Large-scale Municipal Waste Incinerator Research Articles

PAH emissions from coal combustion and waste incineration

The characteristics of PAHs that are emitted by a municipal waste incinerator (MWI) and coal-fired power plant are examined via intensive sampling. Results of flue gas sampling reveal the potential for PAH formation within the selective catalytic reduction (SCR) system of a coal-fired power plant. In the large-scale MWI, the removal efficiency of PAHs achieved with the pilot-scaled catalytic filter (CF) exceeds that achieved by activated carbon injection with a bag filter (ACI+BF) owing to the effective destruction of gas-phase contaminants by a catalyst. A significantly lower PAH concentration (1640ng/g) was measured in fly ash from a CF module than from an ACI+BF system (5650ng/g). Replacing the ACI+BF system with CF technology would significantly reduce the discharge factor (including emission and fly ash) of PAHs from 251.6 to 77.8mg/ton-waste. The emission factors of PAHs that are obtained using ACI+BF and the CF system in the MWI are 8.05 and 7.13mg/ton, respectively. However, the emission factor of MWI is significantly higher than that of coal-fired power plant (1.56mg/ton). From the perspective of total environmental management to reduce PAH emissions, replacing the original ACI+BF process with a CF system is expected to reduce environmental impact thereof.

Mercury contamination and potential impacts from municipal waste incinerator on Samui Island, Thailand

In recent years, mercury (Hg) pollution generated by municipal waste incinerators (MWIs) has become the subject of serious public concern. On Samui Island, Thailand, a large-scale municipal waste incinerator has been in operation for over 7 years with a capacity of 140 tons/day for meeting the growing demand for municipal waste disposal. This research assessed Hg contamination in environmental matrices adjacent to the waste incinerating plant. Total Hg concentrations were determined in municipal solid waste, soil and sediment within a distance of 100 m to 5 km from the incinerator operation in both wet and dry seasons. Hg analyses conducted in municipal solid waste showed low levels of Hg ranging between 0.15–0.56 mg/kg. The low level was due to the type of waste incinerator. Waste such as electrical appliances, motors and spare parts, rubber tires and hospital wastes are not allowed to feed into the plant. As a result, low Hg levels were also found in fly and bottom ashes (0.1–0.4 mg/kg and ≤0.03 mg/kg, respectively). Stack concentration of Hg were less than 0.4 μg/Nm3. Since Hg emissions were at low concentrations, Hg in soil from atmospheric fallout near this incinerator including uptake by local weeds were very low ranging from non detectable to 399 μ g/kg. However, low but elevated levels of Hg (76–275 μ g/kg) were observed in surface soil and deeper layers (0–40 cm) in the predominant downwind direction of incinerator over a distance of between 0.5–5 km. Soil Hg concentrations measured from a reference/background track opposite of the prevailing wind direction were lower ranging between 7–46 μ g/kg. Nevertheless, the trend of Hg build up in soil was clearly seen in the wet season only, suggesting that wet deposition process is a major Hg pollution source. Hg concentrations in the sea bottom sediment collected next to the last station track was small with values between 35–67 μ g/kg. Based upon the overall findings, in terms of current potential environmental risk, the environment has not yet been appreciably contaminated from Hg emissions produced by this incinerator. However the increase of Hg measured in downwind direction of the incinerator should be monitored for future potential risk.

PCDD/F Adsorption and Destruction in the Flue Gas Streams of MWI and MSP via Cu and Fe Catalysts Supported on Carbon

