Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 205-212
205
SYMPOSIA SECTION
I.
Symposium on Municipal and Industrial Wastes as Potential Fertilizer Sources J. C. Barber, Chairman Second Chemical Congress, Las Vegas, Nevada, August 1980
Fertilizer from the Oxidative Ammoniation of Sawdust Yong K. Kim; Wendell M. Plain, and John D. Hatfleld Division of Chemical Development, National Fertilizer Development Center, Tennessee Valley A W r h y , Muscle Shoals, Alabama 35660
Pine sawdust was reacted with air and ammonia over a range of temperatures to incorporate nitrogen into the solid product. The resulting solids contained large amounts of nitrogen in organically bonded forms, which may be a source of slowly available nitrogen fertilizer. A central composke experimental design was used to determine the effects of test conditions: reaction time, temperature, and flow rates of air and ammonia. Major factors which influenced the product were the reaction time and temperature. The flow rate of air and ammonia within the test range affected the product to a lesser degree. Increasing the reaction time and temperature increased the nitrogen concentration in the solid. The optimum conditions for the highest nitrogen content were determined at each rea& time. Maximum nitrogen content of the solid product, 27%, was obtained after 4 h at 320 O C ; reaction periods of 2 h and 1 h gave 24% and 20% N content, respectively.
Introduction Chemical nitrogen fertilizers have played an important role in increasing grain production in recent decades. The low cost and availability of the nitrogen fertilizers made their liberal application to crops a good farm management practice to achieve high yields and profits. However, the supply of natural gas, the main raw material for ammonia synthesis, has been declining in recent years, and the price of the gas has increased steadily. The cost of nitrogen fertilizer products increased likewise and this trend probably will continue in the future. Moreover, the awareness of environmental consequences of agricultural activities has resulted in a reevaluation of traditional farming practices. The nitrogen fertilizers of today, such as ammonia or urea, are only partially utilized by plants because of large losses through leaching by runoff water and through evaporation processes. Inefficient use of fertilizer nitrogen is a waste of valuable resources. Therefore, it is desirable to develop more efficient nitrogen fertilizers. The efficiency may be improved by controlled-release mechanisms which may be achieved by chemical modifications or by physical modifications, such as coatings on the surface of the fertilizer. One approach for making an efficient nitrogen fertilizer by chemical reaction processes may be the incorporation of ammonia in renewable waste materials or other low-cost and abundant resources. Ammonia nitrogen is converted to organic nitrogen through oxidative ammoniation of carbonaceous materials (Car0 and Frank, 1929; Car0 and Frank, 1932; Ehrenberg and Heimann, 1930; Erasmus, 1930; Grosskinsky and Klempt, 1953; Nigro, 1967; Saito et al., 1951; Scholl and Davis, 1933; Sears and Herrick, This article not subject to
U S . Copyright.
1977; Voituron, 1931; Walton and Gardiner, 1932). Sawdust, a waste from the lumber industry, was selected as a suitable waste carbonaceous source for the nitrogen carrier because of its availability (Wiley, 1955) and the amenability of ita physical properties for further processing. In the early 1930's some attempts were made to utilize sawdust for the production of glucose and other chemical intermediates or for conversion to a fertilizer or soil conditioner, but none succeeded as commerically viable products. Voitron (1931) used NOz as an oxidizing agent for his starting material of sawdust or peat, and subsequent ammoniation reactions produced final products containing 2-970 nitrogen. Car0 and Frank (1929,-1932)obtained products containing 10-2070 nitrogen by oxidation and ammoniation reactions with various cellulosic starting materials. Scholl and Davis (1933) treated peat and sawdust under high pressure with ammonia to obtain products containing 5-22% nitrogen. Saito et al. (1951) made products containing up to 30% nitrogen by high-temperature oxidation and ammoniation reaction starting from various cellulosic materials or coal. These studies indicated that sawdust can be ammoniated at an elevated temperature to produce some interesting potential fertilizer materials. Experimental Section The sample of sawdust used in this study was collected from a lumber company in Littleville, AL, where pine lumber is the main product from locally harvested trees. The bulk sample from the mill was dried for 3 days at room temperature and screened to several particlesize fractions. The -20, +32 mesh fraction was used in the testa because
Published 1981 by the American Chemical Soclety
206
Ind. Eng. Chem. Rod. RES. Dev.. Vol. 20, No. 2, 1981 d E X l T G W TO GC
COOLlNG W4TER
CONDENSER
TUElHOCOUPLE
and the center point was replicated seven times.
