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Treatment of Food-Agro (Sugar) Industry Wastewater with Copper Metal and Salt: Chemical Oxidation and Electro-Oxidation Combined study in Batch Mode
Anurag Tiwari, Omprakash Sahu
www.elsevier.comlocate/wri
PII: S2212-3717(16)30041-5
DOI: http ://dx. doi.org/ 10.1016/j .wri .2016.12.001
Reference: WRI75
To appear in: Water Resources and Industry
Received date: 18 May 2016 Revised date: 7 December 2016 Accepted date: 12 December 2016
Cite this article as: Anurag Tiwari and Omprakash Sahu, Treatment of Food-Agro (Sugar) Industry Wastewater with Copper Metal and Salt: Chemica Oxidation and Electro-Oxidation Combined study in Batch Mode, Wate Resources and Industry, http://dx.doi.org/10.10167j.wri.2016.12.001
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Treatment of Food-Agro (Sugar) Industry Wastewater with Copper Metal and Salt: Chemical Oxidation and Electro-Oxidation Combined study in Batch Mode
Anurag Tiwari and Omprakash Sahu
Department of Chemical Engineering, NIT Raipur, Raipur India School of Chemical and Food Engineering, BiT Bahir Dar University Ethiopia Correspondence author. Tel:+251940209034. ops0121@gmail.com
Abstract:
Sugar industry is one of the major industries which have been included in the polluting industries list by the World Bank. Different pollution monitoring agencies like State and National Pollution Control Boards have been made compulsory for each industry to set up a waste water treatment plants. In treatment system, single treatments of effluent are not effective to manage the dischargeable limit. So an attempted has been made to treat sugar industry wastewater with electrochemical and chemical process by using copper as electrode and chemical. Electrochemical process shows 81% chemical oxygen demand and 83.5% color reduction at pH 6, electrode distance 20mm, current density 178Am- and 120 min treatment time.The combined treatment results show 98% chemical oxygen demand and 99.5% color removal at 8mM mass laoding and pH 6 with copper sulphate.
Keywords
Chemical oxygen demand; Color; Inorganic; Settling; Waste
Introduction:
Sugarcane has been cultivated from pre-historic times in India. Indian mythology supports the fact as second largest producer of sugarcane next to Brazil. Sugar industry is seasonal in nature and operates 150 to 180 days in a year (Aradhey, 2014; Vaithiyanathan et al., 2014). A significant large amount of waste are generated during the manufacture of sugar, which
contains a high amount of pollutants in terms of suspended solids, organic matters, biological and chemical oxygen demand effluent including sludge, press mud and bagasse (Yadavand Daulta, 2014). At present 526 sugar mill are operating in India that produced 33.69 million tons of sugarcane in the year of 2015-16 (ISAM, 2016). To crush one tone of sugarcane nearly 2000 liters water required, which generated nearly 1000 liter of wastewater (Khole, 2009). Several methods has been suggested by authors to treat the sugar industry wastewater like adsorbent (Saxena andMadan, 2012), electrochemical (Asaithambi and Matheswaran 2011), anaerobic biological treatment (Alkaya et al 2011), biochemical oxidation (Prasad et al. 2006), etc. The wastewaters treated by above methods are not meeting the discharge limit; it required modification either in individual treatment or separately. Some author has been reported the combination like electrocoagulation and membrane technology (Son et al., 2014), thermolysis and coagulation (Kumar et al., 2009), electrocoagulation and coagulation (Mahesh et al., 2006) etc. The combined technology is better alternative to bring the wastewater into discharge limit. Electrocoagulation has its own impression to treat the various wastewater like textile industry wastewater (Tyagi et al., 2014), electroplating industry wastewater (Lekhlif et al., 2014), Dyes (Zhian et al., 2014), dairy wastewater (Sharma et al., 2014) etc. The electrocoagulation technology possesses manyadvantages viz. in situ production of coagulants (less externalchemicals), easier installation, lower secondary pollution, odorand color removal and lower residence times (Szpyrkowicz et al. 2005). It is complex process with a multitude of mechanisms operating synergistically to remove pollutants from the water.
