Treatment of textile effluent by fly ash and reusing of colour adsorbed fly ash

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1 Journal of Scientific CHANDRASEKARAN & Industrial Research & MALATHY FLY ASH TO ADSORB TEXTILE DYE AND USE COLOURED FLY ASH Vol. 70, March 2011, pp Treatment of textile effluent by fly ash and reusing of colour adsorbed fly ash P Chandrasekaran 1 * and R Malathy 2 1 Department of Civil Engineering, Kongu Engineering College, Perundurai , India 2 Excel Engineering College, Komarapalayam , India Received 16 September 2010; revised 02 February 2011; accepted 04 February 2011 In this study, fly ash from thermal power plant was used as adsorbent for dye effluent emitted from textile processing industries. Sludge [colour adsorbed fly ash (CAF)] from packed column was used to replace cement in different proportions in concrete. CAF concrete was not found equal to strength of conventional concrete but it was above the standard level and comparable. Durability test gave satisfactory results. Keywords: Adsorption, Colour adsorbed fly ash(caf), Fly ash, Packed column Introduction Fly ash (FA) and soil mixture has been used as adsorbents for dye effluents 1. Activated carbon and FA are reported 2 to reduce totally the COD values in domestic wastewater. Reverse osmosis (RO) method is costlier, time consuming and not bearable by small and medium sized industries 3. Fixed bed adsorption FA columns 4,5 exposed to cadmium bearing wastewater was found very effective. Piekos & Pasalawska 6 found that FA removed fluoride completely. FA also adsorbed heavy metal like Cr(VI) 7 and Zn(II) 8 and removed effectively dinitro butyl phenol (DNBP) 9 from aqueous solutions. Adsorption of metal ions onto FA surface depends on proportion of carbon contents. Concentration of various metals in leachates depends on their chemical nature, and association with mineral phases of FA 10. While treating effluent, carbon contents of FA is removed and it becomes more pozzolanic material having predominantly of glass phase, which reacts like pozzolanic martial. Later, it changes FA as cementitious material after reacting with Ca(OH) While using treated liquor and FA in cement and concrete, FA resulted in complete removal of toxicity 12. FA can also be used for soil reclamation 13 and as cold bonded light weight aggregate 14. FA is also used for brick production and for reclamation of alkali soil 15. This study presents FA to adsorb dye effluent and then colour adsorbed fly ash (CAF) was used to replace *Author for correspondence pc_civil@yahoo.com, civilpc1965@gmail.com cement. CAF strength properties were compared with strength of conventional concrete (CC) and ordinary fly ash concrete (OFC). Experimental Section Materials FA was obtained from combustion of pulverized coal in Thermal power station at Mettur, Tamil Nadu. It is generally finer than cement and consists mostly of spherical glassy compounds of complex composition. Dye effluent was collected from textile dyeing industries. Ordinary 53 Grade Portland cement and naturally available river sand (Fineness modulus, 2.6; specific gravity, 2.65) were used. A well graded (size, 20 mm) angular broken aggregate (Flakiness Index, 21.12%) was used as coarse aggregate. A sieve analysis (IS ) was carried out for both fine and coarse aggregate. Based on sieve analysis results, gradation of coarse aggregate was determined as a well graded aggregate (fineness modulus, 6.72) and zonation of fine aggregate confines to zone III (fineness modulus, 2.6). Well graded coarse aggregate reduces air content of concrete and as flakiness Index is less, this increases aggregate-gel (Transition Zone) bond strength. As fine aggregate falls in Zone III, bleeding and segregation of concrete is reduced and hence reduction in strength of concrete is avoided. CAF was taken out from packed column as a sludge and was dried and mixed with designed mix of concrete (1: 1: 2 for cement: sand: coarse aggregate) with w/c ratio of 0.45 for M25 concrete replacing cement in