Results and Discussion Four independent variables were s e l d for this series of tests: reaction time, temperature, and flow rates of ammonia and air. The ranges and levels of the four variables studied are listed in Table 11. The coded values (xl to x 3 were related to the actual variables and their levels by the following expressions Fl = 160 + 30x1 or x1 = (Fl - 160)/30 (1)
t = 2 = ~ or + 'x2 = 3.322 log t
__ I'8.D.
TUBE
COURSE FRIT
1
1
Figure 1. Schematic diagram of experimental equipment.
it was one of the most abundant size fractions. The experimental equipment is illustrated schematically in Figure 1. The reaction tube (1-in. id.) had a coarse, sintered glass partition plate near the middle of the tube. The plate supported the sample and acted as a fluidized grid bed through which the reaction gas mixture of ammonia and air was introduced. The reaction tube was heated by two round, tube-type furnaces in series. The first furnace acta as a preheater for the incoming gas and the second furnace heats the sawdust. The temperature of both furnaces was controlled manually by resistors. An air cooling coil (3" i.d. glass tubing) in the reaction tube was used to adjust the temperature of reaction. Before each test, the furnace and reaction tube temperature were equilibrated at a prefixed temperature with the precalibrated resistor setting with no cooling air circulation. Ten grams of the sawdust that contained 49.7% C, 0.1% N, and 9.1% H20 was used. After introduction of the sample through the top of the reaction tube, the temperature of the sample was equilibrated for 20 min. During this period some volatile organic compounds and water vapor were evolved, with some of them condensing on the wall of the reaction tube where the temperature was low. The test started with the introduction of the mixed gases of ammonia and air from the bottom part of the reaction tube, as shown in Figure 1. The air and ammonia flow rates were regulated to the desired values with needle valves and the two streams combined in a Y-tube before introduction into the reaction tube. Large amounts of volatile compounds condensed during the early part of the test, and thereafter smaller but darker brownish-colored condensates were collected. After each test the reaction tube was separated from the furnace and cooled at room temperature. The solid and condensate were analyzed for carbon and nitrogen contents. During the reaction the exit gases were monitored by a gas chromatograph, Varian Model 3700. A column,6 f t X l / g in. stainless steel, packed with Molecular Seive SA, 30-50 mesh, was used for oxygen and CO measurements, and a similar column packed with Porapak N, 8&100 mesh, was used for NH3 and C02 measurements. A sweeping helium gas flow was maintained at 35 mL/min, and the column temperature was fixed at 130 OC. The gases were detected by a thermal conductivity detector with a setting of 179 mA and 190 "C. The peaks were automatically integrated by a Mini Lab Integrator, Model CS1-38, Columbia Scientific Industries. Results of the tests are summarized in Table I. All tests were duplicated
-1
(2)
TI = 280 + 20x3 or x 3 = (Tl - 280)/20
(3)
F2= 400 + 100x4or x4 = (F2- 400)/1OO
(4)
The experimental design was the central composite type whose model is the complete quadratic surface between each measured property ( r e s p m ) , y , and the independent variables or factors, x,, which was originally used by Box and Wilson (1951). The model can be expressed as
The term bo is the mean of the seven replicates at the center; bl through b4 are the respective effects of each variable for one coded unit of increase; bll through bu indicate curvature for the respective variable; and the coefficient, bi; indicates the interaction of two independent variables or how the level of one variable affects the response caused by a second variable. These interaction terms are completely separable from each other as well as from the main effects because the design is orthogonal in these terms when used in the coded variables. The b coefficients of eq 5 were determined by least squares for each measured response and are summarized in Table 111. The correlation coefficients, R2, indicated the fraction of the total variability of each response ahout its mean that is explained by the model. The standard deviation, u, is frequently called "pure error" because it