1638
© IWA Publishing 2015 Water Science & Technology
|
71.11
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2015
Manufacturing ceramic bricks with polyaluminum chloride (PAC) sludge from a water treatment plant E. M. da Silva, D. M. Morita, A. C. M. Lima and L. Girard Teixeira
ABSTRACT The objective of this research work is to assess the viability of manufacturing ceramic bricks with sludge from a water treatment plant (WTP) for use in real-world applications. Sludge was collected from settling tanks at the Bolonha WTP, which is located in Belém, capital of the state of Pará, Brazil. After dewatering in drainage beds, sludge was added to the clay at a local brickworks at different mass percentages (7.6, 9.0, 11.7, 13.9 and 23.5%). Laboratory tests were performed on the bricks to assess their resistance to compression, water absorption, dimensions and visual aspects. Percentages of 7.6, 9.0, 11.7 and 13.9% (w/w) of WTP sludge presented good results in terms of resistance, which indicates that technically, ceramic bricks can be produced by incorporating up to 13.9% of WTP sludge. Key words
| ceramic bricks, clay-sludge mixtures, WTP sludge
E. M. da Silva Science and Technology Center of the Universidade do Estado do Pará (UEPA), Tv. Enéas Pinheiro, 2626, Belém, Pará, Brazil D. M. Morita Hydraulic and Environmental Engineering Department of Escola Politécnica of the Universidade de São Paulo (EPUSP), São Paulo, Brazil A. C. M. Lima Engineering Department of the Universidade do Estado do Pará (UEPA), Tv. Enéas Pinheiro, 2626, Belém, Pará, Brazil L. Girard Teixeira (corresponding author) Institute of Technology of the Universidade Federal do Pará (UFPA), Rua Augusto Corrêa, 01 - Guamá. CEP 66075-110. Caixa postal 479, Belém, Pará, Brazil E-mail: [email protected]
INTRODUCTION Most of the water treatment plant (WTP) residuals generated in developing countries are: (i) discharged directly into water bodies, which is not reported due to the scarcity of water sources, siltation of water bodies, water quality deterioration and adverse impacts on aquatic biota (Zhao & Babatunde ); (ii) disposed in landfills, which is an expensive method that requires large areas and can contaminate the soil and groundwater if not well operated; or (iii) discharged into publicly owned treatment works (POTW), which can cause operational problems if the POTW was not designed for this purpose and also transfers the sludge disposal problem from the WTP to the wastewater treatment plant. Today, the principle of industrial ecology (Korevaar ) has emerged; sludge should not be considered rejected material but raw material that can be used in productive processes. Furthermore, ever stringent environmental legislation and rising logistical costs have brought into focus the beneficial uses of WTP sludge (US Environmental Protection Agency ). There are several benefits of using WTP sludge in the civil construction industry, such as: eliminating discharges to surface water or POTWs; reducing or eliminating disposal doi: 10.2166/wst.2015.132
to landfill (American Water Works Association/American Society of Civil Engineers/US Environmental Protection Agency ; Lu et al. ); reducing sludge disposal costs; reducing environmental impact of clay mining because the sludge is a substitute for clay; and creating opportunities for sanitation companies and brick industries in the global market, which encourages sustainable growth across all industry sectors, including partnerships between businesses (green economy, industrial symbiosis, etc.). A study by Cantó et al. () was performed at the Saint Joan Despí WTP in Barcelona, Spain. To use WTP sludge to make ceramic bricks, an experimental plant was built, which used heat to dry the sludge and break it down into powder. The material consisted of silicon dioxide (SiO2, 50%), aluminum oxide (Al2O3, 13%), calcium oxide (CaO, 14%), potassium oxide (K2O, 3%) and organic matter (10%). By mixing 70% of the powder produced with 30% clay, the ceramic material obtained was porous and could be used for acoustic and thermal insulation. Rouf & Hossain () demonstrated the viability of using sludge rich in arsenic and iron as a substitute for
