United States Environmental Protection Agency Municipal Environmental Research Laboratory Cincinnati OH 45268 Research and Development EPA-600/S2-84-046 Mar. 1984 Project Summary Characterization of Sewage Sludge and Sewage Sludge-Soil Systems Lee E. Sommers, Darrell W. Nelson, and Allen W. Kirleis Field and laboratory studies were conducted to characterize the chemical properties of municipal sewage sludges. to evaluate the fate of sludge compo- nents in soils, and to determine the distribution of trace metals in milling fractions of grains grown on sludge- treated soils. Specific studies included (1) characterizing the organic compo- nents in sewage sludges, (2) separating sludges into organic and inorganic fractions, (3) examining the capacity of sludge to retain metals, (4) evaluating sludge through spectroscopic, infrared, and electron spin resonance studies, (5) conducting laboratory soil incubation studies to characterize mineralization and nitrification of nitrogen and decom- position of organic carbon in sludge- amended soils, (6) determining metal speciation with analytical data for soil solution samples, and (7) evaluating the uptake of Cd, Zn, Ni, Cu, Fe, and Mn in oats, corn, wheat, and soybeans grown in soils treated with sewage sludge. This Project Summary was developed by EPA's Municipal Environmental Re- search Laboratory, Cincinnati, OH, 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 The recent emphasis on applying municipal sewage sludge to agricultural cropland necessitates a knowledge of the sludge constituents and their fate in soils. Sludges can be used as an alternative fertilizer because they contain not only macronutrients required by plants (i.e., N, P, and K), but also essential micronutri- ents such as Cu, Zn, and Mn. Studies have shown that comparable crop yields can be obtained with conventional fertil- izer materials and sewage sludge, but sludges may also have constituents that can be toxic to plants or to animals or humans consuming products grown on sludge treated soils. Trace metals, or- ganics, and pathogens are the three broad groups of sludge constituents that have received the greatest emphasis in re- search and regulatory activities. Of the metals contained in sludge, Cd has receivedthe most attention asa potential threat to human health, and Zn, Cu, and Ni have been implicated in decreasing crop yields. The polychlorinated biphenyls (PCB's) have received more attention than other sludge-borne organics. This series of studies was conducted to characterize the chemical composition of sewage sludges, to study the fate of sludge components in soils, and to evalu- ate the distribution of metals in crops grown on sludge-treated soils. Chemical Composition of Sewage Sludges The organic components in sludge were characterized by several extraction, chro- matographic, and spectroscopic tech- niques. Fatty acid esters (fats and waxes) and phthalic acid esters (plasticizers) constituted 2% to 10% and <1 % of sludge oven-dry weight, respectively. Palmitic acid esters and dibutyl phthalate were the predominant components in the respec- tive fractions. Upon H2SO4 hydrolysis of the sludges and subsequent analysis of the hydrolyzates by high pressure liquid ------- chromatography and colorimetric proce- dures, hexuronic acids, glucose, and xylose were detected. The sugars were likely monomers of hemicellulose and cellulose polymers, which together made up 0.99% to 2.55% of sludge oven-dry weight. Organic N in the sludges was present primarily as a-amino acid N, constituting 31% to 36.5% of the organic N. The amino acid distribution in sludge hydrolyzates was determined by an amino acid analyzer and revealed that amino acids of bacterial origin were present (i.e., a-amino pimelic, a,e-diaminopimelic, /8- alanine, y-amino butyric, and ornithine) as well as those commonly found in plant and animal protein. Sodium-amalgam reduction of the sludges produced few or no phenolic compounds, indicating small concentrations of humic-type materials. Infrared and X-ray analyses of residues from HF-treated sludges and NaOH ex- tracts (humic acids) of sludges indicated the presence of condensed aromatic rings or quinone-like compounds and little or no inorganic crystalline material. Sludges were separated into light and heavy fractions by an ultrasonic disper- sion and heavy liquid separation tech- nique to provide information on trace metal forms in sludges. The light fraction (organics) was 8% to 