Catalytic destruction has been applied to control polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/Fs) emissions from different facilities. The cost of carbon-based catalysts is considerably lower than that of the metal oxide or zeolite-based catalysts used in the selective catalytic reduction (SCR) system. In this study, destruction and adsorption efficiencies of PCDD/Fs achieved with Cu/C and Fe/C catalysts from flue gas streams of a metal smelting plant (MSP) and a large-scale municipal waste incinerator (MWI), respectively, are evaluated via the pilot-scale catalytic reactor system (PCRS). The results indicate that Cu and Fe catalysts supported on carbon surface are capable of decomposing and adsorbing PCDD/ Fs from gas streams. In the testing sources of MSP and MWI, the PCDD/F removal efficiencies achieved with Cu/C catalyst at 250 degrees C reach 96%, however, the destruction efficiencies are negative (-1,390% and -112%, respectively) due to significant PCDD/F formation on catalyst promoted by copper. In addition, Fe/C catalyst is of higher removal and destruction efficiencies compared with Cu/C catalyst in both testing sources. The removal efficiencies of PCDD/Fs achieved with Fe/C catalyst are 97 and 94% for MSP and MWI, respectively, whereas the destruction efficiencies are both higher than 70%. Decrease of PCDD/F destruction efficiency and increase of adsorption efficiency with increasing chlorination of dioxin congeners is also observed in the test via three-layer Fe/C catalyst. Furthermore, the mass of 2,3,7,8-PCDD/Fs retained on catalyst decreases on the order of first to third layer of catalyst. Each gram Fe/C catalyst in first layer adsorbs 10.9, 6.91, and 3.04 ng 2,3,7,8-PCDD/Fs in 100 min testing duration as the operating temperature is controlled at 150, 200, and 250 degrees C, respectively.

Partitioning and removal of dioxin-like congeners in flue gases treated with activated carbon adsorption

Activated carbon adsorption is commonly used to control dioxin-like congener (PCDD/Fs and PCBs) emissions. Partitioning of PCDD/Fs and PCBs between vapor and solid phases and their removal efficiencies achieved with existing air pollution control devices (APCDs) at a large-scale municipal waste incinerator (MWI) and an industrial waste incinerator (IWI) are evaluated via intensive stack sampling and analysis. Those two facilities investigated are equipped with activated carbon injection (ACI) with bag filter (BF) and fixed activated carbon bed (FACB) as major PCDD/F control devices, respectively. Average PCDD/F and PCB concentrations of stack gas with ACI + BF as APCDs are 0.031 and 0.006 ng-TEQ/N m 3, and that achieved with FACB are 1.74 and 0.19 ng-TEQ/N m 3 in MWI and IWI, respectively. The results show that FACB could reduce vapor-phase PCDD/Fs and PCBs concentrations in flue gas, while the ACI + BF can effectively adsorb the vapor-phase dioxin-like congener and collect the solid-phase PCDD/Fs and PCBs in the meantime. Additionally, the results of the pilot-scale adsorption system (PAS) experimentation indicate that each gram activated carbon adsorbs 105–115 ng-PCDD/Fs and each surface area (m 2) of activated carbon adsorbs 10–25 ng-PCDD/Fs. Based on the results of PAS experimentation, this study confirms that the surface area of mesopore + macropore (20–200 Å) of the activated carbon is a critical factor affecting PCDD/F adsorption capacity.

Characteristics of PCDD/F congener distributions in gas/particulate phases and emissions from two municipal solid waste incinerators in Taiwan

Partitioning of PCDD/F (polychlorinated dibenzo- p-dioxins and polychlorinated dibenzofuran) congeners between gaseous and particulate phases and removal efficiencies of the existing air pollution control devices (APCDs) for PCDD/Fs at two large-scale municipal waste incinerators (MWIs) in Taiwan are evaluated via stack sampling and analysis. Two MWIs investigated are equipped with activated carbon injection (ACI) and selective catalytic reduction system (SCR) as major PCDD/F control devices, respectively. The average PCDD/F concentrations of stack gases are 2.35 and 1.49 ng/N m 3, and the international toxic equivalent quantity (TEQ) are 0.17 and 0.043 ng TEQ/N m 3 in MWI-A and MWI-B, respectively. The average removal efficiency of PCDD/Fs achieved with ACI+BF (bag filters) reaches 95% (MWI-A) while that achieved with the WS (wet scrubber)+SCR system reaches 99% (MWI-B). The results obtained on gas/particulate partitioning in flue gases indicate that particulate-phase PCDD/Fs accounted for 27.7% and 24.7% of the total PCDD/F concentrations at the outlets of cyclone (CY) and electrostatic precipitator (EP) for MWI-A and MWI-B, respectively. But the gas/particulate partitioning in flue gas after PCDD/Fs control devices is quite different in two MWIs. This study also indicates that total 2,3,7,8-substituted PCDD/F discharges are 142.3 μg TEQ/ton waste for MWI-A and 98.6 μg TEQ/ton waste for MWI-B, respectively.

