Waste Management 34 (2014) 1072–1078
Contents lists available at ScienceDirect
Waste Management journal homepage: www.elsevier.com/locate/wasman
Effects of using arsenic–iron sludge wastes in brick making Khondoker Mahbub Hassan a,⇑, Kensuke Fukushi b, Kazi Turikuzzaman a, S.M. Moniruzzaman a a b
Department of Civil Engineering, Khulna University of Engineering and Technology, Khulna 9203, Bangladesh Integrated Research System for Sustainability Science (IR3S), The University of Tokyo, 7-3-1 Hongo, Tokyo 113-8654, Japan
a r t i c l e
i n f o
Article history: Received 29 April 2013 Accepted 20 September 2013 Available online 13 October 2013 Keywords: Arsenic–iron sludge Brick making Leaching potentials Waste recycling
a b s t r a c t The arsenic–iron sludge generated in most of the treatment systems around the world is discharged into the nearest watercourse, which leads to accumulative rise of arsenic and iron concentrations in water. In this study, attempts were made to use the arsenic–iron sludge in making bricks and to analyze the corresponding effects on brick properties. The water treatment plant sludge is extremely close to brick clay in chemical composition. So, the sludge could be a potential substitute for brick clay. This study involved the addition of sludge with ratios 3%, 6%, 9% and 12% of the total weight of sludge–clay mixture. The physical and chemical properties of the produced bricks were then determined and evaluated and compared to control brick made entirely from clay. Results of different tests indicated that the sludge proportion and firing temperature were the two key factors in determining the quality of bricks. The compressive strength of 3%, 6%, 9% and 12% sludge containing brick samples were found to be 14.1 MPa, 15.1 MPa, 9.4 MPa and 7.1 MPa, respectively. These results indicate that the compressive strength of prepared bricks initially increased and then decreased with the increase of sludge proportion. Leaching characteristics of burnt bricks were determined with the variation of pH at a constant temperature. The optimum amount of sludge that could be mixed with clay to produce good bonding of clay–sludge bricks was found to be 6% (safely maximum) by weight. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction The serious arsenic as well as iron contamination in groundwater of Bangladesh has come out recently as the biggest natural calamity in the world. The people in 59 out of 64 districts comprising 126,134 km2 of Bangladesh are suffering due to the arsenic contamination in groundwater (Safiuddin and Karim, 2001). Seventy-five million people are at risk and 24 million are potentially exposed to arsenic contamination. Most of the recognized stages of arsenic poisoning have been identified in Bangladesh and the risk of poisoning in the population is increasing day by day (Safiuddin and Karim, 2001). The millions of shallow and deep wells that had been sunk in various parts of the country are dispensing their own special brand of poison. In consequence, a large number of populations in Bangladesh are suffering from the toxic effects of arsenic contaminated water. On the other hand, arsenic in combination with various metals such as iron causes serious environmental problems which adversely affect the health of millions of people in Bangladesh. The data collected by the governmental bodies, NGOs and private organizations reveal that a large number of populations in Bangladesh are suffering from melanosis, leucomelanosis, keratosis, hyperkeratosis, dorsum, non-petting oedema, ⇑ Corresponding author. Tel.: +880 1714087302; fax: +880 41774780. E-mail address: [email protected] (K.M. Hassan). 0956-053X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.wasman.2013.09.022
gangrene and skin cancer (Karim, 2000). To minimize these adverse effects available technologies and water treatment have been made which helps to remove arsenic and iron from drinking water (Hassan et al., 2010). Therefore, a sludge is got that will contain this arsenic and iron. So far, most of the focus has been given on awareness building and the development of water treatment system removing arsenic from drinking water. The disposal of arsenic rich sludge generated from the treatment processes is one of the issues that have received little attention from the sponsors of the technologies and the users (Eriksen and Zinia, 2001). At present, 18 large scales arsenic and iron treatment plants are working actively in Bangladesh. Each treatment plant generates about 170 m3 arsenic-laden sludge per year (Basak and Islam, 2008). They have sufficient removal capacity (>80–90%) for iron as well as arsenic (Hemal and Zinia, 2001). Landfills are commonly used technique for the disposal of sludge in Bangladesh. However, rapid urbanization is gradually making it difficult to find suitable landfill sites (Lin and Weng, 2001). In some places, sludge is directly disposed to the nearby rivers or low laying areas, which is likely to pollute surface and groundwater (Sullivan et al., 2010). It has been shown recently that arsenic-laden sludge, when disposed into the soil do release toxic elements which accumulate in plants (Huq et al., 2011). Recently, environmental regulations are becoming more stringent and volume of generated sludge continues to increase, traditional sludge disposal methods are coming under
K.M. Hassan et al. / Waste Management 34 (2014) 1072–1078
increasing pressure to change and therefore, there is a strong demand for environmentally safe reuse and effective disposal methods for iron and arsenic contaminated sludge out of water treatment plants. Incineration is costly and contributes to air pollution while landfill space is becoming scarce. A possible long term solution appears to be recycling of the sludge and using it for beneficial purposes. One technique that is available to treat hazardous waste is solidification that stabilizes and solidifies components of waste. The solidified product could be disposed off to a secure landfill site or be recycled as construction materials like bricks if it meets the specific strength requirements and can be shown to leach toxic pollutants within acceptable limits (Rahmat, 2001). In this paper, an attempt has been made to use the arsenic–iron sludge for brick making. For thousands of years, bricks have been made from clay. The major chemical compositions of brick clay were found to be silica, alumina, and ferric oxide which indicate the similar compositions of the water treatment plant sludge (Hegazy et al., 2012). So, the sludge could be a potential substitute for brick clay. Use of arsenic–iron sludge in making brick would be one of the low-cost technologies available in Bangladesh which might significantly contribute to reducing the adverse environmental effects of arsenic-laden sludge. Performance of this technology depends on the concentration of arsenic–iron sludge used as brick ingredient and burning temperature and technique for those bricks. This study mainly aims at blending of arsenic–iron sludge waste with clay for making bricks and to study the physical properties and leaching characteristics of the developed bricks for its potential use in construction works. 