26% of the sludge dry weight, and the heavy fraction (inor- ganics) constituted 69% to 88% of the sludge weight. Most of the metals were associated with the sludge light fraction (organic). Infrared studies were conducted to characterize qualitatively the sewage sludge light (organic) and heavy (inor- ganic) fractions obtained using the heavy liquid separation technique. Infrared spectra of sludge organic fractions re- vealed the presence of proteinaceous and polysaccharide-like materials. Infrared absorptions characteristic of carboxyl groups and aromatic compounds were not observed in the spectra of sludge light fractions. The position of the amide-l band in the infrared spectra of the sludge light fractions was used to obtain direct evidence of metal binding sites involving amide N and possibly amide O. A discrete shift in the position of the amide-l band was initiated by extracting indigenous metal cations from the sludge organic fraction. This shift was reversed by satu- rating the extracted sludge organic frac- tion with Cu2+. Absorption bands of quartz and calcite dominated the infrared spectra of sludge inorganic fractions. Electron spin resonance (ESR) spectros- copy was used to study the mechanism of Cu2+ binding by humic acid (HA) extracted from soil and sewage sludge. The ESR data showed that the addition of pyridine (py) and 1,10-phenanthroline (phen) to the soil and sludge Cu-HA complexes resulted in the added nitrogen ligands replacing water coordinated to Cu2*. The added ligand did not displace HA oxygen donor ligands also coordinated to the Cu2+. The addition of a more basic nitrogen donor, ethylenediamine (en), resulted in the formation of Cu(en)l+ by displacement from Cu2+ or both coordinated aquo ligands and HA oxygen donors. ESR parameters revealed that two HA oxygen atoms were coordinated equatorially to Cu2+ in the original soil and sludge Cu-HA complexes. In the sludge Cu2+-HA com- plex, the Cu2+ ion also appeared to form axial bonds with HA nitrogen donor ligands originating from proteinaceous materials associated with the sludge HA fraction. Characterization of an adduct with glycylglycine showed that the dipep- tide formed coordinate bonds with Cu2+ bound to sludge HA. The metal retention capacities'of calcar- eous and acidic sludges and sludge fractions were determined. The results obtained from the equilibration of Cd, Cu, Ni, or Zn salts with calcareous and acidic sludges indicated that calcareous sludges have a higher capacity to retain added metals than noncalcareous sludges and that metal retention was directly related to sludge pH. As solution pH increased above 5.0, chemical precipitation of metals, most likely as carbonates, became the dominant mechanism in the removal of Cd, Cu, Ni, or Zn from solution. Metal retention was reduced when pH values of sludge and metal solutions were below 5.0. Most of the Cd, Cu, Ni, and Zn retained by sludge at low pH values was likely the result of complexation by organic matter and sorption by amorphous Fe, Al, and Mn hydrous oxides. The retention capacity for Cd and Cu with heavy and light sludge fractions decreased in the following order: light fraction>heavy fraction>whole sludge This order indicates the formation of stable complexes between sludge organ- ics and metal ions. The heavy fraction, which is composed largely of inorganic materials, also retained large proportions of added Cd and Cu. The sludge compo- nents responsible for Cd, Cu, Ni, or Zn retention were estimated by selective extraction procedures. The results indi- cated that three sludge components are primarily involved in Cd, Cu, Ni, or Zi retention. Sludge components are rankei below in decreasing order of their impor tance for retention of each metal: Cd: carbonate>organic matter>hydrou oxides; Cu: carbonate>organic matter = hydrous oxides; Ni: carbonate>organic matter = hydrous oxides; Zn: carbonate>organic matter>hydrous oxides. Fate of Sludge Components in Soils A laboratory soil incubation system was used to study metal extractability (with DTPA), nitrogen mineralization, nitrification, and organic C decomposi- tion in soils amended with municipal and synthetic sludges. The synthetic sludges were prepared to contain varying concen- trations of Cu, Cd, Zn, Pb, and Ni at a constant level of organic C and N. The extent of decomposition of municipal sewage sludges (as measured by C02 evolution) appeared to be a function of the organic C content of the sludges. As much as 