Characteristics of azaarenes and dioxins in gases emitted from waste incinerators

In this study, we propose an analytical method to determine the fourteen of azaarenes present in flue gas samples collected according to Japanese Industrial Standard K 0311, which designates the method for the determination of dioxins in flue gas. Azaarenes can be analyzed using the acidic water phase after shaking extraction with dichloromethane, which is unnecessary for dioxin analysis. Flue gas samples were obtained from 24 waste incinerators in Japan, and azaarenes were detected in all the flue gas samples (0.21–3800 μg/m³ _N). The most abundant of the detected compounds were quinoline and isoquinoline. The concentration of azaarenes had a tendency to increase with that of polychlorinated dibenzo-p-dioxins and dibenzofurans. The isomer distribution of heptachloro-dibenzofurans (HpCDFs) was calculated using the computed Gibbs energy of formation (ΔG _f ) obtained by the semiempirical molecular orbital method at various temperatures. The calculated isomer distribution was fitted to the measured value of HpCDFs. It seems that the temperature obtained from the fitting calculations is an indicator of the cooling capacity of the combustion gas in an incinerator. The computed ΔG _f also explained the measured isomer distributions of azaarenes. It is suggested that the isomer distribution of azaarenes in the combustion process is thermodynamically controlled. This work was presented in part at the International Conference on Combustion, Incineration/Pyrolysis, and Emission Control, 2006, Kyoto     

Distribution of inorganic bromine and metals during co-combustion of polycarbonate (BrPC) and high-impact polystyrene (BrHIPS) wastes containing brominated flame retardants (BFRs) with metallurgical dust

This study focused on the thermal degradation of polycarbonate (BrPC) and high-impact polystyrene (BrHIPS), containing different brominated flame retardants. The evolved inorganic bromine was utilized for the separation of metals present in electric arc furnace dust (EAFD). The thermal degradation of BrPC generated inorganic gaseous HBr (69%) and condensable Br₂ (31%). The bromine evolved from BrHIPS was detected almost entirely in a condensed phase as SbBr₃. When mixed with EAFD, the evolved inorganic bromine reacted immediately with the metallic components of zinc and lead, but not with iron. The best bromination efficiencies were obtained during the isothermal heating (80 min at 550 °C) of the mixtures at mass ratios of 6:1 and 9:1 w/w under oxidizing conditions. The achieved brominating rates reached 78 and 81% for zinc and 90 and 94% for lead in 6:1 and 9:1 BrPC:EAFD, respectively, and 47 and 65% for zinc and 67 and 63% for lead in 6:1 and 9:1 BrHIPS:EAFD, respectively. The oxidizing condition favored complete vaporization of the formed bromides.     

Gasification of the char derived from distillation of granulated scrap tyres

This work reports the effect of pressure on the steam/oxygen gasification at 1000 °C of the char derived from low temperature-pressure distillation of granulated scrap tyres (GST). The study was based on the analysis of gas production, carbon conversion, cold gas efficiency and the high heating value (HHV) of the product. For comparison, similar analyses were carried out for the gasification of coals with different rank.In spite of the relatively high ash (≈12 wt.%) and sulphur (≈3 wt.%) contents, the char produced in GST distillation can be regarded as a reasonable solid fuel with a calorific value of 34 MJ kg⁻¹. The combustion properties of the char (E_A ≈ 50 kJ mol⁻¹), its temperature of self-heating (≈264 °C), ignition temperature (≈459 °C) and burn-out temperature (≈676 °C) were found to be similar to those of a semi-anthracite.It is observed that the yield, H₂ and CO contents and HHV of the syngas produced from char gasification increase with pressure. At 0.1 MPa, 4.6 Nm³ kg_char⁻¹ of syngas was produced, containing 28% v/v of H₂ and CO and with a HHV around 3.7 MJ Nm⁻³. At 1.5 MPa, the syngas yield achieved 4.9 Nm³ kg_char⁻¹ with 30% v/v of H₂-CO and HHV of 4.1 MJ Nm⁻³. Carbon conversion significantly increased from 87% at 0.1 MPa to 98% at 1.5 MPa.It is shown that the char derived from distillation of granulated scrap tyres can be further gasified to render a gas of considerable heating value, especially when gasification proceeds at high pressure.     