1639
E. M. da Silva et al.
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Ceramic bricks with sludge from water treatment plant
clay to manufacture bricks. Different mixtures of clay-sludge were tested, and experiments were performed with clay to evaluate how sludge changes the quality of the brick. The tests showed that the leachate from the sludge had a higher arsenic concentration than the leachate from the brick that had already been burned. The compression tests demonstrated that resistance depended on the quantity of sludge in the brick and, also the burn temperature. Bricks of good quality were also obtained by adding 15% (w/w) of sludge to clay and burning at 1,000 C. The resistance to compression of all of the bricks attained the technical standards for ceramic material used in Bangladesh. Large quantities of sludge in the mixture led to less plastic behavior of the mass. The authors reported that to produce good quality blocks, additions of 15–25% (w/w) sludge in the ceramic paste were appropriate. Recent studies have also suggested the feasibility of using WTP sludge for ceramic production (Cornwell & Roth ; Tartari et al. ; Kizinievič et al. ; Huang & Wang ). In Brazil, several studies have been performed on the laboratory scale and concluded that WTP sludge has mineralogical characteristics similar to that of clay, reduces resistance to bending and increases water absorption and porosity in samples burned at 900–950 C, and that samples with 10% sludge (m/m) burned at 900 C satisfy the values specified by Brazilian standards for red brick materials (Cosin et al. ; Magalhães ; Mothé et al. ; Teixeira et al. ). However, demonstrations in real-world applications have been limited. Thus, the goal of this study was to evaluate the technical viability of using sludge from the Bolonha WTP located in the metropolitan region of Belém, Pará in the local brickworks. W
W
W
MATERIALS AND METHODS The Bolonha WTP, which supplies 65% of the metropolitan region of Belém-Pará-Brazil, contains the Água Preta and Bolonha lakes as its main water sources. The Bolonha WTP operates with a flow of 4 m3 s1 and has a complete treatment cycle, which consists of a Parshall flume, six turbine-type flocculators, six horizontal-flow settling tanks with manual sludge removal, eight rapid dual-media filters and a disinfection unit with gaseous chlorine. The sludge and filter backwashing water are discharged directly into the creek that flows into the Guamá River. Because the WTP does not have a sludge treatment system, to achieve the primary objective of this work, two sludge dewatering units (SDUs) were set up in areas near
Water Science & Technology
|
71.11
|
2015
the Bolonha WTP settling tanks. The drainage beds were made of fiberglass water tanks equipped with a 5-cm layer of crushed stone (size 1), which was covered by a geotextile fabric. The period for monitoring the drainage bed in SDU1 was approximately 23 days and 15 days for SDU2 because the latter was more concentrated. The sludge batches collected after the dewatering phase were transported to the selected brick manufacturing plant. Test procedures for characterizing the sludge and clay followed ABNT standards (Brazilian Association of Technical Standards): NBR 6508/1984 – Determination of soil density (Brazil a); NBR 6457/1986 – Determination of soil moisture (Brazil ); NBR 7181/1984 – Granulometric Analysis (Brazil b). Total organic carbon was determined using the Brazilian Enterprise of Agricultural Research methods (Embrapa ). The X-ray diffraction test consisted of drying the sludge in an oven, which was then passed through a 100 mesh US standard sieve screen; afterward, the powder sample was placed on glass plates. Next, the X-ray machine was turned on over the sample, and a diffractogram was obtained with a Geiger counter. Indexing of the basal peaks in the diffractograms obtained from the prepared materials was performed by comparing them with the standard in the database from the Philips program (X-pert High Score) using the JCPDS-ICDD diffractometric patterns. Scanning electron microscopy (SEM) was performed using Zeiss model LEO-1430 equipment (Zeiss, Oberkochen, Germany). The following were the conditions for analyzing images of the secondary electrons: electron beam current of 90 μA, constant acceleration voltage of 10 kV and working distance of 12–15 mm. The samples were metalized with a gold and platinum alloy. The clay used in preparing the ceramic bricks was from the brickmaking industry; it comprised lean and fat types and was taken from a nearby deposit. At the brickworks, the clay was mixed manually at a ratio of 8:2 of lean to fat clay, respectively. Before mixing the clay with the sludge, sludge samples and ceramic paste were collected to determine the moisture level due to the loss of moisture in the sludge over time. The following percentages of sludge/clay were evaluated: 10, 12 and 20% (v/v). These were established according to Morita et al. (), Magalhães (), Dias et al. () and Novaes (). Before beginning the production of ceramic bricks, the clay was separated and left at a site near to the sludge. Using a shovel, an operator alternately placed the appropriate quantities of sludge and clay mass. The control (brick without sludge) was also prepared.