2. Methodology 2.1. Raw material collection The arsenic–iron sludge waste used for this study was collected from arsenic–iron removal plant (AIRP) at Manikganj (Fig. 1) in Bangladesh. Manikganj water treatment plant uses to dispose the sludge into the bank of a nearby water body. As a result, during rains, the sludge drains into the water body and increases the concentration of arsenic, iron and other elements. To reduce such contamination in water bodies, the utilization of sludge for producing environmentaly stable products such as brick manufacturing for use in construction works would be very effective. In this study, for producing sludge–clay bricks, clay sample was collected from nearby brick field at Fultola of Khulna district. Khulna, the third largest city of Bangladesh, is located in the southern part of the country and situated below the tropic of cancer, around the intersection of latitude 22.49°N and longitude 89.34°E. The area of Khulna city is 47 square km with a population around 1.5 million (BBS, 2009). 2.2. Sample preparation and testing The collected sludge samples were brought to laboratory and oven dried for 24 h at 105 °C. Then, the sludge sample and collected brick clay were crushed and sieved in such a way that the soil sample did not contain any foreign matter. Before taking the soil for sampling, large chunks of soil was crushed manually and mixed thoroughly to get a uniform representation. Water was then added slowly to the soil and mixed it thoroughly by hand until a smooth consistency for molding is achieved. After drying and crushing, the moisture content, arsenic and iron of the sludge were determined in the laboratory. Arsenic content of the sludge was determined by field kits (HACH, USA) using color coding. Arsenic determination by HACH kit involves generation of arsine gas (AsH3) by addition of prepackaged sulfamic acid and zinc powder
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and its entrapment on a strip of paper impregnated with mercuric bromide, followed by comparison of the color of the orange-brown circle on the strip to a reference scale. The iron content was determined by Phenanthroline Method using Spectrophotometer (DR 4000, HACH, USA). The quality assurance/control of samples (QA/ QC) were done using reference materials (spike samples), sample replicates (3 samples) and prepared blanks. The detection limits for the determination of both arsenic and iron was 0.01 mg/L. For the manufacture of bricks, a specific dimension of mold was utilized. In this study, the specific dimension of brick was 250 mm 125 mm 75 mm. Two wooden frames were used for molding of bricks. The side walls of the mold was 12.5 mm thick. The lower end of the mold was fixed with a plate of wood to facilitate the pouring process. A total of 4 brick samples for each sludge–clay mixture proportion of 3%, 6%, 9% and 12% were prepared in the laboratory. For the preparation of bricks, the sludge– clay mixture was placed into the mold and then compacted well to get the desired strength. Drying and burning of the brick sample was done in three stages. At first, the sample was oven dried at a temperature of 105 °C for 2 days. Secondly, the oven dried brick was burnt into a laboratory furnace at 500 °C for 12 h. Finally, the temperature was increased to about 1000 °C and in this stage the sample was burnt for 12 h. In this study, 3-stages burning process was applied to avoid firing shrinkage of the brick samples. Furthermore, for firing of bricks, the temperature had been raised uniformly @ 100 °C. The actual temperature within the laboratory furnace for brick burning was monitored using a simple dilatometer (thermometer). However, a detailed differential thermal analysis was not done in this study. It was observed from previous studies that sudden rise in burning temperature is responsible for fracturing the surface of brick sample. After the completion of burning process, the furnace was switched off and the bricks had not been been removed until they become cool to room temperature. The prepared bricks were then taken to laboratory for the determination of various physical and chemical properties. Various laboratory tests such as moisture content, specific gravity, water absorption capacity and compressive strength of bricks were performed to investigate the physical properties of the prepared sludge–clay bricks. In this study, leaching characteristics of sludge–clay bricks were investigated with the variation in sludge concentration and pH at a constant temperature. Typically, the leaching test removes the mobile component of any analyte present in the solid phase. The extraction fluid employed is a function of the alkalinity of the solid phase of the waste (USEPA, 1992). Three different conditions were selected to analyze the leaching characteristic. These conditions were acidic condition, alkaline condition and neutral condition. Particle size of waste materials will surely impact the leachability due to variation in surface area of the solid phase. Once these arsenic-laden sludge–clay bricks will be used in the construction industry, they will break, construction waste and demolition waste containing these bricks will have various particle sizes and varied leachability. In this study, each of the prepared sludge–clay brick was cut into 6 (six) equal pieces for the determination of arsenic and iron leachability. Triplicate samples were tested for leaching behavior of each mix with sludge and the average values were reported for the assessment.
3. Results and discussion After the collection of sludge sample, various chemical characteristics such as pH, arsenic and iron content were determined in the laboratory. This study found that the arsenic and iron content of the sludge sample were very high (arsenic 0.5 mg/L and iron 7.5 mg/L). The sludge had a pH value of 6.5, indicating that the sludge can be treated as neutral material. When desired bricks were
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Fig. 1. Sludge collection from arsenic–iron treatment plant at Manikganj.
prepared, various physical and chemical properties were tested in the laboratory. Quality of brick usually depends upon its water absorption capacity, moisture content, specific gravity and compressive strength. Fig. 2 represents the physical properties of the sludge–clay bricks with the variation in sludge proportion. With the increase in sludge proportion, the water absorption capacity and specific gravity of the prepared bricks were found to be increased while the moisture content was decreased. The specific gravity of iron content is usually 3 times higher than clay samples which led to gradually higher specific gravity with the increase in sludge proportion in the prepared bricks. The results indicate that the compressive strength of prepared bricks initially increased and then decreased with the increase of sludge proportion possibly due to the strong bonding of iron content with clay particles. The interpretation of this findings are given in Section 3.3.
3.1. Leaching characteristics Table 1 represents the variation in the amount of leaching of arsenic and iron with varied sludge proportions. Test results indicate that the leached arsenic content, for 3% sludge-mix brick, was always below 0.05 mg/L which is the acceptable limit of Bangladesh standard for drinking water. In this case, disposal of arsenic-laden sludge bricks into nearby water bodies appear to be safe and not to contribute to recontamination of the water environment. However, the world health organization (WHO) guideline value for arsenic is 0.01 mg/L for drinking purpose. When 6% sludge-mix was used, it exceeded the allowable limit and for further increase in sludge proportion, the amount of leached arsenic content increased rapidly. On the other hand, leached iron content was always found to be less than standard limit (0.3–1.0 mg/l).