Electrocoagulation treatment methods offer an alternative to the use of metal salts or polymers and polyelectrolyte addition for breaking stable emulsions and suspensions. The destabilization mechanism of the contaminants, particulate suspension, and breaking of emulsions taking place in an EC reactor may be summarized Liu et al. (2010). As a EC
suitable anode materials iron (Sahu and Chaudhari, 2015), aluminum (Cotillas et al., 2014) and other metals like carbon (Narayanan and Ganesam, 2009), mild steel (Vasudevan et al., 2009), copper (Yun et al., 2014) and stainless steel (Olmez, 2009) as well as combination of iron and aluminum (Kobya et al., 2014) are used for treatment of different industrial waste water. Up to till now no author has been reported to treat the sugar industry waste water by copper electrode or combination with coagulation with electrocoagulation.
So the investigations have been done to treat the sugar industry wastewater by copper metal and salt by combination of electro-coagulation and coagulation process. The parameters namely pH, electrode distance, current density, mass loading has been reported. The process generates sludge that necessitates a need of post treatment by separation; hence its separation by settling and filtration was also studied. Material and methods: Material
All the laboratory grades chemical (Sodium Hydroxide, Hydrochloric acid, poly aluminium chloride and Copper Sulphate) were used for analysis. The copper sheet (B96-ASTM) was purchased from market and used as electrode. The waste water collected from Bhoramdev Sugar Industry Ltd. Kavardha (C.G.) India and preserved at 18oC until used. The physicochemical characteristic of effluent is presented in Table 1. Experimental methods
The electrocoagulation experiment was performed in electrochemical reactor (EC). EC is made of transparent fiber glass having capacity of 1.5dm (10.7x10.7x13.7 cm) capacities. The reactor fitted with squared electrode having dimension 7.5 cm x 7.5 cm x 2mm (effective area 56.25 cm ) of copper material. A space of 1cm to 2.5 cm was varies between to two electrodes and 1.5 cm gap was maintained at the bottom of the reactor for the movement of magnetic stirrer. A DC power in range of 0 to 30 (V) voltages and 0 to 5 (A) current was
supplied to respective terminals in parallel arrangement. At fixed variable time measure amount of treated was collected for analysis.
Chemical coagulation process was performed in Jar test apparatus. A 200ml ofsugar industry wastewater (SIWW) was taken in a 500ml glass beaker. First pH of the SIWW was noted and initial pH (pHo) was adjusted by adding aqueous sodium hydroxide (1 M) or sulfuric acid (1 M) solution. A measureweight of the coagulant was added to the wastewater and fast agitated (110 rpm) for 5 min thereafter, slowly agitated (60rpm) for 30 min. Thenwaste water sample was kept for settling (6hrs).Clean liquid was collected and analyses for chemical oxygen demand(COD) and color removal. The percentage removal of COD and color was calculated by eq (1). The experimental setup for treatment of sugar industry waste water is shown in Fig.1.
Removal ( %) = (Ci-C^100 (1)
Where,
Ci= Initial concentration (mg/l)
Cf= Finial concentration (after treatment; mg/l) Analytical Procedure
All the physico-chemical parameter like COD, color, total solids, total dissolved solids, total suspended solid reduced carbohydrate, sulphate, chloride, etc., was determined per standard method of analysis (APHA, 1989). The colour of the sample was measured in terms of the absorbance at X = 420 nm using a UV-vis spectrophotometer (Model Lambda 35) from Perkin-Elmer Instruments, Switzerland. The residual organics in the treated effluent were analyzed by thermogravitmetric analysis (TGA, SHIMADZU, DTG-60H) Results and discussion: Effect of pH:
The effect of initial pH was carried out from pH 3-10.5 at electrode distance (ED) 20mm, current density (CD) 89Am- and time (t) 120min. Four copper electrodes configuration on percentage COD and color reduction is presented in Fig. 2(a) and (b). It can seen that COD 51.5%, 59.5%, 63.5% and color 54%, 62%, 66% removal was increases with increased in pH 3, 4.5 and 6. Further increase in pH 7.5, 9 and 10.5, COD 55%, 46.5% 43% and color 58%, 49%, 44% removal was decreases at 120min of reaction time. The lower percentage of COD and color removal can be explained by amphoteric behavior of Cu(OH)3, which does not precipitated at high acidic and alkaline pH. Similar result was observed by other author when laundry wastewater treated with copper electrode (Yun et al., 2014).