Improved quartz furnace method for chlorine and sulfur determination in municipal solid waste

 A method of determining the chlorine (Cl) and sulfur (S) in municipal solid waste (MSW) was studied. The quartz furnace method was improved in two ways: recovery from ash by hot extraction with dilute nitric acid, and avoidance of the volatilization of alkali (earth) metal chlorides by setting the sample combustion temperature at 600°C. In a comparison with the bomb method, using nine sets of kitchen garbage and waste plastics, the bomb method yielded a 15%–25% lower value than the improved quartz furnace method. Combustion in the bomb was frequently incomplete, resulting in recovery losses of Cl and S. The average kitchen garbage involved 5.2 mg Cl/g, of which at least 24.1% would be converted to HCl. Plastics contained 23 mg Cl/g generating 88.1% HCl on average. In the same way, kitchen garbage contained 3.0 mg S/g, generating 52.3% SO _x , whereas plastics contained 1.1 mg S/g with 55.1% SO _x formation. Received: March 20, 2002 / Accepted: October 13, 2002     

Energy from Waste – Clean,efficient, renewable: Transitions in combustion efficiency and NOx control

Traditionally EfW (Energy from Waste) plants apply a reciprocating grate to combust waste fuel. An integrated steam generator recovers the heat of combustion and converts it to steam for use in a steam turbine/generator set. This is followed by an array of flue gas cleaning technologies to meet regulatory limitations.Modern combustion applies a two-step method using primary air to fuel the combustion process on the grate. This generates a complex mixture of pyrolysis gases, combustion gases and unused combustion air. The post-combustion step in the first pass of the boiler above the grate is intended to “clean up” this mixture by oxidizing unburned gases with secondary air.This paper describes modifications to the combustion process to minimize exhaust gas volumes and the generation of noxious gases and thus improving the overall thermal efficiency of the EfW plant. The resulting process can be coupled with an innovative SNCR (Selective Non-Catalytic Reduction) technology to form a clean and efficient solid waste combustion system.Measurements immediately above the grate show that gas compositions along the grate vary from 10% CO, 5% H₂ and 0% O₂ to essentially unused “pure” air, in good agreement with results from a mathematical model. Introducing these diverse gas compositions to the post combustion process will overwhelm its ability to process all these gas fractions in an optimal manner. Inserting an intermediate step aimed at homogenizing the mixture above the grate has shown to significantly improve the quality of combustion, allowing for optimized process parameters. These measures also resulted in reduced formation of NO_x (nitrogenous oxides) due to a lower oxygen level at which the combustion process was run (2.6 vol% O_2, wet instead of 6.0 vol% O_2, wet).This reduction establishes optimal conditions for the DyNOR? (Dynamic NO_x Reduction) NO_x reduction process. This innovative SNCR technology is adapted to situations typically encountered in solid fuel combustion. DyNOR? measures temperature in small furnace segments and delivers the reducing reagent to the exact location where it is most effective. The DyNOR? distributor reacts precisely and dynamically to rapid changes in combustion conditions, resulting in very low NO_x emissions from the stack.     

Mathematical modeling of MSW combustion and SNCR in a full-scale municipal incinerator and effects of grate speed and oxygen-enriched atmospheres on operating conditions