1640
E. M. da Silva et al.
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Ceramic bricks with sludge from water treatment plant
With the sludge from SDU1, sludge: clay percentages of 7.6 and 9.0% (w/w) were evaluated, and with the sludge from SDU2, 11.7, 13.9 and 23.5% (w/w) were evaluated. The mixtures were first homogenized and then extruded; the bricks were then naturally dried for a period of 7 days and later burned at 500 C for 48 hours. After this stage, the bricks remained in the kiln for 24 hours to cool. Finally, the manufactured bricks were stored in a covered area at the brickworks. According to standard NBR 15270-1 (Brazil a), for a batch of 30 thousand bricks, inspection by direct measurement should be performed by double sampling on 13 bricks. Because the number of bricks produced with the sludge in SDU1 was less than 100, it was decided that at least 11 bricks should be inspected by direct measurement: 6–7 bricks to check the resistance to compression and 5–6 bricks for the water absorption tests. The tests were performed according to NBR 15.270-3 standard (Brazil b). W
RESULTS AND DISCUSSION Total solids obtained for the sludge were 27.9% in SDU1 and 23.4% in SDU2 after dewatering periods of 23 and 15 days, respectively. This result demonstrates the effective drying capacity of the drainage bed, which differs from conventional sand-bed drying due to the lack of a sand layer and the existence of the geotextile fabric coverage. Similar results were obtained by Achon et al. (), which concluded that this type of drainage bed does not suffer from the action of rainfall because the water does not incorporate to the sludge mass. In addition, they can be reused repeatedly after geotextile fabric surface cleaning. According to Cornwell et al. (), the application of sludge in the clay pit is better than application in the brickworks, because it does not require the operator’s attention and the use of equipment in addition to that commonly employed in mining. In this work, the addition of sludge in the brickworks did not represent an impediment to its use in the manufacture of the bricks. In developing countries, it is common practice for small producers of bricks to buy clay because they do not have their own clay pit. So, the use of sludge represents cost savings for them. Total organic carbon was 4.04% in SDU1, 4.23% in SDU2, 1.08% for fat clay and 1.09% for lean clay. The water content of the samples from the Bolonha WTP sludge, lean and fat clays and the ceramic paste at the beginning of the process were 72.1%, 14.4%, 23.9% and 32.2%, respectively, for SDU1. For SDU2, these values were 76.6%,
Water Science & Technology
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71.11
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2015
15.2%, 24.6% and 33.5%, respectively. The difference of 4.4% in the water content of the sludge may be attributed to the test period for dewatering the sludge in SDU1, which was longer (23 days) than that of SDU2 (15 days). Most ceramic industries add 2% of charcoal (w/w) and water to the ceramic paste at the beginning of the brick manufacturing process. The first material has the objective of facilitating the burning of bricks in the furnace and the water improves the mixing of clay and reduces the extrusion pressure. In this study, because of the characteristics of the sludge, it was not necessary to add water or charcoal into the ceramic paste, which represents cost savings for industry. The results obtained for granulometry by sedimentation and specific mass of the sludge samples from SDU1 and SDU2, lean and fat clays and ceramic paste are presented in Table 1. The sludge exhibits granulometric characteristics that are predominantly similar to those of a colloidal clay with a strong tendency to behave as a plastic material that is similar to fat-type clay. These characteristics indicate that the sludge is rich in clay minerals with a slight amount of silt and an absence of sand but with a high level of organic material, which is typical for the Amazon region (Quesada et al. ). Lean clay has characteristics of clayey silt. However, it should be noted that this clay had already been at the brickworks for a period of approximately 6 months due to the need of the brickmaker to stockpile raw material. Fat clay behaves like silty clay soil, with the presence of predominantly fine particles, and is thus highly recommended for use in the ceramic industry. The granulometric composition of the ceramic paste at a ratio of 8:2 for the lean and fat clays was 45.00 ± 4.24% for