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Water absorption capacity (%)
Moisture Content (%)
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6 5 4 3 2 1 0
3%
6%
9%
12%
25 20 15 10 5 0
3%
Proportion of sludge (%) Compressive Strength (MPa)
1.85
Specific gravity
6%
9%
12%
Proportion of sludge (%)
1.8 1.75 1.7 1.65 1.6 1.55
18 15 12 9 6 3 0
3%
Proportion of sludge (%)
6%
9%
12%
Proportion of sludge (%)
Fig. 2. Variation in physical properties of prepared bricks with the variation in sludge proportion. Column values represent the average of triplicate samples, and error bars show the range of standard deviation.
Table 1 Variation in the amount of leaching of arsenic and iron with the variation in sludge proportion. Proportion of sludge in prepared bricks (%)
Standard limits (drinking purpose)
3%
6%
9%
12%
Bangladesh
WHO
Amount of arsenic leaching (mg/L)
After After After After After
24 h 72 h 120 h 168 h 216 h
0.001 0.025 0.050 0.025 0.025
0.001 0.025 0.050 0.075 0.075
0.025 0.075 0.100 0.250 0.500
0.025 0.100 0.250 0.500 0.500
0.05 mg/L
0.01 mg/L
Amount of iron leaching (mg/L)
After After After After After
24 h 72 h 120 h 168 h 216 h
0.177 0.000 0.000 0.000 0.000
0.175 0.355 0.025 0.190 0.080
0.218 0.315 0.183 0.177 0.127
0.280 0.384 0.284 0.159 0.082
0.3–1.0 mg/L
0.3 mg/L
3.1.1. Acidic medium Bricks having 3%, 6%, 9% and 12% sludge-mix showed large variations in leaching behavior. The results of leaching tests at acidic medium (Fig. 3) indicate that leaching of arsenic and iron from burnt bricks increases with the increase in sludge proportion. For 3% sludge containing brick, the rate of leaching was lower than the 6%, 9% and 12% sludge containing bricks. In this study, it was observed that the amount of arsenic and iron leaching increased with the decrease in pH value of the aqueous medium. At a low pH value around 3.0, the leached arsenic content for almost all proportions of sludge–clay bricks were found to be far exceeding the standard limit of 0.05 mg/l. On the other hand, leached iron content was within the acceptable limit (0.3–1.0 mg/l) for 3% and 6% sludge-mix bricks but far exceeded in case of 9% and 12% sludgemix. Thus, the experimental results suggest that the burnt bricks should not be exposed to acidic medium. 3.1.2. Alkaline medium To obtain an alkaline solution, the value of pH was selected to be 12.0. Bricks having 3%, 6%, 9% and 12% sludge mix showed large
variation in leaching behavior. Corresponding test results and their graphical representation are given in Fig. 4. In alkaline medium, the leached arsenic and iron contents from burnt brick samples were found to be within the allowable limit at the initial time period. In case of arsenic, rate of leaching increases as time passes and finally it exceeded the allowable limit. On the other hand, the leached iron content was always found to be within the allowable limit (0.3–1.0 mg/L). Although initially the rate of leaching increased slowly but as the time passes, the rate of leaching decreased gradually. It was observed that in alkaline medium the rate of leaching was remarkably less than that in acidic medium. 3.1.3. Neutral medium To obtain a circum-neutral medium, the pH value was adjusted to 6.50. Bricks having 3%, 6%, 9% and 12% sludge-mix showed large variations in leaching behavior. Fig. 5 indicates that in neutral medium the rate of leaching changes with the proportions of sludge in the brick sample. For small proportion of sludge, the amount of leaching was very less. For 3% and 6% sludge containing brick samples, the leached arsenic content never exceeded the
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Fig. 3. Leaching of arsenic and iron with variable sludge proportion at acidic medium. Line values represent the average of triplicate samples.
Fig. 4. Leaching of arsenic and iron with variable sludge proportion at alkaline medium. Line values represent the average of triplicate samples.
allowable limit of 0.05 mg/L. However, for 9% and 12% sludge containing brick samples, leached arsenic was found to exceed the allowable limit after 72 h and 24 h, respectively. A similar study by Eriksen and Zinia (2001) also concluded that the arsenic treatment units renderd the majority of the arsenic into a stable and non-mobile phase. On the other hand, the leached iron content of burnt brick samples in neutral medium was found to be within the allowable limit (0.3–1.0 mg/L). For 3% sludge containing brick, leached iron content was nolonger observed after 72 h. For 6%, 9% and 12% sludge containing brick samples, there was an increase in the amount of iron leaching initially but as the time passes, the rate of leaching decreased gradually. 3.2. Effects of firing temperature The firing temperature is another important parameter affecting the degree of shrinkage. Test results of this study indicate that
there is an inverse relation between firing temperature and the proportion of sludge. The temperature of burning should be selected in such a manner that it neither very low nor very high. It has been observed from this study that burning temperature ranges between 900 °C and 1000 °C (Fig. 6). Bricks which were burnt at low temperature do not seem to have high compressive strength. On the other hand, at high temperature, brick seems to have fractured surface. So, an optimum range of temperature is required for brick burning. With the increase in sludge proportion, temperature of firing shrinkage decreases, because the swelling of the clay is much lower than that of sludge, an addition of sludge to the mixture widens the degree of firing shrinkage. A similar study (Lin and Weng, 2001) indicated that the sludge proportion and firing temperature were the two key factors determining the quality of bricks and the optimum firing temperature was around 1000 °C for 6 h. Fig. 6 indicates the relation between sludge proportion and firing temperature in the prepared sludge–clay bricks. For the
Fig. 5. Leaching of arsenic and iron with variable sludge proportion at neutral medium. Line values represent the average of triplicate samples.
K.M. Hassan et al. / Waste Management 34 (2014) 1072–1078
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3.4. Proposals for sludge–clay bricks
Fig. 6. Relation between sludge proportion and firing temperature.
sludge proportion of 3%, the firing shrinkage was found to be occured at a temperature around 1000 °C. For further increase in sludge proportion, there was a drop in the temperature of firing shrinkage. Finally, for 12% sludge containing bricks, the temperature of firing shrinkage was found to be around 920 °C. Furthermore, the physical properties of a bricks such as moisture content, specific gravity, water absorption capacity and compressive strength were found to be completely dependent on its burning temperature (Fig. 2).
