Multielement Analysis of Municipal Sewage Sludge Ashes. Absorption of Elements by Cabbage Grown in Sludge Ash-Soil Mixture A. Keith Furr and Thomas F. Parkinson Office of Occupational Health and Safety, and Nuclear Reactor Laboratory, Virginia Polytechnic Institute and State University, Blacksburg, Va. 24061
Timothy Wachs Department of Chemistry, Cornell University, Ithaca, N.Y. 14853
Carl A. Bache, Walter H. Gutenmann, Patricia C. Wszolek, Irene S. Pakkala, and Donald J. Lisk” Pesticide Residue Laboratory, Department of Food Science, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca, N.Y. 14853
rn An analytical survey of 42 elements and polychlorinated biphenyls (PCBs) was conducted on municipal sewage sludge ashes from 10 American cities. T h e concentrations of specific elements in the ashes varied widely. Calcium and iron content reflected the addition of lime and ferric chloride during sewage treatment. Elements such as cadmium, mercury, nitrogen, and selenium were low probably because of volatilization losses during incineration. PCBs were not detected in t h e ash samples. Although the total content of nickel and zinc in the ashes was high, absorption of these elements by cabbage grown on ash-amended soil was surprisingly low, possibly due to their presence in t h e ashes as insoluble compounds formed during incineration. T h e annual production of sewage sludge in the United States presently is in the range of 5 million tons ( I ) . Methods of disposal have included discarding in landfills, ocean dumping, incineration, and more recently its use as a soil amendment in horticulture and agriculture. There is much concern presently about elevated concentrations of Cd, Ni, Zn,Cu, P b , Cr, and other elements in sludges resulting from industrial activities and their possible absorption by crops grown on sludge-amended soils. This area of research has been reviewed ( I , 2). Disposal of municipal sludges by incineration produces an odorless, sterile ash comprising from about 30 t o 60% of t h e weight of t h e original sludge on a dry basis (3).Proper disposition of sludge ash thus constitutes a n appreciable portion of the nation’s total solid waste disposal problem. Farrell and Salotto ( 4 ) reported the content of 23 elements in sludge ashes from three small American cities, but extensive data have not been published on t h e elemental composition of municipal sludge ashes or t h e extent of absorption of elements by crops grown on sludge ash amended soil mixtures. In t h e work reported, 42 elements and polychlorinated biphenyls (PCBs) were determined in sludge ashes from I O American cities. Cabbage was then grown in t h e greenhouse in potted soil amended with these sludge ashes, and t h e extent of specific elemental absorption by t h e plants was compared with t h e total content of t h e respective elements in t h e various ashes. IL~pwimental In 1976 a description of our proposed study was sent t o 16 cities with a request t h a t they participate a n d return a representative sample of their sludge ash t o us for analysis. T h e cities t h a t responded a n d t h e data they provided pertaining t o their sludge incineration process are given in Table I. T h e process may typically include addition of ferric chloride or aluminum sulfate t o precipitate phosphates and the addition of polymer as a settling agent for the suspended solids and phosphate floc during primary sedimentation. Addition of lime may also be used t o precipitate heavy metals and other 0013-936X/79/0913-1503$01,00/0 @ 1979 American Chemical Society
solids. T h e resulting solids are largely dewatered by use of a centrifuge or vacuum filtration. T h e solids may then be fed into the top of t h e incinerator where they are further dried, incinerated, and cooled as they progress toward the bottom where the ash collects and is removed by trucking or sluicing. Exhaust scrubbers remove the fly ash, which may then be conveyed back and added (as a filtering aid) to incoming sewage prior to its primary sedimentation. In some cities the sludge t h a t is incinerated is a mixture of dewatered primary a n d excess activated sludge. T h e sludge ashes received were air dried, pulverized in a hammermill containing a 3-mm sieve, mixed by tumbling, and subsampled for analysis. A study was also made to determine if a crop grown on sludge ash amended soil would absorb elements in proportion to their concentration in the ash. The soil used was a Darian gravelly silt loam (fine loamy, mixed, mesic aeric ochraqualfs), p H 5.5, and with a determined cation exchange capacity of 20.8 mequiv/100 g. T h e soil was air-dried, sifted through a 2-mm screen, and thoroughly mixed. Five percent w/w of the various sludge ashes was mixed with portions of the soil using a cement mixer [or 111.2 metric tons/ha (,SO t o ~ d a c r e ) ]For . each sewage treatment plant, 7 kg of the respective sludge ash-soil mixture was used to fill each of three 7.6-L plastic pots. T h e pots were 21 cm i.d. and contained drain holes. Soil alone