Utilization of water treatment plant sludge in structural ceramics bricks

Applied Clay Science 118 (2015) 171–177

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Research Paper

Utilization of water treatment plant sludge in structural ceramics bricks A. Benlalla a, M. Elmoussaouiti a,⁎, M. Dahhou a, M. Assafi b a b

Department of Chemistry, Laboratory for Materials, Nanomaterials and environment, Faculty of Science University Mohamed V., Rabat, Morocco National Office of Electricity and Drinking Water, International Water and Sanitation Institute Rabat, Morocco

a r t i c l e

i n f o

Article history: Received 13 May 2015 Received in revised form 14 September 2015 Accepted 15 September 2015 Available online xxxx Keywords: Drinking water sludges Terracotta Technological properties Low porosity

a b s t r a c t The main aim of this study is to assess the effect of incorporating water treatment sludges (WTS) of plant Bouregreg on the properties and microstructure of clay used for raw material. This work proposes to test the clays used in the manufacture of a ceramic that could incorporate alumina sludge. The raw materials, alumina sludge and clay, were mixed together in different proportions, were prepared by incorporating from 5 to 30%. Specimens of these mixtures were then fired at 800, 900, and 1000 °C. In order to determine the technological properties, such as bulk density, linear shrinkage, water absorption, compressive strength, X-Diffraction, and Scanning Electron Microscopy. The results obtained showed that the samples tested are dense and have high mechanical resistance, without deformation or defects. These clay materials may be used for the production of terracotta products and also for the formulation of low porosity raw material. © 2015 Elsevier B.V. All rights reserved.

1. Introduction A water treatment plant produces large quantities of sludge as a result of treatment processes of raw water such as flocculation, filtration and coagulation. According to regulations, drinking water sludges are classified as “non-hazardous waste” also known as “banal industrial waste” (BIW). That implies that they are not submitted to the heavy constraints of “hazardous waste” (Miroslav, 2008). This sludge can be dewatered further by thickening, centrifugation and filtration operations in order to recover water and minimize the volume of the waste stream is commonly to dewater the sludge up to about 30% dry matter(DM) and then pay to send it to a commercial landfill (Benlalla et al., 2015). However, this practice is becoming more and more expensive. Consequently, National Office of electricity and drinking water of Bouregreg initiated a research project on alternative methods for utilization of mill sludges. Questions have been raised in regard to the potential environmental impacts of the sludge when used. The recycling of such waste to fabricate structural ceramics can be technologically, economically, and environmentally attractive because it produces materials with greater flexural strengths and provides for adequate treatment of the water treatment plant (WTP) sludge. Therefore this technological innovation for manufacturing news products was able to minimize the impacts of WTP residues and can be seen as an environmental performance of industrial solid waste from WTP.

⁎ Corresponding author. E-mail address: [email protected] (M. Elmoussaouiti).

http://dx.doi.org/10.1016/j.clay.2015.09.012 0169-1317/© 2015 Elsevier B.V. All rights reserved.

The sludge produced by WTP can be used like additive to produce high-alumina refractory ceramics, lightweight aggregate (LWA), Glassceramics, and finally as a prime material for clinker manufacture (Ferreira and Olhero, 2002; Huang and Wang, 2013; Toya et al., 2007; Husillos Rodríguez et al., 2011). The sludge produced by WTP can also be a potential substitute for brick clay because its chemical composition is very close to that of brick clay (Hegazy et al., 2012). In addition, the use of sludge in the construction industry is considered to be an economic and environmentally sound option (Ramadan et al., 2008). The concentration of sludge that can be incorporated into clays in order to produce bricks depends partly on the sludge properties (grain-size distribution and chemical and mineral composition) but even more so on the properties of the raw materials used (Teixeira et al., 2011). Using bench-scale experimentation, (Alleman and Berman, 1984), showed that conventional clay and shale ingredients for bricks could be partially supplemented with sludge. They called this clay product “biobrick”. Bricks manufactured from dried sludge collected from an industrial wastewater treatment plant were investigated by (Lin and Weng, 2001; Weng et al., 2003b). These reports showed that the sludge proportion and the firing temperature were the two key factors determining brick quality (Liew et al., 2004). In accordance with a previous study, bricks produced from sewage sludge of different compositions were investigated by incorporating WTP sludges with different proportions that can reduce the cost due to the utilization of waste and, at the same time, it can help to solve an environmental problem (Pereira et al., 2000). The utilization of WTP sludge in brickmaking eliminates an environmental problem, several economies related to the replacement of a natural raw material are generated, leading to environmentally friendly practices (Beretka, 1975).