Table 1
|
Granulometry and specific mass found in sludge samples from Bolonha WTP, lean clay, fat clay and ceramic paste
Granulometry by sedimentation (%) Sample
Silt (%)
Clay (%)
Specific mass g cm3
SDU1
8
92
2.182
SDU2
4
96
2.349
Lean clay 1
55
46
2.203
Lean clay 2
59
41
2.205
Fat clay 1
37
63
2.650
Fat clay 2
39
61
2.651
Ceramic paste 1
48
52
2.616
Ceramic paste 2
42
58
2.617
1641
E. M. da Silva et al.
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Ceramic bricks with sludge from water treatment plant
clay and 55.00 ± 4.24% for silt with a specific mass of 2.62 ± 0.71 g cm3. The values indicate that there is an absence of a sand fraction in the ceramic paste composition for the Amazon region. The absence of sand in the ceramic paste contributed positively to the mechanical resistance of the ceramic bricks (Teixeira et al. ). Furthermore, its composition is acceptable according to the ideal range proposed in the ‘Winkler Diagram’ (Winkler ). The level of clayey components (φ < 2 μm) is at the upper limit of this range as is the level of deplastifiers. These results confirm the good quality of clay from the Amazon region for the manufacture of ceramic bricks. The images obtained from SEM (Figure 1(a) and 1(b)) show that the sludge samples present micrometric dimensions (
© IWA Publishing 2015 Water Science & Technology
|
71.11
|
2015
Manufacturing ceramic bricks with polyaluminum chloride (PAC) sludge from a water treatment plant E. M. da Silva, D. M. Morita, A. C. M. Lima and L. Girard Teixeira
ABSTRACT The objective of this research work is to assess the viability of manufacturing ceramic bricks with sludge from a water treatment plant (WTP) for use in real-world applications. Sludge was collected from settling tanks at the Bolonha WTP, which is located in Belém, capital of the state of Pará, Brazil. After dewatering in drainage beds, sludge was added to the clay at a local brickworks at different mass percentages (7.6, 9.0, 11.7, 13.9 and 23.5%). Laboratory tests were performed on the bricks to assess their resistance to compression, water absorption, dimensions and visual aspects. Percentages of 7.6, 9.0, 11.7 and 13.9% (w/w) of WTP sludge presented good results in terms of resistance, which indicates that technically, ceramic bricks can be produced by incorporating up to 13.9% of WTP sludge. Key words
| ceramic bricks, clay-sludge mixtures, WTP sludge
E. M. da Silva Science and Technology Center of the Universidade do Estado do Pará (UEPA), Tv. Enéas Pinheiro, 2626, Belém, Pará, Brazil D. M. Morita Hydraulic and Environmental Engineering Department of Escola Politécnica of the Universidade de São Paulo (EPUSP), São Paulo, Brazil A. C. M. Lima Engineering Department of the Universidade do Estado do Pará (UEPA), Tv. Enéas Pinheiro, 2626, Belém, Pará, Brazil L. Girard Teixeira (corresponding author) Institute of Technology of the Universidade Federal do Pará (UFPA), Rua Augusto Corrêa, 01 - Guamá. CEP 66075-110. Caixa postal 479, Belém, Pará, Brazil E-mail: [email protected]
INTRODUCTION Most of the water treatment plant (WTP) residuals generated in developing countries are: (i) discharged directly into water bodies, which is not reported due to the scarcity of water sources, siltation of water bodies, water quality deterioration and adverse impacts on aquatic biota (Zhao & Babatunde ); (ii) disposed in landfills, which is an expensive method that requires large areas and can contaminate the soil and groundwater if not well operated; or (iii) discharged into publicly owned treatment works (POTW), which can cause operational problems if the POTW was not designed for this purpose and also transfers the sludge disposal problem from the WTP to the wastewater treatment plant. Today, the principle of industrial ecology (Korevaar ) has emerged; sludge should not be considered rejected material but raw material that can be used in productive processes. Furthermore, ever stringent environmental legislation and rising logistical costs have brought into focus the beneficial uses of WTP sludge (US Environmental Protection Agency ). There are several benefits of using WTP sludge in the civil construction industry, such as: eliminating discharges to surface water or POTWs; reducing or eliminating disposal doi: 10.2166/wst.2015.132
