IDENTIFICATION THE BENEFICIAL USAGE
OF WATER TREATMENT SLUDGE

MARFIAH AB.WAHID
AZINOOR AZIDA ABU BAKAR
AMINUDDIN MOHD BAKI
FAIZAH KAMARUDDIN
Lecturer of Faculty of Civil Engineering, UiTM Shah Alam 

NURUL IZZA HASSAN
WAN AMIZAH WAN JUSOH
Undergraduate Student of Faculty of Civil Engineering, UiTM Shah Alam 

TAJUL ARIFFIN ADAM
Lecturer of Faculty of Art and Design, UiTM Shah Alam

INTRODUCTION 

Sludge is a byproduct of water treatment. Sludge was produced during clarification and filtration processes. Sludge was also produced from the accumulated solids removed from sedimentation basin or settling tank. The disposal of sludge from water treatment operations has become a major problem in Malaysia. The problem becomes acute because of scarcity of space for installation of treated sludge. The advantage of water sludge is that this kind of sludge is not a hazardous waste. Many people concern about the constituents of the sludge those that affect our body our body system. This study should continue in finding the product which can be produced from water sludge. Figure 1 shows the traditional approach for water sludge management. Figure 2 shows the new approach for water sludge management.

The physical characteristics, mineral compositions and chemical compositions of water treatment sludge are influenced by raw water quality and water treatment processes.

Physical properties of sludge include plasticity limit, moisture content and particle size. For pottery making, the plasticity characteristics permit the sludge to be shaped or molded when mixed with water; and they must have sufficient wet and air-dried tensile strength to maintain their shape after forming. Plasticity behavior and maximum deformation, which depends on moisture content, will be examined using plastic limit and liquid limit test (Attenberg Plasticity limit).The moisture content of samples will be determined by weighing the samples after dried at 110ºC.The percentages of the various grain sizes present in a sludge will be determined by sieving and sedimentation hydrometer test. Finer particles give a smoother and shinier surface than coarser particles (Hammer, 1991). Particles size need for pottery is less than 0.005 mm (5μm). Color is an important source of information for sludge (e.g. a red sludge indicates the presence of iron oxide; blue or grey soil indicates the sludge originated from a marsh). Metallic oxides (particularly those of iron, magnesium and calcium) influence the color of the finished fired product.

The shape, size and specific surface all influence the engineering behavior of sludge minerals. Mineral composition is shown by a chemical formula, which is a shorthand way of indicating the numbers of atoms of different elements that make up the mineral .Mineral composition of the sludge was determined using X-ray Diffraction (XRD).

Chemically, there are compounds of silica and alumina with varying amounts of metallic oxides and other impurities. Although technically metallic oxides are impurities, they act as fluxes, promoting lower temperatures. Chemical composition of the sludge was determined by using X-ray Fluorescence (XRF) and Total Nitrogen Measurement (TNM).

 All standard techniques were done as described in British Soil Standard (BS1377-1990)

RESULTS AND DISCUSSION 

Mineralogical Composition 

The first feature studied was mineral compositions. Mineral compositions as determined by X-ray diffraction are as follows: Silica, kaolinite, muscovite, iron oxide and   iron hydrogen phosphate.

Silica is more prominent compared to others. The result is shown in Figure 4

Figure 4: XRD pattern for water treatment sludge

There are a few forms of silica. The form of free silica (SiO₂) is found in almost all clays, in various forms such as quartz (a constituent of sand, flint and other rocks), tridymite, cristobalite (both formed from quartz geologically or when fired) and amorphous (non crystalline) silica. Water treatment sludge contained high concentration of free form silica. Referring to McKee, 2006, for most clay, kaolinite or Al₂Si₂O₅(OH)₄, Aluminum Silicate Hydroxide is a major component and also sold as ‘kaolin’. Is formed from the alteration (mostly weathering) of aluminum rich silicate minerals such as feldspars. Kaolinite is important to the production of ceramics and porcelain. Muscovite or KA_l2(AlSi3O10)(F, OH)₂, Potassium aluminum silicate hydroxide fluoride. Muscovite is not often valuable as a mineral specimen but is often associated with other minerals of extraordinary beauty and value.  