is based on the agrement hetween and within the replicate runs. The "lack of fit" error, S, is based upon how well the calculated values of the response using eq 5 with the appropriate values of the b's in Table I11 agree with all the observed values in Table I. If eq 5 were to predict exactly the mean of the replicates for each test condition, then S would equal u, except for the degrees of freedom involved for each. The fact that S and u are the same order of magnitude indicates that the model describes the results with about the same precision that they could be duplicated by the experimental technique. The total nitrogen content, NT, in the solid product varied from 8.3 to 27.1%, depending on the test conditions. Since this property is of major interest in this study, a more detailed description of the nitrogen content will be made for different experimental conditions. The maximum content of nitrogen in the solid product as a function of gas flow rates, time, and temperature is obtained by setting the partial derivatives aNT/axl, aNT/aX,,aNT/aX3,and aNT/aX, of eq 5 to zero, solving the four equations for xl*, x2*, x3*, and x4* (which is the set of optimum conditions), and then suhstituting thew values in eq 5 to obtain the maximum percent nitrogen. Thus, a maximum of 30.3% N is predicted at 314 O C using 81 cm3 of NH3/min and 159 cm3 of air/min for a period of 17.5 h. All these conditions are within the ranges studied with the exception of time, which makes the prediction less reliable, and the process becomes less attractive at very
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 2, 1981 207 1
,
,
600 AIR
NH3
on??" 220
TEMP c J / m i n Oc
6 5 0
320
600
I
I_: ,\
/ i
I
3
E
303
I
,
k
2 00
240
260
MO
280
320
TEMPERATURE, Oc
130
-1
2
05
I
2
TIME, h
8
4
300
8" c"
p
46
li
5
45
105
4.5 3 5
44
IO
4.0
85
25
i
Figure 3. Effect of temperature and air flow rate on nitrogen fixation in solid when ammonia flow rate is 147 cm3/min and time is 4 h (numbers on curves denote N, %).
25
8 B = Q SOLIDIIOO q SAWDUST, CURVE C : g N/100 g SMDUST.
OCURVE
Figure 2. Optimum conditions for (a) maximum percent nitrogen and (b) other properties of solid producb for various retention times.
long retention times. Consequently, the optimum conditions of xl, x3, and x4 were calculated for fixed shorter retention times, x 2 , and the results are shown in Figures 2a and 2b. The maximum nitrogen concentration ranged from about 17% in 30 min to about 28% in 8 h, as seen in the w e in Figure 2b. It is possible, however, to attain nearly 27% N in 4 h, 24% N in 2 h, and more than 21% N in 1 h. The optimum conditions of temperature and the flows of NH3and air for the various retention times are shown in Figure 2a. The optimum ammonia flow rate changed from 211 to 126 cm3/min, and the optimum temperature changed only from 324 to 317 "C as the reaction time changed from 30 min to 8 h. The optimum air flow rate, however, decreased from 685 to 342 cm3/min as the reaction time increased. Other important properties of the solid are plotted in Figure 2b along with the nitrogen concentration line (A) for the same condition of maximum nitrogen concentration. The solid weight (B) decreased in similar patterns as the reaction time increased from l/z h to a minimum value at 3-4 h and then increased as the time increased further. The total weight of nitrogen in the solid (C) increased continuously as the reaction time increased for the optimum N concentration conditions at each time. The ratio of the total weight of nitrogen in the solid (C) to the solid weight (B) produces the % N in the solid (A) within experimental error. Figure 3 shows the contours of constant nitrogen concentration in the solid as a function of temperature and air flow rate when the reaction time is fixed at 4 h and the ammonia flow rate is 147 cm3/min. These equinitrogen lines indicate that the gradient along the temperature axis is very large, especially in the lower temperature range, but the surface flattens out as the optimum temperature (320 "C)is approached. The gradient along the air flaw rate axis is small, so that any appreciable change in the air flow rate from the optimum
2M) 240
260
280
jo3
320
TEMPERATURE, t
Figure 4. Effect of temperature and air flow rate on nitrogen fixation in solid when ammonia flow rate is 147 cm3/min and time is 2 h (numbers on curves denote N, %).
