Environmental impacts of a large-scale incinerator with mixed MSW of high water content from a LCA perspective

Large-scale incinerators are applied widely as a result of the heavy burden of municipal solid waste（MSW） generated, while strong opposition is arising from the public living nearby. A large-scale working incineration plant of 1500 ton/day was chosen for evaluation using life cycle assessment. It was found that the corresponding human toxicity impacts via soil（HTs）, human toxicity impacts via water（HTw） and human toxicity impacts via air（HTa）categories are 0.213, 2.171, and 0.012 personal equivalents（PE）, and global warming（GW100）and nutrient enrichment（NE） impacts are 0.002 and 0.001 PE per ton of waste burned for this plant. Heavy metals in flue gas, such as Hg and Pb, are the two dominant contributors to the toxicity impact categories, and energy recovery could reduce the GW100 and NE greatly. The corresponding HTs, HTw and HTa decrease to 0.087, 0.911 and 0.008 PE, and GW100 turns into savings of- 0.007 PE due to the increase of the heating value from 3935 to5811 k J/kg, if a trommel screener of 40 mm mesh size is used to pre-separate MSW. MSW sorting and the reduction of water content by physical pressure might be two promising pre-treatment methods to improve the combustion performance, and the application of stricter standards for leachate discharge and the flue gas purification process are two critical factors for improvement of the environmental profile identified in this work.

Silver impregnated carbon for adsorption and desorption of elemental mercury vapors

The Hg 0 vapor adsorption experimental results on a novel sorbent obtained by impregnating a commercially available activated carbon （Darco G60 from BDH） with silver nitrate were reported.The study was performed by using a fundamental approach,in an apparatus at laboratory scale in which a synthetic flue gas,formed by Hg 0 vapors in a nitrogen gas stream,at a given temperature and mercury concentration,was flowed through a fixed bed of adsorbent material.Breakthrough curves and adsorption isotherms were obtained for bed temperatures of 90,120 and 150°C and for Hg 0 concentrations in the gas varying in the range of 0.8–5.0 mg/m 3 .The experimental gas-solid equilibrium data were used to evaluate the Langmuir parameters and the heat of adsorption.The experimental results showed that silver impregnated carbon was very effective to capture elemental mercury and the amount of mercury adsorbed by the carbon decreased as the bed temperature increased.In addition,to evaluate the possibility of adsorbent recovery,desorption was also studied.Desorption runs showed that both the adsorbing material and the mercury could be easily recovered,since at the end of desorption the residue on solid was almost negligible.The material balance on mercury and the constitutive equations of the adsorption phenomenon were integrated,leading to the evaluation of only one kinetic parameter which fits well both the experimentally determined breakthrough and desorption curves.

Fast indirect measurement of PCDD/F TEQ emission from municipal solid waste incineration:a review

Landfilling,a traditional and major method for municipal solid waste management,is gradually being taken place by incin-eration.However,the contamination problem caused by polychlorinated dibenzo-p-dioxin and dibenzofuran(PCDD/F)emissions from incineration has also brought much concerns.Traditional offline method based on high-resolution gas chromatography coupled with high-resolution mass spectrometry for the determination of PCDD/F emissions is expensive,infrequent and time-lagging.Use of PCDD/F indicators to achieve fast indirect measurements for PCDD/Fs is a much more promising method.Six categories of potential PCDD/F indicators are discussed in this paper:CO,total hydrocarbons,specific PCDD/F congeners,polycyclic aromatic hydrocarbons,chlorophenols and chlorobenzenes.Their performance as PCDD/F indicators are verified in the following criteria:(1)structural similarities;(2)known mechanistic arguments;(3)known cor-relation values from the literature and(4)detectability.Comprehensively considering the four factors,chlorobenzenes may be the best suitable PCDD/F indicator.One analytical method based on Photon Ionization coupled with Time-of-Flight Mass Spectrometry has been proved effective for the online/atline measurements for PCDD/F indicators for the prediction of TEQ in incineration process.Moreover,thermal desorption and gas chromatography can be applied to provide extra separation and concentration for very complex matrices with extremely low concentrations.

The co-removal of PCDD/Fs by SCR system in a full-scale municipal solid waste incinerator:Migration-transformation and decomposition pathways

Polychlorinated dibenzo-p-dioxins and furans(PCDD/Fs)generated from municipal solid waste(MSW)incineration are considered as the key pollutants,which could pose serious risks to the environment and ecology.This study comprehensively investigated the effect of selective catalytic reduction(SCR)system on PCDD/F removal,phase distributions,and migrationtransformation characteristics of 17 congeners in a full-scale MSW incinerator.The three flue gas samples and two fly ash samples were separately collected for PCDD/F analysis.The results showed that the SCR system reduced the I-TEQ concentration of PCDD/Fs from 0.135 to 0.010 ng I-TEQ Nm^(−3)with a remarkable toxicity removal efficiency of 92.6%,through oxidation decomposition over V_(2)O_(5)-WO_(3)/TiO_(2)catalysts and chlorination process of low-chlorinated congeners.In addition,the de novo synthesis observed along the flue between SCR system and stack regenerated unexpected PCDD/Fs,which might enhance the PCDD/F emission level.This study verified the three pathways of SCR system on PCDD/F removal and inspired operating suggestions for SCR system,i.e.,keeping SCR system operated in stable and consistent conditions,regularly replacing V_(2)O_(5)-WO_(3)/TiO_(2)catalysts,and timely cleaning the dusts and inlet materials of SCR system,which would be beneficial for achieving the ultra-low emission of PCDD/Fs in full-scale MSW incinerators.