During the electrocoagulation pH change was also observed with time, which is shown in Fig.3. The effluent pH after ECT would increase for acidic influent but would decrease for alkaline influent. The initial pH of effluent 3, 4.5, 6, 7.5, 9, 10.5 was found to be change pH 5.54, 5.85, 6.13, 6.24, 7.11 and 7.52 at 120min of reaction. The general cause of the pH increase can be explained from the following equation. 2 H2O + 2e- = H2 (g) + 2OH- (cathode) (2)
This reaction shows that the cathode generates hydrogen gas,and this causes the pH to increase as the hydroxide-ion concentration in the water increases (Thakur et al., 2009). Effect of electrode distance:
The effect of electrode distance (10mm to 25mm) was examine at current density (CD), 89Am- , optimum pH 6 and time 120min, which is shown in Fig.4(a) and (b). It was found that increased in electrode distance the COD and color reduction increase with time. When electrode distance is 10mm, 15mm, 20mm the COD 48%, 54%, 63.5% and color reduction was 53.5%, 58%, 66% respectively. Again when electrode distance was increases 25mm the COD 57% and color reduction was reduced to 61.5%. This may be due to the increases in internal resistance at same current density the internal resistance drop between electrode
increase and that lead to the decrease of ion production and therefore a decrease in removal efficiency (Rahmanand Borhan, 2014). Effect of current density:
The influence of current density on the removal rates of COD and color was investigated at initial COD 3682mg/l, color 350PCU, pH 6 and electrode distance 20mm. It was found that COD and color reduction increase with increase with current density and time and decrease with further increase in current density. In Fig. 5(a) and (b) the maximum 81% COD and 83.5% color reduced when current density was
178Acm. At maximum current density 222.5Am- it was 75% COD and 79% color reduction and at minimum current density 44.5Am- 57.5% COD and 60% color reduction was found. Slowly it increases when CD 89Am-2, 133.5Am-2, 63.5%, 70% COD and 66%, 73.5% color reduction. This might be attributed to the fact that large amounts of copper (II) ions were generated at long electrolysis times which can react with the dissolved oxygen in the wastewater. This leads to lowering the amount of oxygen in the treated wastewater (Hong et al., 2014). Electrocoagulation fallowed by coagulation process:
The effect of coagulation has been carried out with waste sludge (WS), copper sulphate (CuSO4) and poly-aluminum chloride (PAC) for untreated SIWW (CODo =3682mg/l, color=350PCU) and pretreated with electrocoagulation (CODo= 699.58mg/l, color = 57.75 PCU).
pH optimization
The effect of pH0 in the range of pH 3-9 on without treated (initial mass loading 30mM) and pre-treated with electrocoagulation (initial mass loading 4mM) sugar industry wastewater (SIWW) has been investigated.In Fig. 6(a) without treated SIWW is showing maximum 49.2% COD and 52.4% color reduction at pH 6 with copper sulphate. Similarly same mass loading and pH range, poly aluminium chloride shows 47.8% COD and 51.3% color
reduction at pH 7.5. Waste sludge was not used for without treated SIWW. It has been observed that coagulationhas significant effect on further increasing the percent CODand color reductions when it is applied after electrocoagulation treated SIWW, which is shown in Fig. 6(b). An increase in COD reduction of about 11% (from 81% to 92%) and color reduction 11.5% is achieved at pH 6 and 4mM mass loading with CuSO4. Similarly poly-aluminum chloride shows COD 10.5% (from 81% to 91.5%) and color reduction 11% (from 83.5% to 94.5%) at pH 7.5 respectively. The generated sludge after electrolysis was also used as coagulant after dried and grind. It shows only 6% (from 81% to 87%) COD and 5.4% (from 83.5% to 88.9%) color reduction at pH 6 with same mass loading. Mass loading
The effect of mass loading was carried out at range of 2mM to 12mM at optimum (CuSO4 (pH 6), PAC (pH 7.5)), which is shown in Fig. 7. It was observed that COD and color removal increase with increase in mass loading. Maximum 17% (from 81% to 98%) COD and 16% (from 83.5 to 99.5%) color reduction was found at 8mM (mass loading) with copper sulphate (CuSO4). Poly-aluminum shows 16.5% (from 81% to 97.5%) COD and 15.6% (from 83.5% to 99.1%) color reduction at 10mM of mass loading. From this it can be concluded that after adding coagulant at optimum pH and mass, unreactant organic pollutant fully react and settle down. Thus results show that the electrolysis followed by coagulationis the most effectivemethod of treatment of sugar industry wastewater giving close to 100% reduction of COD as well ascolor. Physicochemical analysis of solid-liquid suspension Settling
The settling study was carried out for combined treated effluent at different pH and optimum mass loading, which shown in Fig. 8 (a) and sludge volume index is shown in Fig 8(b).The
Kynch theory was used to analyze the settling process (Richardson et al., 2003). The concentration of sludge at a time t was determined by using the following expression:
C0xTotal height Height of suspension after time t
The interface between the supernatant andthe sludge is identifiable for the electrocoagulation and coagulation treated SIWW. From Fig.8 (a) electrochemical and chemical treated sludge interface can be easily observed between the pH 7.5 and 9. It was found that the settling rate of the solids was faster initially and after some time, it decreased. The settling rate was found in the order of pH 7.5 > pH 9 > pH 6 > pH 4.5 > pH 3. The best settling shown at pH 7.5, this may be due to the formation of heavy flocks at this pH, which settle down. Flocs and flakes deposited on the anode surfaces lower the COD removal efficiency and also the sludge volume in the cell liquor, which can be clearly identified from Fig. 8(b). Under acidic pH, the electrode is attacked by H+ ions which enhance the Cu dissolution (Golder et al. 2007). The sludge characteristics at different pH are mention in Table 2.
