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Research Paper
The effect of incorporation of a Brazilian water treatment plant sludge on theproperties of ceramic materials
S.R. Teixeira , G.T.A. Santos, A.E. Souza, P. Alessio, S.A. Souza, N.R. Souza
Department of Physics Chemistry and Biology, Univ. Estadual Paulista, UNESP, Rua Roberto Simonsen, 305, P.O. Box 266, 19060-080, Presidente Prudente, SP, Brazil
a b s t r a c ta r t i c l e i n f o
Article history:
Received 14 September 2010
Received in revised form 2 May 2011Accepted 4 May 2011
Available online 8 June 2011
Keywords:
Water treatment sludge
Clay
Texture
Red ceramic
Physical properties
We evaluated thefeasibilityof incorporating sludgefrom decantation ponds of a water treatmentplant (WTP)
into a ceramic body used in ceramic brick manufacturing. The sludge grain-size distribution (silt, sand andclay) and the effects of its incorporation on the properties of the ceramic body were studied. Samples were
collected during a period of ten months. The chemical and mineralogical compositions of the WTP sludgevaried according to the month of sludge production, but the compositions are similar to those of the natural
raw material used by the red ceramic industry. Technological tests of ceramic probes showed that this residuecan be incorporated into clays used to produce ceramic bricks. The concentration of sludge to be incorporateddepends on its properties (grain-size distribution and chemical and mineral composition), but mainly on the
properties of the raw material (matrix) used.
2011 Elsevier B.V. All rights reserved.
1. Introduction
Conventional water treatment plants (WTPs) transform crude
water into potable water utilizing a series of processes: coagulation,occulation, decantation and ltration. The process of coagulation
involves the use of Fe or Al salts that form occules with impurities inwater, which sediment (or oat) and are later ltered out. Thistreatment produces a solid residue (alum or ferric sludge) with a highwater content, whose composition depends on the origin of the crude
water collected (surface water or groundwater through wells), thetype of soil of the region, the material discharged into the river,chemical products present, the process of treatment employed, etc.The main components of the sludge from WTPs are (sometimes
known as water treatment residues): clay minerals, very ne-grainedminerals (mainly oxides and hydroxides of aluminum and iron),organic matter and contaminants from the discharge of urban andindustrial efuents and other human activities.
In general, this sludge is dumped directly into rivers and streamsor into the drain system, causing a signicant environmental impact,which compromises the quality of drinking water and the health ofthe public and animals that utilize it. The growing concern of
environmental organizations, due to the risks to health and to theenvironment, has led to the restriction or prohibition of dischargingthis residue into the environment (streams, landlls, soil, etc.).
Currently, there are more than 7500 complete cycle (or conventional)WTPs in Brazil, and even though there is legislation prohibiting it, the
amount of sludge released into waterways is still substantial
(Monteiro et al., 2008). A comprehensive study about biosolids waspublished byAndreoli (2006)where he presented the state of the art
in alternatives for recycling of sanitation waste in the manufacture ofred ceramics.
The sludge generated in WTPs is a solid residue that should beproperly treated and disposed without causing harm to the environ-ment. One of the techniques used to prepare sludge for disposal isdehydration, resulting in a cake with a concentration of solids of 60 to
70%. This cake can be used as fertilizer, incinerated, disposed in landllsfor urban waste, and composted with urban waste, among otheralternatives. More recently, the alternatives in which the residue isutilized or transformed into products that are useful to society
have been studied. An important one of them is the utilization ofresidues in making cement and ceramic bodies. Its incorporationinto ceramic bodies for the production of bricks and roof tiles is aviable practice, and could be of interest to ceramic manufacturers
(Andreoli, 2006; El-Mahllawy and El-Sokkary, 2008; Huang et al., 2001,2005; Jordan et al., 2005; Kayaci et al., 2010; Li et al., 2005, 2006;Menezes et al., 2002; Monteiro et al., 2008; Oliveira et al., 2006; Teixeira,2006; Teixeira et al., 2002, 2006; Ueno and Leite, 2007; Vieira et al.,
2008; Weng et al., 2003; Zou et al., 2009).The recycling of residues can reduce environmental impacts,
increase the useful life of the mineral raw materials used, and lower
nal production costs. The ceramic industry is a very important sectorin Brazil and is widespread. Brazilian consumption of clay hassurpassed 150 million tons/year since 2005 (MME, 2009). Sludgefrom WTPs, mainly from the treatment of surface water, can be
incorporated into ceramic bodies; sludge contains minerals that arecommon in clays, and therefore, its composition facilitates the clay/
Applied Clay Science 53 (2011) 561565
Corresponding author. Tel.: +55 18 322953 55; fax: +55 18 3221 5682.
