Emission levels and phase distributions of PCDD/Fs in a full-scale municipal solid waste incinerator: The impact of wet scrubber system

Abstract

The emission of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) from municipal solid waste (MSW) incinerations will pose serious risk to ecological environment and human health. To further understand the memory effect of wet scrubber system (WSS) on PCDD/Fs emission and phase distribution characteristics, a field study was conducted in a full-scale (850 t d−1) MSW incinerator where a WSS was newly adopted. The four exhaust flue gas samples and the two scrubbing solution samples inside WSS were separately collected for PCDD/Fs analyzing. The results indicated that the memory effect of WSS obviously enhanced the I-TEQ concentration of PCDD/Fs from 0.007 to 0.033 ng I-TEQ Nm−3 after flue gas passed through WSS, owing to increasing the total mass concentration of PCDD/Fs and the proportion of low-chlorinated congeners. The gas-phase PCDD/Fs was dominant (62.5%–88.9%) in flue gas, among which the PCDD/Fs enriched in condensed water notably contributed to nonnegligible proportions of 25.0%–67.6%. The adsorption/desorption process of PCDD/Fs was considered as one of the reasonable mechanisms of memory effect, based on the PCDD/Fs phase distribution and the congeners profile inside the WSS. Besides, the I-TEQ concentration of PCDD/Fs determined in scrubbing solution was up to 50.2 pg I-TEQ L−1, which might be a potential source to cause the enhancement of PCDD/Fs emission. This study verified the enhancement impact of WSS on PCDD/Fs emission and inspired the optimal design of WSS, i.e., choosing more suitable filling materials and timely replacing them to reduce the negative impact of memory effect, keeping WSS operated in relatively stable and consistent conditions, and safely disposing the scrubbing solution to mitigate the secondary pollution of PCDD/Fs.