2 236 J SCI IND RES VOL 70 MARCH 2011 PACKED COLUMN CYLINDER Fig. 1 Packed column layout proportions of 0%(Specimen I), 10%, 20% and 30% (Specimen II). Packed Column Typical PVC packed column (diam, 20 cm; ht, 60 cm) was adopted (Fig. 1). Experiment was done by using single layered FA. Bottom of column was filled with sand (thickness, 20 cm) and above which a mixer of FA and sand at 3:1 (thickness, 20 cm) was provided. Perforated cloth filter (1 µ) was provided at the bottom of column to avoid washout of FA. Removal of dyes by adsorption on column composed of FA and sand mixtures reaches saturated condition when adsorbent mixture stops adsorbing solute dyes. Concentration of dye in effluent, when becomes equal to initial concentration, indicates reaching of adsorbent to equilibrium point. Absorbance Absorbance Wavelength (Nanometer) a) Tests on Dye Effluent Chemical characteristics tests [ph, total dissolved solids (TDS), suspended solids (SS), chlorides, sulphate, COD and BOD] were conducted on raw and treated dye effluents. Optical density of raw and treated dye effluent samples (Fig. 2) was measured with spectrophotometer (APHA 16, 1996). Experiments conducted on Concrete Samples Mean compressive strength tests were carried out for 28 days old cubes of M25 CC, M25 OFC and M25 CAF concrete (CAFC) with replacement of cement by FA and CAF ash of 10%, 20% and 30%. For durability tests, other sets of cube samples (size, 150 mm) from CC and CAF replaced concrete with replacement of cement by CAF in the proportion of 10%, 20% and 30% were prepared, water cured for 28 days and dried for one day. Weights of these cubes were found out. Wavelength (Nanometer) b) Fig. 2 Optical density for: a) Untreated sample; b) Treated sample For acid attack test, 1N H 2 SO 4 (3%, ph 2) was used. For chloride attack, 1N NaCl (3%, ph 7) was used. For alkaline test, NaOH (3%) was added with water. Sets of cubes were immersed in these solutions for 90 days. Concentration of solution was maintained throughout this period. After 90 days, specimens were taken out, surfaces were cleaned and weights of specimens were measured. Compressive strength and loss/gain in weight of concrete of cubes were found. Rapid Chloride Penetration test (RCPT) was performed as per ASTM C 1202 to determine electrical conductance of CC and 30% of CAFC mix for M25 concrete at the age of 28 days curing and to provide a

3 CHANDRASEKARAN & MALATHY FLY ASH TO ADSORB TEXTILE DYE AND USE COLOURED FLY ASH 237 Compressive strength, N/mm 2 Fig. 3 Chemical characteristics of untreated and treated samples rapid indication of its resistance to penetration of chloride ions as a quality control measure. Test method consists of monitoring amount of electrical current passed through 51 mm thick slices of 102 mm nominal diameter of cylindrical specimens for 6 h. For preparation of specimens, coarse aggregates passing through sieve (size, 12.5 mm) were used. RCPT apparatus consists of two reservoirs. Specimen was fixed between two reservoirs using an epoxy bonding agent to make test set up leak proof. One reservoir (connected to positive terminal of DC source) was filled with 0.3 N NaOH solutions and other reservoir (connected to negative terminal of DC source) with 3% NaCl solution. A DC of 60 V was applied and maintained across specimen using two stainless steel electrodes (meshes) and current across specimen was recorded at 30 min interval for duration of 6 h. Total charge passed during this period was calculated in terms of coulombs using trapezoidal rule (ASTM C ) as Q = 900 (Io + 2 I I I I 360 ) (1) where Q, charge passed (C); I o, current (A) immediately after voltage is applied; and I t, current (A) at t min after voltage is applied. Standard chloride ion penetrability in specimens based on current passed is given as: high, 4000; moderate, ; low, ; very low, ; and negligible, <100. Results and Discussion Dye Effluent Chemical characteristics (Fig. 3) of untreated (ph 8) dye effluent got reduced in treated (ph 7.2) samples as follows: ph, 10, BOD, 66.21; COD, 65; chlorides, 20; Compressive strength, N/mm 2 Fig. 4 Compressive strength of concrete (1:1:2) Fig. 5 Compressive strength of concrete after immersion in acid, chloride and alkaline environment TDS, 16.67; hardness, 13.33; SS, 50; and sulphate, 50.3%. In spectrometer test (Fig. 2) around wavelength of 620 nm, colour absorbance is maximum, indicating that colour is totally removed and other toxic contents are reduced by 50%. Hence, by using FA as adsorbent for dye effluent by suitable method, work load is reduced to half. Concrete Compressive Strength Test Varying percentage of CAF % replacement of CAF Under 28 days mean compressive strength tests (Fig. 4), carried out for M25 CC cubes, M25 OFC and M25 CAFC cubes with partial replacement of cement by FA and CAF ash of 10%, 20% and 30%. even though, CAFC results into a slightly lesser strength than OFC, these values are higher than target mean strength of M25 concrete of 31.6 MPa. Hence, CAF can be effectively used as a raw material for concrete in construction industries.

