Coprecipitation of phthalic acid complexed with iron during iron precipitation. Methane gas production resulting from anaerobic microbial waste degradation. Microbial reduction of sulfates to sulfides. Reduction of ferric to ferrous iron resulting from E h and pH changes due to microbial waste degradation. Retention of organic waste acids by adsorption and anion exchange on the injection-zone mineral constituents. Although limited degradation of the organic waste constituents did occur in the subsurface after waste injection, the reaction products are as detrimental to the groundwater quality as the waste itself. In addition, the formation of iron hydroxide, iron carbonate, terephthalic acid precipitates, and the production of carbon dioxide gas probably were factors in the plugging of the injection zone adjacent to the wells and eventual abandonment of the system. The corrosive nature of the organic acids may have been a factor in causing waste leakages into shallower zones a t the two injection wells and at certain observation wells. This study has shown that the organic wastes of this plant were reactive rather than inert after injection into the subsur-
face environment a t this study site, and that the nature of this reactivity should be an important factor in ascertaining the compatibility of an industrial organic waste with the subsurface, into which it is to be placed.
Literature Cited (1) Hall, C. W., Ballentine, R. K., “Underground Waste Management and Artificial Recharge”, New Orleans, September 1973,2, 783-9 (1973). (2) Warner, D. L., Orcutt, D. H., ibid., pp 687-697. (3) Leenheer, J. A,, Malcolm, R. L., ibid., 1,565-84 (1973). (4) Peek, H. M., Heath, R. C., ibid., 2,851-75 (1973). (5) Malcolm, R. L., Leenheer, J. A., I n s t . Enuiron. Sei. Proc., Anaheim, Calif., April 1973, 336-40 (1973). (6) White, W. R., Leenheer, J. A., J . Chromatogr. Sci., 13,386-390 (1975). (7) Lawrence, A. W., McCarty, P. L., Water Pollut. Control Fed. J., 1, Part 2, 1-17 (1969). (8) Siebert, M. L., Hattingh, W. H. J., Water Res., 1,13-19 (1967). (9) DiTommaso, A,, Elkan, G. H., “Underground Waste Management and Artificial Recharge”, New Orleans, September, 1973, 1,585-99 (1973). (10) Oborn, E. T., Hem, J. D., U.S. Geol. Suru. W a t e r S u p p l y , Paper 1459-H, 213-35 (1961). Received for review J u n e 2,1975. Accepted December 3,1975.
Municipal Incinerator as Source of Polynuclear Aromatic Hydrocarbons in Environment Ian W. Davies, Roy M. Harrison’, Roger Perry*, Don Ratnayaka, and Roger A. Wellings Public Health Engineering, Department of Civil Engineering, Imperial College, London SW7 2BU U.K.
Polynuclear aromatic hydrocarbons, formed by the incomplete combustion of municipal refuse in a continuous feed incinerator, are released into the environment in the ash waste from the incinerator. In addition they are discharged in both the stack gases and wastewaters from the plant. The balance between the three emission modes is discussed in relation to combustion conditions and incinerator operation.
Incineration is a valuable means of waste disposal, being highly effective both in reduction of the volume of waste and in the elimination of noxious materials, and, as such, is coming increasingly into use. Combustion processes are a known source of polynuclear aromatic hydrocarbons (PAH), and the release of these compounds from municipal refuse incinerators has been reported both in the stack gases ( I ) and the ash residues (2). Despite isolated measurements of PAH emissions, however, it appears that no assessment has been made of the relative contributions of the various routes of emission from a municipal incinerator to the total output of these compounds. Accordingly, as part of a broader study of PAH levels in the environment, such an evaluation has been attempted.
Experimental S t a c k Gas Sampling a n d Analysis. Isokinetic samples were taken using a sampling train built to EPA specification with an out-of-stack filter ( 3 ) .Samples were composites from 15 points across the gas stream, and simultaneous Present address, Dept. of Environmental Sciences, University of Lancaster, Lancaster, U.K. LA1 4YQ.
