United States Environmental Protection Agency Municipal Environmental Research Laboratory Cincinnati OH 45268 Research and Development EPA-600/S2-80-199 Mar. 1981 Project Summary Production of Non-Food-Chain Crops with Sewage Sludge Lilia A. Abron-Robinson, Cecil Lue-Hing, Edward J. Martin, and David W. Lake A beneficial use for sewage sludge? This study investigated the feasibility of using sewage sludge in cultivating three non-food-chain crops currently sold on the open market or with good potential for marketability. A cost analysis determined how cultivation costs using sewage sludge compared with costs using commercial fertilizer. Cotton, sod, and energy biomass trees were determined to have the best potential for cultivation using sewage sludge, based on the market values and nutrient requirements for each crop and on the hectares pres- ently under cultivation for production of these crops. Results indicate that large quanti- ties of sewage sludge can be used, based solely on the nitrogen and phosphorus requirements for the cul- tivation of these crops. In addition, although the total costs for fertiliza- tion using commercial fertilizer are less than the costs for using sewage sludge, the latter would be viewed more favorably if the municipality generating the sludge bore the costs. This Project Summary was devel- oped by EPA's Municipal Environ- mental Research Laboratory, Cincin- nati. OH 45268. to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction Sewage sludge has historically been viewed as a spent by-product of sewage treatment. Recognition of the valuable properties of sludge, including its high concentrations of plant nutrients and organic matter, has led to increasing emphasis on its beneficial uses for re- claiming disturbed lands and fertilizing agricultural soils. The prospect of wide- spread application on agricultural land has, however, been accompanied by concern over possible accumulations of toxic substances in soils and potential translocation of toxics throughout the human food chain. The purpose of this study was to evaluate the feasibility and market potential of land application of munic- ipal sewage sludge in the cultivation of non-food-chain crops (NFCC). Using sludge in this manner would realize the advantages of its beneficial properties while circumventing the potential prob- lems associated with the unknown impacts of toxic materials on the human food chain. This study entailed three broad activities: (1) assessing the fertil- izer value of sludge, (2) selecting NFCC amenable to cultivation using sewage sludge, and (3) determining land re- quirements and costs associated with producing NFCC using sludge and com- paring these costs to the costs of pro- ducing the same crops using commer- cial fertilizer. The analyses were based on data available in the literature or obtained through personal interviews. Fertilizer Value of Sludge The nutrient content of municipal sewage sludge was found to vary with the composition of the influent waste- water and the sewage and sludge treat- ------- ment processes employed. Municipal sludges were found to have a total nitrogen (N) content of 1 % to 6%, a phos- phorus (P) content of 1% to 6%, and a potassium (K) content of 0.04% to 6.1 %. Because of its low potassium levels, sludge is generally not considered to be a good source of this nutrient. Based on mean sludge N, P, and K values of 3.2%, 1.8%, and 0.3%, respec- tively; on inorganic, N, P, and K prices of $0.253/kg ($0.115/lb), $1.37/kg ($0.621/lb), and $0.259/kg ($0.1176/lb); and on a projected 1985 U.S. sludge production rate of 16,012 dry metric tons/day (17,650 dry tons/day), the total daily sludge produced in the United States has an estimated chemical fertilizer equivalent market value of $537,000 per day for the year 1985 (based on 1980 dollars). Other benefits of using sewage sludge, such as improvements in tilth and water holding capacity of soils, are difficult to quantify. It is crucial also to consider that using sewage sludge in place of or as a supplement to chemical fertilizer avoids or reduces the high energy costs associated with both commercial fertil- izer production and sludge incineration. NFCC Amenable to Sewage- Sludge Cultivation The next step was to identify NFCC and determine which of these are amenable to cultivation using sewage sludge. Food-chain crops are defined as (1) tobacco; (2) crops grown for human consumption; and (3) pasture, forage, and feed grain for animals whose prod- ucts are consumed by humans. NFCC are, therefore, the crops that remain. These crops were first identified using the Standard Industrial Code (SIC), to which were added research crops such as jojoba, euphorbia, guayule, and bio- mass crops. Cotton and soybeans were also included because these crops have significant inedible uses, both respond favorably to commercial fertilization, and cotton clearly has a high N demand. The selection of NFCC feasible for cultivation using sewage sludge was based on a developed set of criteria. The most important of these criteria were: (1) the crop must not produce edible matter that could easily become a part of man's food chain; (2) the crop must have a demonstrated or a high probability of future market potential; (3) the land used to raise the crop must have a high probability of being continuously used exclusively for production of that crop; and (4) data must be available giving the response of the crop to sludge, or suffi- cient data must be available for similar crops, to enable a probable response determination using data extrapolation and inference. Six crop categories composed of 20 crops were studied in relation to the above criteria: timber tracts (five hard- wood and three softwood varieties); forest nurseries; flax; horticultural specialties (greenhouse varieties, shrubs, sod and turf grasses, lawn grasses); research crops (jojoba, guayule, euphorbia, energy biomass crops); and oil crops (cotton, soybeans). Using sludge for cultivating hardwood forests was deemed unacceptable because hardwoods are best grown in the open forest environment. These sites are generally remote from sludge generating centers and