3.3. Characteristics of prepared clay–sludge bricks In this study, the quality of prepared bricks was determined on the basis of laboratory tests (ASTM C67). Four brick samples of each sludge proportion have been made and various tests were performed on those bricks to justify the effectiveness of arsenic– iron sludge as a substitute for clay. It can be said on the basis of test results that properties of prepared bricks were slightly different from the properties of controlled bricks. The durability of the brick is largely dependent upon their water absorption. The water absorption of control clay brick generally ranged between 10.0% to 11.2%. In case of this study, test results show that water absorption capacity of prepared bricks ranges from 15.2% to 19.6%. The apparent specific gravity of controlled clay brick generally ranged between 1.8 and 2.0. While apparent specific gravity test results of prepared bricks were found in the range between 1.66 and 1.79. Compressive strength significantly determines the potentiality of bricks for its application. Compressive strength is usually affected by the porosity, pore size, and type of crystallization. It is usually defined as the failure stress measured normal to the bed face of the brick. AASHTO standards for brick requirements: 150 kg/cm2 (14.7 MPa) for a first-class brick. The compressive strength of 3%, 6%, 9% and 12% sludge containing brick samples were found to be 14.1 MPa, 15.1 MPa, 9.4 MPa and 7.1 MPa, respectively. These results indicate that the compressive strength of prepared bricks initially increased and then decreased with the increase of sludge proportion possibly due to the strong bonding of iron content with clay particles. Typically, clay particles are negatively charged colloids while ferric iron hydroxides show positively charged surface sites (Dzombak and Morel, 1990) at circum neutral pH. This study found the optimum amount of sludge 6% (safely maximum) by weight could be mixed with clay to produce good bonding of clay–sludge bricks. In this case, most of the free negative changes in clay particles would form electrostatic bondings with iron hydroxide solid phase. For further increment of sludge proportion, the iron content might nolonger find free available charges for bond formation and thus gradually decreases strength. In another observation, Mahzuz et al. (2009) found that arsenic contaminated sludge could be safely used up to 4% for making ornamental bricks.
On the basis of test results of this study, it can be said that quality of sludge-brick depends upon the sludge concentration, technique of molding, degree of compaction, method of burning and firing temperature. In order to yield a good quality brick, the proportion of sludge and the firing temperature are the two key factors controlling the shrinkage in the firing process. Specific gravity, moisture content and compressive strength of the burnt brick samples are also dependent on the sludge proportion and the firing temperature. As the amount of leaching and toxicity of the burnt bricks are higher both in acidic and alkaline mediums, the prepared bricks should not be exposed to those mediums. In this study, hand molding was used for the preparation of bricks. For future works, mechanical molding should be used to compare the brick properties. For burning the sludge–clay bricks, laboratory furnace was used in this study. However, it is recommended that brick samples should be burnt alternately in the brick field and the change in brick properties should be observed. Furthermore, in this study, leaching characteristic of burnt brick samples was determined with the variation in pH at a constant temperature and one specific particle size (one sixth of a brick). A detailed investigation should be done with the variation of temperature and particle sizes in combination with the variable pH to check the leaching behavior of prepared bricks. The rate of increase in firing temperature was also considered to be a key factor. Sudden increase in temperature affects the shrinkage in the firing process. Thus, the rate of increase should be slow to avoid firing shrinkage.
4. Conclusions This work endeavoured to demonstrate a feasible way of using arsenic–iron sludge as a clay substitute for brick manufacturing. Different measurements of both clay–sludge mixtures were carried out to evaluate the factors that could affect the brick quality. The results of compressive strength tests on the bricks indicate that the strength is greatly dependent on the amount of sludge in the brick and the firing temperature. This study found that the compressive strength of prepared bricks initially increased and then decreased with the increase of sludge proportion. Moreover, the specific gravity and water absorption capacity of prepared bricks were found to be increased with the gradual increase in sludge proportion. Test results also indicate that moisture content of the prepared bricks decreases with the increase in sludge proportion. Tests on leaching characteristic identified that the amount of arsenic and iron leaching from the sludge-bricks were higher for both acidic and alkaline mediums and thus the prepared bricks should not be exposed to those mediums. Based on the laboratory test results, it can be concluded that arsenic-laden sludge could be effectively used as a component of raw materials for brick making. The optimum amount of sludge that could be mixed with clay to produce good bonding of clay– sludge bricks was found to be 6% (safely maximum) by weight. The firing shrinkage of brick was also remain unaffected in this case. Furthermore, the amount of leaching in 6% sludge content brick was less in comparison to higher sludge-mix bricks. Thus, the arsenic–iron sludge from the groundwater treatment plant would be cautiously blended with clay materials for brick manufacturing and hence be recycled as construction materials.
Acknowledgements Appreciation goes to the Department of Civil Engineering, KUET for the financial support to complete this Project.
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References Basak, R., Islam, M.S., 2008. A study on the use of arseniciron contaminated sludge in making construction materials. BSc thesis, Department of Civil and Environmental Engineering, Shahjalal University of Science and Technology, Sylhet, Bangladesh. BBS, 2009. Statistical pocket book of Bangladesh, Bangladesh Bureau of Statistics, pp. 8. Dzombak, D.A., Morel, F.M.M., 1990. Surface Complexation Modeling: Hydrous Ferric Oxide. Willey-Interscience, New York. Eriksen, N., Zinia, B.K.N., 2001. A study of arsenic treatment technologies and leaching characteristics of arsenic contaminated sludge. Technologies for Arsenic Removal from Drinking Water, ISBN 984-31-1305-6, pp. 209–213. Hassan, K.M., Fukushi, K., Nakajima, F., Yamamoto, K., 2010. Evaluation of groundwater arsenic treatment process in response to organic matter inclusion in feed water. Water Practice and Technology 5 (3), 1–11. Hegazy, B.E., Fouad, H.A., Hassanain, A.M., 2012. Brick manufacturing from water treatment sludge and rice husk ash. Australian Journal of Basic and Applied Sciences 6 (3), 453–461. Hemal, N.E., Zinia, B.K.N., 2001. A study of arsenic technology and leaching characteristics of arsenic contaminated sludge. Technology for arsenic removal from drinking water. ISBN 984-31-1305-6, pp. 207–208.