Investigation on the emission factors and removal efficiencies of heavy metals from MSW incinerators in Taiwan.

Two large-scale municipal waste incinerators (MWIs) equipped with different air pollution control devices (APCDs) were selected for conducting flue gas sampling and determination of heavy metals emissions including lead, zinc, cadmium, chromium, copper and mercury. In addition, the emission characteristics and removal efficiencies of heavy metals were evaluated via simultaneous sampling of flue gas upstream and downstream of APCDs. The average removal efficiency of particulate matter was 99.47%, and the removal efficiency of heavy metals could reach 95% or higher (except for Hg) for MWI-A. Preliminary results indicated that the average removal efficiency of particulate matter was 99.94%, and the removal efficiency of heavy metals could reach 98% or higher (except for Hg) for MWI-B. The average removal efficiencies of Hg for MWI-A and MWI-B were 47% and 30% respectively. The removal efficiencies achieved with existing APCDs were close to that reported in the US EPA document (AP-42) for MWIs. The average concentrations of heavy metals and particulate matter emitted from stack could meet current emission standards in Taiwan for both MWIs, but particulate matter, Pb and Cd concentrations of MWI-A were higher than the current emission regulations in Germany and the Netherlands.

Sampling and analysis of ambient dioxins in northern Taiwan

In this study, ambient air samples were taken concurrently in the vicinity area of a large-scale municipal waste incinerator (MWI) and the background area for measuring polychlorinated dibenzo- p-dioxins and furans (PCDD/Fs) concentrations from November 1999 through July 2000 in northern Taiwan. The results obtained from eighteen ambient air samples indicate that the mean PCDD/F concentration of seventeen 2,3,7,8-substituted congeners in wintertime (188–348 fg-I-TEQ/m 3) is significantly higher than that measured in summertime (56–166 fg-I-TEQ/m 3). In addition, the seasonal PCDD/F concentrations are compared with the ambient air quality data including CO, NO 2, PM 10 and TSP sampled from Taipei area to gain better insights. It indicates that the variation of ambient air PCDD/F concentrations is closely correlated with that of PM 10 concentrations. Besides, the results indicate that the I-TEQ concentration of ambient air in sampling site B (directly downwind of the MWI) is of the highest while the sampling site A (upwind of MWI) is of the lowest among all sampling sites. This implies that existing MWI can be a significant emitter of PCDD/Fs in this area. Furthermore, the patterns of the PCDD/F congener distribution at all sampling sites (including the background site in Taoyuan) are quite similar. OCDD concentration is of the highest among seventeen PCDD/F congeners investigated and accounts for about 35% of the total concentration. As for the I-TEQ concentrations, 2,3,4,7,8-PeCDF is the most significant contributor, generally being responsible for 30–45% of the total I-TEQ values depending on the sampling sites and seasons.

Formation and presence of polyhalogenated and polycyclic compounds in the emissions of small and large scale municipal waste incinerators

Polyhalogenated compounds included polychlorinated dibenzo-p-dioxins and dibenzofurans were identified and quantified in the emissions of small (batch-wise operated) and continuous operated municipal wasteincinerators. In addition, the amount of emitted polycyclic aromatics was determined. The results are represented and possible correlations between the concentration levels of the different compound groups are discussed.