are only inter- mittently accessible; also, the impacts of sludge on the open forest environment are poorly understood. Furthermore, hardwoods have a slow rotation period and low N and P requirements. Flax was deleted because the market for this crop is declining and a reasonable possibility exists that land used to raise this crop could be used to grow food-chain-crops. Of the research crops, all were rejected except biomass crops because not enough data were available to deter- mine feasibility. Based on the above criteria, crops retained for further study included monoculture timber tract operations using softwood, forest nurseries, sod, and energy biomass trees, and cotton and soybeans. Of these, cotton, sod, and biomass trees were selected for detailed case study analysis. These three crops are currently sold on the open market or, in the case of biomass crops, are being actively researched. Thus, information was readily available describing the preferential climatic condition for the crop, nutrient requirements of the crop, land required, and minimum size of a city that could generate enough sludge to support crop production. Land Requirements and Costs Given both the sludge quantities generated and the land currently under harvest for each crop in each state, the following were determined: (1) the maximum amount of land that could be fertilized for each crop in each state, constrained by either the amount of sludge generated in that state or by the| land currently harvested; (2) the unitf costs (excluding land costs) of using sludge to fertilize this land (by three application modes—injection, surface irrigation, truck spreading); and (3) the unit costs of fertilizing this land using custom application of commercial fertil- izer. Application rates of sludge and commercial fertilizer were calculated in two different ways: rates needed to satisfy crop nitrogen requirements and rates needed to satisfy crop phosphorus requirements. Aqueous ammonia containing 30% NHa was used as the basic source of commercial N; phos- phorus pentoxide containing 40% P was used as the basic source of commercial P. The current cost of commercial fertil- izer was determined from the chemical marketing literature, and the costs of transport and custom application were based on information from companies providing these services. The cost of the sludge itself was taken as zero, and the sludge transportation costs from the centers of sludge generation to the application sites were considered separately. Conclusions and Recommendations | The cost comparisons for sludge and commercial fertilizer are compared in Table 1 . Of the three sludge application modes, injection is the most expensive and truck spreading appears to be the cheapest. Using sludge in lieu of com- mercial fertilizer appears to be most cost effective when applying sludge to biomass crops via truck spreading and surface irrigation at rates sufficient to satisfy nitrogen requirements. Research on the use of sewage as a substitute for commercial fertilizers for the production of biomass crops should be encouraged. Using sludge for sod production is the most feasible beneficial sludge use option at this time. Sod production would conservatively use 5% to 10% of the total sludge generated in the sod producing states. As stated previously, biomass crops are still in the research stage. Although most of the cotton being produced is used in part for food- chain products, the possibility does exist whereby a portion of this crop could be grown for non-food-chain purposes only. It became evident from the case study analysis of the three crops that all of the * sewage sludge generated cannot be| ------- Table 1. Cost Comparisons for Sludge Versus Commercial Fertilizer (Fertilizer Costs Include Both N and P) Cotton Average Total Annual Cost ($/ha) Sod Biomass Application Mode N(S) P(S) Fertilizer' NfSJ P(S) Fertilizer' NfS) P(SJ Fertilizer" Injection Surface Irrigation Truck Spreading 1,229 1,034 290 1,364 1,156 709 1,127 290 660 1,048 296 290 290 704 336 350 1,197 350 350 255 417 746 361 338 432 432 432 'All fertilizer costs are custom application. used to produce NFCC. Based only on the crops analyzed in this study, how- ever, at least 20% of the sludge gener- ated could be used for NFCC production. This is significant. The problem of generating more sludge than that required for application raises other concerns such as the need for storage facilities and the need for other benefi- cial sludge use options. These needs should be addressed if the eventual objective is to use and recycle sludge to the greatest extent possible. Transportation costs from the centers of sludge generation to the application site will have a significant impact on cost. When transport costs are added to the costs presented in Table 1, the dif- ference between costs for sludge and commercial fertilizer become even more pronounced. Clearly, if sewage sludge is to compete with commercial products, the costs for the operation will have to be borne by the municipality generating the sludge. If the municipality were to transport the sludge to the application site and provide the application equip- ment, the sludge would be a sought- after commodity. Lilia A. Abron-Ftobinson and Cecil Lue-Hing are with PEER Consultants, Inc., Rockville. MD 20852; Edward J. Martin and David W. Lake are with Environ- mental Quality Systems, Inc., Rockville, MD 20852. Gerald Stern is the EPA Project Officer (see below). The complete report, entitled "Production of Non-Food-Chain Crops with Sewage Sludge," (Order No. PB 81-125296; Cost$11.OO, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Municipal Environmental Research Laboratory U. S. Environmental Protection Agency Cincinnati, OH 45268 « U.S.QOVERMMBIT PRINTING OFFKC:1M1-757-Ol2/70l7 ------- Unit»— •"*-— Center for Environmental Research Postage and _ r-ees raia "j Environmental 90 UNITED STATES Protection ENVIRONMENTAL PROTECTION AGENCY &MB Cincinnati, Ohio 45268 Offi ~~~~~~~~~~~~~~~ Pa,. OFFICIAL BUSINESS PENALTY FOR PRIVATE USE $300 AN EQUAL OPPORTUNITY EMPLOYER Region 5 Library 2D3o%En£:rrs Chicago, IL 60604 EPA-353(Cin) (Rev. 11-80) ------- |