Suspended Solids Sedimentation of River Water Influenced by Electrocoagulation

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1 International Conference on Transport, Civil, Architecture and Environment engineering (ICTCAEE'212) December 26-27, 212 Dubai (UAE) Suspended Solids Sedimentation of River Water Influenced by Electrocoagulation Sudatta. Mohanty, Prof. Fadil Bin Hj. Othman, and Ahmed Rozlan Nazmi Abstract River Water generally contains much lower suspended solids concentration, Bio-chemical Oxygen Demand and Chemical Oxygen Demand than industrial waste water. But even in river water treatment, electro-coagulation proves effective in removing up to 3% suspended solids with Fe electrode and up to 45% in case of electrode. The optimum density for electrocoagulation was found to be around 7 A/m 2, optimum distance between electrodes was 1mm and optimum time for electrocoagulation of 1L sample was between 2-3. The study showed that time, distance between electrodes and settling time were most important parameters for electrode and density was most important parameter for Fe electrode. At lower density, performance of Fe electrode was better than electrode. However, as density and time was increased, performance of electrode was better. Hence, this experiment proves feasibility of electro-coagulation in suspended solids removal from river water. Keywords Electrocoagulation, Suspended Solids, Sedimentation, Iron/uium electrodes, Settling Time I. INTRODUCTION RINKING water contains several suspended and dissolved impurities, both chemical and biological. These Dcompounds may come from natural sources or due to leaching of waste deposits. Inorganic compounds, in general, originate from weathering and leaching of rocks, soils, and sediments, which principally are calcium, magnesium, sodium and potassium salts of bicarbonate, chloride, sulphate, nitrate, and phosphate. Organic compounds originate from decaying plants and animal matters and from agricultural runoffs, which constitute natural humic material to synthetic organics used as detergents, pesticides, herbicides, and solvents [2]. These constituents and their concentrations influence the quality and use of the natural water resource. Traditionally water was coagulated by chemical reagents like alum to neutralize the charge on particles, form flocs of metal hydroxides and cause coagulation. However this requires large area and continuous supply of chemicals which is costly. Electro-coagulation, on the other hand helps to increase active cations without increasing salinity of water [3]. Other advantages of electro-coagulation over chemical coagulation are less sludge, no requirement of removing excess chemicals, lower maintenance, bubbles produced carry pollutants to the surface and faster removal of SS by filtration. Electro-coagulation is now considered an effective pretreatment technique prior to biological treatment, ultrafiltration, UV radiation, etc [4]. Electro-process has been tested successfully treating variety of wastewater samples such as restaurant wastewater, urban wastewater, de-fluoridation separation of suspension ultrafine particle, and removal of nitrate from water [5].According to Abraham[6], this is able to remove COD, total carbon, total dissolved solid, total suspended solids and heavy metal such as chromium, molybdenum and zinc. But performance of this approach in treating river wastewater is not well defined. In this paper, we aim to study feasibility of electrocoagulation in treating river water. We also intend to find out effect of changing various parameters like, distance between electrodes, duration and settling time on removal percentage [1]. I. MATERIALS AND METHODS A. Waste-Water Characteristics The general characteristics of the river water sample are as given in table II A 1 below: TABLE I WASTEWATER CHARACTERISTICS SL.NO. CHARACTERISTICS VALUE 1. Suspended Solid concentration 28 ppm (SS) 2. Bio-chemical Oxygen Demand 2.8 mg/l (BOD) 3. Chemical Oxygen Demand (COD) 15mg/L 4. ph 6.7 Sudatta Mohanty is a 3 rd Year B.Tech student in Civil Engineering at Indian Institute of Technology (IIT), Delhi ( sudatta.mohanty.993@gmail.com). Prof. Fadil Bin Hj. Othman is teaching at the Environmental Engineering department in Faculty of Civil Engineering, Universiti Teknologi Malaysia(UTM)( dfadilos@utm.my). Ahmed Rozlan Nazmi has just completed Masters degree at Universiti Teknologi Malaysia (UTM). 25

