Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 212-216
212
T
ERROR OF PREDICTIW
4
,
I
240
260
280
3C0
320
TEMFERATUFE ,' c
Figure 15.
Effect of temperature and time on ammonia consump-
tion.
The total nitrogen concentration in the liquid product varied only slightly when the temperature increased, but increased when the time increased (Figure 12). Since most of the nitrogen in the liquid is ammonia nitrogen, as indicated in Table I, the ammonia and air flow rates affect the nitrogen concentration because higher ammonia partial pressure in the exit gas leads to the higher concentration of ammonia in the liquid product. Since our analysis is based on the fixed air and ammonia flow rates of 400 and 160 cm3/min, respectively, the reaction time is the major factor affecting nitrogen concentration because the amount of ammonia in the exit gas is small during the first hour of reaction and then gradually increases in the latter part of reaction time. The exit gases were monitored by gas chromatography (GC) for 02,NH3, CO, and COP. Figure 13 is an example of the results, and the consumption of oxygen and ammonia is shown in Table I (last two columns). Oxygen consumption was highest at the start of the reaction, and almost all ammonia was consumed during the first 30 min.
Only a small fraction of the oxygen was utilized in the latter part of the reaction. The total consumptions were evaluated by integrating the areas under the curves. Carbon monoxide and carbon dioxide formed during the early part of the reaction, but only small amounts of carbon dioxide were detected after 40 min of reaction. Oxygen consumption is the same when the temperature is 240 "C, regardless of the reaction time variation; however, it is increased when the temperature and time are increased, as shown in Figure 14. Ammonia consumption as a function of time and temperature is shown in Figure 15. This ammonia consumption occurs in both solid and liquid products. Since our error in the gas chromatographic measurement is so large and the fit is poor, the prediction is only valid to denote the trend of the changes. Under one of the optimum conditions of 2 h reaction time and 310 O C , ammonia and oxygen consumptions are 4300 and 2500 cm3, respectively, and the mole ratio NH3:02 consumed is about 1.7 to form both solids and liquids as well as escaping CO and COPgases. Conclusions Pine sawdust was treated with ammonia and oxygen to obtain products that contained as much as 27% nitrogen. Initial test results indicate that the nitrogen in the products has a limited solubility, and the products may be useful as controlled-release nitrogen fertilizers. Literature Cited BOX,0. E. P.; Wilson, K. B. J . R . Stet. SOC.( B ) 1951, 13(1), 1-45. Caro, N.; Frank, A. R. British Patent 347841, Jan 30, 1929. Caro, N.; Frank, A. R. German Patent 559254, Sept 17, 1932. Ehrenberg, C.; Heimann, H. German Patent 507320, Sept 15, 1930. Erasmus, P. German Patent 514510, Dec 23, 1930. Klempt, W. German Patent 883 809, July 20, 1953. Grosskinsky, 0.; Nigro, C. Agrochimica 1967. XII(l), 52-59. Saito, H.; Torii, Y.; Nada, T. J. Chem. Soc. Jpn. Ind. Chem. Sect. 1851, 54, 122-123. Schoil, W.; Davis, R. 0. E. I d . €ng. Chem. 1933, 25(10), 1074-1078. Sears, K. D.; Herrick, F. W. US. Patent 4002457, Jan 11, 1977. Voituron, E. German Patent 518792, Feb 24, 1931. WaAon. G.; Ciardiner, R. F. U.S. Patent 1 858230, May 10, 1932. Wiley, A. J. Ind. Eng. Chem. 1955, 47(7), 1397-1404.
Receiued for review October 8, 1980 Accepted F e b r u a r y 9, 1981 T h i s paper was presented at t h e 180th N a t i o n a l M e e t i n g of t h e American Chemical Society, L a s Vegas, NV, Aug 1980.