30% to 47% of the C02-C evolved from the sludge-treated soils was due to dissolution of calcium carbonate present in the sludges. Significant inhibition of nitrification was found in soils amended with synthetic sludges at rates greater than 60 metric tons/ha, whereas stabi- lized municipal sludges showed rapid nitrification of all application rates. Generally, the percent of sludge organic N mineralized increased with sludge appli- cation rate. Metals (Zn, Cu, Ni, and Cd) extracted from soil with DTPA generally increased with incubation time and were directly related to the amount of sludge- borne metal added to the soil. Similar correlations were obtained between added and DTPA-extractable metals for synthetic and municipal sludges. In gen- eral, synthetic sludges offer promise for studying the decomposition rate of munic- ipal sludges in soils. The decomposition of liquid and dried municipal sewage sludges was deter- mined in soils under laboratory and field conditions. Evolved COs was continuously monitored in soil + sludge mixtures incubated in the laboratory. Primary, raw, and waste-activated sludges showed the greatest degree of decomposition, where- as digested and composted sludges had the lowest decomposition values during a 112-day incubation. The data indicate that the percentage of sludge organic C ------- composed in soil will be less for those idges subjected to intensive stabiliza- n processes at the treatment plant. rbon dioxide evol ution i n the field study is monitored for a 24-hr period by jaling cylinders containing soil-sludge nixtures. The cylinders remained open to he environment between sampling >eriods. Soil moisture and temperature were also monitored. Evolution of C02 was initially rapid in all soil and sludge ;ombinations, but it decreased with time swing to consumption of easily decom- posable organic substrates in the sludge md gradual lowering of soil temperature n the late fall and winter. Carbon dioxide evolution rates for all treatments were affected by temperature and increased in sarly spring. Dewatering an anaerobically digested sludge by air-drying reduced the extent of decomposition in soil. Because of C02 release from carbonate dissolution, he presence of inorganic C in sludges can interfere with organic C decomposi- ion calculations based on COj evolution. Data from both the laboratory incubation md field study show good agreement loncerning relative order and magnitude >f sludge decomposition. A first-order i odel adequately predicts decomposition >' most sewage sludges under field ; >nditions. The model failed to predict an ncrease in the rate of C02 evolution in jarly spring. This increase is possibly due o increased organic C availability induced >y freezing and thawing cycles during the )revious winter. Incubation studies using carboxyl- abeled 14C dibutyl phthalate (DBF) added o soils at 0.1% (w/w) indicate that 90% >f the DBF was degraded within 80 days. Decomposition of DBF was shown to be nicrobially mediated and was a function jf soil type, pH, and temperature. Applica- ion of DBF at rates of 0.4% (w/w) and the addition of ammonium and CaCOa or iewage sludge had little effect on the sxtentof DBF degradation. Dibutyl phthal- ate contained in sewage sludge or other waste materials to soils should not pose a long-term persistence problem in soils. Humic acids (HA) extracted from siudge, soil, and sludge-amended soil were char- acterized by elemental and functional group analyses, and by visible and infra- red spectroscopy. When compared with a soil HA, the sludge HA appeared to be a more aliphatic, N-enriched polymer with decreased amounts of carboxyls and phenolic hydroxyls. Proteinaceous mate- rials associated with the sludge HA appeared to be the major source of N enrichment. Sludge organic matter was apparently recovered in HA extracted from soil 2 and 14 months after sludge applica- tion. The association of sludge-borne proteinaceous and aliphatic materials with the sludge and sludge-amended soil HA fractions was indicated by increased amide and C-H stretch infrared absorp- tions, as well as by the increased N contents and decreased C:H ratios. The observation of proteinaceous materials associated with HA extracted from sludge- amended soil 14 months after application suggested that these proteinaceous materials were resistant to decomposi- tion, possibly as a result of their incorpo- ration into the HA structure. Infrared spectroscopy was used to identify the