Iron Oxides are minerals that are form by combination of cation with oxygen. These are in the category of non silicate minerals. This mineral creates the reddish color of the sludge.

Iron Hydrogen Phosphate, FeH₂P₂O₇ is a non silicate mineral.

Chemical composition 

Chemical composition is vital because of its effect on the product behavior. The chemical composition of water treatment sludge was determined by X-ray fluorescence is shown in Table 1. Water treatment sludge is compared with clay. Water sludge has less SiO₂ and K₂O than clay but more Al₂O₃ and Fe₂O₃.Percentage of Al₂O₃ is high   due to coagulation process during water treatment process. Whereas Fe₂O₃ is iron oxide which give the reddish color of water sludge

TABLE 1: Chemical composition of water treatment sludge (percentage) 

 SiO₂ (Silicon Dioxide, Silica): Silica is found in nature in several forms, including quartz and opal. In fact, it has 17 crystalline forms. Silica is manufactured in several forms including as a major ingredient in Portland cement, glass, porcelain ceramic and is also used as a homeopathic remedy to treat impure blood, brittle nails and lack lustre hair (Hansen, 2003).

Al₂O₃ (Aluminium Oxide, Alumina): Alumina has a very high melting temperature and alumina ceramics can maintain up to 90% of their strength above 1100C. They are thus employed in many refractory materials. Aluminum oxide is an excellent thermal and electrical insulator. In its crystalline form, called corundum, its hardness makes it suitable for use as an abrasive and as a component in cutting tools. Powdered aluminum oxide is frequently used as a medium for chromatography (Hansen, 2003).

Fe₂O₃ (Iron Oxide, Ferric Oxide): Iron compounds are the most common coloring agent in ceramics. On one hand, they are nuisance impurities where they stain otherwise white clay or glaze or where they muddy an otherwise bright color. Iron oxides, along with oxides of other metals, provide the colors in some glazes after being fired at a high temperature. They are also used as pigments (Hansen, 2003).

K₂O (Potassium Oxide): K₂O is considered together with sodium, since the two almost always occur together and have very similar properties. When taken together the two are often labeled KNaO. K₂O generally promotes higher melt viscosity than Na₂O.It is an important auxiliary flux in high temperature glazes. It is a heavy oxide and in general hosts the brightest colors of all fluxes except for lead. It is usually preferred even to soda for a more brilliant glossy glaze and longer firing range. K₂O is considered as a very stable and predictable oxide (Hansen, 2003).

MgO (Magnesium oxide): is a white solid mineral that occurs naturally as periclase and is a source of magnesium is used by many libraries for preserving/deacidifying books, and as an insulator in industrial cables. It is also used as a medication to relieve heartburn, sour stomach, or acid indigestion. Medical uses of Magnesium oxide also include as a short-term laxative, or used to supplement a diet with magnesium. Magnesium oxide is used as a basic refractory material for lining crucibles. Magnesium oxide is a principle ingredient in construction materials used for fireproofing. It is used as a reference white color in colorimetric (Hansen, 2003).

CaO (Calcium oxide): Commonly known as lime, quicklime or burnt lime. It is also used in water and sewage treatment to reduce acidity, to soften, as a flocculants and to remove phosphates and other impurities; in paper making to dissolve lignin, as a coagulant and in bleaching; in agriculture to improve acidic soils; and in pollution control - in gas scrubbers to desulphurize waste gases and to treat many liquid effluents. It is a refactory and a dehydrating agent and is used to purify citric acid, glucose, dyes and as a CO₂ absorber. It is also used in pottery, concrete, paints and the food industry, where it is sometimes used (in conjunction with water) to heat items like MREs (Meals Ready to Eat) and coffee (Hansen, 2003).

SO₃ (Sulphur): SO₃ refers to the sulfur material that burns away during firing. It can be used in an analysis to make clear the nature of LOI components. Since it is lost during firing, a formula weight of zero should be used so there is no impact on the calculated formula or calculated properties. Many raw clays contain some sulfur (Hansen, 2003).