TEMPERATURE,
Oc
Figure 5. Effect of temperature and air flow rate on nitrogen fixation in solid when ammonia flow rate is 147 cm3/min and time is 1 h (numbers on curves denote N, 7'0).
condition will decrease the nitrogen concentration in the solid only slightly as long as the temperature is maintained. A similar situation prevails at reaction times of 2 h (Figure 4) and 1h (Figure 5). Figures 2-4 may be superimposed on each other to obtain a three-dimensional picture including time as the vertical 2 axis. The contributions to the nitrogen concentration by temperature, air flow rate, and time can be seen easily by this construction when the ammonia flow rate is optimized in each case. Figure 6 shows the equinitrogen lines as functions of temperature and ammonia flow rate when the reaction time is fixed at 2 h and the air flow rate a t 514 cm3/min. These contours are similar to those of Figure 3, indicating a very small effect on the ammonia flow rate when the air flow rate is fmed, as long as the temperature is maintained. In summarizing the above analysis it is concluded that the major factors which influence the nitrogen concentration are the reaction temperature and time; and vari-
208
[nd. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 2, 1981
0000000000000000000000000000000000000000000
0000000000000000000000000000000000000000000
Ommmmm~mmMmmmmmm~uammuauauamuauauauauamuauaNNwwddddddd
000000000
000000000000000000000000000000000
w w w w w w w w o 8 o o o o o o w w w w w w w w o o o o o o o o m m w m ~ ~ ~ ~ m w m
0.10.10.10.1N~0.1NmmmmmmmmNNN0.1~~~~~mmmm~mm~0.10.10.1~Nmm0.10.10.1
Y
a
8
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 2, 1981 209
TEMPERATURE,
Oc
Figure 6. Effect of temperature and ammonia flow rate on nitrogen fixation in solid when air flow rate is 514 cm3/min and time is 2 h (numbers on curves denote N, %).
7.
\
I
I
\ \
0
3
si
4t
i 240
2ko
2kO
300
320
TEMPERATURE, ' c
Figure 7. Mect of temperature and reaction time on weight of solid product when air and ammonia flow rates are 400 and 160 cms/min, respectively (numbers on curves denote reaction time, hours).
cd 0
00000
000000
ooooo8oooooo
d d d d d d d d d d d d
.-me a
000000000000
Wddddddddddd
fi & l
2 'a 0 ~ 0 0 0 0 0 0 0 0 0 03 i.)
(0
o~cva(0a(DcBaa+.'