The rising popularity of incineration of municipal solid waste (MSW) calls for detailed mathematical modeling and accurate prediction of pollutant emissions. In this paper, mathematical modeling methods for both solid and gaseous phases were employed to simulate the operation of a 450 t/d MSW-burning incinerator to obtain detailed information on the flow and combustion characteristics in the furnace and to predict the amount of pollutant emissions. The predicted data were compared to on-site measurements of gas temperature, gas composition and SNCR de-NO_X system. The major operating conditions considered in this paper were grate speed and oxygen concentration. A suitable grate speed ensures complete waste combustion. The predictions are as follows: volatile release increases with increasing grate speed, and the maximal value is within the range of 700–800 kg/m² h; slow grate speeds result in incomplete combustion of fixed carbon; the gas temperature at slow grate speeds is higher due to adequate oxygenation for fixed carbon combustion, and the deviation reaches 200 K; NO_X emission decreases, but CO emission and O₂ concentrations increase, and the deviation is 63%, 34% and 35%, respectively. Oxygen-enriched atmospheres promote the destruction of most pollutants due to the high oxygen partial pressure and temperature. The furnace temperature, NO production and CO emission increase as the oxygen concentration increases, and the deviation of furnace exit temperature, NO and CO concentration is 38.26%, 58.43% and 86.67%, respectively. Finally, oxygen concentration is limited to below 35% to prevent excessive CO and NO_X emission without compromising plant performance. The current work greatly helps to understand the operating characteristics of large-scale MSW-burning plants.     

Treatment of municipal landfill leachate by catalytic wet air oxidation: Assessment of the role of operating parameters by factorial design

The wet air oxidation (WAO) of municipal landfill leachate catalyzed by cupric ions and promoted by hydrogen peroxide was investigated. The effect of operating conditions such as WAO treatment time (15-30 min), temperature (160-200 °C), Cu²⁺ concentration (250-750 mg L⁻¹) and H₂O₂ concentration (0-1500 mg L⁻¹) on chemical oxygen demand (COD) removal was investigated by factorial design considering a two-stage, sequential process comprising the heating-up of the reactor and the actual WAO. The leachate, at an initial COD of 4920 mg L⁻¹, was acidified to pH 3 leading to 31% COD decrease presumably due to the coagulation/precipitation of colloidal and other organic matter. During the 45 min long heating-up period of the WAO reactor under an inert atmosphere, COD removal values up to 35% (based on the initial COD value) were recorded as a result of the catalytic decomposition of H₂O₂ to reactive hydroxyl radicals. WAO at 2.5 MPa oxygen partial pressure advanced treatment further; for example, 22 min of oxidation at 200 °C, 250 mg L⁻¹ Cu²⁺ and 0-1500 mg L⁻¹ H₂O₂ resulted in an overall (i.e. including acidification and heating-up) COD reduction of 78%. Amongst the operating variables in question, temperature had the strongest influence on both the heating-up and WAO stages, while H₂O₂ concentration strongly affected the former and reaction time the latter. Nonetheless, the effects of temperature and H₂O₂ concentration were found to depend on the concentration levels of catalyst as suggested by the significance of their 3rd order interaction term.     

Limits and dynamics of methane oxidation in landfill cover soils

In order to understand the limits and dynamics of methane (CH₄) oxidation in landfill cover soils, we investigated CH₄ oxidation in daily, intermediate, and final cover soils from two California landfills as a function of temperature, soil moisture and CO₂ concentration. The results indicate a significant difference between the observed soil CH₄ oxidation at field sampled conditions compared to optimum conditions achieved through pre-incubation (60 days) in the presence of CH₄ (50 ml l⁻¹) and soil moisture optimization. This pre-incubation period normalized CH₄ oxidation rates to within the same order of magnitude (112-644 μg CH₄ g⁻¹ day⁻¹) for all the cover soils samples examined, as opposed to the four orders of magnitude variation in the soil CH₄ oxidation rates without this pre-incubation (0.9-277 μg CH₄ g⁻¹ day⁻¹).Using pre-incubated soils, a minimum soil moisture potential threshold for CH₄ oxidation activity was estimated at 1500 kPa, which is the soil wilting point. From the laboratory incubations, 50% of the oxidation capacity was inhibited at soil moisture potential drier than 700 kPa and optimum oxidation activity was typical observed at 50 kPa, which is just slightly drier than field capacity (33 kPa). At the extreme temperatures for CH₄ oxidation activity, this minimum moisture potential threshold decreased (300 kPa for temperatures <5 °C and 50 kPa for temperatures >40 °C), indicating the requirement for more easily available soil water. However, oxidation rates at these extreme temperatures were less than 10% of the rate observed at more optimum temperatures (∼30 °C). For temperatures from 5 to 40 °C, the rate of CH₄ oxidation was not limited by moisture potentials between 0 (saturated) and 50 kPa. The use of soil moisture potential normalizes soil variability (e.g. soil texture and organic matter content) with respect to the effect of soil moisture on methanotroph activity. The results of this study indicate that the wilting point is the lower moisture threshold for CH₄ oxidation activity and optimum moisture potential is close to field capacity.No inhibitory effects of elevated CO₂ soil gas concentrations were observed on CH₄ oxidation rates. However, significant differences were observed for diurnal temperature fluctuations compared to thermally equivalent daily isothermal incubations.     