Filtration
Gravity filtration was used for electrochemical and chemical treated wastewater, to generatethe experimental data (pH 3 to pH 9). Gravity filtration can be considered as a constant pressure filtration by neglecting the effect of change in the hydrostatic head on the total pressure. The force balance for the gravity filtration using a filter paper on a Buchner funnel can be written as a McCabe and Smith, (2001).
— = ^-.V + .Rm (4)
AV A2 AP AAP m
where, At is the time interval of filtration, (s), AV is the filtrate volume collected up to that
■5 O
time intervalAt, (m ), C is the solids concentration in the slurry, (kg/m ), V is the total liquid
filtrate volume collected up to the time interval t (m ), ^ is the viscosity of the liquid filtrate,
(Pa.s), AP is the pressure drop across the filter =pgh, (Pa), A is the filtration area, (m ), Rmis the resistance of the filter medium, (m-1), a is the specific resistance to filtration, also called as SCR
After recording the observations on the volume of the filtrate as a function of time, a plot of At/AV may produce a straight line, which is shown in Fig.9. The values of Rmand a can be calculated from the slope and the intercept, respectively are given in Table 3. Value of cake resistance are found in the order 0.032x1012(pH 4)<0.310x1012(pH9)<1.39x1012(pH4.5)< 3.53x1012(pH7.5)<5.26x1012(pH6). At pH 6 with copper sulphate show good filtration, this may due to size of particles. Thermal analysis
The TGA, differential thermal analysis (DTA) and differential thermal gravimetery (DTG) curves of the electrocoagulation scum and sludge in oxidizing atmosphere is shown in Fig. 10 (a) and (b) respectively. The DTAtrace shows dehydration and volatilization (removal of volatiles) of the sample up to 300oC losing weight of 21.84% for filtrate treated water and 31.05% for precipitated sludge. The results reflect to contain of less volatile materials in filtrate as compared to settled sludge. The peak rate of weight loss 0.79mg/min was seen at temperature Tmax137oC for filtrate and 5.3mg/min at259oC for sludge.Oxidizing of solids was found exothermic, showing the heat evolution 1020 J/g for filtrate and for settling sludge it was 1740 J/g. Oxidation seems to be completed at 600oC for scum and 800oC for bottom sludge. In 1000 C the 49.28% weight of filtrate and 60.09% weight of settled sludge as ash found to remain. Thus settled sludge contains less inorganic material as compare the filtrate. Thus, the amount of ash in sludge is lower than that of filtrate which showed 10.81% ash. Hence, the calorific value of sludge is expected to be higher than that of filtrate (Shak and Wu, 2015). Conclusion:
The sugar industry wastewater treatment with electrocoagulation and coagulation shows promiseable result up to discharge limit. It is possible to reduced 81% COD and 83.5% color reduction at pH 6, electrode distance 20mm and current density 178Am- and 120 min treatment time. Addition of coagulant CuSO4 has shown 98% COD and 99.5% color removal at 8mM loading and PAC had shows 97.5%COD and 99.1% color removal at 10mM loading with electrocoagulation treated wastewater. The combined treated SIWW shown better settling at pH 7.5 and filtration at pH 6. The settling sludge shows less inorganic material as compared to filtrate at optimum pH. The dried sludge is grindinable and it can add in cements for constructing material.