rll+rl"rlrlrlrldrlrl
41 U
ations of air or ammonia flow rates from 400 and 160 cm3/min, respectively, have small, but significant, effects on the nitrogen concentration in the solid. Therefore, all the other properties or responses of the process are shown only for the effect of the temperature and time, with the air and ammonia flow rates fixed at 400 and 160 cm3/min, respectively. Starting from 10 g of pine sawdust (dry weight base is 9.1 g), the solid product weight ranged from 3.9 to 6.9 g, depending on the experimental conditions. The solid weight decreased when the temperature or reaction time increased, as shown in Figure 7, for 1and 4 h of reaction time. It approached a minimum value of about 4 g or 40% of the starting sawdust weight at about 300 "C and 4 h reaction time, although most of its weight loss occurred during the first part of the reaction. The oxidation reaction of the sawdust liberates C02and other low molecular weight organic compounds. Ammoniation of the oxidized product probably does not increase the weight because ammonia reacted with acidic groups results in amide groups with the release of one H20 molecule (mole weight = 18) for one NH3 (mole weight = 17) addition. The total weight of nitrogen fixed in the solid product is the product of the solid weight and the nitrogen content in the solid. The total nitrogen weight ranged from 0.48 to 1.25 g, depending on the reaction conditions. An increase in temperature or reaction time increased the total nitrogen fixed, as shown in Figure 8. However, the increase in fixed nitrogen becomes progressively smaller a t longer reaction time and at higher temperature, which can be contrasted with the maximum nitrogen concentration curve, C, of Figure 2b. If the reaction time is 2-4 h (for
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 2, 1981
210
Table 11. Range and Level of Variables coded level
coded variable
actual variable F, = ammonia flow rate, cm3/min, STP t = reaction time, h T, = temperature, "C F, = air flow rate, cm3/min, STP
Xl
x2
x3 x4
-2 100 0.5 24 0 200
0 160 2 280 400
-1 130 1 26 0 300
2 220 8 320 600
1 190 4 300 500
Table 111. Coefficients of the Second-Degree Model for Various Properties of Oxidized and Ammoniated Pine Sawdust solid product coefficient
liquid product
N total
atomic ratio C:N
wt, g
%
3.349 -0.102 -1.057 -0.732 -0.135 0.078 0.392 0.210 0.087 0.143 0.140 -0.076 0.346 0.176 -0.009 0.441 0.470 0.907
10.314 0.147 1.417 1.093 -0.067 -0.233 -0.139 -0.561 -0.158 -0.099 0.086 0.118 0.036 -0.545 -0.130 0.546 0.647 0.919
14.943 0.718 1.515 -0.026 -0.719 -0.279 0.178 0.090 -0.164 -0.136 0.128 0.299 -0.059 -0.392 -0.229 0.675 0.848 0.864
gas used
N total,
o,, cm3 NH,, cm3 2295.0 4168.8 51.8 167.5 b2 1014.5 359.6 b3 285.0 268.3 b, -0.081 -591.2 71.0 bll -0.025 -248.1 53.6 b 22 -0.050 251.9 68.6 b 33 -0.187 - 89.5 -153.1 b44 0.032 23.1 -65.1 bl, -0.172 31.3 -21.9 '13 0.034 -1 59.4 340.6 b 14 0.166 -27.8 99.9 b23 -0.653 -294.9 185.3 b, -0.159 -619.3 -31.9 b34 -0.128 55.6 149.9 ua 0.686 240.7 470.4 Sb 0.612 1219.9 297.9 RZ 0.791 0.871 0.708 a u = pure error for standard deviation of replicates. S = standard deviation of calculated vs. observed responses. R' = fraction of total variability of a response about its mean that is explained by model. bo b,
wt, g
%
g
NK, %
4.486 0.069 -0.165 -0.590 -0.310 0.027 0.133 0.246 0.133 -0.022 0.091 -0.041 0.034 0.203 0.016 0.332 0.381 0.827
20.686 0.165 3.785 3.185 0.569 -0.308 -0.733 -0.852 -0.533 -0.222 -0.141 0.266 0.003 -0.703 0.278 1.596 1.754 0.911
0.925 0.022 0.166 0.06b -0.022 -0.011 -0.014 -0.014 -0.001 -0.014 0.007 0.006 -0.025 -0.019 -0.001 0.061 0.072 0.886
3.971 -0,010 0.881 -0.a73
N N H ~%, 12.271 0.786 1.232 -0.368 -1.002 -0.197 -0.241 0.134 0.111 -0.029 0.008 -0.016 0.009 -0.104 -0.429 0.642 0.763 0.882
I T
1
ERROR OF A SINGLE RUN
I
-
ir
0 51
I
240
1
260
280
300
320
I ~
TEMPERATURE, ' c
Figure 8. Effect of temperature and time on the weight of nitrogen d 160 cm3/min, fixed in solid when air and NH3flow raks ate 400 a respectively (numbers on curves denote reaction time, hours).