4 Table 238 J SCI IND RES VOL 70 MARCH 2011 Table 1 Quantitative difference in weight loss/gain of CAF replaced concrete with conventional concrete Specimen Acid test Chloride test Alkaline test Weight loss, % Weight gain, % 10% CAF % CAF % CAF Durability Test Table 2 Gain in weight characteristics Specimen Weight Weight Increase weight before after in weight gain% RCPTkg RCPTkg kg Specimen-I (M25 (Conven.) Specimen-II (M25 by 30% replacement) Table 3 Current penetrability characteristics Period of Current penetrability measurement C min Specimen I Specimen II (M25 (M25 by 30% Conven.) replacement) Compressive strength of M25 specimens after conducting durability tests at the age of 90 days immersion was found out (Fig. 5a). Quantitative difference in weight loss in acid immersion and weight gain in chloride and alkaline immersion has occurred when CAFC replaced with CC (Table 1). In acid, compressive strength is not much affected in M25 concrete due to presence of calcium oxide, which imparts strength with age. It is the CAF, which acts as a filler material and easily combines with basic oxides to form various silicates, thereby increasing impermeable nature. In NaCl and NaoH solutions, compressive strength is not much affected compared with conventional cubes. Current, A Time, min 30%CAF M25 Conven M25 Fig. 6 Penetration characteristics of conventional and CAF replaced concrete Chloride Ions Penetrability Characteristics Weight gain of specimen shows chloride penetration for normal fly ash concrete is more when compared with 30% replaced CAFC due to increase of powder content and filler effect (Table 2). Current penetrability values in coulombs are given in Table 3. Using Eq. (1) for specimen I (M25 CC), Q = coulombs and for specimen II (M25 by 30% CAF replacement), Q = coulombs, indicating chloride ion penetrability as moderate in both cases. If average chloride penetrability is low, quality assessed is good. Overall quality of concrete with 30% partial replacement of cement by CAF seems to be good. Decrease in water content combined with the production of additional cementitious compounds reduces pore interconnectivity of concrete thus decreasing permeability. Reduced permeability results in improved long-term durability and resistance to various forms of deterioration. Comparative Study of Current With Time Chloride ion reduces electrical resistance of concrete. For CC cubes, chloride ion penetrability is more, when compared with 30% replacement of CAF, due to increase of impermeability by adding CAF as a filler material (Fig. 6). Conclusions This experimental study has proved to be better in reducing dye effluent pollutant concentration in dyeing industry and giving solution to disposal problem of colour adsorbed Fly ash by using it to treat dye effluent, thereafter to be used in concrete manufacturing. Dye effluents are drastically reduced by this treatment method. Strength and durability of CAF mixed concrete also was found to be good. Thus disposal of sludge after effective

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