E-mail address:rainho@fct.unesp.br(S.R. Teixeira).
0169-1317/$ see front matter 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.clay.2011.05.004
Contents lists available at ScienceDirect
Applied Clay Science
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c l a y
http://dx.doi.org/10.1016/j.clay.2011.05.004http://dx.doi.org/10.1016/j.clay.2011.05.004http://dx.doi.org/10.1016/j.clay.2011.05.004mailto:rainho@fct.unesp.brhttp://dx.doi.org/10.1016/j.clay.2011.05.004http://www.sciencedirect.com/science/journal/01691317http://www.sciencedirect.com/science/journal/01691317http://dx.doi.org/10.1016/j.clay.2011.05.004mailto:rainho@fct.unesp.brhttp://dx.doi.org/10.1016/j.clay.2011.05.0047/25/2019 ladrillos de lodo
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sludge mixture (Monteiro et al., 2008). One of the main contaminantsof sludge is associated with the type of occulants used for itsprecipitation. In previous work, we observed that the sludge obtainedwith aluminum-based chemical is more deleterious to ceramic
properties than those obtained with iron compounds (Teixeira et al.,2002, 2006).
This paper presents the results of a study conducted over ten
months with the aim of evaluating the variation of grain-size
distribution (texture) in sludge from water treatment. Also, weassessed the technological properties of ceramic bricks obtained withthe addition of sludge to clayey material used by ceramic industry.
2. Materials and methods
From 2001 to 2004, samples were collected on the washing dates
of the rst decanter of the WTP of the state sanitation companySABESP (Companhia de Saneamento Bsico do Estado de So Paulo) inPresidente Prudente County, located 558 km west of So Paulo, thecapital city of the state of So Paulo. This company uses the
conventional coagulationocculationsedimentation pretreatmentsin its water purication system. During this period, three differentcoagulants were utilized (aluminum sulfate, ferric chloride andaluminum polychloride), and samples were collected monthly overten months. The aluminum polychloride coagulant was adopted by
SABESP due to its higher efciency in the coagulation of solid particlesin treated water. Therefore, the sludge incorporated in the ceramicmaterial for technological tests was obtained with this chemical andcalled sludge-Al. The tank was divided into six parts, and two liters of
sludge were obtained from each one, totaling twelve liters persampling. The samples were mixed and dried in an oven at 110 C,broken up and pulverized in a blade mill, and the resultant materialwas then passed through a # 40 sieve (0.42 mm).
Concentrations of organic matter (OM) were determined by theWalkleyBlack method (EMBRAPA, 1998) and the concentrations ofthe sand, silt and clay fractions by the pipette method, in the samplesof sludge and clay, with prior oxidation of the organic matter using
hydrogen peroxide (Dixon and White, 1996; Klute, 1986). The mainminerals in the clay were determined in a previous study (Teixeira etal., 2001). The sludge minerals were identied using a D/MAX-2100/
PC, Rigaku X-ray diffractometer (copper radiation, Ni lter and 0.02step). These samples were K or Mg saturated andoriented (spread) onglass plates (Dixon and White, 1996; Moore and Reynolds, 1997).Chemical analysis of a sample of sludge, to test for the presence of
heavy metals, was carried out in a laboratory certied for chemicalanalysis using atomic absorption spectrophotometry (AAS), inaccordance with established standards. A thermogravimetric system(TG-209, NETZSCH Instruments)and a differential scanning calorimetry
apparatus (DSC 291A, TA Instruments) were used to characterize thesamples, at 10 C/min in air (50 ml/min).