mode by which carboxylates of a soil HA complexed Cu2+ and Fe3+. Carboxylic acid groups of soil HA were converted to carboxylates (CO-?) by form- ing coordinate bonds with Cu2+ and Fe3+. The separation of the antisymmetrical, va (COi), and symmetrical, vs (COi), stretch- ing vibrations of COI obtained from spectra of metal-HA complexes indicated that COz formed a unidentate complex (i.e., a single M-O bond) with Cuz+ and Fe3+. The formation of bidentate or bridging complexes between COi of HA and Cu or Fe3* was not observed. Metal-chelate stability diagrams were developed as a function of pH and redoxto predict the behavior of five synthetic chelating agents in soils. The metals evaluated include H+, Fe3*, Fe2+, AI3+, Mn2*, Ca2*, Mg2+, Zn2+, Cu2+, Cd2+, Pb2*, and Ni2*. In acid systems, Ni2+ at 10 5 to 10~7 M was the predominant ligand species for all chelating agents. Similar results were obtained in alkaline systems when NiCO3 controlled Ni2* solubility. In the absence of Ni2*, either Cda* or Pb2* ligand species dominated at alkaline pH for all chelating agents. In acid systems, Cu, Pb, Fe, and Zn are the major chelated species. These chelating agents deserve further study in acid soils as extractants for metals and as reagents for determining metal ion activities through competitive equilibria. The results identify ligands that may be useful in determining various metal ion activities in soils. The diethyl- enetriamine pentaacetic acid (OPTA) soil test appears to have a sound theoretical basis for evaluating the plant-available Pb, Cd, and Ni in soils. A cooperative study was conducted with the Tennessee Valley Authority to determine the effects of sewage sludge applications on the heavy metal status of a soil. Sewage sludge from Tuscumbia, Alabama, was applied to an acid soil (pH ~ 5) as a single treatment in 1971 or as annual treatments from 1971 through 1974 in amounts totaling 50 to 800 metric tons/ha. Soil samples (0- to 15-cm depth) obtained from the plots in 1977 were moistened to -0.33 bar water potential and equilibrated for 7 days before displacement of the soil solution. The soil solutions were analyzed for Zn, Cd, Cu, Ni, Pb, Mn, Fe, Ca, Mg, Al, Na, K, PO*, SO4, Cl, conductivity, pH, and organic C. The metal species present were calcu- lated with a computer program (GEO- CHEM). Sludge application increased soil solution concentrations of Zn, Mn, and Cd, but Cu, Ni, and Pb levels in most solutions were below the detection limits of the analytical methods used. Cd, Zn, and Mn in the soil solution appeared to exist predominately as the free ion. Depending on the model used to represent metal interaction with soluble organic C, complexation by inorganic and organic ligands ranged from 9% to 33%. 3% to 22%, and 3% to 31 % of the total soluble Cd, Zn, and Mn, respectively. Cd was complexed with organic ligands to a greater extent than were Zn or Mn. Sulfate, phosphate, and chloride formed inorganic complexes with Cd, Zn, and Mn, but they constituted less than 10% of the total metal present. The general degree of metal complexation by organic and inor- ganic ligands increased in the following order: Zn = Mn = Ni < Cd < Cu Speciation of Zn and Cd into free metal ion and complexed forms was essentially the same in the soil solution, regardless of metal concentrations in solution and rate or frequency of sludge application. Calculated activities of Cd2* indicated undersaturation with respect to known Cd solid phases, whereas Zn2* activities were comparable with those of ZnFezCu, soil Zn, and Zn2SiO.t. Soluble Zn and Cd were directly related to the amount of metal added and to the extractability of added metal with DTPA. The solubility and DTPA-extractability of Cd were in- creased more by a single application of si udge than by multiple, annual additions. This relationship was not as consistent for added Zn. Distribution of Trace Metals in Milling Fractions of Grains Grown on Sludge-Treated Soils Oats, corn, wheat and soybeans were grown on soils treated with stabilized sewage sludge from three Indiana cities. ------- Sludges were applied to a Chalmers silty clay loam soil at rates of 56 to 448 metric tons/ha. Oat samples were separated into groats and hulls, and concentrations of Cd, Zn, Cu, Fe, and Mn were determined in each fraction by atomic absorption spectrophotometry. The effect of sludge application rates on the concentrations of trace metals in whole oats, groats, and hulls was similar for all three