Simulation of co-incineration of sewage sludge with municipal solid waste in a grate furnace incinerator

Incineration is one of the most important methods in the resource recovery disposal of sewage sludge. The combustion characteristics of sewage sludge and an increasing number of municipal solid waste (MSW) incineration plants provide the possibility of co-incineration of sludge with MSW. Computational fluid dynamics (CFD) analysis was used to verify the feasibility of co-incineration of sludge with MSW, and predict the effect of co-incineration. In this study, wet sludge and semi-dried sludge were separately blended with MSW as mixed fuels, which were at a co-incineration ratios of 5 wt.% (wet basis, the same below), 10 wt.%, 15 wt.%, 20 wt.% and 25 wt.%. The result indicates that co-incineration of 10 wt.% wet sludge with MSW can ensure the furnace temperature, the residence time and other vital items in allowable level, while 20 wt.% of semi-dried sludge can reach the same standards. With lower moisture content and higher low heating value (LHV), semi-dried sludge can be more appropriate in co-incineration with MSW in a grate furnace incinerator.     

Influence of bromine on metal volatilization in waste combustion

Co-combustion tests of municipal solid waste and bromine-containing waste plastics have been performed in the TAMARA test incinerator in order to investigate the fate of bromine in waste combustion. HBr is the main bromine combustion product. Approximately 50% of the bromine inventory stays in the grate ashes, which is much more than is found for chlorine. The percentage of bromine transferred into the fly ash also exceeds that of chlorine. There is a strong indication that bromine has a promoting effect upon the volatility of most of the heavy metals that are typically mobilized by chlorine. Received: February 2, 2000 / Accepted: March 3, 2000     

Inertization of pyrite cinders and co-inertization with electric arc furnace flue dusts by pyroconsolidation at solid state

The viability of a pyroconsolidation process to render pyrite cinders inert and to co-inert pyrite cinders with a hazardous polymetallic residue such as electric arc furnace flue dusts (EAF) containing Pb, Cu, Zn, As, Cr, Ni and Mo were investigated. The effects of pyroconsolidation temperature (800-1200 degrees C), milling pyrite cinders and additions of both CaO and EAF on the resulting microstructure of the pellets were determined. The microstructural changes were then compared with the results of the standard leaching tests. Full inertization of pyrite cinders was achieved after milling to < 100 micron followed by a pelletization and pyroconsolidation process at a temperature of 1200 degrees C. This process also allows co-inertization of pyrite cinders with controlled additions of EAF (up to approximately to 10%). Following pyroconsolidation at 1200 degrees C, the metallic elements were inert components in the four main phases: traces of Cr in hematite; Cr, Cu, Zn and Ni in spinel-phase; traces of Cr and Zn in calcium ferrites; and Pb and traces of Cu, Zn and Ba in K-Ca-Al-Fe glassy silicate.     

