characterization of insular sewage sludge stabilization
CHARACTERIZATION OF INSULAR SEWAGE SLUDGE STABILIZATION BY LIMING AND THERMAL TREATMENT F. FEDRIZZI1, A.R. FINOTTI**, S.R. SOARES** AND A.R. CABRAL* 1
Postdoctoral fellow at Université de Sherbrooke (Dept. Civil Eng.). Previously with Universidade Federal de Santa Catarina, Florianopolis, Brazil * Department of Civil Engineering, Université de Sherbrooke, Sherbrooke, Quebec J1K 2R1 Canada ** Department of Environmental and Sanitary Engineering, Universidade Federal de Santa Catarina (UFSC), Florianopolis, Brazil
SUMMARY: Sewage sludge production and management are worldwide problems,
mainly in developing countries such as Brazil. The sewage sludge produced at the Insular Wastewater Treatment Plant located in Florianopolis, Brazil, was used in this study. This paper addresses the characterization of stabilized sewage sludge from two different treatment methods, namely liming and thermal stabilization. Results showed that stabilized biosolids could be applied to a limited number of beneficial uses, such as a landfill cover layer or as a light aggregate in very low-risk civil engineering or forestry structures.
1. INTRODUCTION There is a worldwide increase in sewage sludge production, which is increasing interest in the management and use of this particular waste stream. In Brazil, 48.6% of its 200 million inhabitants are connected to a wastewater collection system (IBGE, 2013). However, the actual amount of sewage sludge generated has not been properly assessed. Based on an estimate made between 2000 and 2001, 12 million Brazilians living in an area with wastewater collection and treatment annually generated approximately 151,000 metric tons of sludge as total suspended solids (33 g TSS day-1 per capita) (Leblanc et al., 2008; Machado, 2001). Thus, it can be roughly estimated that 1.2 million metric tons of dry sludge is the annual potential generation for only half of the country’s population. In addition, inadequate disposal of sludge remains a major environmental, economic and social problem for municipal authorities in Brazil. This study was carried out with sludge generated at the Insular Wastewater Treatment Plant (IWTP) located in Florianopolis, the state capital of Santa Catarina, Brazil. The current practice at IWTP is to send sewage sludge to landfills, which is costly and is thus both an environmental and economic concern. There is a need for the development of stabilization strategies that can promote mass reduction, prevention of vector attraction, elimination of organic pollutants and pathogens, as well as the reduction of odor emission, which could be a new sewage sludge management alternative for the city. Given the fact that incineration is not an option in
Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2 - 6 October 2017 S. Margherita di Pula, Cagliari, Italy / © 2017 by CISA Publisher, Italy
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Florianopolis, other alternatives had to be tested. The goal of this study was to characterize stabilized sewage sludge produced by two different treatment methods, namely liming and thermal stabilization. 2. MATERIALS AND METHODS Methods based on lime addition and thermal drying are frequently applied among several other solutions for sewage sludge treatment (Bień and Bień, 2016; Pająk, 2013; Wong and Selvam, 2006). In this study, the liming treatment was applied by mixing sludge and lime in percentages of 15%, 30% and 45% (on a dry weight basis) and storingin a greenhouse for 90 days. The thermal treatment was applied by dehydration of sludge samples in drying beds for 30 days, followed by drying in an oven at 105 °C for 24 hours, and exposure to higher temperatures at 300 oC (2 hours), 550 oC (2 hours) and 700 oC (1 hour). Incineration was not an option. All stabilized sludge samples were milled and sieved in a 2-mm sieve. A flowchart of the stabilization process is shown in Figure 1. Raw Sewage Sludge Liming treatment
Thermal treatment
90 days
Drying bed
30 days
105 °C
15% CaO
30% CaO
45% CaO
L15
L30
L45
24 h
2 mm
300 °C 2h
550 °C 2h
700 °C 2h 2 mm
Biosolids T300
T550
T700
Biosolids
Figure 1. Flowchart of raw sewage sludge treatment by liming and thermal methods. All samples of treated sludge and of raw sewage sludge were characterized by physicochemical and bacteriological parameters. In addition, samples from each type of treatment were analyzed for x-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, as well as leaching and solubilization of several potential pollutants. 3. RESULTS AND DISCUSSION The results presented in Table 1 show that the sludge samples were stabilized after the application of the liming and thermal methods. The wastewater produced in Florianopolis does not receive an industrial load and consequently does not have a high contamination ratio. In terms of bacteriological parameters, helminth eggs remained in the liming samples (L15, L30 and L45). Despite the presence of toxic compounds and pathogen decay or elimination, heavy metal concentrations remained in the samples after the thermal treatment. In addition, the concentrations of some metals increased with the treatment temperature (°C) because of the increased mass loss, while the mass of heavy metals did not change. In general, after the
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
treatment, the samples could be classified as Class A sludge according to local legislation (BRASIL, 2006). In this class, Brazilian legislation allows several beneficial uses, including spreading in agricultural lands. Table 1. Biosolids characterization by biological, chemical and physical parameters.
