Ind. Eng. Chem. Rod. Res. Dev. lS81, 20,217-222
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Sludge Disposal: Predictive Modeling for Assessing Impact on Agricultural Lands Danlel A. McLean," Kenneth E. Osborn, Mlchael J. Vandaveer, and Henry Y. Kokka Wafer Pollutbn Contrql Department, East Bay Municipal Uti/@ District, Oakland, Callfornh 94623
Sewage sludge was applled in liquid form to marginal agriculture land as a nitrogen source. Using four years of data the auttfop developed mathematical models to dedcribe the behavior of ca'dpiup, copper, zinc, and nickel in the test plots. Data collected in the fifth year of the study were used to verify the validity of the models. A project lifetip6 gf 150 years was calculat9 using the qdmium model. The ca~cyia!ed project iifetime was based on nitrogen requirement of the crop (field corn), nb6gen content of the sludge, and an assumed EPA mandated soil limit for.+cgdmiumof 10 mg/kg,
Introduction Special District No. 1 af the East Bay Municipal Utility District provides wastewater treatment and disposal for seven cities located on the eastern shore of San k'rargisco Bay. The District has a s9rvice area of 83 square miles and serves a population of approximately 575 000 and over 7000 businesses and industkies. Iq response to changing state and federal requirements, the District began design of secondary treatment facilities in the late 1960's. The primary regulations which impacted this decision were those contained in the 1972 amendments to the Federal Water Pollution Control Act (Clean Water Act). T4e Act mandated 85% BOD removal for all municipally owned treatment plants which was essentially a mandate for biological secondary tpeatment. As design of treatm$nt plant expansions got under way, there was a realization among treatment plant operators of the enormous increase in sludge production thgt would accompany implementation of secondary treatment. At the same time that this increase in sludge production was being forecast, options for disposal of digested sludge from treatment plants were being foreclosed. In the Bay Area, sanitary landfills were reaching capacity and incineration was rapidly becoming too costly due to increasing fuel costs ahd air pollution control requirements. Disposal of sludge in the ocean was foreclosed by the EPA under authority of the Clean Water Act. Because of these contingencies, numerous agencies began to explore the disposal of digested sludge on land that was to be used for agricultural purposes. In 1973, the District started a land disposal study. The purpose of this study was to evaluate the upe of sludge for the reclamation of marginal agricultural land that existed within reasonable transport distance of the treatment plant. At the time this test program was begun, there was already a general awareness of the potential for heavy metals toxicity from sewage sludge applied to cropland (Council for Agricultural Science and Technology, 1976). This problem can be evidenced both by phytotoxicity to crops grown on sludge amended soil and toxicity to human or animal users due to uptake of metals from the soil by the plants. Because the District has fairly high levels of heavy metals in the sludge (Table I) (Capar et al., 1975; Burpee et al., 1979; San Francisco Bay Region Wastewater Solids Study, 1978), we were aware that the potential for heavy metals toxicity would be the primary issue in this study. This study evaluated the effect of sludge application on crop yield and on metals uptake by the plants. A grain crop was chosen because of the known reduced transport 0196-4321/81/122O-0217$01.25/0
of heavy metals into the grain compared to other parts of the plant and because the crop would not be used directly for hwnan consumption. Possible metals of interest were reviewed for significant concentrations in the sludge and fqr *possibletoxicity to plants or end users of the crop. Based on this review, it was decided to monitor soil and plant tissue concentratipns of cadmium, cdpper, nickel, and zinc. The soil in the test plot area is alkaline, apd it is well known that plant uptake of heavy metals is reduced when plants are grown on alkaline sQil. Because Cif this, it was dpcided to perform a full-scale field trial using a forage crop and local farming techniques to evaluate the potential of sewage sludge as a soil aniendment.