Quantification of multiple methane emission sources at landfills using a double tracer technique

A double tracer technique was used successfully to quantify whole-site methane (CH₄) emissions from Fakse Landfill. Emissions from different sections of the landfill were quantified by using two different tracers. A scaled-down version of the tracer technique measuring close-by to localized sources having limited areal extent was also used to quantify emissions from on-site sources at the landfill facility, including a composting area and a sewage sludge storage pit. Three field campaigns were performed. At all three field campaigns an overall leak search showed that the CH₄ emissions from the old landfill section were localized to the leachate collection wells and slope areas. The average CH₄ emissions from the old landfill section were quantified to be 32.6 ± 7.4 kg CH₄ h⁻¹, whereas the source at the new section was quantified to be 10.3 ± 5.3 kg CH₄ h⁻¹. The CH₄ emission from the compost area was 0.5 ± 0.25 kg CH₄ h⁻¹, whereas the carbon dioxide (CO₂) and nitrous oxide (N₂O) flux was quantified to be in the order of 332 ± 166 kg CO₂ h⁻¹ and 0.06 ± 0.03 kg N₂O h⁻¹, respectively. The sludge pit located west of the compost material was quantified to have an emission of 2.4 ± 0.63 kg h⁻¹ CH₄, and 0.03 ± 0.01 kg h⁻¹ N₂O.     

Dry-thermophilic anaerobic digestion of organic fraction of municipal solid waste: methane production modeling

The influence of particle size and organic matter content of organic fraction of municipal solid waste (OFMSW) in the overall kinetics of dry (30% total solids) thermophilic (55 °C) anaerobic digestion have been studied in a semi-continuous stirred tank reactor (SSTR). Two types of wastes were used: synthetic OFMSW (average particle size of 1 mm; 0.71 g Volatile Solids/g waste), and OFMSW coming from a composting full scale plant (average particle size of 30 mm; 0.16 g Volatile Solids/g waste).A modification of a widely-validated product-generation kinetic model has been proposed. Results obtained from the modified-model parameterization at steady-state (that include new kinetic parameters as K, Y_pMAX and θ_MIN) indicate that the features of the feedstock strongly influence the kinetics of the process. The overall specific growth rate of microorganisms (μ_max) with synthetic OFMSW is 43% higher compared to OFMSW coming from a composting full scale plant: 0.238 d⁻¹ (K = 1.391 d⁻¹; Y_pMAX = 1.167 L CH₄/gDOC_c; θ_MIN = 7.924 days) vs. 0.135 d⁻¹ (K = 1.282 d⁻¹; Y_pMAX = 1.150 L CH₄/gDOC_c; θ_MIN = 9.997 days) respectively.Finally, it could be emphasized that the validation of proposed modified-model has been performed successfully by means of the simulation of non-steady state data for the different SRTs tested with each waste.     

Distribution of copper,silver and gold during thermal treatment with brominated flame retardants

The growing consumption of electric and electronic equipment results in creating an increasing amount of electronic waste. The most economically and environmentally advantageous methods for the treatment and recycling of waste electric and electronic equipment (WEEE) are the thermal techniques such as direct combustion, co-combustion with plastic wastes, pyrolysis and gasification. Nowadays, this kind of waste is mainly thermally treated in incinerators (e.g. rotary kilns) to decompose the plastics present, and to concentrate metals in bottom ash. The concentrated metals (e.g. copper, precious metals) can be supplied as a secondary raw material to metal smelters, while the pyrolysis of plastics allows the recovery of fuel gases, volatilising agents and, eventually, energy. Indeed, WEEE, such as a printed circuit boards (PCBs) usually contains brominated flame retardants (BFRs). From these materials, hydrobromic acid (HBr) is formed as a product of their thermal decomposition.In the present work, the bromination was studied of copper, silver and gold by HBr, originating from BFRs, such as Tetrabromobisphenol A (TBBPA) and Tetrabromobisphenol A-Tetrabromobisophenol A diglycidyl ether (TTDE) polymer; possible volatilization of the bromides formed was monitored using a thermo-gravimetric analyzer (TGA) and a laboratory-scale furnace for treating samples of metals and BFRs under an inert atmosphere and at a wide range of temperatures. The results obtained indicate that up to about 50% of copper and silver can evolve from sample residues in the form of volatile CuBr and AgBr above 600 and 1000 °C, respectively. The reactions occur in the molten resin phase simultaneously with the decomposition of the brominated resin. Gold is resistant to HBr and remains unchanged in the residue.     

