Correspondence Comment on “Formation of Dioxins during the Combustion of Newspapers in the Presence of Sodium Chloride and Poly(vinyl chloride)” SIR: A recent paper in Environ. Sci. Technol. reported on the correlation between organic and inorganic chlorine content in newspapers versus formation of dioxins from waste materials using a lab incinerator apparatus (1) with batch feed for the fuels. In this study the exhaust gases from the combustion of newspaper, from branches of a London plane tree, and from newspapers mixed with sodium chloride (NaCl), polyethylene, or poly(vinyl chloride) (PVC) were collected and analyzed for dioxin levels. The reported results showed that feed samples with a higher chloride content produced more dioxins. The authors concluded that there is a correlation between dioxin formation and chloride content. The amount of dioxins formed in the samples according to the number of chlorides was Cl5 > Cl4 > Cl6 > Cl7 > Cl8 in PCDD isomers and Cl4 > Cl5 > Cl6 > Cl7 > Cl8 in PCDF isomers, except in the case of newspapers alone. The results reported inferred that NaCl and PVC contribute significantly to dioxin formation from waste materials combusted in incinerators. This article (1) also included a number of results previously published and similarly interpreted (2) from the same apparatus. The results from this experimental study provide useful information on the correlation between chlorine content and formation of dioxins in combustion of municipal wastes but only under non-steady-state operation. We point out that since the runs were performed by batch feed, these results are not necessarily representative of a modern continuous feed municipal waste incinerator, operating under steady state and excess air conditions. A significant difference exists between batch-feed and continuous-feed incinerators for the combustion of materials. Early municipal waste combustors (MWC) prior to 1950s were usually batch-feed furnaces that utilized manual stoking on stationary grates. In the 1950s, continuous-feed of refuse, mechanized stoking on moving grates, and water-based air pollution control (APC) systems became common (3). The batch-feed incinerators experience several problems such as nonuniform turbulence, temperature variations due to batch processing, and over-charging of furnaces relative to plant design capacity, i.e., fuel rich operation. The occurrence of puffs and oxygen deficiency produced from the combustion of organics at the time of fuel inlet is a common problem in batch-feed incineration (4). Continuous-feed incinerators are operated under a uniform, steady-state operation, in which the operation pa-
10.1021/es025516s CCC: $22.00 Published on Web 03/27/2002
2002 American Chemical Society
rameters including furnace temperature, solid (waste) residence time, and gas and solid flow rates are kept constant throughout the incineration process. The CO, CO2, and O2 levels are usually monitored for control and a fuel-lean operation is maintained to ensure continuous uniform conversion from the combustion of municipal wastes. The results in the referenced article (1) could result from very fuel rich operation at the time of initial batch inlet or a combination of fuel rich/fuel lean operation and do not necessary represent dioxin effluents from continuous feed and air flow municipal incinerators. The research group of Rivera has recently shown that, for a modern municipal solid waste incinerator (MSWI), levels of dioxin in the effluent are similar to levels in feed (5-7). Non-steady-state operation is unlikely to result in such low dioxin levels in the effluent. The results of Yasuhara et al. could be valuable for the correlation between chlorine content in the newspapers and dioxin formation under nonuniform or non-steady-state operation incinerators. They are not fully appropriate for modern, continuous feed, steady-state operation MSWIs. It is important that the data be evaluated objectively, relative to both environmental concerned community and industry or municipal incinerator operation. An experimental procedure which applies a continuous-feed incinerator under steady-state operation at recommended conditions would be more appropriate to evaluate dioxin effluent levels and for use in prediction of PCDD/F effluent from modern municipal waste incinerators.
Literature Cited (1) Yasuhara, A.; Katami, T.; Okuda, T.; Ohno, N.; Shibamoto, T. Environ. Sci. Technol. 2001, 35, 1373-1378. (2) Katami, T.; Ohno, N.; Yasuhara, A.; Shibamoto, T. Bull. Environ. Contam. Toxicol. 2000, 64, 372-376. (3) Walsh, D.; Chillrud, S.; Simpson, H.; Bopp, R. Environ. Sci. Technol. 2001, 35, 2441-2447. (4) Hart, J. Chemosphere 2001, 42, 559-569. (5) Abad, E.; Adrados, M. A.; Caixach, J.; Fabrellas, B.; Rivera, J. Chemosphere 2000, 40, 1143-1147. (6) Fabrellas, B.; Sanz, P.; Abad, E.; Rivera, J. Chemosphere 2001, 43, 683-688. (7) Abad, E.; Adrados, A.; Caixach, J.; Rivera, J. Environ. Sci. Technol. 2002, 36, 92-99.
Hsien-Tsung Chern and Joseph W. Bozzelli* Department of Chemistry and Environmental Science New Jersey Institute of Technology Newark, New Jersey 07102 ES025516S
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