to landfill (American Water Works Association/American Society of Civil Engineers/US Environmental Protection Agency ; Lu et al. ); reducing sludge disposal costs; reducing environmental impact of clay mining because the sludge is a substitute for clay; and creating opportunities for sanitation companies and brick industries in the global market, which encourages sustainable growth across all industry sectors, including partnerships between businesses (green economy, industrial symbiosis, etc.). A study by Cantó et al. () was performed at the Saint Joan Despí WTP in Barcelona, Spain. To use WTP sludge to make ceramic bricks, an experimental plant was built, which used heat to dry the sludge and break it down into powder. The material consisted of silicon dioxide (SiO2, 50%), aluminum oxide (Al2O3, 13%), calcium oxide (CaO, 14%), potassium oxide (K2O, 3%) and organic matter (10%). By mixing 70% of the powder produced with 30% clay, the ceramic material obtained was porous and could be used for acoustic and thermal insulation. Rouf & Hossain () demonstrated the viability of using sludge rich in arsenic and iron as a substitute for
1639
E. M. da Silva et al.
|
Ceramic bricks with sludge from water treatment plant
clay to manufacture bricks. Different mixtures of clay-sludge were tested, and experiments were performed with clay to evaluate how sludge changes the quality of the brick. The tests showed that the leachate from the sludge had a higher arsenic concentration than the leachate from the brick that had already been burned. The compression tests demonstrated that resistance depended on the quantity of sludge in the brick and, also the burn temperature. Bricks of good quality were also obtained by adding 15% (w/w) of sludge to clay and burning at 1,000 C. The resistance to compression of all of the bricks attained the technical standards for ceramic material used in Bangladesh. Large quantities of sludge in the mixture led to less plastic behavior of the mass. The authors reported that to produce good quality blocks, additions of 15–25% (w/w) sludge in the ceramic paste were appropriate. Recent studies have also suggested the feasibility of using WTP sludge for ceramic production (Cornwell & Roth ; Tartari et al. ; Kizinievič et al. ; Huang & Wang ). In Brazil, several studies have been performed on the laboratory scale and concluded that WTP sludge has mineralogical characteristics similar to that of clay, reduces resistance to bending and increases water absorption and porosity in samples burned at 900–950 C, and that samples with 10% sludge (m/m) burned at 900 C satisfy the values specified by Brazilian standards for red brick materials (Cosin et al. ; Magalhães ; Mothé et al. ; Teixeira et al. ). However, demonstrations in real-world applications have been limited. Thus, the goal of this study was to evaluate the technical viability of using sludge from the Bolonha WTP located in the metropolitan region of Belém, Pará in the local brickworks. W
W
W
MATERIALS AND METHODS The Bolonha WTP, which supplies 65% of the metropolitan region of Belém-Pará-Brazil, contains the Água Preta and Bolonha lakes as its main water sources. The Bolonha WTP operates with a flow of 4 m3 s1 and has a complete treatment cycle, which consists of a Parshall flume, six turbine-type flocculators, six horizontal-flow settling tanks with manual sludge removal, eight rapid dual-media filters and a disinfection unit with gaseous chlorine. The sludge and filter backwashing water are discharged directly into the creek that flows into the Guamá River. Because the WTP does not have a sludge treatment system, to achieve the primary objective of this work, two sludge dewatering units (SDUs) were set up in areas near