Evaluation of respiration in compost landfill biocovers intended for methane oxidation

A low-cost alternative approach to reduce landfill gas (LFG) emissions is to integrate compost into the landfill cover design in order to establish a biocover that is optimized for biological oxidation of methane (CH₄). A laboratory and field investigation was performed to quantify respiration in an experimental compost biocover in terms of oxygen (O₂) consumption and carbon dioxide (CO₂) production and emission rates. O₂ consumption and CO₂ production rates were measured in batch and column experiments containing compost sampled from a landfill biowindow at Fakse landfill in Denmark. Column gas concentration profiles were compared to field measurements. Column studies simulating compost respiration in the biowindow showed average CO₂ production and O₂ consumption rates of 107 ± 14 g m⁻² d⁻¹ and 63 ± 12 g m⁻² d⁻¹, respectively. Gas profiles from the columns showed elevated CO₂ concentrations throughout the compost layer, and CO₂ concentrations exceeded 20% at a depth of 40 cm below the surface of the biowindow. Overall, the results showed that respiration of compost material placed in biowindows might generate significant CO₂ emissions. In landfill compost covers, methanotrophs carrying out CH₄ oxidation will compete for O₂ with other aerobic microorganisms. If the compost is not mature, a significant portion of the O₂ diffusing into the compost layer will be consumed by non-methanotrophs, thereby limiting CH₄ oxidation. The results of this study however also suggest that the consumption of O₂ in the compost due to aerobic respiration might increase over time as a result of the accumulation of biomass in the compost after prolonged exposure to CH₄.     

Thermal decomposition of electronic wastes: mobile phone case and other parts

Pyrolysis and combustion runs at 850°C in a horizontal laboratory furnace were carried out on different parts of a mobile phone (printed circuit board, mobile case and a mixture of both materials). The analyses of the carbon oxides, light hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), polychlorodibenzo-p-dioxin, polychlorodibenzofurans (PCDD/Fs), and dioxin-like PCBs are shown. Regarding semivolatile compounds, phenol, styrene, and its derivatives had the highest yields. In nearly all the runs the same PAHs were identified, naphthalene being the most common component obtained. Combustion of the printed circuit board produced the highest emission factor of PCDD/Fs, possibly due to the high copper content.     

Effect of aeration modes on the characteristics of composting emissions and the NH3 removal efficiency by using biotrickling filter

A pilot biotrickling filter (BTF) packed with ZX02 fibrous balls as packing material was tested for the treatment of ammonia (NH₃) released from a composting plant of dairy manure. In order to investigate the effects of three compost aeration modes (mode Co-I, Co-II and In-II) on the NH₃ removal efficiency, a field experiment was continuously carried out for more than eight months. The results demonstrated that under the intermittent aeration mode (In-II), the NH₃ removal efficiency reached 99.2 ± 0.1% when the inlet NH₃ concentration was 7.5-32.3 mg m⁻³ (9.8-42.5 ppmv). The maximum and critical elimination capacity of the biotrickling filter was 22.6 and 4.9 g NH₃ m⁻³ h⁻¹, respectively. The effluent concentration of NH₃ was lower than 1.0 mg m⁻³, which meets the first class discharge standards of GB14554-93. When the concentration of free ammonia in the trickling liquid was varied from 0.1 to 0.4 mg L⁻¹, the nitrification yield was between 47.9% and 103.8%. In addition, the optimum liquid tricking velocity (LTV) of the biotrickling filter was 0.5 m³ m⁻² h⁻¹ for low inlet concentrations and 2.2 m³ m⁻² h⁻¹ for high inlet concentrations. Therefore, the use of the biotrickling filter for the compost under the third aeration mode (In-II) yielded an effective optimum NH₃ removal and reduced the nitrogen loss in the compost.     