P₂O₅ (Phosphorus Pentoxide): Phosphorus along with calcium is an essential element in plant and animal growth, thus its principal source is organic ash (i.e. calcined cattle bones). Phosphoric oxide is normally present in only trace amounts in ceramic materials. Phosphorus Pentoxide is an extremely good dehydrating agent. When combined with a carboxylic acid, the result is an anhydride. Phosphorite mineral Ca₃(PO₄)₂ and Apatite 3Ca₃(PO₄)₂ Ca(Cl,F)₂ are the parent rocks of phosphate fertilizers (Hansen, 2003).

TiO₂ (Titanium dioxide): The TiO₂ group is composed of rutile, anatase, and brookite. This product is mainly for pottery-porcelain and enamel industry. Titanium dioxide (TiO₂) is a multifaceted compound. TiO₂ is also a potent photocatalyst that can break down almost any organic compound when exposed to sunlight, and a number of companies are seeking to capitalize on TiO₂'s reactivity by developing a wide range of environmentally beneficial products, including self-cleaning fabrics, auto body finishes, and ceramic tiles. Also in development is a paving stone that uses the catalytic properties of TiO₂ to remove nitrogen oxide from the air, breaking it down into more environmentally benign substances that can then be washed away by rainfall. Other experiments with TiO₂ involve removing the ripening hormone ethylene from areas where perishable fruits, vegetables, and cut flowers are stored; stripping organic pollutants such as trichloroethylene and methyl-tert-butyl ether from water; and degrading toxins produced by blue-green algae. It remains to be seen, however, whether the formation of undesirable intermediate products during these processes outweighs the benefits offered by TiO₂'s photocatalytic properties (Hansen, 2003).

MnO (Manganese Oxide): Manganese is a constituent in many igneous rocks, and thus occurs in many clays weathered from these parent rocks (Hansen, 2003).

ZrO₂ (Zirconium Dioxide): Zirconium oxide is an extremely refractory material and its metallic form likewise melts very high. Zircon can be added to transparent glazes to produce a harder surface (Hansen, 2003).  

PHYSICAL CHARACTERISTICS 

Sample selection 

In this research, sludge sample from water treatment plant were selected .A representative sample was taken and graded in size ranges of less than 425 µm. As a pilot study, this research only emphasize on the behavior of sludge sample when mixed with Kaolin. 

Sample preparation 

Wet sieve was used to make size fractions .Both samples, water sludge and clay were classified by using wet sieving method namely hydrometer test. For Atterberg limit test, water sludge which passed a 425 µm test sieve was prepared to mix with clay weighing about 500 g. The mixture was then added with distilled water to become a paste. Sample about 300 g from the paste was used for cone penetration test to get the liquid limit and the rest of the paste was used for plastic limit test. 

Moisture Content and Plasticity 

TABLE 2: Moisture content of Water sludge and Clay

TABLE 3: Comparison of Plasticity Index for water sludge   and the mixture of water sludge with clay

Plasticity is very important in any ceramic product. Moisture content and plasticity behavior for water treatment sludge when mixed with natural clay in this study is shown in Table 2 and Table 3 respectively. It is clearly shown that the plastic limit of the sample will increase after added with clay. Result in Figure 5 shown that the plasticity index for raw water sludge is in the category of silt with high plasticity and the mixture of water sludge with 50% clay and 10% clay is in the category of silt with intermediate plasticity. Logical explanation for this is because water sludge is not clay even though kaolinite existed in the composition but kaolinite is the lowest category of clay. The content of silica is high and to increase the plasticity index for ceramic product need to add with high quality of clay.  Calculation of the mixture is very important for good quality ceramic product.

Figure 5: Plasticity Index chart for different mixture of water sludge and clay

RECOMMENDATIONS AND CONCLUSION 

Sludge is a byproduct of water treatment process. It has always been considered as waste, which needs to be disposed with its associated costs. This paper has reviewed the potential of turning this waste into a resource. As a resource it has potential to generate wealth from the resulting products. Apart from direct benefits, turning waste into wealth will also reduce disposal costs and eliminate the need for disposal sites, hence saving in land usage. Reduction in waste handling will definitely lead towards a more sustainable development, which is thus lead towards sustainable environment. Further study for producing water sludge as a construction material is recommended.