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Table 1 Chemical compositions of raw materials determined by XRF. Raw materials

SiO2

Al2O3

Fe2O3

TiO2

CaO

MgO

Na2O

K2O

P2O5

LoI

Total

WTP sludge Clay

27.12 54.17

62.66 15.27

1.16 6.81

0.16 0.91

1.25 10.88

0.37 7,74

0.24 0.76

0.83 2.85

0.19 0.12

5.11 10.29

99.09 99.51

LoI: loss Ignition.

Utilization of water treatment sludge in the industry of construction products is promising and economically reasonable, and the products produced are not contaminated with hazardous impurities (Liew et al., 2004). Therefore, the objective of the research is to determine the influence of drinking water treatment sludge, which is composed from a large amount of Al2O3, on physical and mechanical properties, structural parameters, mineralogical composition of the ceramic body burned at 800 to 1000 °C temperatures. In addition, the possibility to utilize this additive in the production of ceramic products was studied. 2. Experimental This section describes the materials and methods used to investigate the feasibility of using WTS for brick production and characterize the structural properties of the resulting bricks. 2.1. Sludge and clay samples The sludge used in this work was collected from the water treatment plant of Bouregreg located in the city of Rabat (Morocco). In this industry, the water is treated with aluminum sulfates, and cationic polyelectrolytes. The sludge was collected from thecoagulation/flocculation tank once a week during 12 months. The material was sun-dried during 72 h and stocked after each collection. All the collected materials were homogenized. The dried materials were then milled and passed through a 0.6 mm sieve before use. The used clays were supplied by a local bricks industry (Rabat. Morocco). The samples of clay were also sun-dried during 72 h and sieved to 0.6 mm particles. In order to get a uniform particle size. Both sludge and clay were dried with an electric heater during 48 h at 105 °C in order to remove moisture, to get a representative samples for a number of chemical–physical analyses. 2.2. Characterization of raw materials Tables 1 and 2 show the chemical composition by XRF and a range of metals including Pb, Cd, Cu, Cr, Zn and Ni analyzed using ICP. All of these metals and their concentration in the sludge is an important indicator for the quality for sludge. It can be seen that Alumina is the most abundant element in the sludge, which also contains a significant amounts of Silica, as well as minor amounts of Fe2O3, CaO, MgO, Na2O and K2O. Environmental safety testing based on heavy metals concentration in WTS tested shows the satisfactory in comparison to the permitted standards (TCVN 5945–2005: Fe b 5, Ni b 0.5, and Cr6 + b 0.1 ppm) (Degirmenci, 2008). 2.3. Preparation blocks sludge bricks Bricks containing 5 to 30% WTS by weight were produced in accordance with the mix compositions as shown in Table 3. The mixture of brick clay and WTS slurry was placed in a commercial kitchen mixer Table 2 Concentrations of main heavy metals of WTP sludge determined by ICP (⁎ppm on dry material). Element

Cd

Cr

Cu

Ni

Pb

Zn

Sludge

˂5

31

17

15

36

35

⁎ ppm: parts per million.