was used for growth of the control crop. Appropriate quantities of sulfur were mixed with the various sludge ash-soil mixtures so their resultant pH ranged from 5.2 to 5.7. T h e crop grown was “Golden Acre” cabbage (Brassica oleracea var. c a p i t a t o ) . Cabbage was the crop chosen, since it has been found to be quite resistant to possible phytotoxic constituents in municipal sludge, yet actively a b sorbs heavy metals ( 5 ) .One cabbage plant was grown to maturity in the greenhouse in each of four pots representing a given sewage treatment plant. The period of growth was from May to September. T h e plants were fertilized weekly with 1000 m L of a solution containing reagent grade K H 2 P 0 4 (0.001 M ) and KNO:j (0.005 M) (6). All plants were watered daily, care being taken t o avoid splashing soil on t h e aerial portions of t h e plants. At maturity the cabbage was harvested with only the edible leaf head portion taken for analysis. Prior to analysis the leaves were rinsed with distilled water to remove adhering dust. The respective replicated cabbage heads grown on sludge ash from a particular treatment plant were combined and suhdivided in a food cutter. T h e plant material was mixed, freeze dried, milled to a powder, again mixed, and subsampled f’or analysis. T h e ash and crop samples were analyzed for 32 elements using nondestructive neutron activation analysis as previously described ( 3 ) .Arsenic was distilled as arsine and det,ermined spectrophotometrically using the silver diethyldithiocarbamate procedure ( 7 , 8 ) .Boron was determined by the curcumin colorimetric procedure (9). Cadmium, lead, and zinc were determined by conventional stripping voltammetry ( I O ) . Volume 13, Number 12, December 1979
1503
Table 1. Data Pertaining to Municipal Sewage Sludge Incinerator Ashes Studied sewage treatment plant
city
Dunkirk, N.Y. Grand Rapids, Mich. Greensboro, N.C. Hilton, N.Y. Indianapolis, Ind. Kalamazoo, Mich. Lorton. Va. Naugatuck, Conn.
Saginaw , Mich. Youngstown, Ohio
a
ratio ( O h ) industrial: domestic contribution
Dunkirk Wastewater 60:40 Treatment Plant Grand Rapids Waste- 30:70 water Treatment Plant North Buffalo Sewage 3Q:70 Treatment Plant 2:98 Northwest Quadrant Treatment Plant Dept. of Public Work$ 76:30 City of Kalamazoo Treatment Plant Lower Potomac Treatment Plant Borough Naugatuck Wastewater Treatment Plant Saginaw Wastewater Treatment Plant Youngstown Wastewater Treatment Plant
50:50 10:90
50:50
heavily industrial 25:79
combustion temp, "C
feed rate, tons/ ha
multiple (5) hearth multiple (7) hearth
870
3
up to 980
4
vacuum filtration vacuum filtration vacuum filtration vacuum filtration vacuum filtration vacuum filtration
multiple (5) hearth multiple (6) hearth multiple (8) hearth multiple (7) hearth multiple (6) hearth multiple (7) hearth
870
vacuum filtration vacuum filtration
multiple (6) hearth multiple (7) hearth
dewatering scheme
combustion unit
vacuum filtration vacuum filtration
additives
ultimate ash disposal method
ferric chloride, lime ferric chloride, lime
landfill
2.5
polymer
landfill
775-870
4
landfilI
800- 1000
5
775
7
aluminum sulfate dry sludge ash none
775-870
5
sandf iII
775-870
6
870-925
5
800
6
ferric chloride, lime ferric chloride, lime, aluminum sulfate, polymer ferric chloride, lime ferric chloride, lime
landfill
landfill landfilI
landfill
landfill landfill
Moist sludge cake.
Mercury was measured by flameless atomic absorption analysis (11). Nickel was analyzed by the furnace atomic absorption method. Phosphorus was measured by the molybdivanadophosphoric acid spectrophotometric procedure (12). Selenium was measured by the fluorometric method of Olson (13). Nitrogen was assayed by the Kjeldahl method. The determination of pH was done by the method of Peech et al. (14). y emission was measured with a Packard y scintillation spectrometer equipped with a Model 9012 multichannel analyzer. Total y radiation in the range of 5-505 keV was integrated and recorded for 10 g of each sample over a period of 1000 s. Relatively little y radiation was recorded above 505 keV. Analytical precision in repetitive counting of duplicates of the same sample was within 62%. PCBs were sought as Aroclor 1254 using electron-capture gas chromatography to analyze the supernatant solutions obtained from vigorously shaking 5 g of each ash sample with 25 mL of toluene for 2 h. A Tracor 220 gas chromatograph equipped with a ""Ni detector and a glass column (180 cm X 4 mm i d . ) packed with 3%OV-17 on 100/120 mesh Gas-Chrom Q was used for these analyses. Flow rate through the column was 60 cm.3/min nitrogen and the column temperature was 185 OC. Detector and injector temperatures were 310 and 230 "C, respectively. Results were confirmed for selected ash samples using negative ion electron-capture chemical ionization mass spectrometry. Negative ions were formed by electron capture in a chemical ion source using methane as the reagent gas (15). These negative ions were detected using a modification of a conversion dynode system previously described (16).