Huq, I.S.M., Nesa, L., Chowdhury, M.T.A., Joardar, J.C., 2011. Disposal of arsenic filter sludge in soil and its consequences. Environmental Science and Engineering 5, 165–176. Karim, M., 2000. Arsenic in groundwater and health problems in Bangladesh. Water Resources 34 (1), 304–310. Lin, D.F., Weng, C.H., 2001. Uses of sewage sludge ash as brick material. Journal of Environmental Engineering 127 (10), 922–927. Mahzuz, H.M.A., Alam, R., Alam, M.N., Basak, R., Islam, M.S., 2009. Use of arsenic contaminated sludge in making ornamental bricks. Journal of Environmental Science and Technology 6 (2), 291–298. Rahmat, M.N., 2001. Development of Environmentally Friendly Building Material: An Analysis of the use of Solidified Industrial Waste. Safiuddin, M., Karim, M.M., 2001. Ground water arsenic contamination in Bangladesh: causes, effects and remediation. In: Proceedings of the 1st IEB International Conference and 7th Annual Paper Meet. Institution of Engineers, Bangladesh, Chittagong, Bangladesh. Sullivan, C., Tyrer, M., Cheeseman, C.R., Graham, N.J.D., 2010. Disposal of water treatment wastes containing arsenic – a review. Science of the Total Environment 408, 1770–1778. US EPA (US Environmental Protection Agency), 1992. Method 1311: Toxicity Characteristic Leaching Procedure. (accessed 25.07.13).
Contents lists available at ScienceDirect
Waste Management journal homepage: www.elsevier.com/locate/wasman
Effects of using arsenic–iron sludge wastes in brick making Khondoker Mahbub Hassan a,⇑, Kensuke Fukushi b, Kazi Turikuzzaman a, S.M. Moniruzzaman a a b
Department of Civil Engineering, Khulna University of Engineering and Technology, Khulna 9203, Bangladesh Integrated Research System for Sustainability Science (IR3S), The University of Tokyo, 7-3-1 Hongo, Tokyo 113-8654, Japan
a r t i c l e
i n f o
Article history: Received 29 April 2013 Accepted 20 September 2013 Available online 13 October 2013 Keywords: Arsenic–iron sludge Brick making Leaching potentials Waste recycling
a b s t r a c t The arsenic–iron sludge generated in most of the treatment systems around the world is discharged into the nearest watercourse, which leads to accumulative rise of arsenic and iron concentrations in water. In this study, attempts were made to use the arsenic–iron sludge in making bricks and to analyze the corresponding effects on brick properties. The water treatment plant sludge is extremely close to brick clay in chemical composition. So, the sludge could be a potential substitute for brick clay. This study involved the addition of sludge with ratios 3%, 6%, 9% and 12% of the total weight of sludge–clay mixture. The physical and chemical properties of the produced bricks were then determined and evaluated and compared to control brick made entirely from clay. Results of different tests indicated that the sludge proportion and firing temperature were the two key factors in determining the quality of bricks. The compressive strength of 3%, 6%, 9% and 12% sludge containing brick samples were found to be 14.1 MPa, 15.1 MPa, 9.4 MPa and 7.1 MPa, respectively. These results indicate that the compressive strength of prepared bricks initially increased and then decreased with the increase of sludge proportion. Leaching characteristics of burnt bricks were determined with the variation of pH at a constant temperature. The optimum amount of sludge that could be mixed with clay to produce good bonding of clay–sludge bricks was found to be 6% (safely maximum) by weight. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction The serious arsenic as well as iron contamination in groundwater of Bangladesh has come out recently as the biggest natural calamity in the world. The people in 59 out of 64 districts comprising 126,134 km2 of Bangladesh are suffering due to the arsenic contamination in groundwater (Safiuddin and Karim, 2001). Seventy-five million people are at risk and 24 million are potentially exposed to arsenic contamination. Most of the recognized stages of arsenic poisoning have been identified in Bangladesh and the risk of poisoning in the population is increasing day by day (Safiuddin and Karim, 2001). The millions of shallow and deep wells that had been sunk in various parts of the country are dispensing their own special brand of poison. In consequence, a large number of populations in Bangladesh are suffering from the toxic effects of arsenic contaminated water. On the other hand, arsenic in combination with various metals such as iron causes serious environmental problems which adversely affect the health of millions of people in Bangladesh. The data collected by the governmental bodies, NGOs and private organizations reveal that a large number of populations in Bangladesh are suffering from melanosis, leucomelanosis, keratosis, hyperkeratosis, dorsum, non-petting oedema, ⇑ Corresponding author. Tel.: +880 1714087302; fax: +880 41774780. E-mail address: [email protected] (K.M. Hassan). 0956-053X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.wasman.2013.09.022
gangrene and skin cancer (Karim, 2000). To minimize these adverse effects available technologies and water treatment have been made which helps to remove arsenic and iron from drinking water (Hassan et al., 2010). Therefore, a sludge is got that will contain this arsenic and iron. So far, most of the focus has been given on awareness building and the development of water treatment system removing arsenic from drinking water. The disposal of arsenic rich sludge generated from the treatment processes is one of the issues that have received little attention from the sponsors of the technologies and the users (Eriksen and Zinia, 2001). At present, 18 large scales arsenic and iron treatment plants are working actively in Bangladesh. Each treatment plant generates about 170 m3 arsenic-laden sludge per year (Basak and Islam, 2008). They have sufficient removal capacity (>80–90%) for iron as well as arsenic (Hemal and Zinia, 2001). Landfills are commonly used technique for the disposal of sludge in Bangladesh. However, rapid urbanization is gradually making it difficult to find suitable landfill sites (Lin and Weng, 2001). In some places, sludge is directly disposed to the nearby rivers or low laying areas, which is likely to pollute surface and groundwater (Sullivan et al., 2010). It has been shown recently that arsenic-laden sludge, when disposed into the soil do release toxic elements which accumulate in plants (Huq et al., 2011). Recently, environmental regulations are becoming more stringent and volume of generated sludge continues to increase, traditional sludge disposal methods are coming under
K.M. Hassan et al. / Waste Management 34 (2014) 1072–1078