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Fig. 1: Experiment setup (1) wastewater sample, (2) pump, (3) electrode, (4) magnetic stirrer, (5) DC supply, (6) agitator, (7) beaker for coagulation, (8) discharge
Time (min)
-0-pH3 -Q- pH4.5
pH6 -0-pH7.5
-*-pH9 --X-pHlO.5
¡//PS
60 80 Time in (min)
Fig.2: Effect of initial pH on (a) COD (b) color removal at ED=20mm COD=3682mg/l, Color=350PCU
, CD=89Am-2,
i« 6 5
tl D :s
4.5 6 7.5
Initial pH of WW
Fig.3: Effect of initial pH on pH change at 120min reaction time
60 80 Time (mill)
■o- 10 mm
■A- 20mm
/ / / o','
'/V / * / / / / / /
■o 15 mm
O 25 mm
60 80 Time (min)
Fig.4: Effect of electrode distance on (a) COD (b) color removal at pH6, CD=89Am- ,
COD=3682mg/l, Color=350PCU.
-c— CD=4 4. 5A/m2 HCHCD=S9A/m2 ■ö-CD=133.5A/m2 OCD=178A/m2 -X- CD=222.5A/m2
Time (min)
-<0- CD=44.5 A/m2 -O- CD=89A/m2 -A- CD=133.5A/m2 -O- CD=178A/m2 - x- CD=222.5A/m2
PS.--'
<//p '///
iff* it/f №
Time (min)
Fig.5: Effect of current density on (a) COD (b) color removal at ED=20mm, pH6,
COD=3682mg/l, Color=350PCU
■^CuS04 COD -C-PACCOD
CuS04-Color ■o- PAC-Color
Sample pH
^^WS-COD —A—CuS04-C0D ^^PAC-COD -O- WS-Color -A- CuS04-Color -O- PAC-Color
Sample pH
88 ¡-©
Fig.6: Effect of initial pH on COD and colour removal (a) without treatedSIWW at 30mM mass loading COD = 3682mg/l and (b) pre-treated with electrocoagulation at
4mM mass loading, COD= 670mg/l.
Fig.7: Effect of mass loading on (a) COD and (b) color removal at optimum pH, COD=
690mg/l.
Time (min)
100 120
50 300
Sample pH
Fig.8:
(a) Settling of sludge at different pH,
(b) Sludge volume index
10 20 30 40 50 60 70
VxlOfiim3)
Fig.9: Filterability of the flocculated slurry
-100.0
-150.0
-200.0
-250.0
-300.0
137 Cel 0.79 mg/min
244 Cel
1011 C 49.28 % 0.0
-1.00 g= E
-1.50 o I—
500 600
Temp Cel
-200.0
-400.0
259 Cel
-15.0 ct E
O I— Q
100 200 300 400
500 600
Temp Cel
700 800 900 1000
Fig. 10: Thermal oxidation characteristics of the (a) scum and (b) sludge by copper electrode. Heating rate = 100 K/min; sample weight = 10.5 mg.
Table 1: Characteristic of sugar industry waste water
S.No Characteristics Quantity
1 Color Dark brown
(350PCU)
2 pH 5 . 5
3 COD 3682
5 Phosphate 5.9
6 Protein 43
7 Total solid 1987
8 Suspended solid 540
9 Dissolved solid 1447
10 Chloride 50
11 Hardness 900
All the values except pH and color is in mg/dm3
Table 2: Analysis of residue obtained after EC (Copper) and coagulation (CUSO4) at
different pH.
S.No Parameter /pH 3 4.5 6 7.5 9
1 Weight of residue(kg/m ) 7.12 7.49 8.12 9.05 8.58
2 Color Light greenish Light greenish dark bluish green bluish green bluish green
3 Nature Flakey &Tough to grind Flakey & Tough to grind Flakey &easy to grind Flakey &easy to grind Flakey & Tough to grind
4 Size(mm) 1-4 2-6 2-6 1-5 1-5
6 Percentage convertible COD 86 87 92 89 88
7 Percentage of color 87.25 88.5 95 91 89.5
Table 3: Filterability of the treated waste water
S.No Initial pH Kpx10"12 ßx10-6 C ax10-14 Rmx10-12
s/m6 s/m3 Kg/m3 m/Kg
1 3 0.609 0.093 5.6 1.61 0.032
2 4.5 0.609 3.886 1.21 7.45 1.39
3 6 0.641 3.552 3.64 2.60 5.26
4 7.5 0.702 9.866 7.55 1..38 3.53
5 9 0.74 0.866 1.58 6.94 0.310