Results and Discussion The results of analysis of the sludge ashes are given in Table 11. T h e concentrations of specific elements may vary widely depending on their concentration in the initial wastewater, those added during sewage treatment (aluminum, calcium, and iron), and losses during incineration. The calcium and iron contents of the ashes were reflective of the use of lime and 1504
Environmental Science & Technology
ferric chloride in the treatment process (see Table I). Elements such as bromine, chlorine, cadmium, mercury, nitrogen, and selenium were probably lost by vaporization during incineration. Other elements such as barium, chromium, copper, and lead can be lost in small amounts as constituents of particulates in the stack gases ( 4 , 17). In an analytical survey of sludges from American cities conducted earlier ( 3 ) ,PCBs were detected in nearly all samples. No evidence was found for the presence of PCBs in the sludge ashes in this study. Farrell and Salotto ( 4 ) also found PCBs and chlorinated pesticides to be absent in ashes resulting from sludge incineration. As they point out, however, the absence of PCBs may not result entirely from thermal decomposition but also as volatilized condensates on escaping particulates. Others have shown the thermal decomposition of PCBs at elevated temperatures (18, 19). The concentrations of selected toxic and nutrient elements in the cabbage are given in Table 111. The errors in these elemental analyses were within 610%. Whereas elements such as arsenic and lead tend to be excluded by plants, others such as nickel and zinc should expectedly have been absorbed to a much greater extent by the cabbage in the p H range (5.2 to 5.7) of the soil-sludge ash mixture based on the total nickel and zinc contents of the sludge ashes. I t is possible that the formation of refractory, insoluble compounds of these elements occurred in the ash during incineration which reduced their equilibrium concentration in the soil solution and, therefore, availability for plant root absorption. Interestingly, elements such as iron, manganese, and lead were higher in the control cabbage than in any grown in the various sludge ashes. It is possible that a portion of these elements present natively in the soil was fixed in unavailable form by the sludge ash and this was reflected by a lower concentration in the cabbages. These observations could be important when considering sludge ash disposal in landfills where rainfall percolating through the landfill may dissolve heavy metals, yhich may ultimately reach water supplies. Also, the decomposition of
Table II. Element Concentration, pH, and Radioactivity in Sludge Ashes Surveyed parts per milllon (dry wt) In sludge ash from (see Table I) element
AI As Au B Ba Br Ca Cd Ce CI co Cr cs cu
DY Eu Fe Hf Hg K La Lu Mg Mn Na N Ni P Pb Rb Sb sc Se Sm Sn Sr Ta Ti V
Dunkirk
11220 9.5 a 48 5 439 8.1 274 900 3.8
16040 0.9
56 295 2.7 273 500 10.9 77 14610 11270 69 8.2 9 696 3 345 0.4 1.,l 2 180 513 4.3 2.8 0.4 0.2 91450 38110 1.1 0.08 0.18 4 080 2 291 4.2 22 14 620 555 1671 1200 2 660 20 000 277
w
5817 739 1473 600 4 200 10000 120 7 5.5 0.9 0.2 4.5 330 1090 0.1 1265 21 1 194
Yb Zn
700
5 050
5 163 0.8 0.2 6.0 87 1170 0.3 2 945 25 16
9.8 3.9
DH kadioact. a
Grand Rapids
Greensboro
Hliton
54410 1.5
83810 58 730 19 9.3 5.0 3.0 17 17 40 2 087 5401 1035 0.8 1.2 2.9 102800 42390 84970 31 22 1.5 160 403 36 563 1044 1050 45 18 9.2 4 777 1949 41 1 0.3 1.3 1.o 1140 1225 3 225 3.6 7.7 4.6 1.7 0.5 51 130 36630 29950 5.6 4.7 5.5 0.04 0.06 0.04 12110 8037 10480 39 52 12 0.3 13100 14420 16010 756 1019 910 6 006 5 959 7217 800 800 1000 350 89 680 27000 65000 52 000 559 248 1333 13 31 73 21 69 8.8 4.9 2.2 4.3 0.04 0.04 0.04 14 10 19 1204 1103 344 824 4 600 720 0.5 1.7 1.8 7 994 2 889 6814 110 23 70 9.2 4.2 163 3.1 740 400 1070
10.3 9.1
9.1 6.8
Kalamaroo
indlanapoiis
8.4 8.2
Absence of data was due to analytical interference which prevented analysis.