sludges used, and they generally decreased in the following order: Zn = Fe > Mn > Ni > Cu > Cd Except for Mn, the concentrations of trace metals increased with increasing rates of sludges applied, but the groats contained greater concentrations of Cu, Ni, Zn, Cd, and Mn than the hulls. The metal concentrations in whole- kernel corn were not significantly in- creased by sewage sludge applications of 56 to 448 metric tons/ha. Except for one Cd-enriched sludge, Cd concentrations in whole corn and fractions from dry-milling were less than 0.05 mg/kg. As expected, the germ fraction contained the greatest proportion of the fat, ash, and trace metals, and most of the protein was found in the grits fraction. Both the concentra- tion and the percent distribution of metals in dry-milling fractions decreased in the following order: germ > hulls > flour > meal > grits The metal concentrations in both wheat and soybean grain were increased by sludge applications. For wheat, the bran contained significantly higherconcentra- tions of all metals than did the flour. Metal concentrations were similar in whole soybean gram and the resulting meal. Conclusions 1. Characterization of the organic com- ponents in sewage sludges indica- ted that fatty acid esters and phthalates were predominant forms present in nonaqueous extracts of sludge. 2. A heavy liquid extraction procedure developed to separate sewage sludges into organic and inorganic fractions indicated that most metals naturally present in the sludge were associated with the fraction en- riched in organic matter. 3. Municipal sludges had the capacity to retain appreciable amounts of Cd, Cu, Ni, and Zn. The most likely primary mechanisms involved in sludge retention of added metal salts were precipitation as carbon- ates and sorption by organic matter and hydrous oxides. 4. Studies conducted to evaluate the spectroscopic properties of sludge organic matter indicated that sludge humic acids were more aliphatic and contained fewer carboxyl and phenolic hydroxyl functional groups than soil humic acids. 5. Infrared investigations indicated that the amide group in residual proteinaceous materials could be involved in the retention of Cu by sludge. 6. Electron spin resonance studies indicated that Cu (II) was bound to oxygen-containing donor ligands in the humic acid fraction of sewage sludge. 7. In laboratory incubation experi- ments, evolution of COz from sludge-treated soils indicated that elevated amounts of trace metals may temporarily inhibit decomposi- tion, but they do not do so over an extended period. Some temporary inhibition of nitrification was ob- served in sludge-amended soils. 8. Studies conducted u nder laboratory and field conditions indicated that the extent of sludge decompositic in soils was inversely related to tr intensity of treatment and proces ing within the sewage treatmei plant. 9. Laboratory incubation studies using dibutyl phthalate indicated that more than 90% of this compound will be degraded within 80 days after application to soils. 10. The free metal ion was the primary species of Zn and Cd found in soil solutions, regardless of total metal concentrations or the rate or fre- quency of sludge application. 11. For oats, metal concentrations were significantly greater in the groats than in the hulls. 12. Minimal increases in grain metal content were observed when corn was grown on sludge-amended soils. 13. Concentrations of Zn, Cu, Cd, and Ni in wheat and soybean grain were increased by sludge applications. Bran and meal contained the high- est metal concentrations for wheat and soybeans, respectively. The firll report was submitted in fulfill- ment of Grant No. R804547-02 by Purdue University under the sponsorship of the U.S. Environmental Protection Agency. L. E. Sommers. D. W. Nelson, A. W. Kirleis. S. D. Strachan. J. C. In/nan, S. A. Boyd, J. G. Graveel, and A. D. Behel are with Purdue Unversity, West Lafayette. IN 47907. James A. Ryan is the EPA Project Officer (see below). The complete report, entitled "Characterization of Sewage Sludge and Sewage Sludge-Soil Systems." (Order No. PB 84-158 898; Cost: $28.00. 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 ------- United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 BULK RATE POSTAGE & FEES P> EPA PERMIT No. G-35 Official Business Penalty for Private Use $300 LUU W T1LLEV HbblUN V tHA LIHkARIAN 230 6 UtAKBORN S CHitAGU IL 60604 {, U.S. GOVERNMENT PRINTING OFFICE: 1984-759-102/909 ------- |