Parameters pH Total solids content (%) Organic Matter (%) Chemical oxygen demand -1 (mg g ) Total nitrogen (%) Phosphorus (%) Aluminum (%) Calcium (%) Magnesium (%) -1 Iron (mg kg ) -1 Copper (mg kg ) -1 Zinc (mg kg ) -1 Cadmium (mg kg ) -1 Lead (mg kg ) -1 Chrome (mg kg ) Moisture content (%) -3 Density (g cm ) -1 Total coliforms (MPN g TS) -1 Fecal coliforms (MPN g TS) -1 Escherichia coli (MPN g TS) Helminthn eggs(viable -1 eggs g TS)
Sewage Sludge Raw 6.6 12.9 63.2
Liming Treatment L15 9.4 90.1 45.3
L30 9.8 90.4 44.9
626.2
896.7
5.9 2.2 1.1 0.9 0.6 12850.0 204.0 445.5 0.6 22.8 38.4 87.1 0.9
3.1 0.9 0.7 7.9 5.0 7828.0 115.0 454.0 < 0.5 11.4 21.6 9.9 0.7
2.2E+08
1134.2
Thermal Treatment L45 10.0 93.2 32.5
T300 6.7 96.5 64.2
T550 8.6 97.7 52.5
T700 8.8 97.9 52.1
593.0
1493.8
1548.6
1110.1
2.6 0.7 0.5 10.1 5.9 4778.0 81.0 272.0 < 0.5 22.7 15.4 9.6 0.7
2.5 0.5 0.4 13.7 8.1 4168.0 65.0 215.0 < 0.5 7.4 11.2 6.9 0.9
6.7 2.0 1.5 1.2 0.7 12468.0 266.0 742.0 < 0.01 46.6 48.0 3.5 0.7
5. 3.9 3.5 3.2 2.8 3.4 2.0 2.2 1.2 1.3 20798.0 22983.0 452.0 486.4 1283.0 1419.0 1.7 1.2 73.0 75.5 50.2 52.2 2.3 2.1 0.7 0.7
0.0
0.0
0.0
0.0
0.0
0.0
2.2E+08
0.0
0.0
0.0
0.0
0.0
0.0
2.2E+08
0.0
0.0
0.0
0.0
0.0
0.0
0.2
0.3
0.3
0.1
0.0
0.0
0.0
Based on the results above, one sample for each type of treatment was selected (L45 and L300) for a detailed characterization. The L45 sample was selected because it was the only one that reached an adequate level of stabilization following the liming treatment. The T300 sample was selected because incineration at higher temperatures is not possible in Florianopolis. Further analysis of the economic viability was out of the scope of this study. Figure 2 shows a morphological comparison between samples from raw sewage sludge, liming and thermal treatment. The raw sewage sludge sample had a homogeneous and filamentous composition, as well as small particle aggregation (Figure 2A). The biosolids samples, L45 and T300, had an irregular grain distribution and a crystalline phase. The L45 micrograph shows small particles, needle-shaped crystals and typical formations of hydrated compounds (e.g., CaO) (Figure 1B), whose presence normally leads to the formation of
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
particles with a crystalline phase (Cyr et al., 2007). The T300 micrograph shows irregular grains, some in a honeycomb format, and needle-shaped crystals (Figure 2C). The general characteristics of thermal biosolids (e.g., sewage sludge ash – SSA) have been reported in the literature and show that elements have a crystalline phase (Cyr et al., 2007; Monzó et al., 2003) and variable morphology (Taylor, 1990).