Plant Nutrients from Municipal Sewage Sludge Paul M. Glordano' and David A. Mays National Fertilizer Development Center, Tennessee Valley Authority, Muscle Shoals, Alabama 35660
Municipal sewage sludge from Florence, AL, compared favorably with commercial fertilizers as a source of plant nutrients for field crops. Results after one growing season indicated that soil injection of liquid, aerobically digested sewage sludge at a rate of 11 metric tonslha provided adequate amounts of plant nutrients to sustain high yields of corn (Zea mays L.), cotton (OossSpium hhutum L.), and soybeans (Glycine maxL.). Heavy metal concentrations were about the same in plants fertilized with sludge as with commercial fertilizer; hence, there was no indication in these crops that toxic metals omnipresent in sewage sludge were excessive in either the vegetative or reproductive plant parts. Sludge from Florence is typical of that from other small municipalities without heavy industry, and early indications are that such sludge can be utilized safely and beneficially for crop fertilization and soil improvement because of its relatively low heavy metal content.
Introduction The fertilizer and soil conditioning values of sewage sludge have been recognized for many years (Kirkham,
1974). However, the high cost of liquid sludge transportation and the relatively low cost of commercial fertilizers have not made land application of sludge economically
This article not subject to U.S. Copyright. Published 1981 by the American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 2, 1981 213
attractive. Furthermore, considerable concern has been expressed over the potential toxicity to plants of heavy metals associated with sludge and the long-term threat to crop production (Allaway, 1977). Doyle (1977) also reviewed the impact of low-level Cd intake on human health. Experimentation with laboratory animals has indicated that Cd may impair growth, cause hypertension and Na retention, and adversely affect some enzyme systems, reproduction, and other metal levels. Despite these concerns, land application of sludge is increasing, especially in rural areas where cropland is close to water treatment plants and industrial inputs of potential pollutants are minimal (Lockeretz, 1978). Only small acreages, usually in close proximity to the treatment plant, are required to accept the entire annual production of sludge from small municipalities. Large metropolitan areas such as Chicago, Denver, Indianapolis, Milwaukee, etc., however, have instituted sophisticated programs to deal with sludge recycling because of the large quantity of waste generated, often with significantly high industrial 6r agricultural contribution, and the greater distance to the disposal destination. Since ocean dumping and incineration are no longer acceptable means of elimination, and landfills are scarce and expensive to construct, the only viable alternative is land application. For example, sludge farms such as Werribee at Melbourne, Australia, have been operated successfully for many years by employing suitable management practices. The purpose of this study was to evaluate the grain or seed yield response of corn, cotton, and soybeans to soilinjected liquid, aerobically digested sewage sludge from Florence, AL, relative to the response to conventional fertilizer practices. These are the principal row crops grown in north Alabama. In addition to ascertaining the beneficial effects from nutrients contained in sludge and the soil conditioning properties of the organic component, heavy metal accumulations in the crops and soil were monitored. Experimental Section The experimental site is located on a l-ha portion of a 70-ha tract owned by the city of Florence and situated approximately 10 km from the wastewater treatment plant. The soil on the site is a Decatur silt loam (Rhodic Paleudult) with a plow layer pH of 5.4, cation-exchange capacity of 10 mequiv/100 g of soil, and an organic matter content of about 0.8%. The area had been in row crops (cotton and soybeans) for many years, and soil tests indicated medium P and high K levels. Liquid, aerobically digested sludge (3-4% solids) was injected below the soil surface during late fall of 1978. Application equipment consisted of an 8325-L tank mounted on a four-wheel drive, high-flotation