The Hg reduction ratio increases as the flue gas temperature decreases. The Hg reduction ratio is closely related to the inlet Hg concentration and was expressed with a Langmuir-type adsorption isotherm.     

污泥活性炭的表征及其对Cr（Ⅵ）的吸附特性

以城市污水处理厂污泥为原料，采用磷酸活化一微波热解法制备得到污泥活性炭，并将其用于吸附水溶液中的Cr（Ⅵ）。分别采用元素分析仪（VarioELcube）、比表面积孔径分布测定仪（ASAP2020）、扫描电镜（SEM）和傅里叶红外光谱（FT—IR）等仪器对原污泥及污泥活性炭的表面组成和结构进行表征，探讨污泥活性炭的孔隙结构参数和表面化学性能。通过静态吸附实验，考察了溶液初始pH，接触时间，初始Cr（Ⅵ）浓度对污泥活性炭吸附Cr（Ⅵ）效果的影响，并探讨了污泥活性炭去除Cr（Ⅵ）的机理。实验结果表明，pH越低吸附效果越好，吸附平衡时间为100h。不同温度下吸附过程均符合Langmuir等温吸附模型，30℃时最大吸附容量为27．55mg／g；吸附动力学过程符合准二级速率方程（R2〉0．99）；污泥活性炭对Cr（Ⅵ）的去除是一个吸附-还原耦合的过程。