Ceramic probes (CPs) were pressed uniaxially (19 MPa, 60
20~5 mm3
) in triplicate, using clay from the oodplains of theParan River (on the Bauru Sandstone), which is also used to producebricks by the ceramic industry located in the Presidente Prudenteregion, So Paulo state, Brazil. This raw material has 57 wt.% clay,37 wt.% silt, 6 wt.% sand, a high plasticity limit (40.6%) and low
concentration of organic matter (5.57 wt.%) (Teixeira et al., 2001). Thesludge concentration added to the clay ranged from 0 to 30 wt.%. After
ring in a laboratory kiln at ve temperatures varying from 850 to1200 C, the CPs were submitted to technological tests according to
Brazilian norms for the evaluation of ceramic properties. Waterabsorption (WA), apparent porosity (AP) and apparent specic mass(ASM) were determined using an analytical balance and theArchimedes method. Linear shrinkage was determined by measuring
the length of the samples before and after ring using a caliper. The
exural rupture strength (FS) was determined by the three-point
bending test using a universal machine (EMIC, model DL 2000)(Santos, 1989; Teixeira, 2006).
3. Results and discussion
3.1. Grain-size distribution
Texture analysis showed that the fractions of clay, silt and sand of
the sludge varied monthly. The percentages of these fractions differaccording to the time of the year in which the sludge was produced.Fig. 1 shows the variation of the fractions and of organic matter, in theten sampling months and, the variation of the water level measured
using a xed ruler in the river where water was drawn for the WTP.The changes in river levels were associated with the amountof rainfallin the region. The concentration of organic matter showed noapparent variation. On the other hand, sand showed a tendency tovary inversely with the level of the river, while clay decreased at the
lowest river level. During the sampling period (10 months), clayconcentration varied from 30 to 60 wt.%. As shown by the lowest riverlevels (Fig. 1), the months of June to September had the lowest rainfallin the region, which is normal at this time (winter) in the southern
hemisphere.The ideal grain-size distribution for each type of product for the
red ceramic industry is represented in the classical Winkler diagram
(Monteiro and Vieira, 2004). It consists of a triaxial scheme whereeach axis represents the sand, silt and clay fractions and, it can beorganized in regions in which each component may have a variablecomposition as shown in Table 1. According to these ranges, the
sludge had a concentration of clay that gave it an ideal plasticity formaking roof tiles and ridge caps. It was also evident that theconcentrations of clay greater than 40% conferred high plasticity tothe ceramic body, causing problems in the dryingand ring of ceramic
pieces. In some cases, the concentration of sand (non-plastic material)was also very high, which can worsen the properties of the ceramicmaterial. Therefore, the sludge to be used for mixing with the ceramicraw material should have concentrations of clay and non-plastic
materials compatible with those ranges shown in the Winkler
diagram. As the raw material used in this paper has high plasticity,we used the sludge with the highest concentration of sand.
3.2. X-ray diffraction and chemical analysis
X-ray diffraction analysis (Fig. 2) of the clay material and of
oriented clay plates showed kaolinite (0.723 and 0.359 nm) as thepredominant clay mineral, along with the presence of mica (1.068 and
Fig. 1. Variation of the grain-size fractions and of organic matter in the sampling
months and, the variation of the river water level at the point of water collection.
562 S.R. Teixeira et al. / Applied Clay Science 53 (2011) 561565
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0.500 nm), goethite (0.415 nm) and quartz (0.333 nm). This clay alsocontained, at lower concentrations, other iron oxides, titanium oxides,gibbsite and other 2:1 type minerals such as smectites ( Dixon andWhite, 1996; Moore and Reynolds, 1997). The ceramics factories of
the region use oodplain clays which have a similar mineralogicalcomposition, as observed in a previous work (Teixeira et al., 2001).Considering the major minerals and texture of the sludge used, weobserved that this material has a composition similar to that
characteristic of non-plastic material (high concentration of sandand silt) used to mix with raw material (predominantly kaoliniticclays) with high plasticity (high concentration of clay minerals). Thesludge collected during the rainy season (October to May) has a
particle size distribution (high plastic clay concentration and lowconcentration of non-plastic material) close to that observed forkaolinitic clays used in brick production (Monteiro et al., 2008;Teixeira et al., 2001).Fig. 3shows the diffractogram of the oriented
clay slide of the sludge sample, collected in the month of August,obtained using aluminum polychloride as coagulant. Here, the mainclay minerals noted above can be identied.