Methods A test site was located in the San Joaquin/Sacramento River delta in eastern Solano County. The test plot site and plot layout are shown in Figures 1 and 2. The sludge application rates used in the test plot program shown were 0,3,6,12, and 25 dry tons per acre. These application rates were selected based on use of sludge as a soil amendment. Sludge was applied to achieve an appIication of 0,100,200, 400, and 800 lb of nitrogen per acre as q K N allowing for a mineralization rate of 15% of thg TKN applied in the first year, 10% of the remaining TKN after the first year, and 5% of the remaining TKN after the second year (Hyde, 1976). All of the sludge applied in this program was primary sludge. The program was terminated prior to completion of the District's secondary treatment facilities. Planning of the crop irrigation and harvest were under control of the farmer who owned the test plot area. The crop chosen for this test program was field corn. Soil metals concentrations were determined by extracting the soil with diethylenetriaminepentaacetic acid followed by flame or flameless atomic absorption spectrometry (AAS) (Lindsay, 1972). This extraction technique was selected because it was widely reported in the literature and was considered to estimate the soil metals fraction available to plants. Whole plant samples were dried, ground and digested with nitric and perchloric acids. Grain samples were shelled from the cob by hand, dried, ground, and similarly digested. Metals concentrations were determined by flame or flameless AAS.
Results When compared to the results of similar studies conducted by other agencies, the results of this study were 0 1981 American Chemical Society
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Table I. Trace Metal Concentrationsin Various Sludges (mg/kg)
EBMUD Cd
60
Chicago
feed lot
500
1
San Jose 40 -.
900 200 1800
Figure 1. EBMUD Special District No. 1wMee area and test plot site location.
San Francisco Novato, CA
__
Rn 600 100 1800
Denver
in 1800 120 1900
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800
... 2000
plication. This project was continued through the 1978 harvest. It is not the purpoae of this paper to report this study in detail. It has been well covered elsewhere (Hyde, 1976; Hyde et al., 1979; San Francisco Bay Region Wastewater Solids Study, 1978). Rather, if a project of this type is to he undertaken, it is important to know what the potential lifetime of that project may he. This is particularly important due to the EPA requirement that the discharger agency maintain total control of the use of the land in perpetuity. In the case of land to be used for growing crops, it is important to plan the sludge application such that a 15- to 25-year lifetime of the project area can he assured. Therefore, it was our purpose to develop models relating sludge application to soil and plant tissue metals concentrations. Linear Models Data of the type generated in this study are usually analyzed with standard statistical techniques such as correlation of coefficients, linear regression, or Student’s t or other tests of signiicance between groups of data. The precision of the analysis using these techniques improves with larger data bases and with sample replication. We applied these statistical techniques where there were sufficient data to do so. In addition, during our data evaluation it became obvious that there was a need for both sampling and analytical replication in order to provide sufficient data to allow statistical interpretation of the results. The study included triplicate test and control plots and some replicate samples were collected. However, in programs like this the analytical resources available are often limiting. Therefore, it is desirable to be able to find relationships that will allow reduction in the number of analvses oerformed but that will SUDD~V “ the necessarv infoimatibn. Standard data analysisaaseases the relationship between sludge auulication and metal uotake. This was the orieinal approalh used in evaluating the data from the s&dy. However, the ultimate goal of a project of this type is to be able to predict the long-term impacts of sludge . - aupli.. cation on cropland. Review of the data (Osborn and McLean. 1980) indicated that the extractable metal concentrations or crop metal concentrations might he sensitive to either the amount of metal applied in an individual year (annual model) or to the total amount of metal applied to the test plot over the life of the project (cumulative model). The cumulative model would apply if the metal applied to the soil did not change chemical state or otherwise become unavailable to the plant over time. However, if chemical interactions in the soil reduced the availability of metal to the plant over time, the uptake by the plant would be more sensitive to the amount of metal applied in a given year and the annual model would be followed. The concept of these two models is~ illustrated in Figures 3 and 4. In Figure 3 the DTF’A extractable soil cadmium concentration is compared to the total amount of sludge applied over the life of the project. It can be seen that the slope of the regression line decreases between 1974 and 1975 and would he expected to remain approximately constant thereafter although the intercept increases he-
__
1 ITYPI
Figure * 2. Agricultural land application test plot layout. c
unremarkable. In general, crop yield was found to be positively correlated with sludge application rate and the uptake of metals by the crop was related to sludge ap-
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 2, 1981 219 Cumulative Application, kglha D
Cumulative Application, kglha
Figure 3. Linear regression lines for DTPA extractable soil cadmium as a function of cumulative sludge application.