truck with a set of four injection knives spaced 0.8 m apart. Rates of sludge application were 11 and 78 metric tons/ha. Nutrient and heavy metal compositions of the sludge and amounts applied at the above rates are shown in Table I. Rye (Secale cereale L.), sown as a winter cover crop, was mowed and plowed under in the spring of 1979. Treatments in addition to the two sludge rates included a nofertilizer control and a commercial fertilizer application considered to be adequate for the particular crop (168 kg of N, 45 kg of P, 112 kg of K/ha for corn and cotton, and the same rates of P and K only for soybeans). A lime variable was superimposed over these treatments such that the soil pH value was 5.4 in the no-lime plots and 6.5 with liming. A pH value of 6.5 or higher has been recommended in interim EPA criteria as a safeguard against excessive
Table I. Partid Chemical Composition of Dry Sewage Sludge from Florence, AL, and Amounts of Elements Applied t o Soil
content, element
N P K Ca
Mg
Cd Zn B cu Mn
cr
Ni Pb
%
2.5 1.9 0.2 1.3 0.2 0.0015 0.0700 0.0465 0.0375 0.0660 0.1000 0.0180 0.0300
amount applied (kg/ha) at sludge rate of 11 metric 78 metric tons tons
275 209 22 143 22 0.2 7.7 5.1 4.1 7.3 11.0 2.0 3.3
1950 1482 156 1014 156 1.2 54.6 36.3 29.3 51.5 78.0 14.0 23.4
Cd uptake by crops grown on sludged soils (Federal Register, 1979). Two varieties each of corn, cotton, and soybeans were planted in the spring of 1979 (Table 11). Plots consisted of four rows, 10 m in length and spaced at 0.9 m. Three replicates were provided for each treatment. At maturity the two center rows of each plot were harvested for yield determination and chemical analysis. In addition, vegetative tissue was sampled at silking (corn) or early bloom (cotton and soybeans) for assay of N, P, K, Ca, Cu, Ni, Cd, and Zn. Plant samples were oven dried at 70 O C , ground in a Wiley mill equipped with stainless steel blades and screens, dry ashed at 450 OC, and analyzed according to standard atomic absorption or emission spectrophotometric techniques. Separate samples were used for Kjeldahl N determination and P analysis by the vanadomolybdate method. Soil was sampled in the fall of 1979 after all crops had been harvested. A 2.5-cm diameter core sampler was used to remove soil at 15-cm increments to a depth of 60 cm. Four cores were taken from each plot, and subcores of equal depth were composited for subsequent analysis. Air-dried samples were extracted for Zn, Cd, and Cu with a DTPA-TEA mixed reagent according to the soil test developed by Lindsay and Norvell (1978) for available micronutrients. Although originally intended and calibrated for Zn, Mn, Fe, and Cu in calcareous soils, this test has been widely used for other metals such as Cd, Ni, and Pb in both acid and calcareous soils. Total N was determined by the macro-Kjeldahl procedure, and N03-N by the phenoldisulfonic acid colorimetric method. Potassium and P were extracted with a double-acid reagent consisting of 0.05 N HC1 and 0.025 N H2S04and analyzed, respectively, by flame emission and the vanadomolybdate method. Discussion of Results The nutrient and heavy metal compositions of the sludge used in this study are typical of those in sludges generated in small, nonindustrialized metropolitan areas (Table I). At the rates of sludge applied, EPA interim regulations relating to allowable annual and cumulative Cd levels would permit land application for 25 years and 4 years for the 11- and 78-metric ton rates, respectively (Federal Register, 1979). Based on the crop yields and plant analyses obtained in this study, the ll-metric ton sludge rate provided adequate N and P to replace that removed in harvested plant parts; however, K removal exceeded that supplied at the ll-ton rate.
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Chem. Prod. Res. Dev., Vol. 20, No. 2, 1981
Table 11. Chemical Analysis of Corn Ear Leaves and Immature Cotton and Soybean Leaves %
treatment lime
N
P
K
Ca
Zn
Cd
PPm Ni Cu Corn
%
N
P
K
-
fertilizer low sludge high sludge
+
t -
+
-
t
1.35 1.27 2.84 2.72 2.79 2.52 2.47 2.59
0.44 0.39 0.59 0.59 0.64 0.59 0.67 0.64
2.15 2.29 2.66 2.56 2.54 2.54 2.62 2.56
0.70 0.64 0.60 0.80 0.97 0.80 0.97 1.10
13 12 34 27 49 48 66 76
Zn
Cd
PPm Ni
(Pioneer 3369A)
(Funk’s 4507) control
Ca
0.28 0.25 0.32 0.20 0.17 0.17 0.60 0.46