Chemical analysis (X-ray uorescence XRF) of a sample of
sludge showed that iron, silicon, aluminum and titanium were themain components of the sample, with a small concentration ofcalcium. Quantitative analysis by atomic absorption spectropho-
tometry (AAS) showed that the concentrations of the heavy metalsPb (0.42 ppm), Cr (4.60), Zn (31), Mn (121), Al (0.43) and Cu (15)were below the limits recommended for agricultural recycling of
sewage sludge (Mota, 2003). This result was expected since this isa farming region with little industry. The concentration of Fe(130,800 ppm) was high due to the coagulant used, which has aniron base. The presence of heavy metals in the sludge does notprohibit its incorporation into ceramic materials, considering that
these metals can be incorporated and made inert in the crystallinestructure of vitreous phases formed during the sintering process ofceramics.
3.3. Thermal analysis
Fig. 4 shows the thermograms (TG/DTG) for two samples of sludgewith iron and one with aluminum, collected in different periods. Thethermogravimetric analysis data showed that there was a loss of
moisture of approximately 9% (near 65 C), loss of water due todecomposition of hydroxides (aluminum and iron) and burning oforganic matter on the order of 7% (close to 265 and 315 C), and loss ofstructural water from kaolinite of 7% (around 500 C) (Monteiro et al.,
2008; Teixeira et al., 2008).Fig. 5shows the data for differential scanning calorimetry (DSC) of
WTP sludge with two different coagulants used (Fe and Al), clay usedfor the production of bricks, and kaolin from Georgia (USA).
Comparing the diagrams, it can be seen that all three samples showedkaolinite as the main clay mineral. Besides the loss of free water(~70 C), there was an exothermic band (200450 C) that wasgreater in the samples with WTP sludge, characteristic of organic
matter oxidation and also to the crystallization of amorphous phasesof iron and aluminum (gels) (Gastuche et al., 1964), formed duringthe chemical treatment of the water to precipitate the sludge. Thenarrow peak observed at 573 C is characteristic of thephase
transition of quartz, present in the clay sample. The book edited byDixon and Weed discusses the possible transformations of iron(Schwertmann and Taylor, 1989) and aluminum (Hsu, 1989)hydroxides into oxides and polymorphic transformations of silica.
Table 1
Ideal grain-size distribution for ceramic masses according to the Winkler diagram
(Monteiro and Vieira, 2004).
Type Clay2m Silt 220 m Sand20 m
I. Plasticity very high
(difcult workability)
40 to 50 20 to 40 20 to 30
II. Roof tiles and ridge caps 30 to 40 20 to 50 20 to 40
III. Perforated bricks 20 to 30 20 to 55 20 to 50
IV. Heavy bricks 15 to 20 20 to 55 25 to 55
Fig. 2. X-ray diffraction pattern of clay material used by ceramic industry (Enclosed
XRDP of saturated (K and Na) and oriented clay slides).
Fig. 3.X-ray diffraction pattern of oriented clay minerals in the WTP sludge.
Fig. 4. Thermogravimetric data TG and DTG (Derivative TG curve) of WTP sludge (using
iron chloride and aluminum sulfate).
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3.4. Technological tests
The results with sludge obtained using the coagulant aluminum
sulfate (sludge-Al) were always poorer than those with ferric chloride(sludge-Fe) as observed in a previous work. In general, the aluminumincreased the refractivity and the friability of ceramic material, whilethe iron improved the properties of material resulting from the
reaction with mica in the formation of a glassy phase (Teixeira et al.,2006).