measurement of stack gas flow at the point of sampling using a pitot tube allowed precise maintenance of isokinetic flows. Gas temperatures’were measured with a thermocouple and the stack gas composition and moisture content were determined by standard procedures. Particulates were collected by passage from the heated (150 “C) quartz probe through a cyclone and a 50-mm diameter glass fiber filter (Whatman type GF/C). The total air sample was 1-2 m3 (corrected to NTP). Condensed total liquid fraction and deposited particulates were washed from the cyclone, and all sample-exposed surfaces prior to the filter were washed with distilled dichloromethane. Particles and the glass fiber filter were extracted in a Soxhlet apparatus with dichloromethane for 35 h. After purification of the combined solvent extracts by the procedure of Hoffmann and Wynder ( 4 ) , gas chromatographic analysis for PAH was performed with a Hewlett-Packard 7620 instrument with balanced dual columns (3.5 m X 0.3 cm 0.d. stainless steel; 3% OV7 on 60/80 mesh AW-DCMS Gas Chrom Q) and nitrogen carrier (35 ml min-l) fitted with dual flame ionization detectors. A column temperature of 260 OC was maintained for 8 min and then increased to 300 “C at 8” min-l. Octacosane was used as an internal standard, and the response of the instrument was calibrated using standard PAH solutions in dichloromethane. Analysis of Residues. The residues were dried, crushed, sieved, and extracted with dichloromethane according to the procedure of Hrudey et al. (2). After purification of the extract by a modification of the procedure of Hoffmann and Wynder (41, gas chromatographic analysis was carried out as above. Analysis of Water Samples. Samples (9.5 1.) were collected in borosilicate glass vessels, stoppered, and returned immediately to the laboratory. Dichloromethane (600 ml) Volume 10, Number 5, May 1976 451
Table I. Composition of Refuse
Item
Range of Average composition, composition, '10 by wt "/o by wt
Fine dust a n d cinder Vegetable and putrescibies Paper Metal Glass a n d ceramic Textile a n d wood Plastic a n d rubber Unclassified
13-23 12-18 27-37 8-10 5-10 6-10 4-6 3-8
I
Flgure 1. Layout of incinerator-ground
18.0 15.0 32.0 9.0 7.5 8 5 5.5
I
plan
was added and the resultant liquids were emulsified with an Ultra-Turrax high-speed blender a t 80% full revolutions for 5 min. The mixture was stoppered and left overnight in the absence of light. The bulk of the aqueous layer was decanted and the resultant liquids were filtered under vacuum through a glass fiber filter paper subsequently washed with dichloromethane. The filtrate and washings were transferred to a separating funnel and the dichloromethane layer was separated, dried (CaS04), and evaporated by distillation through a 15-cm Vigreux column. When reduced to a small volume, the extract was purified as above prior to chromatographic analysis. In calculation of the concentrations of PAH in the samples, a correction for extraction efficiency was applied on the basis of earlier experiments with standard materials ( 5 ) .
trolled supply of primary air that entered under the grate. Primary air supply varied between 15-20% excess of the theoretical air requirements. Secondary air was also supplied periodically through the front wall of the furnace to maintain a furnace temperature of between 800 and 1090 "C. Secondary air supply depends on the need to control the furnace temperature and in turn depends on the calorific value of the refuse. In general the secondary air supply could vary in the range nil to about 75% excess air. The residue dropped from the grate into a tank where it was quenched, freed of magnetic materials, and discharged. The gases leaving the furnace entered an upflow water spray tower where they were cooled to 250-300 "C, and larger particles of fly ash were removed. Two induced draft fans drew the gases from the spray towers through an electrostatic precipitator prior to discharging them through a 55-m high concrete chimney (Figure 3). There are three distinct modes of release of PAH from the incinerator into the environment. Gases leaving the furnace contain PAH both as vapor and adsorbed on fly ash particulates. A reduction in levels as a result of passage through the spray tower and electrostatic precipitator would be expected. Solid residues made up of combinations of quenched ash residues and fly ash collected by the spray tower and electrostatic precipitator, also contain PAH as do the wastewaters from the incinerator. The water used is drawn from the final effluent of a neighbouring sewage works and this is used in the quench trough and spray tower where much is lost by evaporation. After use, the water is periodically discharged to the sewage works input. The level of suspended solids in the discharged water is high and PAH are present in the water both in solution and adsorbed on the solids. Isokinetic sampling of the stack gases was performed between the electrostatic precipitator and the chimney, and samples of residues and discharged water were collected. All samples were extracted with dichloromethane and analyzed by gas-liquid chromatography after an appropriate clean-up procedure. Results of the analyses appear in Table I1 together with estimated total daily emissions. Such figures are naturally subject to some fluctuation. Variations in the level of emissions with the combustion temperature and refuse composition might be anticipated
+4
Discussion and Results The incinerator selected for study (Figure 1) was a modern continuous feed municipal refuse incinerator rated a t 9.14 tonnes of refuse per hour. The refuse varies widely by areas, by seasons, by days, and by deliveries arriving a t the incinerator. At the refuse reception pit every effort is made to mix the refuse so that the feed to the furnace is of uniform composition. Table I gives the analysis and the range of refuse composition. The furnace was 2.54 m wide, having a Heenan-Nichols rocking bar-type grate with three sections, each 3.45 m long and inclined a t an angle of 1 1 O . The grate area was 25.1 m2, hence the average burning rate was 364 kg md2 h-l. The furnace has' been designed to burn refuse of calorific value in the range 5860-11 600 kJ/kg with approximately 12% excess air. The furnace was refractory lined and had a continuous feed of refuse from a chute filled by a cactus-type grab crane. The refuse moved down the sloping grate by the action of rocking teeth (Figure 2). Each section of the grate had an independently con452
Environmental Science & Technology
Figure 3. Layout of incinerator-elevation
A-A
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Table I I . Levels and Daily Emissions of Polynuclear Aromatic Hydrocarbons Water Stack gases Compound
Mg/1000 m 3 Mg day’’a
Residues
1-19kg-1
Mg day-lb
Input,
pg I.-*
output,
1-19 I.-’
output, mg day-lc
Fluoranthene 0.58 274 58 1360 0.08 0.62 15.5 Pyrene 1.58 745 49 1150 0.08 0.54 13.5 Benzo(a)anthracene + chrysene 0.72 340 171 4010 0.03 0.64 16.0 Benzo(b)fluoranthene + Benzo(k)fluoranthene + Benzoo) fluoranthene 0.32 151 292 6850 0.03 0.14 3.5 Benzo(a)pyrene + benzo(e)pyrene 0.02 9 147 3450 0.03 0.14 3.5 Per y Iene 0.18 85 82 1920 0.02 0.13 3.3 Benzo(ghi)perylene 0.42 198 47 1100
