Non-Peer ReviewedSewage sludge and crushed elemental sulphur (S0) were combined in various ratios, and incubated under controlled conditions. Sulphur oxidation was strongly enhanced by addition of sewage sludge, though acidification of the mixtures prevented more than 4% of the initial sulphur to be converted to sulphate. Sub-samples of these incubated mixtures were then added to soil, and compared to soil amended with S0 and Na2S04. The sludge and S0 mixtures oxidized rapidly when introduced to the soil environment. Nearly 60% of the S0 from these mixtures oxidized within six weeks, compared to about 25% oxidation of S0 applied without sewage sludge. Indigenous S0 bacterial oxidizers in the sludge may explain the observed enhancement of S0 oxidation. Combinations of S0 and de-watered sewage sludge may provide an inexpensive and effective sulphur fertilizer source for western Canadian farmers in the future

Cowell, L.E.

Schoenau, J.J.

English

eCommons@USASK

Potential use of combined elemental sulphur and sewage sludge as a fertilizer

University of Saskatchewan Research Archive

ABSTRACT Potential Use of Combined Elemental Sulphur and Sewage Sludge as a Fertilizer L. E. Cowell and J. J. Schoenau Dept. Soil Science, University of Saskatchewan, Saskatoon Sewage sludge and crushed elemental sulphur (So) were combined in various ratios, and incubated under controlled conditions. Sulphur oxidation was strongly enhanced by addition of sewage sludge, though acidification of the mixtures prevented more than 4% of the initial sulphur to be converted to sulphate. Subsamples of these incubated mixtures were then added to soil, and compared to soil amended with So and Na2S04. The sludge and So mixtures oxidized rapidly when introduced to the soil environment. Nearly 60% of the So from these mixtures oxidized within six weeks, compared to about 25% oxidation of So applied without sewage sludge. Indigenous So bacterial oxidzers in the sludge may explani the observed enhancement of So oxidation. Combinations of So and dewatered sewage sludge may provide an inexpensive and effective sulphur fertilizer source for western Canadian farmers in the future. Key Words: Elemental sulphur, sulphur oxidation, sewage sludge INTRODUCTION Elemental sulphur fertilizer (So) has not proven to be an effective fertilizer source in western Canada, due to its very low rate of biological oxidation to plant-available sulphate (Swan et al, 1986; Noellemeyer et al, 1981; Solberg and Nyborg, 1986; Solberg et al, 1987). Granular forms of So, though easier and safer to handle, are very slow to oxidize. Very finely divided So, which may be applied in an emulsion, is more rapidly oxidized, but difficult to handle and apply (Ukrainetz, 1982; Janzen and Bettany, 1986 and 1987; Chapman, 1989; Nuttall et al, 1990; Karamanos and Janzen, 1991). Maximum oxidation occurs if the So is thoroughly mixed in the soil (Solberg and Nyborg, 1986; Janzen, 1989; Janzen and Bettany, 1987), and if the soil is warm and moist (Janzen and Bettany, 1984). Soil pH also plays an important role. So oxidation acidifies the soil, and the activity of oxidizing bacteria is depressed in acid soil conditions (Gupta et al, 1988; Lawrence et al, 1988). Recent studies have suggested that heterotrophic oxidation of So is stimulated by sources of organic matter (Cifuentes and Lindemann, 1993). Combination of so with a readily available carbon source may therefore provide a simple method of improving So as a fertilizer. This project examined dewatered sewage sludge as a potential amendment for stimulating So oxidation. MATERIALS AND METHODS The potential amendment of So with dewatered sewage sludge for production of a fertilizer product was envisioned to follow two steps. First, the So would be combined with sludge, and preincubated for a period of time to stimulate bacterial activity. Then, the combined So and sewage sludge would be applied to a sulphur deficient soil well before the crop was planted, in order to allow continued oxidation. This experiment thus followed two steps - a preincubation trial of various combinations of So and sewage sludge, followed by an incubation trial with the combinations added to a sulphur deficient soil. The preincubation trial included mixtures of So and sludge at ratios of 8:2, 5:5,2:8 and 0: 10 on a dry weight basis. These mixtures were incubated for 10 weeks in plastic 1 . bags. ·The incubation chamber was maintained at 30°C and 90% Rh. Subsamples of each mixture were removed weekly for measurement of S042- and pH. After sampling, the mixtures were wetted to 80% of their water holding capacity. The mixtures were thoroughly mixed twice per week to improve conditions for aerobic oxidation. For the soil incubation, treatments included subsamples from the preincubation trial from week 1, 2, 3, 5, and 7. In addition, treatments