increasing pressure to change and therefore, there is a strong demand for environmentally safe reuse and effective disposal methods for iron and arsenic contaminated sludge out of water treatment plants. Incineration is costly and contributes to air pollution while landfill space is becoming scarce. A possible long term solution appears to be recycling of the sludge and using it for beneficial purposes. One technique that is available to treat hazardous waste is solidification that stabilizes and solidifies components of waste. The solidified product could be disposed off to a secure landfill site or be recycled as construction materials like bricks if it meets the specific strength requirements and can be shown to leach toxic pollutants within acceptable limits (Rahmat, 2001). In this paper, an attempt has been made to use the arsenic–iron sludge for brick making. For thousands of years, bricks have been made from clay. The major chemical compositions of brick clay were found to be silica, alumina, and ferric oxide which indicate the similar compositions of the water treatment plant sludge (Hegazy et al., 2012). So, the sludge could be a potential substitute for brick clay. Use of arsenic–iron sludge in making brick would be one of the low-cost technologies available in Bangladesh which might significantly contribute to reducing the adverse environmental effects of arsenic-laden sludge. Performance of this technology depends on the concentration of arsenic–iron sludge used as brick ingredient and burning temperature and technique for those bricks. This study mainly aims at blending of arsenic–iron sludge waste with clay for making bricks and to study the physical properties and leaching characteristics of the developed bricks for its potential use in construction works. 2. Methodology 2.1. Raw material collection The arsenic–iron sludge waste used for this study was collected from arsenic–iron removal plant (AIRP) at Manikganj (Fig. 1) in Bangladesh. Manikganj water treatment plant uses to dispose the sludge into the bank of a nearby water body. As a result, during rains, the sludge drains into the water body and increases the concentration of arsenic, iron and other elements. To reduce such contamination in water bodies, the utilization of sludge for producing environmentaly stable products such as brick manufacturing for use in construction works would be very effective. In this study, for producing sludge–clay bricks, clay sample was collected from nearby brick field at Fultola of Khulna district. Khulna, the third largest city of Bangladesh, is located in the southern part of the country and situated below the tropic of cancer, around the intersection of latitude 22.49°N and longitude 89.34°E. The area of Khulna city is 47 square km with a population around 1.5 million (BBS, 2009). 2.2. Sample preparation and testing The collected sludge samples were brought to laboratory and oven dried for 24 h at 105 °C. Then, the sludge sample and collected brick clay were crushed and sieved in such a way that the soil sample did not contain any foreign matter. Before taking the soil for sampling, large chunks of soil was crushed manually and mixed thoroughly to get a uniform representation. Water was then added slowly to the soil and mixed it thoroughly by hand until a smooth consistency for molding is achieved. After drying and crushing, the moisture content, arsenic and iron of the sludge were determined in the laboratory. Arsenic content of the sludge was determined by field kits (HACH, USA) using color coding. Arsenic determination by HACH kit involves generation of arsine gas (AsH3) by addition of prepackaged sulfamic acid and zinc powder
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and its entrapment on a strip of paper impregnated with mercuric bromide, followed by comparison of the color of the orange-brown circle on the strip to a reference scale. The iron content was determined by Phenanthroline Method using Spectrophotometer (DR 4000, HACH, USA). The quality assurance/control of samples (QA/ QC) were done using reference materials (spike samples), sample replicates (3 samples) and prepared blanks. The detection limits for the determination of both arsenic and iron was 0.01 mg/L. For the manufacture of bricks, a specific dimension of mold was utilized. In this study, the specific dimension of brick was 250 mm 125 mm 75 mm. Two wooden frames were used for molding of bricks. The side walls of the mold was 12.5 mm thick. The lower end of the mold was fixed with a plate of wood to facilitate the pouring process. A total of 4 brick samples for each sludge–clay mixture proportion of 3%, 6%, 9% and 12% were prepared in the laboratory. For the preparation of bricks, the sludge– clay mixture was placed into the mold and then compacted well to get the desired strength. Drying and burning of the brick sample was done in three stages. At first, the sample was oven dried at a temperature of 105 °C for 2 days. Secondly, the oven dried brick was burnt into a laboratory furnace at 500 °C for 12 h. Finally, the temperature was increased to about 1000 °C and in this stage the sample was burnt for 12 h. In this study, 3-stages burning process was applied to avoid firing shrinkage of the brick samples. Furthermore, for firing of bricks, the temperature had been raised uniformly @ 100 °C. The actual temperature within the laboratory furnace for brick burning was monitored using a simple dilatometer (thermometer). However, a detailed differential thermal analysis was not done in this study. It was observed from previous studies that sudden rise in burning temperature is responsible for fracturing the surface of brick sample. After the completion of burning process, the furnace was switched off and the bricks had not been been removed until they become cool to room temperature. The prepared bricks were then taken to laboratory for the determination of various physical and chemical properties. Various laboratory tests such as moisture content, specific gravity, water absorption capacity and compressive strength of bricks were performed to investigate the physical properties of the prepared sludge–clay bricks. In this study, leaching characteristics of sludge–clay bricks were investigated with the variation in sludge concentration and pH at a constant temperature. Typically, the leaching test removes the mobile component of any analyte present in the solid phase. The extraction fluid employed is a function of the alkalinity of the solid phase of the waste (USEPA, 1992). Three different conditions were selected to analyze the leaching characteristic. These conditions were acidic condition, alkaline condition and neutral condition. Particle size of waste materials will surely impact the leachability due to variation in surface area of the solid phase. Once these arsenic-laden sludge–clay bricks will be used in the construction industry, they will break, construction waste and demolition waste containing these bricks will have various particle sizes and varied leachability. In this study, each of the prepared sludge–clay brick was cut into 6 (six) equal pieces for the determination of arsenic and iron leachability. Triplicate samples were tested for leaching behavior of each mix with sludge and the average values were reported for the assessment.