Water Science & Technology
|
71.11
|
2015
the Bolonha WTP settling tanks. The drainage beds were made of fiberglass water tanks equipped with a 5-cm layer of crushed stone (size 1), which was covered by a geotextile fabric. The period for monitoring the drainage bed in SDU1 was approximately 23 days and 15 days for SDU2 because the latter was more concentrated. The sludge batches collected after the dewatering phase were transported to the selected brick manufacturing plant. Test procedures for characterizing the sludge and clay followed ABNT standards (Brazilian Association of Technical Standards): NBR 6508/1984 – Determination of soil density (Brazil a); NBR 6457/1986 – Determination of soil moisture (Brazil ); NBR 7181/1984 – Granulometric Analysis (Brazil b). Total organic carbon was determined using the Brazilian Enterprise of Agricultural Research methods (Embrapa ). The X-ray diffraction test consisted of drying the sludge in an oven, which was then passed through a 100 mesh US standard sieve screen; afterward, the powder sample was placed on glass plates. Next, the X-ray machine was turned on over the sample, and a diffractogram was obtained with a Geiger counter. Indexing of the basal peaks in the diffractograms obtained from the prepared materials was performed by comparing them with the standard in the database from the Philips program (X-pert High Score) using the JCPDS-ICDD diffractometric patterns. Scanning electron microscopy (SEM) was performed using Zeiss model LEO-1430 equipment (Zeiss, Oberkochen, Germany). The following were the conditions for analyzing images of the secondary electrons: electron beam current of 90 μA, constant acceleration voltage of 10 kV and working distance of 12–15 mm. The samples were metalized with a gold and platinum alloy. The clay used in preparing the ceramic bricks was from the brickmaking industry; it comprised lean and fat types and was taken from a nearby deposit. At the brickworks, the clay was mixed manually at a ratio of 8:2 of lean to fat clay, respectively. Before mixing the clay with the sludge, sludge samples and ceramic paste were collected to determine the moisture level due to the loss of moisture in the sludge over time. The following percentages of sludge/clay were evaluated: 10, 12 and 20% (v/v). These were established according to Morita et al. (), Magalhães (), Dias et al. () and Novaes (). Before beginning the production of ceramic bricks, the clay was separated and left at a site near to the sludge. Using a shovel, an operator alternately placed the appropriate quantities of sludge and clay mass. The control (brick without sludge) was also prepared.
1640
E. M. da Silva et al.
|
Ceramic bricks with sludge from water treatment plant
With the sludge from SDU1, sludge: clay percentages of 7.6 and 9.0% (w/w) were evaluated, and with the sludge from SDU2, 11.7, 13.9 and 23.5% (w/w) were evaluated. The mixtures were first homogenized and then extruded; the bricks were then naturally dried for a period of 7 days and later burned at 500 C for 48 hours. After this stage, the bricks remained in the kiln for 24 hours to cool. Finally, the manufactured bricks were stored in a covered area at the brickworks. According to standard NBR 15270-1 (Brazil a), for a batch of 30 thousand bricks, inspection by direct measurement should be performed by double sampling on 13 bricks. Because the number of bricks produced with the sludge in SDU1 was less than 100, it was decided that at least 11 bricks should be inspected by direct measurement: 6–7 bricks to check the resistance to compression and 5–6 bricks for the water absorption tests. The tests were performed according to NBR 15.270-3 standard (Brazil b). W