2 International Conference on Transport, Civil, Architecture and Environment engineering (ICTCAEE'212) December 26-27, 212 Dubai (UAE) Fig 3. Iron Electrodes Fig 1. River Water Sample in front of UTM Civil Engineering Department B. Laboratory Apparatus A laboratory batch electro reactor was designed and performed in a cylindrical glass cell (volume 1 ml) with stirring at constant speed. Stirring was provided by a plate impeller from plastic material ( 3 cm) at a rotating velocity of 1 rpm (HEIDOLPH RZR-211 Electronic) (Fig II B 2). The experiments carried out in this work were setup into static methods. The mono-polar iron (Fe) and aluium () electrodes were used in this work (Fig 2 & Fig 3). The total effective electrode area was cm 2 and the net spacing between the electrodes (d) was varied between 1 and 2 mm. Electrodes were immersed in 1 litre of river-water sample and applied density of between 35 A/m 2 and 7 A/m 2 (Fig 4). The electrodes were connected to terals of a DC Power Supply (LODESTAR 817; 3VI loa) with potensio-static or galvano-static operational options. A magnetic stirrer (3mm dia) was used to provide constant stirring at 3 rpm. Before each run, electrodes were washed properly to remove surface grease. 1% acid solution was used to remove rust from surface of Fe electrode. At the end of run, the electrodes were washed thoroughly with water to remove any solid residues on the surfaces, and dried. Fig 4. Final Apparatus for Electro-coagulation C. SS Removal Technique The suspended solid concentration was found before electro-coagulation and 2hrs (settling time) after electrocoagulation. The natural-water samples were filtered through standard GF/F glass filter paper (Fig II C 1). The residual retained on the filter paper was oven dried at 15 o to a constant weight (Fig II C 2 & Fig II C 3). Fig 5. Filteration Apparatus D. Settling Time To analyse the effect of settling time on SS removal efficiency, turbidity was used as the parameter. A standard turbidity meter (Fig II D 1) was used to analyse change of turbidity of the sample with time (Fig II D 2). Fig 2. uum Electrodes II. ANALYSIS A. SS Removal The removal efficiency of suspended solids was calculated as CR (%) = [(C o C)/C o ]*1 26

3 International Conference on Transport, Civil, Architecture and Environment engineering (ICTCAEE'212) December 26-27, 212 Dubai (UAE) where C o and C are concentration of suspended solids before and after electro-coagulation B. Turbidity Removal From analysis during settling, it is clear that Concentration (of SS) α Turbidity dc/dt α c (where dc/dt is the change in concentration of SS with time and c is the concentration of SS at time t ) Let dc/dt = -kc (where k is a positive constant and negative sign indicates that concentration of SS decreases with time) Solving, c = c o e -kt (where c o is the initial concentration of SS in the sample) The value of k shows the effectiveness of the process. III. RESULTS AND DISCUSSIONS A. SS Removal i. Under Influence of density Current density was a more influential parameter in case of Fe electrode than electrode. However, as time of electrocoagulation was increased, it also became an important parameter in case of electrode. For electro-coagulation time of 3, as density was increased from 35A/m 2 to 7A/m 2, the SS removal efficiency increased from 36% to 46% in case of electrode and from 21.4% to 36% in case of Fe electrode. (Fig 6) For electro-coagulation time of 2, the corresponding increase was from 25% to 28.28% in case of electrode and from 17.84% to 32.14% in case of Fe electrode. (Fig 7) Electrocoagulation time = 3, distance between electrodes=1mm % removal in %removal in Fe Fig 6 % removal in %removal in Fe Fig 7 density=7a/ Electrocoagulation time=2, distance between electrodes=1mm density=7a/ ii. Under influence of distance between electrodes Distance between electrodes was a very important parameter influencing SS removal efficiency in both electrode and Fe electrode. As distance between electrodes was decreased from 2mm to 1mm, the SS removal efficiency increased from 1.71% to 28.28% in case of electrode and from 1.71% to 26.15% in case of Fe electrode. (Fig 8) % removal in %removal in Fe Fig 8. iii. Under Influence of Time of Electrocoagulation Time of electro-coagulation was varied to detere optimum time required for substantial SS removal. As time of electro-coagulation was increased from 1 to 3, there was great increase in SS removal efficiency in electrode from 11.89% to 46%. However, in case of Fe there was more gradual change from 19.3% to 36% From experiments, the optimum time for electrode is around 3 and optimum time for Fe electrode is between 2 and 3. (Fig 9) %removal Electrocoagulation time=2, curren m time Fig 9 distance=1m m distance=2m m Current density = 7A/m 2, distance between electrodes = 1mm %removal in electrode %removal in Fe electrode iv. Under Influence of type of electrode At density of 35A/m 2, the performance of Fe electrode was better. But as density and time was increased to 7A/m 2, performance of electrode was slightly better. (Fig 9) This is because, at high densities or time of electrocoagulation, particles of iron oxide move into the solution providing reddish colour and increasing SS concentration. In case of distance between electrodes was more influential (Fig 1) whereas in case of Fe density was more influential. (Fig 11) 27