3. Results and discussion After the collection of sludge sample, various chemical characteristics such as pH, arsenic and iron content were determined in the laboratory. This study found that the arsenic and iron content of the sludge sample were very high (arsenic 0.5 mg/L and iron 7.5 mg/L). The sludge had a pH value of 6.5, indicating that the sludge can be treated as neutral material. When desired bricks were
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Fig. 1. Sludge collection from arsenic–iron treatment plant at Manikganj.
prepared, various physical and chemical properties were tested in the laboratory. Quality of brick usually depends upon its water absorption capacity, moisture content, specific gravity and compressive strength. Fig. 2 represents the physical properties of the sludge–clay bricks with the variation in sludge proportion. With the increase in sludge proportion, the water absorption capacity and specific gravity of the prepared bricks were found to be increased while the moisture content was decreased. The specific gravity of iron content is usually 3 times higher than clay samples which led to gradually higher specific gravity with the increase in sludge proportion in the prepared bricks. The results indicate that the compressive strength of prepared bricks initially increased and then decreased with the increase of sludge proportion possibly due to the strong bonding of iron content with clay particles. The interpretation of this findings are given in Section 3.3.
3.1. Leaching characteristics Table 1 represents the variation in the amount of leaching of arsenic and iron with varied sludge proportions. Test results indicate that the leached arsenic content, for 3% sludge-mix brick, was always below 0.05 mg/L which is the acceptable limit of Bangladesh standard for drinking water. In this case, disposal of arsenic-laden sludge bricks into nearby water bodies appear to be safe and not to contribute to recontamination of the water environment. However, the world health organization (WHO) guideline value for arsenic is 0.01 mg/L for drinking purpose. When 6% sludge-mix was used, it exceeded the allowable limit and for further increase in sludge proportion, the amount of leached arsenic content increased rapidly. On the other hand, leached iron content was always found to be less than standard limit (0.3–1.0 mg/l).
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Water absorption capacity (%)
Moisture Content (%)
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6 5 4 3 2 1 0
3%
6%
9%
12%
25 20 15 10 5 0
3%
Proportion of sludge (%) Compressive Strength (MPa)
1.85
Specific gravity
6%
9%
12%
Proportion of sludge (%)
1.8 1.75 1.7 1.65 1.6 1.55
18 15 12 9 6 3 0
3%
Proportion of sludge (%)
6%
9%
12%
Proportion of sludge (%)
Fig. 2. Variation in physical properties of prepared bricks with the variation in sludge proportion. Column values represent the average of triplicate samples, and error bars show the range of standard deviation.
Table 1 Variation in the amount of leaching of arsenic and iron with the variation in sludge proportion. Proportion of sludge in prepared bricks (%)
Standard limits (drinking purpose)
3%
6%
9%
12%
Bangladesh
WHO
Amount of arsenic leaching (mg/L)
After After After After After
24 h 72 h 120 h 168 h 216 h
0.001 0.025 0.050 0.025 0.025
0.001 0.025 0.050 0.075 0.075
0.025 0.075 0.100 0.250 0.500
0.025 0.100 0.250 0.500 0.500
0.05 mg/L
0.01 mg/L
Amount of iron leaching (mg/L)
After After After After After
24 h 72 h 120 h 168 h 216 h
0.177 0.000 0.000 0.000 0.000
0.175 0.355 0.025 0.190 0.080
0.218 0.315 0.183 0.177 0.127
0.280 0.384 0.284 0.159 0.082
0.3–1.0 mg/L
0.3 mg/L
3.1.1. Acidic medium Bricks having 3%, 6%, 9% and 12% sludge-mix showed large variations in leaching behavior. The results of leaching tests at acidic medium (Fig. 3) indicate that leaching of arsenic and iron from burnt bricks increases with the increase in sludge proportion. For 3% sludge containing brick, the rate of leaching was lower than the 6%, 9% and 12% sludge containing bricks. In this study, it was observed that the amount of arsenic and iron leaching increased with the decrease in pH value of the aqueous medium. At a low pH value around 3.0, the leached arsenic content for almost all proportions of sludge–clay bricks were found to be far exceeding the standard limit of 0.05 mg/l. On the other hand, leached iron content was within the acceptable limit (0.3–1.0 mg/l) for 3% and 6% sludge-mix bricks but far exceeded in case of 9% and 12% sludgemix. Thus, the experimental results suggest that the burnt bricks should not be exposed to acidic medium. 3.1.2. Alkaline medium To obtain an alkaline solution, the value of pH was selected to be 12.0. Bricks having 3%, 6%, 9% and 12% sludge mix showed large
variation in leaching behavior. Corresponding test results and their graphical representation are given in Fig. 4. In alkaline medium, the leached arsenic and iron contents from burnt brick samples were found to be within the allowable limit at the initial time period. In case of arsenic, rate of leaching increases as time passes and finally it exceeded the allowable limit. On the other hand, the leached iron content was always found to be within the allowable limit (0.3–1.0 mg/L). Although initially the rate of leaching increased slowly but as the time passes, the rate of leaching decreased gradually. It was observed that in alkaline medium the rate of leaching was remarkably less than that in acidic medium. 3.1.3. Neutral medium To obtain a circum-neutral medium, the pH value was adjusted to 6.50. Bricks having 3%, 6%, 9% and 12% sludge-mix showed large variations in leaching behavior. Fig. 5 indicates that in neutral medium the rate of leaching changes with the proportions of sludge in the brick sample. For small proportion of sludge, the amount of leaching was very less. For 3% and 6% sludge containing brick samples, the leached arsenic content never exceeded the
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Fig. 3. Leaching of arsenic and iron with variable sludge proportion at acidic medium. Line values represent the average of triplicate samples.
Fig. 4. Leaching of arsenic and iron with variable sludge proportion at alkaline medium. Line values represent the average of triplicate samples.
allowable limit of 0.05 mg/L. However, for 9% and 12% sludge containing brick samples, leached arsenic was found to exceed the allowable limit after 72 h and 24 h, respectively. A similar study by Eriksen and Zinia (2001) also concluded that the arsenic treatment units renderd the majority of the arsenic into a stable and non-mobile phase. On the other hand, the leached iron content of burnt brick samples in neutral medium was found to be within the allowable limit (0.3–1.0 mg/L). For 3% sludge containing brick, leached iron content was nolonger observed after 72 h. For 6%, 9% and 12% sludge containing brick samples, there was an increase in the amount of iron leaching initially but as the time passes, the rate of leaching decreased gradually. 3.2. Effects of firing temperature The firing temperature is another important parameter affecting the degree of shrinkage. Test results of this study indicate that
there is an inverse relation between firing temperature and the proportion of sludge. The temperature of burning should be selected in such a manner that it neither very low nor very high. It has been observed from this study that burning temperature ranges between 900 °C and 1000 °C (Fig. 6). Bricks which were burnt at low temperature do not seem to have high compressive strength. On the other hand, at high temperature, brick seems to have fractured surface. So, an optimum range of temperature is required for brick burning. With the increase in sludge proportion, temperature of firing shrinkage decreases, because the swelling of the clay is much lower than that of sludge, an addition of sludge to the mixture widens the degree of firing shrinkage. A similar study (Lin and Weng, 2001) indicated that the sludge proportion and firing temperature were the two key factors determining the quality of bricks and the optimum firing temperature was around 1000 °C for 6 h. Fig. 6 indicates the relation between sludge proportion and firing temperature in the prepared sludge–clay bricks. For the
Fig. 5. Leaching of arsenic and iron with variable sludge proportion at neutral medium. Line values represent the average of triplicate samples.