Annual Application. kglha
Figure 6. Comparison of predicted and measured soil metal concentrations for the annual and cumulative models. (Legend as in Figure 5.) Cumulative Application. kglha 1
0
0
2 Annual AppliCatiOn. k g l h a
Figure 4. Linear regression lines for DTPA extractable soil cadmium as a function of annual sludge application.
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Figure 7. Comparison of predicted and measured soil metal concentrations for the annual and cumulative models. (Legend as in Figure 5.) Cumulative Application. kglha
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tween 1975 and 1976. Figure 4 shows the relationship between extractable metal and annual application. In this case, the slope of the regression line increases for each year of the project. The test of which model best represents the data is constancy of slope from one year to the next.
Annual Application, kglha
Figure 8. Comparison of predicted and measured soil metal concentrations for the annual and cumulative models. (Legend as in Figure 5.)
Thus, in this case, it may be seen that cadmium appears to best fit the cumulative model and that DTPA extractable soil cadmium is related to the total amount of cadmium applied to the test plot. Comparison of the two
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Ind. Eng. Chem. Prod.
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1981 Cumulative Application. kglha
Cumulative Application. kglha
Annual
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Figure 9. Comparison of predicted and measured plant metal concentrations for the annual and cumulative models. The solid and broken lines represent the predicted values for the cumulative and annual models, respectively. The circles and triangles are the 1977 data points for the cumulative and annual models, respectively.
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Annual Application, kg/ha
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Figure 11. Comparison of predicted and measured plant metal concentrations for the annual and Cumulative models. (Legend as in Figure 9.) Cumulative Application, kg/ha
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models for soil cadmium, copper, nickel, and zinc, the four metals studied in this project, is shown in Figures 5 through 8. In each case, data through 1976 were used to project the response of extractable metal to the application in 1977 and the curve based on both models is shown in the figure. From this analysis, it is apparent that soil cadmium and zinc are related to the cumulative amount of metal applied while copper is related to the annual application. Nickel is not related to either cumulative or annual application. It was found throughout these studies that nickel behaves differently from other metals but the reasons for this behavior were not explored. This same analysis was performed for the whole plant tissue burdens of the four metals (Figures 9 through 12). In the case of whole corn plants, the interpretation of the data is not as straightforward as for soil. Cadmium u p w e into the plant (Figure 9) does not appear to fit either model very well. Copper (Figure 10) appears to be related to the cumulative application while nickel (Figure 11)and zinc (Figure 12), like cadmium, do not appear to fit either model. The most probable explanation for these observations is that the DTPA extractable soil metal concentration does not represent the metal uptake by corn plants
Figure 12. Comparison of predicted and measured plant metal concentrations for the annual and cumulative models. (Legend as in Figure 9.)
very well, at least for the type of soil found on these test plots. As can be seen from Table 11, this method of analysis would break down completely if applied to grain metal concentrations. So little metal is translocated to the grain that grain metal concentrations are not sensitive to sludge application. This, of course, is a highly desirable situation from the standpoint of sludge disposal. Conclusions As an example of the predictive use of these metals, Table I11 shows the projection for cadmium in soil based on the cumulative model. The annual sludge application rate is calculated based on an assumed annual nitrogen requirement for the crop to be planted (Baier, 1975). From this, an annual application rate for cadmium of 0.5 kg/ha is calculated. As assumed soil limit for cadmium of 10 mg/kg results in a lifetime limitation for cadmium application of 77 @/ha and a project life of 154 years for this example. The results of an analysis of this type would be determined by regulatory constraints on the concentration of metal in the soil, by the fraction of metal applied to the soil that is extracted in the analytical procedure, and by the nutrient requirements of the crop to be grown. One major constraint of these models is that they must rely on the results of field trials to generate the necessary data.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 2, 1981 221