(20 L capacity) and mixed for 60 min while water was added after 10% moistening by weight. The plastic mixtures prepared in this way were stored in plastic bags for one day to achieve a homogenous distribution of moisture. The plastic mixtures were molded in a pilot scale screw mold of size 80 × 30 × 20 mm. the shaped samples were held for one day and then dried in an oven at 105 °C until constant weight was achieved. The dried samples were then fired in an electric furnace at three different test temperatures; 800 °C, 900 °C and 1000 °C at an average heating rate of 5 °C/min with a 2 h soaking time at the respective peak temperatures. The samples were furnace cooled for further experiments. Fig. 1 shows aspect of raw samples and fired at 800 to 1000 °C. 2.4. Brick testing method Because water content is an important factor affecting the quality of the brick, tests compaction, and Atterberg limits were conducted, to obtain the plastic nature of the sludge–clay mixtures and to determine the optimum moisture content (OMC) in the brick manufacturing process. Using this OMC, the mixtures with various proportions of sludge and clay were prepared in batches. The methylene blue value (BV) reflects the activity of the clay fraction, thus, it gives an indication of the mineralogy of this fraction and the cation exchange capacity (CEC) of clay minerals. Methylene blue tests performed in this study are based on the French standard Norme Française NF P 94–068 AFNOR (1993). This procedure is continued by adding further 5 mL portions of the methylene blue solution to the clay suspension until a halo of light blue dye surrounds the dark blue spot on the filter paper (Türköz and Tosun, 2011). The produced bricks then underwent a series of tests including firing shrinkage, weight loss on ignition, water absorption, bulk density, and open porosity were conducted according to ASTM C373-88 (ASTM C373-88, 2006a; ASTM C674-88, 2006; ASTM C326-03, 2006), and compressive strength to determine the quality of bricks. As the major properties of the ceramics materials are intimately connected to their mineralogical composition, the samples were finely crushed and analyzed by X-ray diffraction. The different phases formed after firing at 1000 °C were identified using the XPERT DATA COLLECTER software. The samples microstructure was evaluated using scanning electron (SEM). 3. Results and discussion 3.1. Atterberg limits of clay–sludge mixtures Atterberg limits are an important indicator for several properties of clayey soils: plasticity, sensitivity, consistency and shrinkage/swelling potential. Their determination gives a first insight for the mineralogical composition of clays. The liquid and the plastic limits are highly and Table 3 Samples of bricks masses with WTP sludge (wt.%). Firing temperature

Formulations of mixtures containing WTP sludge 5%

10%

15%

20%

25%

30%

800 °C 900 °C 1000 °C

S1 SA SG

S2 SB SH

S3 SC SI

S4 SD SJ

S5 SE SK

S6 SF SL

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Fig. 2. Compaction proctor test curve.

sludge–clay mixtures show that incorporating the sludge with different concentration did not influence the value of placticité. It can be noted that clay–sludge mixtures are highly plastic clays with a very soft consistency. The plastic limit values shown in Table 4 indicate that up to 30% of sludge can be applied into brick without losing its plastic behavior. 3.2. Proctor compaction test

Fig. 1. Aspect of raw samples (A) and fired (B) at 800 °C to 1000 °C.

mainly influenced by the ability of clay minerals to interact with liquids (Schmitz et al., 2004). Several studies had determined a direct link between the mineralogy of clays and geotechnical properties (Mitchell, 1993; Kaya, 2009). Table 4 gives the results of the determination of Atterberg limits of sludge–clay mixtures. According to these results, the effect of moisture on the pulverized material's plastic behavior is demonstrated in accordance with the Atterberg Limits test. The results of Atterberg's tests of

Table 4 Values of plasticity parameters of sludge–clay mixtures.

Liquid limit (WL) Plastic limit (WP) Plasticity index (IP) *S: Sample.

S1 5%

S 2 10%

S3 15%

S4 20%

S5 25%

S6 30%

63.6 39.1 25

62.9 31.6 31

65.4 32.3 33

60.9 31 30

52.5 28.9 24

61.7 31.3 30

A standard compaction test was used to determine the OMC which is an important factor affecting the properties of brick. The OMC of a mixture was based on the moisture requirement in which maximum bonding among the mixture particles is retained. The test results show that the OMC is 23% for clay mixture. Increasing the sludge proportions in the mixture resulted in an increase of OMC (Fig. 2). 3.3. Methylene blue value The methylene blue value (MBV) represents the amount of MB sorbed by 100 g of sludge sample. The MBV is calculated according to Eq (1), where Vcc represents the volume of methylene blue solution (ml) consumed by the sludge suspension and f′ is the dry weight of the sludge sample (g). Table 5 Methylene blue value (MBV) for sludge and clay minerals.

BV (g·100 g−1)

Sludge

Kaolinite

Chlorite

Illite

Smectite

0.32

1

3

–

31

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Fig. 3. The weight loss on ignition of bricks. Fig. 5. The density and porosity of bricks.