economic considerations), then we can eTpect that 1-1.12 g of nitrogen will be fixed in a solid product of about 4.3 g from 10 g of starting pine sawdust. The KMn0,-soluble nitrogen in the solid product ranged of the total nitrogen from 2.5 to 6.5%, which is about 'I4 content. Therefore, the available nitrogen for plant growth would be a small fraction of the total nirogen if KMnO, solubility is a criterion of availability. The reaction time and temperature have major effects on the KMn04-soluble nitrogen, as shown in Figure 9. An increase in the reaction time increased the KMnO4-so1uble nitrogen at low temperature (240-280 "C),but had very little effect in the temperature range 300-320 "C. Also, the KMn04-soluble
01
1
240
, 260
1
280
300
, 320
TEMPERATURE, ' c
Figure 9. Effect of temperature and time on KMn0,-soluble nitrogen in solid when air and NH3 flow rates are a0 and 160 cm3/ min, respectively (numbers on curves denote reaction time, hours).
nitrogen increased with temperature increase for 1-h rum, remained somewhat constant for 2-h runs, and decreased for the 4-h runs. This is the result of the large interaction coefficient, bZ3,in Table 111. A high KMn0,-soluble, nitrogen-containing product is a desirable result, but it also should contain a high total nitrogen content, the latter requiring a temperature of about 310 "C as discussed earlier. Under this temperature condition, KMnOcsoluble nitrogen in the solid product will be about 3.5%, regardless of the reaction time variation. However, for the 4-h runs at 260 "C, the fraction of total nitrogen in the solid in
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 2, 1981 211 81
I
I
,
I
,
I
"BE6 ON C U M S
CENOTE
REACTION
I
240
280
260
300
I
,
320
TEMPERPTURE , ' c
Figure 10. Effect of temperature and time on ratio C:N in solid when air and NH3flow rates are 400 and 160 cm3/min, respectively (numbers on curves denote reaction time, hours).
I
r7
I4O;
I
0
OXYGEN CONSUMED
0
AMMONIA CONSUMO
A
CARBON DIOXIDE PROWCED
1
2-
01
1
,
I
,
240
260
280
300
I 320
TEMFWATURE , 'c
Figure 11. Effect of temperature and time on liquid product weight when air and NH3 flow rates are 400 and 160 cm3/min, respectively (numbers on curves denote reaction time, hours).
KMnOcsoluble form approached about because of the low total nitrogen fixed at this temperature. The atomic ratio of C:N in the solid is a significant factor for fertilizer efficiency. A large ratio C:N product is believed to be an inefficient nitrogen fertilizer. The ratio C:N decreases when reaction time or temperature increases, as shown in Figure 10. The large interaction coefficient, bZ3, explains the relatively large decrease in C:N at 240 "C when time is changed from 1 to 4 h compared to that at 320 "C. The positive coefficients, bz and b%, indicate that the ratio C:N approaches a minimum value at about 300 "C and longer reaction time than 8 h. The ratio C:N will be less than 3 if the reaction time is about 2 h and the temperature is 300 "C or above. The liquid product collected in the condenser at the exit of the reaction tube is a byproduct which contains large amounts of ammonia and water. It also contains condensable nitrogen compounds and oxidized hydrocarbons of low molecular weight. Some of these are yellowish, viscous materials. The total liquid weights as functions of reaction temperature and time are illustrated in Figure 11. Increasing the reaction time or temperature increased
0
25
50
75
100
125
REACTION TIME, MINUTES
Figure 13. Concentration variation of exit gas components during experiments 49 and 50,measured by gas chromatography.
i
NUMBERS ON C U M S DENOTE REACTION TlME h
2--
I
i 240
269
280
300
320
TEMF€RATURE,"c
Figure 14. Effect of temperature and time on oxygen usage.
the liquid weight, but it reached a maximum value a t a reaction temperature of about 300 OC for each isochron.
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 consumption.
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 February 9, 1981 T h i s paper was presented at t h e 180th National Meeting of the American Chemical Society, Las 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