Parameters affecting the stability of the digestate from a two-stage anaerobic process treating the organic fraction of municipal solid waste

This paper focused on the factors affecting the respiration rate of the digestate taken from a continuous anaerobic two-stage process treating the organic fraction of municipal solid waste (OFMSW). The process involved a hydrolytic reactor (HR) that produced a leachate fed to a submerged anaerobic membrane bioreactor (SAMBR). It was found that a volatile solids (VS) removal in the range 40-75% and an operating temperature in the HR between 21 and 35 °C resulted in digestates with similar respiration rates, with all digestates requiring 17 days of aeration before satisfying the British Standard Institution stability threshold of 16 mg CO₂ g VS⁻¹ day⁻¹. Sanitization of the digestate at 65 °C for 7 days allowed a mature digestate to be obtained. At 4 g VS L⁻¹ d⁻¹ and Solid Retention Times (SRT) greater than 70 days, all the digestates emitted CO₂ at a rate lower than 25 mg CO₂ g VS⁻¹ d⁻¹ after 3 days of aeration, while at SRT lower than 20 days all the digestates displayed a respiration rate greater than 25 mg CO₂ g VS⁻¹ d⁻¹. The compliance criteria for Class I digestate set by the European Commission (EC) and British Standard Institution (BSI) could not be met because of nickel and chromium contamination, which was probably due to attrition of the stainless steel stirrer in the HR.     

Fluorescence excitation-emission matrix combined with regional integration analysis to characterize the composition and transformation of humic and fulvic acids from landfill at different stabilization stages

Fluorescence excitation-emission matrix spectroscopy (EEMs) combined with fluorescence regional integration (FRI) analysis was used to investigate the composition and transformation of humic acid (HA) and fulvic acid (FA) from landfill. The EEMs of HAs at different landfill ages were characterized by two typical fluorescence chromophores with Ex/Em pairs at Ex = 420-470 nm/Em = 490-530 nm and Ex = 345-375 nm/Em = 450-465 nm. EEMs of FA were featured by other two distinctly different fluorophores with Ex/Em pairs at Ex = 315-335 nm/Em = 420-440 nm and Ex = 255-275 nm/Em = 425-455 nm. The results show that HA extracted from the refuse disposed in the year of 1989 was formed by connecting small-condensed aromatic structures with protein-like chains. Compared with HA extracted from the refuse disposed in the year of 1992, HA extracted from the refuse of 1996 had a higher fluorescence intensity and lower r_(B,A) (the ratio of the fluorescence intensities of peak B and peak A) value. It contained low molar mass components, low aromatic condensation degree, and more easily oxidized substituents. This indicates that the landfill time strongly affects the EEMs characteristics of HA, and that the humification degree of HA increases with the landfill time. A red shift to a longer wavelength region and an increase of fluorescence intensity were observed when the concentration of HA was increased, suggesting that concentration had a great influence on the fluorescence characteristics of HAs. pH (2-12) also had significant effects on the fluorescence intensity, although it exerted no effect on the peak position of fluorescence of HA and FA. The results of FRI show that increasing concentration lead to more interactions among various structure components and that small molecular weight units tend to aggregate or be masked into more complicated and larger structures. The pH influence on the fluorescence intensity of HA seems mainly through molecular configuration, while the fluorescence intensity change with pH may be due to various substituents of FA.     

Absorption behavior of chlorine and sulfur by Ca(OH)<Subscript>2</Subscript> under simulated conditions with a fluidized bed combustor

This study was carried out to investigate the absorption reaction of chlorine and sulfur with Ca(OH)₂ under simulated conditions related to the co-combustion of refuse-derived fuel and sewage sludge in the fluidized bed combustor, such as high temperature, moisture and a mixing of samples. The combustion experiments were carried out in an electrical furnace with PVC and sulfur powders as the waste samples. High-purity slaked lime powder was used to capture the chlorine and sulfur. The experimental results showed that the removal efficiencies of both chlorine and sulfur were over 90% when the mole ratios of Ca on Cl and S were over 2.5. Furthermore, simultaneous absorption was helpful in improving the removal efficiency of chlorine and sulfur. The presence of chlorine markedly increased the removal efficiency of sulfur. The removal efficiency of chlorine was the highest at 700°C in both independent and simultaneous absorption. The removal efficiency of sulfur increased as the temperature increased, but the removal efficiency of chlorine sharply decreased from 95 to 83% when the moisture content in gases increased from 0 to 20 vol%. These results were confirmed by the combustion test of granular CaCl₂.