Table 5. shows the results of the methylene blue test which are compared to values assigned to clay minerals (Tran, 1980) presented in the same table. g   VccðmlÞ  0:01 g ml  100 MBV =100g ¼ 0 f ðgÞ

ð1Þ

This test is based on the interaction of the MB dye cation (MB +) with either exchangeable interlayer cations present in a clay mineral (e.g. in smectites) and/or surface adsorbed cations. Clay minerals possessing exchangeable interlayer cations, a highly negative charge and a large specific surface area exhibit the highest capacity for cation exchange (Türköz and Tosun, 2011; Teresa et al., 2001; Hang and Brindley, 1970). According to the data above, the Methylene blue value of WTS (0.32 g) is lower than those of values assigned to clay minerals (Tran, 1980; Eslinger and Peaver, 1988) presented in the Table 5. WTS are of low and/or medium electrochemical activity and cation exchange capacity because of the absence of exchangeable interlayer cations. These clay minerals can interact with MB only via surface adsorption. Finally, according to the Atterberg limits, the methylene blue values WTS are silty sands characterized by a highly plastic clay fraction, has low to medium shrink swell capacity and cation capacity exchange linked to clay group.

Fig. 4. The brick firing shrinkage.

3.4. Brick weight loss on ignition Fig. 3 shows that increasing the sludge proportion and temperature resulted in increases in brick weight loss on ignition. The weight loss on ignition criterion for a normal clay brick is 15%, (AASHTO, AASHTO T-99, 1982). With 5% to 15% sludge addition, the produced bricks all meet the criteria. Visual observation showed that an uneven surface was found for the sludge brick. It is speculated that the formation of this unwanted surface was mainly due to the organic component burnt off during the firing process. The brick weight loss on ignition is not only attributed to the organic matter content in the clay, but it also depends on the organic content in the clay and sludge being burnt off during the firing process. In order to avoid the uneven surface texture of bricks, both sludge and clay was oven dried at 105 °C for about 24 h. Upon drying these samples were crushed into powder and then mixed well in required proportion by weight. 3.5. Brick firing shrinkage The quality of brick can be further assured according to the degree of firing shrinkage. Normally, a good quality of brick exhibits a shrinkage below 8%. As shown in Fig. 4, the percentage of shrinkage increases with the increasing sludge addition. For a clay −30% sludge brick, the shrinkage is: 1.9, 2.4 and 2.9% at firing temperatures of 800, 900 and

Fig. 6. The water absorption of bricks.

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3.6. Bulk density and apparent porosity of bricks

Fig. 7. Compressive strength of bricks.

1000 °C, respectively. The produced bricks all meet the criteria. However, the firing temperature is another important parameter affecting the degree of shrinkage. In general, increasing the temperature results in an increase of shrinkage. Thus, the proportion of sludge in the mixture and the firing temperature are the two key factors to be controlled to minimize the shrinkage in the firing process.

The bricks made with clay normally have a bulk density of 1.8 to 2.0 kg/cm3. The measurements of bulk density for different proportions of sludge fired at three temperatures are demonstrated in Fig. 5. As shown, the bulk density of the bricks is inversely proportional to the quantity of sludge added in the mixture. A linear relationship between the bulk density and sludge proportion in the mixture for all three temperatures is observed. The results obtained from the determination of total porosity as a function of firing temperature (Fig. 5). Apparent porosity increases as decreases bulk density. In addition this property decreases with temperature. This finding is closely related to the quantity of water absorbed as demonstrated in Fig. 6. When bricks absorb more water, it exhibits a large pore size than the one with less water absorption. As a result, the bulk density becomes smaller. The firing temperature can also affect the bulk density of the bricks. The results show that increasing the temperature results in an increase in bulk density. 3.7. Brick water absorption Water absorption is a key factor affecting the durability of brick. The less water infiltrates into brick, the more durability of the brick and resistance to the natural environment are expected. Fig. 6 shows the results of the water absorption tests for various sludge

Fig. 8. XRD Spectra of samples fired at 800 °C to 1000 °C.

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clay mixtures fired at three different temperatures. As shown in Fig. 6, the value of water absorption is directly proportional to the quantity of sludge added. Increasing the firing temperature resulted in a decrease of water absorption, thereby increasing the weathering resistance. According to the criterion of water absorption of bricks in ASTM C373-88, ASTM (2006a); ASTM (2006b), the ratio is below 15% for first- class brick and 15 to 20% for second-class brick. According to this guideline bricks with 5 wt.% fired at 900 °C and 5–10 wt.% fired at 800 °C to 1000 °C are first class category, and bricks with 5–15 wt.% fired at 800 °C, 5–20 wt.% fired at 900 °C and 5–25 wt.% fired at 1000 °C are within second-class category. The curves for water absorption and linear shrinkage are realized. This type of curves is also known as gresification diagram, which is associated with the efficiency of the sintering process. The sintering of a material usually causes many changes in its properties (Edemarino Araujo Hildebrando et al., 2013). Gresification diagrams were plotted for the temperature range of 800 °C to 1000 °C for each mixture. The corresponding curves exhibit an increase in water absorption and a decrease in linear shrinkage up to 930 °C, it can be observed that above 930 °C a sharp change occurs in the trend of the curves. It is observed that the specification for bricks was achieved in the studied temperature range (910–930 °C) for samples with up to 20% sludge while the sample above 25% sludge attained only 890 °C.