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3.4. Proposals for sludge–clay bricks
Fig. 6. Relation between sludge proportion and firing temperature.
sludge proportion of 3%, the firing shrinkage was found to be occured at a temperature around 1000 °C. For further increase in sludge proportion, there was a drop in the temperature of firing shrinkage. Finally, for 12% sludge containing bricks, the temperature of firing shrinkage was found to be around 920 °C. Furthermore, the physical properties of a bricks such as moisture content, specific gravity, water absorption capacity and compressive strength were found to be completely dependent on its burning temperature (Fig. 2).
3.3. Characteristics of prepared clay–sludge bricks In this study, the quality of prepared bricks was determined on the basis of laboratory tests (ASTM C67). Four brick samples of each sludge proportion have been made and various tests were performed on those bricks to justify the effectiveness of arsenic– iron sludge as a substitute for clay. It can be said on the basis of test results that properties of prepared bricks were slightly different from the properties of controlled bricks. The durability of the brick is largely dependent upon their water absorption. The water absorption of control clay brick generally ranged between 10.0% to 11.2%. In case of this study, test results show that water absorption capacity of prepared bricks ranges from 15.2% to 19.6%. The apparent specific gravity of controlled clay brick generally ranged between 1.8 and 2.0. While apparent specific gravity test results of prepared bricks were found in the range between 1.66 and 1.79. Compressive strength significantly determines the potentiality of bricks for its application. Compressive strength is usually affected by the porosity, pore size, and type of crystallization. It is usually defined as the failure stress measured normal to the bed face of the brick. AASHTO standards for brick requirements: 150 kg/cm2 (14.7 MPa) for a first-class brick. The compressive strength of 3%, 6%, 9% and 12% sludge containing brick samples were found to be 14.1 MPa, 15.1 MPa, 9.4 MPa and 7.1 MPa, respectively. These results indicate that the compressive strength of prepared bricks initially increased and then decreased with the increase of sludge proportion possibly due to the strong bonding of iron content with clay particles. Typically, clay particles are negatively charged colloids while ferric iron hydroxides show positively charged surface sites (Dzombak and Morel, 1990) at circum neutral pH. This study found the optimum amount of sludge 6% (safely maximum) by weight could be mixed with clay to produce good bonding of clay–sludge bricks. In this case, most of the free negative changes in clay particles would form electrostatic bondings with iron hydroxide solid phase. For further increment of sludge proportion, the iron content might nolonger find free available charges for bond formation and thus gradually decreases strength. In another observation, Mahzuz et al. (2009) found that arsenic contaminated sludge could be safely used up to 4% for making ornamental bricks.
On the basis of test results of this study, it can be said that quality of sludge-brick depends upon the sludge concentration, technique of molding, degree of compaction, method of burning and firing temperature. In order to yield a good quality brick, the proportion of sludge and the firing temperature are the two key factors controlling the shrinkage in the firing process. Specific gravity, moisture content and compressive strength of the burnt brick samples are also dependent on the sludge proportion and the firing temperature. As the amount of leaching and toxicity of the burnt bricks are higher both in acidic and alkaline mediums, the prepared bricks should not be exposed to those mediums. In this study, hand molding was used for the preparation of bricks. For future works, mechanical molding should be used to compare the brick properties. For burning the sludge–clay bricks, laboratory furnace was used in this study. However, it is recommended that brick samples should be burnt alternately in the brick field and the change in brick properties should be observed. Furthermore, in this study, leaching characteristic of burnt brick samples was determined with the variation in pH at a constant temperature and one specific particle size (one sixth of a brick). A detailed investigation should be done with the variation of temperature and particle sizes in combination with the variable pH to check the leaching behavior of prepared bricks. The rate of increase in firing temperature was also considered to be a key factor. Sudden increase in temperature affects the shrinkage in the firing process. Thus, the rate of increase should be slow to avoid firing shrinkage.
4. Conclusions This work endeavoured to demonstrate a feasible way of using arsenic–iron sludge as a clay substitute for brick manufacturing. Different measurements of both clay–sludge mixtures were carried out to evaluate the factors that could affect the brick quality. The results of compressive strength tests on the bricks indicate that the strength is greatly dependent on the amount of sludge in the brick and the firing temperature. This study found that the compressive strength of prepared bricks initially increased and then decreased with the increase of sludge proportion. Moreover, the specific gravity and water absorption capacity of prepared bricks were found to be increased with the gradual increase in sludge proportion. Test results also indicate that moisture content of the prepared bricks decreases with the increase in sludge proportion. Tests on leaching characteristic identified that the amount of arsenic and iron leaching from the sludge-bricks were higher for both acidic and alkaline mediums and thus the prepared bricks should not be exposed to those mediums. Based on the laboratory test results, it can be concluded that arsenic-laden sludge could be effectively used as a component of raw materials for brick making. The optimum amount of sludge that could be mixed with clay to produce good bonding of clay– sludge bricks was found to be 6% (safely maximum) by weight. The firing shrinkage of brick was also remain unaffected in this case. Furthermore, the amount of leaching in 6% sludge content brick was less in comparison to higher sludge-mix bricks. Thus, the arsenic–iron sludge from the groundwater treatment plant would be cautiously blended with clay materials for brick manufacturing and hence be recycled as construction materials.
Acknowledgements Appreciation goes to the Department of Civil Engineering, KUET for the financial support to complete this Project.
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