Lorton
103 900 8815 7.5 5.3 0.5 1.o 8.4 61 1043 686 0.5 10 29800 337400 0.7 1.3 132 117 29 210 954 14 16 346 503 1.7 0.2 570 525 6.4 7.5 0.5 0.9 17660 91 720 28 3.0 0.12 0.04 2317 4017 20 33 0.1 0.4 30 000 16 100 3 095 342 3 940 846 600 1000 40 55 34 000 38 000 82 406 34 18 15 4.0 6.6 13 0.04 0.9 24 9.8 1892 302 7313 1006 14 2.4 32 900 5 230 104 387 33 18 1.5 1.4 2 250 1040
8.2 15.6
Naugatuck
Saglnaw
Youngstown
36 820 22 0.4 17 536
24 190 12 0.3 40 634 3.7 173 900 127 46 6212 16 721 1.7 570 5.1 0.6 57 970 2.7 0.04 8 199 15 0.2 16 100 1805 2 713 800 209 21 000 412 41 10 2.5 0.2 10 670 385 0.5 1354 40 28 0.5 3 700
45 590 6.1 7.8 38 804 10 142 500 4.8 71 6 587 18 754 2.5 485 3.8 0.6 43 320 4.7 0.06 4 799 15 0.1 13200 849 2 185 800 480 37 000 123 23 13 2.7 0.1 8.i 1230 1690 3.8 1739 50 190
8.6 6.6
9.9 4.5
5.0
203 400 5.6 73 6 365 15 468 1.7 1990 4.8 0.4 50 430 2.6 0.12 4410 12 0.3 6 030 875 2 704 800 700 21 000 156 44 11 2.0 0.1 10 1008 1.o 1912 89 48 1.6 8 000
12.2 9.8
6.9 11.8
9.1 4.6
1650
y radiation (cprnlg) above background.
Table 111. Concentrations of Selected Elements in Cabbage Cultured on Soil Amended with the Various Sludge Ashes parts per million (dry wt) In cabbage grown in soli amended with sludge ash from element
controla
Dunklrk
Grand Rapids
Greensboro
Hliton
Indianapolis
Kaiamaroo
Lorton
Naugatuck
As Cd co cu Fe Mn Ni Pb Zn
0.4 0.5 0.8 11.6 425 118 0.6 1.4 31
0.4 0.2 1.7 10.3 353 80 0.5 0.6 18
0.4 0.2 0.8 16.4 164 34 0.6 0.7 16
0.2 0.7 0.9 13.9 399 61 0.8 1.o 41
0.6 0.3 1.1 14.6 22 1 31 0.3 0.5 13
0.2 0.7 1.3 19.4 345 66 0.7 0.7 23
0.4 0.2 0.8 13.0 262 42 0.3 0.5 37
0.4 0.2 0.8 14.3 220 42 0.1 0.6 12
0.6 0.1 1.1 8.5 292 58 0.2 0.6 16
Saginaw
0.4 0.9 0.8 36.6 257 60 n.d.b 0.6 17
Youngstown
0.4 0.2 1.1 7.9 250 22 n.d. 0.6 12
* Soil with no sludge ash added. Not detectable, i.e., less than 0.1 ppm. Volume 13, Number 12, December 1979
1505
PCBs and the loss of some volatile toxic elements during sludge incineration would serve to minimize contamination of leachates when the resulting ash is disposed in landfills. Acknowledgments
T h e authors thank L. F. Armitage, H. J. Arnold, H. G. Corneil, J. G. Doss, T. H. Greweling, H. G. Knight, R. D. Lahr, J. H. Martini, R. Sheldrake, L. E. St. John, Jr., and D. R. Van Campen for their assistance during this investigation. Literature Cited (1) Cahill, H. P., Jr., “Application of Sewage Sludge to Cropland: Appraisal of Potential Hazards of the Heavy Metals to Plants and Animals”, U S . Environmental Protection Agency Publication No. EPA 430/9-76-013, 1976. (2) Page, A. L., “Fate and Effects of Trace Elements in Sewage Sludge When Applied to Agricultural Lands”, U.S.Environmental Protection Agency Publication No. EPA-67012-74-005, 1974. (3) Furr, A. K., Lawrence, A. W., Tong, S. S. C., Grandolfo, M. C., Hofstader. R. A,. Bache. C. A,. Gutenmann. W. H.. Lisk. D. J.. Enuiron. Sci. Technol., 10,683’(1976). (4) Farrell.