3.8. Compressive strength of bricks The compression test is the most important test for assuring the engineering quality of a building material. The results of the compressive strength test on the bricks made from clay and sludge mixtures are shown in Fig. 7. The results indicate that the strength is greatly dependent on the amount of sludge in the brick and the firing temperature. Compressive strength of bricks decreases with increase of sludge mix in the bricks but increases with the increase of firing temperature. As shown, with up to 30% sludge in the bricks at 1000 °C, the strength is even higher than that of normal clay bricks. When a 5 to 10% sludge is added in the brick, the achieved brick strength at 900 °C and 1000 °C lies in the scope of the 1st-class category. With up to 20% sludge added to the bricks, the strength measured at temperatures of 800 to 1000 °C, met the requirements of a 2nd class brick standard (Weng et al., 2003a). It is concluded that alumina sludge can be blended with clay in different proportions to produce a good quality brick under a certain temperature.

3.9. Micro-structure and phase analysis To further investigate the crystalline composition and microstructure of samples. XRD and SEM analyses were carried out, and the results are shown in Figs. 8 and 9, respectively. The results revealed the co-presence of several phases in each one.

Fig. 9. SEM images of the ceramic bricks fired at 1000 °C.

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The crystalline phases of thermal treatment of the drinking water sludge are muscovite KAl2 [(OH, F) 2 | AlSi3O10] and quartz and common lines between muscovite and quartz. These phases seem more reactive to thermal treatment, only quartz is stable during this treatment. The higher the temperature the more we witness the crystallization of solid phases that contain calcium, iron, aluminum, potassium, aluminum silicate, forsterite Mg2SiO4. In turn, the clay is constituted mostly by the mineral phases such as hematite, quartz. It can be not observed a trend or, alternatively, the presence of a typical phase in a group of samples. XRD Fig. 8 analysis shows predominant peaks of quartz at 27.78 and 20.89, and illite peaks at 19.76 and 50.1302. In addition, the diopside peaks at 27.90, 31.17 and 70.01 and anorthite peaks at 31.26 and 35.81 have also been observed. The sintered specimens produced dense matrix material with good surface characteristics. It can be seen from scanning electron micrograph Fig. 9. that the samples are mainly composed of rounded and rhombic shaped quartz crystals along with the lath and cubic crystals of clay. 4. Conclusion The present study was conducted to develop and to characterize a clay product with the addition of alumina sludge as a clay substitute. The feasibility in the use of this material was demonstrated. There is a good correlation between all the properties tested. Ceramics materials could be prepared by using clay and sludges waters as source of alumina. The combination of techniques XRD, SEM, and the characterization of the technological parameters allowed a better analysis of the structural and mineralogical evolution after sintering at 1000 °C. The environmental characterization of the product indicates that a material containing alumina sludge can be used safely. The technological properties are compatible with those specified for ceramic bricks. The proportion of sludge in the mixture and the firing temperature are the two key factors affecting the quality of brick. In all, the recommended proportion of sludge in brick is 20%, with a 30% optimum moisture content, prepared in the molded mixtures and fired between 900 °C and 930 °C to produce a good quality brick. Acknowledgments This study was conducted in the laboratory of quality control (DCEONEEP). The authors acknowledge support from National Office of Hydrocarbons and Mines (ONHYM). Authors would like to thank “National Office of electricity and drinking water” (ONEEP) for supplying the drinking water sludge. References AASHTO, AASHTO T-99, 1982. Standard test methods for moisture–density relations of soils and soil–aggregate mixtures using 5.5 lb rammer and 12 in drop. Standard Specifications for Highway Materials and Methods of Sampling and Testing, Part II. American Association of State Highway and Transportation Officials, Washington, DC. AFNOR, 1993. Mesure de la quantité et de l'activité de la fraction argileuse (norme française NF). association française de normalization (ANFOR), La Défense, Paris, France, pp. 68–94.

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