Figure 2. Scanning electron micrographs of samples from A) raw sewage sludge, B) liming treatment (45%) and C) thermal treatment (300 oC). The results from dispersive energy spectroscopy and x-ray diffraction analysis of the liming and thermal samples are shown in Figures 3 and 4, respectively. For both samples (L45 and T300), the main chemical elements were organic elements (C, O, N e P) and some minerals (Si, Fe, Al, Ca, K, Mg and Na) (Figure 3). In terms of the mineral content, L45 contained calcite (CaCO3), brucite (Mg(OH)2), quartz (SiO2), vaterite (CaCO3) and dolomite (CaMg(CO3)2) (Figure 4A), while T300 contained quartz (SiO2), dolomite (CaMg(CO3)2), rutile (TiO2) and kaolinite (Al2Si2O5(OH)4) (Figure 4B). The main crystalline phases were quartz (SiO2), calcium phosphate (Ca3(PO4)2) and haematite (Fe2O3) (Donatello et al., 2010; Vouk et al., 2017). The presence of a crystalline phase prevents using biosolids in some civil construction projects because of its low strength (Cyr et al., 2007; Monzó et al., 2003; Vouk et al., 2017).
Figure 3. SEM/EDS (dispersive energy spectroscopy) results of biosolids from (A) liming and (B) low temperature thermal treatment methods.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Figure 3. X-ray diffraction (XRD) patterns of samples from (A) liming and (B) thermal treatment methods. The leaching analysis are presented in Tables 2 and 3 by comparing the raw sewage sludge and biosolids samples. The leachate extract from the raw sewage sludge shows a high contaminants content, mainly pathogens. In contrast, the L45 and T300 leachate extracts were below the limits established by local Brazilian legislation (ABNT, 2004). These results demonstrate that liming and thermal treatment methods were efficient in the sewage sludge stabilization. Table 2. Leached elements from L45 and T300 biosolids – Bacteriological parameters Parameters Thermotolerant coliform (MPN 100 mL-1) Total coliform (MPN 100 mL-1) Escherichia coli (MPN 100 mL-1) Fecal streptococci (MPN 100 mL-1) Helminth eggs (viable eggs g-1 TS) Protozoa (cysts g-1 ST) (Entamoeba Coli)
Raw sewage sludge 1300000 1300000 present present 0.04 0.02
L45
T300
< 1.8 < 1.8 < 2.0 0.0 0.004
< 1.8 < 1.8 < 2.0 0.0 absent
0.005
absent
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Table 3. Leached elements from L45 and T300 biosolids – Physicochemical parameters Parameters
Raw sewage sludge -1
Arsenic content (µg L ) Barium content (mg L-1) Cadmium content (mg L-1) Lead content (mg L-1) Chromium content (mg L-1) Mercury content (µg L-1) Selenium content (µg L-1) Fluoride content (mg L-1) Silver content (mg L-1)
< 1.5 < 0.5 < 0.001 0.074 0.047 < 0.05
Postdoctoral fellow at Université de Sherbrooke (Dept. Civil Eng.). Previously with Universidade Federal de Santa Catarina, Florianopolis, Brazil * Department of Civil Engineering, Université de Sherbrooke, Sherbrooke, Quebec J1K 2R1 Canada ** Department of Environmental and Sanitary Engineering, Universidade Federal de Santa Catarina (UFSC), Florianopolis, Brazil
SUMMARY: Sewage sludge production and management are worldwide problems,
mainly in developing countries such as Brazil. The sewage sludge produced at the Insular Wastewater Treatment Plant located in Florianopolis, Brazil, was used in this study. This paper addresses the characterization of stabilized sewage sludge from two different treatment methods, namely liming and thermal stabilization. Results showed that stabilized biosolids could be applied to a limited number of beneficial uses, such as a landfill cover layer or as a light aggregate in very low-risk civil engineering or forestry structures.