RESULTS AND DISCUSSION Total solids obtained for the sludge were 27.9% in SDU1 and 23.4% in SDU2 after dewatering periods of 23 and 15 days, respectively. This result demonstrates the effective drying capacity of the drainage bed, which differs from conventional sand-bed drying due to the lack of a sand layer and the existence of the geotextile fabric coverage. Similar results were obtained by Achon et al. (), which concluded that this type of drainage bed does not suffer from the action of rainfall because the water does not incorporate to the sludge mass. In addition, they can be reused repeatedly after geotextile fabric surface cleaning. According to Cornwell et al. (), the application of sludge in the clay pit is better than application in the brickworks, because it does not require the operator’s attention and the use of equipment in addition to that commonly employed in mining. In this work, the addition of sludge in the brickworks did not represent an impediment to its use in the manufacture of the bricks. In developing countries, it is common practice for small producers of bricks to buy clay because they do not have their own clay pit. So, the use of sludge represents cost savings for them. Total organic carbon was 4.04% in SDU1, 4.23% in SDU2, 1.08% for fat clay and 1.09% for lean clay. The water content of the samples from the Bolonha WTP sludge, lean and fat clays and the ceramic paste at the beginning of the process were 72.1%, 14.4%, 23.9% and 32.2%, respectively, for SDU1. For SDU2, these values were 76.6%,
Water Science & Technology
|
71.11
|
2015
15.2%, 24.6% and 33.5%, respectively. The difference of 4.4% in the water content of the sludge may be attributed to the test period for dewatering the sludge in SDU1, which was longer (23 days) than that of SDU2 (15 days). Most ceramic industries add 2% of charcoal (w/w) and water to the ceramic paste at the beginning of the brick manufacturing process. The first material has the objective of facilitating the burning of bricks in the furnace and the water improves the mixing of clay and reduces the extrusion pressure. In this study, because of the characteristics of the sludge, it was not necessary to add water or charcoal into the ceramic paste, which represents cost savings for industry. The results obtained for granulometry by sedimentation and specific mass of the sludge samples from SDU1 and SDU2, lean and fat clays and ceramic paste are presented in Table 1. The sludge exhibits granulometric characteristics that are predominantly similar to those of a colloidal clay with a strong tendency to behave as a plastic material that is similar to fat-type clay. These characteristics indicate that the sludge is rich in clay minerals with a slight amount of silt and an absence of sand but with a high level of organic material, which is typical for the Amazon region (Quesada et al. ). Lean clay has characteristics of clayey silt. However, it should be noted that this clay had already been at the brickworks for a period of approximately 6 months due to the need of the brickmaker to stockpile raw material. Fat clay behaves like silty clay soil, with the presence of predominantly fine particles, and is thus highly recommended for use in the ceramic industry. The granulometric composition of the ceramic paste at a ratio of 8:2 for the lean and fat clays was 45.00 ± 4.24% for
Table 1
|
Granulometry and specific mass found in sludge samples from Bolonha WTP, lean clay, fat clay and ceramic paste
Granulometry by sedimentation (%) Sample
Silt (%)
Clay (%)
Specific mass g cm3
SDU1
8
92
2.182
SDU2
4
96
2.349
Lean clay 1
55
46
2.203
Lean clay 2
59
41
2.205
Fat clay 1
37
63
2.650
Fat clay 2
39
61
2.651
Ceramic paste 1
48
52
2.616
Ceramic paste 2
42
58
2.617
1641
E. M. da Silva et al.
|
Ceramic bricks with sludge from water treatment plant
clay and 55.00 ± 4.24% for silt with a specific mass of 2.62 ± 0.71 g cm3. The values indicate that there is an absence of a sand fraction in the ceramic paste composition for the Amazon region. The absence of sand in the ceramic paste contributed positively to the mechanical resistance of the ceramic bricks (Teixeira et al. ). Furthermore, its composition is acceptable according to the ideal range proposed in the ‘Winkler Diagram’ (Winkler ). The level of clayey components (φ < 2 μm) is at the upper limit of this range as is the level of deplastifiers. These results confirm the good quality of clay from the Amazon region for the manufacture of ceramic bricks. The images obtained from SEM (Figure 1(a) and 1(b)) show that the sludge samples present micrometric dimensions (