of So alone, Na2S04 and a control with no sulphur addition were included. These treatments were added at an equivalent rate of 100 Jlg S per g soil to a Black Chernozemic sandy loam ('Meota') soil. Incubation conditions were identical to the preincubation study. The amended soil was sampled each week for six weeks for measurement of S042- and pH. RESULTS AND DISCUSSION Characteristics of Sludge, Sulphur and Soil The So used in the experiment was a commercial grade of crushed elemental sulphur. As particle size of So decreases, potential oxidation increases. The So was passed through 60 and 100 mesh sieves to provide an estimate of particle size; 17.5% > 60 mesh (250 J.Lm) 21.5% < 100 mesh (160 J.Lm) The small amount of sulphur in the sludge would play an insignificant role as a supply of sulphur in the sludge and so mixtures (Table 1 ). The S042- content of the sludge exceeded 1300 ppm, which suggests an active population of sulphur-oxidizing bacteria was probably present. However, this S042- would again be insignificant at the rates of sludge and So which would be used as a fertilizer source. More importantly, the carbon and other nutrients supplied with the sludge may stimulate So oxidation. Previous measurement of possible pollutant elements in the Saskatoon sewage sludge indicate that these would pose no threat to the environment or food chain (Cowell and de Jong, 1991). Table 1. Nutrient characteristics of Saskatoon dewatered sewage sludge. Element s N p K c Concentration(%) 0.50 0.90 1.45 0.37 9.80 The soil used in the incubation experiment was sampled from the surface 10 em of a farm field which had no previous applications of sulphur. The initial S04-S content of the soil was 9.8 ppm, which would be deficient for normal plant growth. Preincubation Experiment The final S042- concentration of the mixtures did not exceed 1% after 10 weeks of incubation (Figure 1). The S042- concentration of sludge alone remained stable during the preincubation period. For the mixtures, the S042- concentration was higher when the sewage sludge fraction of the mixture was increased. Sewage sludge stimulated So oxidation, but did not result in a high concentration of S042- accumulated at the end of the preincubation. 2 1.0 ;? 0 ~ 0.8 c 0 ~ ..... c Q) (.) c 0 (.) 0 en 0.6 0.4 0.2 ------------~------' o.o~~~~~~~~~~~,~~~~ 1 2 3 4 5 6 7 8 9 10 Week of Incubation • Sludge Sulphur 80% Sludge 20% Sulphur 50% Sludge 50% Sulphur 20% Sludge 80% Figure 1. Sulphate concentration of sewage sludge alone and in mixture with S0 during the preincubation period. The fraction of So oxidized to S042- was calculated for each treatment, while accounting for the original S042- contributed by the sludge. So oxidation was increased as the proportion of sewage sludge was increased in the mixtures (Figure 2). Over a 10 week period, only 0.3% of the So was oxidized to S042- when the mixture consisted of 20% sludge, but increased to 4.2% when the mixture was 80% sludge. Sharply reduced pH due to So oxidation appeared to limit continued oxidation in the mixtures, and this effect was buffered by a higher proportion of sludge in the mixture (Figure 2). Soil Incubation Incubation of soil with the subsamples from the preincubation trial and with so and Na2S04would mimic activity in a fertilized fields soil, though probably at an increased rate of S0 oxidation. Nearly 100% of the added S042- from the NaS04 source was accounted for at each sampling point throughout the soil incubation (Figure 3). This suggests that S042- immobilization and gaseous loss would have been minimal in the soil for all treatments .. The So added without sewage sludge oxidized to S042- slowly (Figure 1 ). After six weeks, and accounting for soil S042- content, only 25%/ofthe So was accounted for as S042-. In contrast, all combinations of So and sewage sludge were effectively oxidized to · S042-. There was no appreciable difference in oxidation rates between combinations of S0 and sewage sludge which had been preincubated for various lengths of time. There was also little difference in the final S042- release between different ratios ofSo and sewage sludge, although increased sewage sludge content did favour oxidation initially. Mter accounting for soil S042-, the average release of S042- from the combinations of So with sewage sludge was 57%. This amount was well over twice as high as so alone, and about 70% of the Na2S04 source. 3 -tJ) ca s:::: ·-C) ·.:: 0 ...... 0 '#--Cl) U) ca Cl) -Cl) a:. tJ) 5 4 3 2 Sulphur 80o/o Sludge 20o/o " · .... --.-~~~~1-_.s_pH~R~el-e~ase ~ . . . . . . . 6 5 4 3 1 o+-~~r----r----~---.-----.----+2 5 4 3 2 1 0 2 4 6 8 10 12 Sulphur SOo/o Sludge SOo/o S Release pH \__ ~-~.~.1·~··~·~·~·~··~···--· 6 5 4 3 o+----.