1. INTRODUCTION There is a worldwide increase in sewage sludge production, which is increasing interest in the management and use of this particular waste stream. In Brazil, 48.6% of its 200 million inhabitants are connected to a wastewater collection system (IBGE, 2013). However, the actual amount of sewage sludge generated has not been properly assessed. Based on an estimate made between 2000 and 2001, 12 million Brazilians living in an area with wastewater collection and treatment annually generated approximately 151,000 metric tons of sludge as total suspended solids (33 g TSS day-1 per capita) (Leblanc et al., 2008; Machado, 2001). Thus, it can be roughly estimated that 1.2 million metric tons of dry sludge is the annual potential generation for only half of the country’s population. In addition, inadequate disposal of sludge remains a major environmental, economic and social problem for municipal authorities in Brazil. This study was carried out with sludge generated at the Insular Wastewater Treatment Plant (IWTP) located in Florianopolis, the state capital of Santa Catarina, Brazil. The current practice at IWTP is to send sewage sludge to landfills, which is costly and is thus both an environmental and economic concern. There is a need for the development of stabilization strategies that can promote mass reduction, prevention of vector attraction, elimination of organic pollutants and pathogens, as well as the reduction of odor emission, which could be a new sewage sludge management alternative for the city. Given the fact that incineration is not an option in
Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2 - 6 October 2017 S. Margherita di Pula, Cagliari, Italy / © 2017 by CISA Publisher, Italy
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Florianopolis, other alternatives had to be tested. The goal of this study was to characterize stabilized sewage sludge produced by two different treatment methods, namely liming and thermal stabilization. 2. MATERIALS AND METHODS Methods based on lime addition and thermal drying are frequently applied among several other solutions for sewage sludge treatment (Bień and Bień, 2016; Pająk, 2013; Wong and Selvam, 2006). In this study, the liming treatment was applied by mixing sludge and lime in percentages of 15%, 30% and 45% (on a dry weight basis) and storingin a greenhouse for 90 days. The thermal treatment was applied by dehydration of sludge samples in drying beds for 30 days, followed by drying in an oven at 105 °C for 24 hours, and exposure to higher temperatures at 300 oC (2 hours), 550 oC (2 hours) and 700 oC (1 hour). Incineration was not an option. All stabilized sludge samples were milled and sieved in a 2-mm sieve. A flowchart of the stabilization process is shown in Figure 1. Raw Sewage Sludge Liming treatment
Thermal treatment
90 days
Drying bed
30 days
105 °C
15% CaO
30% CaO
45% CaO
L15
L30
L45
24 h
2 mm
300 °C 2h
550 °C 2h
700 °C 2h 2 mm
Biosolids T300
T550
T700
Biosolids
Figure 1. Flowchart of raw sewage sludge treatment by liming and thermal methods. All samples of treated sludge and of raw sewage sludge were characterized by physicochemical and bacteriological parameters. In addition, samples from each type of treatment were analyzed for x-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, as well as leaching and solubilization of several potential pollutants. 3. RESULTS AND DISCUSSION The results presented in Table 1 show that the sludge samples were stabilized after the application of the liming and thermal methods. The wastewater produced in Florianopolis does not receive an industrial load and consequently does not have a high contamination ratio. In terms of bacteriological parameters, helminth eggs remained in the liming samples (L15, L30 and L45). Despite the presence of toxic compounds and pathogen decay or elimination, heavy metal concentrations remained in the samples after the thermal treatment. In addition, the concentrations of some metals increased with the treatment temperature (°C) because of the increased mass loss, while the mass of heavy metals did not change. In general, after the
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
treatment, the samples could be classified as Class A sludge according to local legislation (BRASIL, 2006). In this class, Brazilian legislation allows several beneficial uses, including spreading in agricultural lands. Table 1. Biosolids characterization by biological, chemical and physical parameters.
Parameters pH Total solids content (%) Organic Matter (%) Chemical oxygen demand -1 (mg g ) Total nitrogen (%) Phosphorus (%) Aluminum (%) Calcium (%) Magnesium (%) -1 Iron (mg kg ) -1 Copper (mg kg ) -1 Zinc (mg kg ) -1 Cadmium (mg kg ) -1 Lead (mg kg ) -1 Chrome (mg kg ) Moisture content (%) -3 Density (g cm ) -1 Total coliforms (MPN g TS) -1 Fecal coliforms (MPN g TS) -1 Escherichia coli (MPN g TS) Helminthn eggs(viable -1 eggs g TS)