In general, the results of the technological tests showed that theincorporation of sludge from WTP consistently worsened the
technological properties of the ceramic materials, as also observedin other studies (Jordan et al., 2005; Monteiro et al., 2008; Teixeiraet al., 2006; Weng et al., 2003). However, research results show that it
is possible to produce materials within the limits specied by theregulations of each country, controlling the amount of sludge to be
added to the ceramic material and the sintering temperature.Figs. 6 to 8 show the results of technological tests for clay with
sludge-Al (10, 15 and 20%) collected in the month of August, whichhad a greater concentration of sand. In general, the variation in theproperties of the samples was approximately equal for the additionsof 15 and 20% sludge. The graphs show that the incorporation of
sludge increased water absorption and decreased apparent specicmass (Fig. 6) and exural strength (Fig. 7). These effects are mainly
due to the high concentration (29%) of organic matter in sludge,which increases the porosity of the sample during ring.
The behavior of the properties (WA, ASM, LS) of ceramic bodieswith sludge were similar to those of pure clay material (Teixeira et al.,
2004), showing that it determines the nal properties of the material.All the properties of clay with sludge showed little variation below1000 C. At this temperature up to 1100 C, the variation was abrupt,and then for the greater concentrations of sludge the properties
tended to stabilize. This effect, of the improvement of ceramicproperties with increase in temperature, was already expected sincea liquid phase occurs above 1000 C, with greater densication of theceramic probe. However, the slowdown of the reaction between 1100
and 1150 C was not expected, indicating that with sludge thedensication reactions occurred at temperatures lower than those forpure clay, and crystallization of new phases could have occurred withthe production of microssures. The highest concentration of quartz
due to the sludge may contribute to an increase in porosity andmicrocracks generated by its alpha-beta transition (573 C) duringcooling of the ceramic bodies. These microssures tend to increase
water absorption and decrease apparent specic mass andmechanicalresistance.
Linear ring shrinkage (Fig. 8) changed little at low temperatures(up to 900 C) due to the high concentration of sand (non-plastic
material) in sludge. Above this temperature there was a substantial
Fig. 5.Differential scanning calorimetry (DSC) data of clay material, kaolin and sludge
using different coagulants.
Fig. 6. Water absorption (WA) and apparent specic mass (ASM) of ceramic probes
with (0, 10, 15 and 20 wt.%) incorporated sludge.
Fig. 7. Three-pointexuralstrength (FS) forceramicprobeswith(0, 10,15 and20 wt.%)
incorporated sludge.
Fig. 8. Linear ring shrinkage of ceramic probes with (0, 10, 15 and 20 wt.%)
incorporated sludge.
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increase in linear shrinkage due to the formationof a liquid phase,up to1100 C. At this temperature range, LS was more evident for CPs withadded sludge due the presence ofuxing material (mica and goethite)in sludge (Fig. 3). Again, there was a change in behavior at 1150 C for
samples with a greater (15 and 20%) concentration of sludge.Despite the fact that the addition of sludge worsened the
technological parameters, some of these values were still in
accordance with the Brazilian standards established for ceramics:
exural strength (bricksN
2.0 MPa, perforated bricksN
5.5 MPa, rooftilesN6.5 MPa), water absorption (perforated bricksb25%, rooftilesb18%), linearring shrinkage (bricksb6%), and apparent specic
mass (N1.6 g/cm3) (Santos, 1989; Teixeira, 2006). These limits areapproximately equal to the values established by the Chinese NationalStandards (CNS) (Weng et al., 2003).
4. Conclusions
Particle size analysis showedthat the amounts of sand, silt andclay
varied depending on the time of year that the sludge was produced.The sludge shows characteristics of a plastic material due to the highconcentration (N30%) of clay minerals and organic matter. In general,ceramic industries mix two or more clays with different grain-size
compositions to obtain the ceramic body appropriate for eachproduct. Thus, sludge can be one of the components of the mixture.The quantity of sludge that can be incorporated will be determined bythe ring temperature, the properties of the sludge and mainly by the
raw material properties used as the matrix.Considering the Brazilian technical standards, we can conclude
that: (a) the addition of 10% sludge allows the manufacture of solidbricks for ring temperatures lower than 1000 C; (b) above this
temperature, up to 20% sludge can be incorporated into the rawmaterial for the production of bricks and also roof tiles.
Acknowledgements
The authors thank SABESP of Presidente Prudente for their
collaboration, FAPESP for fellowships and grant support (PROC.2008/04368-4), andthe CNPq/PIBIC program forthe Student ScienticInitiation grants. Dr. A. Leyva helped with the English editing of themanuscript.
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