----~----~--~----,-----+2 5 4 3 2 1 0 2 4 6 8 10 12 Sulphur 20o/o Sludge 80o/o 0 • SRelease pH 6 5 4 3 o+-----~--~----~----~--~~---+2 0 2 4 6 8 10 12 Week of Incubation :r:: c. Figure 2. Percentage of So oxidized to S042- and pH of the mixtures over the course of the preincubation period. 4 -0 100 c Soil C/) C> • Na2804 :I... CD 80 So10 a. C> :::1. • So882 -c 60 ~ So585 0 :.;:::::; * So288 Cd :I... - 40 c CD (.) c 0 20 (.) CD -Cd ..s:: 0 a. ::J 0 1 2 3 4 5 6 Cf) Week Figure 3. Sulphate content of soil during incubation after amendment with So, Na2S04, and combinations of So and sewage sludge at a rate of 100 J.1g S per g soil. Soil pH was not measurably affected by sulphur addition in the soil incubation. After six weeks, the pH of soil amended So and sewage sludge combinations averaged 7.98, while soil without any sulphur added had a pH of 8.07. CONCLUSIONS Sulphur oxidation was stimulated when combinations of So and dewatered sewage sludge were incubated together, and when they were added to soil. Based on these results, the preincubation step would probably not need to exceed one week if combinations of so and dewatered sewage were produced as a fertilizer. There is apparently an active population of sulphur oxidizing bacteria present in the sewage sludge, which quickly respond to the presence of So. The sewage sludge also provides a carbon and nutrient source for microbial growth. However, there was little difference in the effectiveness of the So and dewatered sewage combined in different ratios when added to soil. Oxidation of so rapidly proceeded after all of the combinations were added to a soil. In comparison, oxidation of So applied without sewage sludge was very slow during incubation in soil. Acidification of the preincubation mixtures appeared to limit So oxidation, and S042- content did not exceed 1%. If a fertilizer product is required that immediately supplies a high concentration of S042-, this problem would need to be overcome. The results of these initial incubation trials are very promising. Combining So with sewage sludge may produce an effective and inexpensive fertilizer for farmers. ACKNOWLEDGEMENTS This project was funded by Imperial Oil-Chemicals Division and the Natural Science and Engineering Research Council (NSERC). 5 REFERENCES Chapman, M. 1989. Oxidation of microionized sulphur in soil. Plant and Soil 116: 69-76. Cifuentes, F.R. and Lindeman, W.C. 1993. Organic matter stimulation of elemental sulfur oxidation in a calcareous soil. Soil Sci. Soc. Am. J. 57: 727-731. Cowell, L.E. and de Jong, E. 1991. Application of Saskatoon's dewatered sewage sludge to agricultural land. Proc. 1991 Soils and Crops Workshop. University of Saskatchewan, Saskatoon. pp. 249-268. Gupta et al. 1988. Impact of elemental sulfur fertilization on agricultural soils. I. Effects on microbial biomass and enzyme activity ... CJSS. 68: 463-473. Janzen, H.H. 1989. Elemental sulfur oxidation as influenced by plant growth and degree of dispersion within soil. Can. J. Soil Sci. 70:499-502. Janzen, H.H. and Bettany, J.R. 1984. Sulfur nutrition of rapeseed: I. Influence of fertilizer nitrogen and sulfur rates. Soil Sci. Soc. Am. J. 48: 100-112. Janzen, H.H. and Bettany, J.R. 1986. Release of available sulfur from fertilizers. Can. J. Soil Sci. 66: 91-103. Janzen, H.H. and Bettany, J.R. 1987. Oxidation of elemental sulfur under field conditions in central Saskatchewan. Can. J. Soil Sci. 67: 609-618. Janzen, H.H. and Bettany, J .R. 1987. The effect of temperature and water potential on sulfur oxidation in soils. Soil Science 144: 81-89. Karamanos, R.E. and Janzen, H.H. 1991. Crop response to elemental sulfur fertilizers in central Alberta. Can. J. Soil Sci. 71: 213-225. Lawrence, J.R., Gupta, V.V.S.R., and Germida, J.J. 1988. Impact of elemental sulfur fertilization on agricultural soils. II. Effects on sulfur-oxidizing populations and oxidation rates. Can. J. Soil Sci. 68: 475-483. Noellemeyer, E.J., Bettany, J.R., and Henry, J.L. 1981. Sources of sulfur for rapeseed. Can. J. Soil Sci. 61: 465-467. Nuttall, W.F., Boswell, C. C., and Swanney, B. 1990. Influence of sulphur fertilizer placement, soil moisture and temperature on yield response of rape to sulphur-bentonite. Fertilizer Research 25: 107-114. Solberg, E.D. and Nyborg, M. 1986. Banding versus incorporation of elemental sulphur fertilizers. 1986 Manitoba Soil Science Meeting. pp. 81-86. · · Solberg, E.D., Laverty. D.H., and Nyborg, M. 1987. Effects of rainfall, wet-dry, and freeze-thaw cycles on the oxidation of elemental sulphur fertilizers. 1987 Alberta Soil Science Workshop. pp. 120-125. Ukrainetz, H. 1982. Oxidation of elemental sulphur fertilizers and response of rapeseed to sulphur on a Grey-Wooded soil. 1982 Alberta Soil Science Workshop. · 6 

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Potential use of combined elemental sulphur and sewage sludge as a fertilizer

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