Sewage Sludge Raw 6.6 12.9 63.2
Liming Treatment L15 9.4 90.1 45.3
L30 9.8 90.4 44.9
626.2
896.7
5.9 2.2 1.1 0.9 0.6 12850.0 204.0 445.5 0.6 22.8 38.4 87.1 0.9
3.1 0.9 0.7 7.9 5.0 7828.0 115.0 454.0 < 0.5 11.4 21.6 9.9 0.7
2.2E+08
1134.2
Thermal Treatment L45 10.0 93.2 32.5
T300 6.7 96.5 64.2
T550 8.6 97.7 52.5
T700 8.8 97.9 52.1
593.0
1493.8
1548.6
1110.1
2.6 0.7 0.5 10.1 5.9 4778.0 81.0 272.0 < 0.5 22.7 15.4 9.6 0.7
2.5 0.5 0.4 13.7 8.1 4168.0 65.0 215.0 < 0.5 7.4 11.2 6.9 0.9
6.7 2.0 1.5 1.2 0.7 12468.0 266.0 742.0 < 0.01 46.6 48.0 3.5 0.7
5. 3.9 3.5 3.2 2.8 3.4 2.0 2.2 1.2 1.3 20798.0 22983.0 452.0 486.4 1283.0 1419.0 1.7 1.2 73.0 75.5 50.2 52.2 2.3 2.1 0.7 0.7
0.0
0.0
0.0
0.0
0.0
0.0
2.2E+08
0.0
0.0
0.0
0.0
0.0
0.0
2.2E+08
0.0
0.0
0.0
0.0
0.0
0.0
0.2
0.3
0.3
0.1
0.0
0.0
0.0
Based on the results above, one sample for each type of treatment was selected (L45 and L300) for a detailed characterization. The L45 sample was selected because it was the only one that reached an adequate level of stabilization following the liming treatment. The T300 sample was selected because incineration at higher temperatures is not possible in Florianopolis. Further analysis of the economic viability was out of the scope of this study. Figure 2 shows a morphological comparison between samples from raw sewage sludge, liming and thermal treatment. The raw sewage sludge sample had a homogeneous and filamentous composition, as well as small particle aggregation (Figure 2A). The biosolids samples, L45 and T300, had an irregular grain distribution and a crystalline phase. The L45 micrograph shows small particles, needle-shaped crystals and typical formations of hydrated compounds (e.g., CaO) (Figure 1B), whose presence normally leads to the formation of
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
particles with a crystalline phase (Cyr et al., 2007). The T300 micrograph shows irregular grains, some in a honeycomb format, and needle-shaped crystals (Figure 2C). The general characteristics of thermal biosolids (e.g., sewage sludge ash – SSA) have been reported in the literature and show that elements have a crystalline phase (Cyr et al., 2007; Monzó et al., 2003) and variable morphology (Taylor, 1990).
Figure 2. Scanning electron micrographs of samples from A) raw sewage sludge, B) liming treatment (45%) and C) thermal treatment (300 oC). The results from dispersive energy spectroscopy and x-ray diffraction analysis of the liming and thermal samples are shown in Figures 3 and 4, respectively. For both samples (L45 and T300), the main chemical elements were organic elements (C, O, N e P) and some minerals (Si, Fe, Al, Ca, K, Mg and Na) (Figure 3). In terms of the mineral content, L45 contained calcite (CaCO3), brucite (Mg(OH)2), quartz (SiO2), vaterite (CaCO3) and dolomite (CaMg(CO3)2) (Figure 4A), while T300 contained quartz (SiO2), dolomite (CaMg(CO3)2), rutile (TiO2) and kaolinite (Al2Si2O5(OH)4) (Figure 4B). The main crystalline phases were quartz (SiO2), calcium phosphate (Ca3(PO4)2) and haematite (Fe2O3) (Donatello et al., 2010; Vouk et al., 2017). The presence of a crystalline phase prevents using biosolids in some civil construction projects because of its low strength (Cyr et al., 2007; Monzó et al., 2003; Vouk et al., 2017).
Figure 3. SEM/EDS (dispersive energy spectroscopy) results of biosolids from (A) liming and (B) low temperature thermal treatment methods.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Figure 3. X-ray diffraction (XRD) patterns of samples from (A) liming and (B) thermal treatment methods. The leaching analysis are presented in Tables 2 and 3 by comparing the raw sewage sludge and biosolids samples. The leachate extract from the raw sewage sludge shows a high contaminants content, mainly pathogens. In contrast, the L45 and T300 leachate extracts were below the limits established by local Brazilian legislation (ABNT, 2004). These results demonstrate that liming and thermal treatment methods were efficient in the sewage sludge stabilization. Table 2. Leached elements from L45 and T300 biosolids – Bacteriological parameters Parameters Thermotolerant coliform (MPN 100 mL-1) Total coliform (MPN 100 mL-1) Escherichia coli (MPN 100 mL-1) Fecal streptococci (MPN 100 mL-1) Helminth eggs (viable eggs g-1 TS) Protozoa (cysts g-1 ST) (Entamoeba Coli)
Raw sewage sludge 1300000 1300000 present present 0.04 0.02
L45
T300
< 1.8 < 1.8 < 2.0 0.0 0.004
< 1.8 < 1.8 < 2.0 0.0 absent
0.005
absent
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Table 3. Leached elements from L45 and T300 biosolids – Physicochemical parameters Parameters
Raw sewage sludge -1
Arsenic content (µg L ) Barium content (mg L-1) Cadmium content (mg L-1) Lead content (mg L-1) Chromium content (mg L-1) Mercury content (µg L-1) Selenium content (µg L-1) Fluoride content (mg L-1) Silver content (mg L-1)
< 1.5 < 0.5 < 0.001 0.074 0.047 < 0.05