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222
Table 111. Application of Cumulative Model for Soil Cadmium in a Hypothetical Example to Determine Predicted Project Lifetime annual nitrogen need 260 g/ha nitrogen in sludge 26 g/mT 10 mT/ha annual applied sludge annual applied sludge 1 0 mT/(ha/year) cadmium in sludge annual applied cadmium EPA cadmium soil limit
(hypothetical)
50 mg/kg 0.5 kg 10 mg/kg
cumulative model slope 0.13 (mg/kg)/ for cadmium (kg/ha) lifetime applied cadmium lifetime applied cadmium 77 kg/ha annual applied cadmium 0.5 kg project lifetime
7 7 kg/ha 154 years
It is not possible to project the results from one soil type to another. The results of these projections would also be sensitive to the type of sludge used and to the type of crop grown. Another major constraint is the apparent lack of relationship between either cumulative or annual sludge application and whole plant tissue concentrations. Thus,
these models appear applicable for projecting project lifetimes based on soil metals concentrations but do not appear to be useful for projecting plant tissue burdens. L i t e r a t u r e Cited Bairer, D. C. “Soli Enrichment Study 1974 Row Crop FieM Trials”; (Progress Report No. 3) East Bay Municipal Utility District, Oakland, CA, 1975. Burpee, L.; Osborn, K. E.; McLean, D. A. “Soil Enrichment Demonstration Project, Novato Sanltary Dlstrict“, San Franclsco Bay Region Wastewater Solids Study, Oakland, CA, 1979. Caper, S. G.; Tanner, J. T.; Frledman, M. H.; Boyer, K. W. Environ. Sci. Technol. 1978, 72, 705. Council for Agricultural Science and Technology, Report No. 64, Ames, IA, 1976. Hyde, H. C.; Page, A. L.; Bingham, F. T.; Mahier, R. J. J . Wafer Poiiuf. ControlFed. 1979, 51, 2475. Hyde, H. C. Presented in part at the 48th Annual Conference, California Water Pollution Control Association, Lake Tahoe, CA, April 1976. Lindsay, W. L. Adv. Agron. 1972, 24, 147. Osborn, K. E.; McLean, D.A. “Soli Enrichment Demonstration ProJect,Solano County”, unpubllshed data. “San Franclsco Bay Region Sludge Management Pian”; San Francisco Bay Region Wastewater SolMs Study, Oakland, CA, 1978.
Receioed for review October 9, 1980 Accepted February 23, 1981
Presented at the Second Chemical Congress of the North American Congress, Las Vegas, NV Aug 25-28, 1980.
11. Symposium on Recent Advances in Viscose Rayon Technology G. C. Daul, Chairman Second Chemical Congress, Las Vegas, Nevada, August 1980
Viscose Rayon: Recent Developments and Future Prospects John Dyer” and George C. Daul I77 Rayonier Inc., Eastern Research Division, Whippany, New Jersey 0798 1
By the end of the 1970’s, viscose rayon was recovering and consolidating its position in the marketplace following
a period of decline partly attributable to competition with and an overabundance of synthetic petroleum based fibers. Now a number of rayon markets such as fashion fabrics and nonwovens are experiencing strong growth. Improvements in present manufacturing processes together with the development of improved fibers such as high crimp HWM, Modal, hollow fibers, flame retardant, highly absorbent, and alloy-rayons have shown the versatility of the viscose rayon process. Rayon enjoys a unique position as a textile fiber in that it can be tailored to fit numerous end-use applications. Today’s rayons offer superior performance alone and in blends with other fibers such as polyester, wool, and cotton. Considering the availability of raw materials and the need to feed a growing population, viscose rayon will assuredly remain as one of the most versatile, engineered fibers in the foreseeable future.
It was more than 12 years ago at the Second International Symposium on Viscose Technical Questions that a statement was made that the viscose process had reached a state of development which left scarcely any room for the discovery of new or superior properties by economically feasible methods (1). There have been many improvements on both counts since then and the total world production of rayon has been maintained at 6-7 billion pounds per year (Figure 1) fluctuating according to the economic climate in producing countries (2). In the past decade production in Western Europe, the United States, 0196-4321/81/1220-0222$01.25/0
and Japan has declined somewhat from the peak production years of the 1960’s, but this has been balanced by continued growth in the Soviet Union, Eastern Europe, and other African, Asian, and Oceanic countries. Much of the change in the worldwide production pattern can be associated with price, availability relative to other competitive fibers, and the imposition of regulations relating to safety and the environment that presented a capital burden to the mature viscose rayon industry. In most cases the required investments in equipment and facilities to satisfy regulatory demands have now been made. How0 1981 American Chemical Society