4 International Conference on Transport, Civil, Architecture and Environment engineering (ICTCAEE'212) December 26-27, 212 Dubai (UAE) Electrocoagulation time=2, curren m % removal in %removal in Fe Fig 1. Fig 11. B. Turbidity Removal The result of turbidity vs settling time after electrocoagulation is displayed below (Fig 12 & Table II). Turbity (FTU) % removal in %removal in Fe 5 Fig 12. distance=1 mm distance=2 mm Electrocoagulation time=2, distance between electrodes=1mm Turbidity vs Settling Time 5 1 Time (Hrs) density=7a/ electrocoag ulation 1Am, 1mm, 3.5Am, 1mm, 3.5Am, 2mm, 3 1Am, 1mm, 2 electrocoagulation 1Am, 1mm, 3.5Am, 1mm, 3.5Am, 2mm, 3 1Am, 1mm, 2 Fig 12 shows actual variation of turbidity with settling time and Table II shows the approximation of the curve with exponential curve. From the values of k, it is clear that electro-coagulation helps speed up the settling process 2-4 times. It also shows that distance between electrodes is a more influential parameter than density in case of electrode. Time of electrocoagulation is also an important parameter influencing SS removal. In case of Fe due to mixing of iron oxide in the sample, the initial turbidity was high. Initially, the rate of settling was high due to electro-coagulation. But as more iron oxide mixed into the sample, turbidity didn t decrease much. The variation of k with various factors is as shown : i. Under Influence of density TABLE II ANALYSIS OF TURBIDITY VS SETTLING TIME Co k Equation electrocoagulation time=3, Distance between electrodes=1mm C= 7.668exp (-.52t) C= exp (-.196t) C= exp (-.164t) C= exp (-.88t ) C= exp (-.112t) electr Fig A/ 7A/

5 International Conference on Transport, Civil, Architecture and Environment engineering (ICTCAEE'212) December 26-27, 212 Dubai (UAE) ii. iii. Under Influence of Electrocoagulation time Current Density=7A/, Distance between electrodes=1mm electrocoagu Fig 14 Under influence of distance between electrodes Current, Electrocoagulation time= mm 2mm ACKNOWLEDGEMENT The authors are grateful to Department of Environmental Engineering, Faculty of Civil Engineering, Universiti Teknologi Malaysia. REFERENCES [1]Application of Electro Process for Water and Wastewater Quality Improvement, Fadil Othman l, Moh Faiqun Niam, Nur Shaylinda Mohd ZinJ, 27 [2]Drinking Water Treatment Plant Status In India, Central Pollution Control Board, 22 [3]Electro-coagulation as a Wastewater Treatment, Peter Holt, Geoffrey Barton and Cynthia Mitchell, 26 [4]Electrochemical processes for clean technology, H Inan, A Dimoglo, H Şimşek, 24 [5]Electro-coagulation of reactive textile dyes and textile, wastewater. Journal of Chemical Engineering, 44, insafi, A, Khemis, M., Pons, M. N., Leclerc,.P, Yaacoubi, A., Benhammou, A., and Nejmeddine, A. (24) [6]Environmental chemistry ofdyes and pigments, Canada: John Wiley & Sons. Inc. Abraham, R., and Freeman, H. S. (1996). iv. Fig 15 Under influence of type of electrode Current density=7a/, Electrocoagulation time=3, Distance between electrodes=1mm Fig 16 IV. CONCLUSION Fe The analysis showed that the SS and turbidity removal increases with increase in density, decrease in distance between electrodes and increase in electro-coagulation time. The most suitable density was 7A/m 2. The optimum distance between electrodes was 1mm. The optimum time of electro-coagulation was around 3 for electrode and between 2-3 for Fe electrode. The curves for turbidity vs settling time showed that optimum settling time was around 2-4hrs for electrode and around 1-2hrs for Fe electrode. We get SS removal of around 45% in case of electrode and around 3% in case of Fe electrode. Hence, we can conclude that electro process can enhance settling velocity and reduce settling time. It is feasible even for river water treatment. It can be used as an effective pretreatment prior to biological treatment, ultra-filtration, UV radiation, etc. 29