Analytical & Bioanalytical Electrochemistry

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1 Anal. Bioanal. Electrochem., Vol. 2, No. 3, 2010, Analytical & Bioanalytical Electrochemistry 2010 by CEE Full Paper Phosphorous removal from wastewater effluent using electro-coagulation by aluum and iron plates Hamed Gharibi, 1 Amir Hossein Mahvi, 1,2,* Mohammad Chehrazi, 3 Razih Sheikhi, 1 Sara Sadat Hosseini 1 1 School of Public Health and Center for Environmental Research, Tehran University of Medical Sciences, Tehran, Iran 2 National Institute of Health Research, Ministry of Health, Tehran, Iran 3 Department of biostatistics and epidemiology, Tehran university of medical sciences, Tehran, Iran * Corresponding Author; Tel.: ; Fax: ahmahvi@yahoo.com Received: 24 July 2010 / Accepted: 5 October 2010 / Published online: 20 October 2010 Abstract- In this study, phosphorous removal from wastewater effluent performed using electro-coagulation by aluum and iron plates. This work had 3step: assessment of electrocoagulation for phosphate removal with phosphate concentration based on wastewater effluent in standard conditions (6mg/l), and evaluation of ph (3, 5.5, 7, 8.5, 10), voltage (20 V, V, 40 V), and contact time(10, 20, 40, 60 ) for elucidation of best condition in phosphate removal; evaluation of the process according to the best conditions obtained in step 1 in different concentrations of 4, 8, and 10 mg/l; test of optimum conditions obtained in first two steps on real wastewater. Result obtained from synthetic waste water showed that the most effective phosphate removal with AL/AL plates is % in ph 8.5 and 40 V and 40 after starting process and for IR/IR plates is % in ph 5.5 and 40 V and 40 after starting process. Result obtained from 2th step revealed that the removal efficiency was high whenever concentration of phosphate decreased and efficiency of removal with AL plates is higher than IR plates. In 3th step, efficiency of phosphorous removal using electro-coagulation assessed and efficiency of this step with aluum plates on real wastewater under different conditions is %. Keywords- Phosphorous removal, Electro-coagulation, Wastewater effluent

2 Anal. Bioanal. Electrochem., Vol. 2, No. 3, 2010, INTRODUCTION As known, phosphate discharged into the surface waters, accelerates eutrophication [1, 2]. This can in turn disturb the balance of organisms present in the water and affect water quality, mainly through the depletion of oxygen level as the algae decay. Reduced oxygen level can have harmful effects on fish and other aquatic life, causing reductions in biodiversity. Eutrophication can also affect the recreational value of natural resources [3]. Phosphorus removal techniques are chemical treatments like adsorption, chemical precipitation, ion exchange, electro dialysis, hybrid systems containing fly-ash adsorption and membrane filtration and electrocoagulation [4].Biological treatment for phosphorous removal also used but removal efficiency usually does not exceed %, which means that remaining phosphate should be removed by another technique [5]. Phosphate removal with adsorption and chemical precipitation also have been explored [6,7], but chemical precipitation with use of aluum sulphate and ferric chloride need further costs for purchase and installation of dosing equipment and operating costs for power, disposal of additional sludge, manpower, and surely chemicals used [8]. Electrocoagulation for wastewater treatment has been tested in recent years. Electrocoagulation is a process that creating metallic hydroxide flocks within the wastewater by electro-dissolution of soluble anodes, usually made of iron or aluum [9]. Phosphate removal with electrocoagulation has a several advantages, such as no need of additional chemical matter after or before treatment, relatively low area demand [10], also sludge from this process is intensive and has low water [11]. For this reasons, in this work, phosphate removal from wastewater effluent has been studied with electrocoagulation. Choosing plates for this process is very important and common plate materials are aluum and iron. They are cheap, readily available, and proven effective [12]. As known, Al 3+ and Fe 3+ ions dissolve and combine with hydroxyl ions in the water [13], when direct current passes through the Al and Fe anodes, they form metal hydroxides, which are partly soluble in the water under definite ph values. This step results in the colloidal particles formation with metal hydroxides as nuclei of the latter. Around a nucleus, the adsorption layer of cations and anions is being organized. Taken together, the nucleus and adsorption layer form a granule of the colloidal particle, which has a small positive charge. To compensate the charge, a diffusion layer is being formed around the granule, which makes the particle a neutral one. The main reactions that occur during the electrolysis reactions are shown in below. When aluum is used as plate materials, the reactions are as follows: At the cathode: 3H 2 O + 3e 3/2 H 2 O+3OH (1)

3 Anal. Bioanal. Electrochem., Vol. 2, No. 3, 2010, At the anode: Al Al 3+ +3e (2) In the solution: Al 3+ (aq)+3h 2 O Al(OH) 3 + 3H + (aq) (3) When iron is used as plate materials, the reactions are: At the cathode: 3H 2 O + 3e 3/2 H 2 (g) + 3OH (4) At the anode: 4Fe(s) 4Fe 2+ (aq) + 8e (5) And with dissolved oxygen in solution: 4Fe 2+ (aq) + 10H 2 O(l) + O 2 (g) 4Fe(OH) 3 + 8H + (aq) (6) Overall reaction: 4Fe(s) + 10 H 2 O (l) + O 2 (g) Fe (OH) 3(S) + 4H 2 (g) (7) As seen in the above reactions, electrocoagulation is a combination of oxidation, flocculation and flotation. Electrocoagulation has occurred in three steps. In first step, coagulant has formed because of oxidation of anode. In second step, pollutants have destabilized. In last step, destabilized matters have united [14]. Aim of this work was to study the feasibility of phosphorous removal with electrocoagulation and detere the optimum operating conditions under different values such as ph, current density(cd), contact time and different plates (aluum and iron) for doing the best conditions that found in real wastewater effluent. 2. EXPERIMENTAL 2.1. Reagent and Solutions All chemicals used were analytical grade and used without further treatment. All chemical were purchased from Merck chemicals. Distilled water was used in step 1 and 2 of study and for 3th step reactor was filled with real wastewater that collected from wastewater treatment effluent. Phosphate solutions were prepared from KH 2 PO 4 (Merck) in 1 and 2th step. NaCl 1%(Merck), was used as supporting electrolyte. When necessary, ph was adjusted by using 0.1N HCl or 0.1N NaOH. After collecting samples, in distinguished time (10, 20, 40, 60 ) spectrophotometer (PERKINELMER lambda25) was used for the analysis of

4 Anal. Bioanal. Electrochem., Vol. 2, No. 3, 2010, phosphate in accordance with the standard methods (vanadomolybdophosphoric acid calorimetric method) [16] Experimental setup For this study, a glass tank in 1 litter volume with two plates (5 11 cm) was used Fig. 2. The plates were vertically in to the tank and the gap between the plates was 1.5 cm. One of the aims in this study was detere of operating efficiency between aluum and iron plates for phosphorous removal with electro-coagulation and in according this, plates were made of aluum and iron separately. Plates were connected to teral of direct supply power characterized by 5 A for current and the ranges 0 40 V for voltage. Temperature (21-22 c) was stable in during of the work. Synthetic phosphate solutions(6 mg/l) was used in the first step and in 2th step, in best efficiencies that elucidated in the first step, concentration of phosphate changed to 4 mg/l and 8 mg/l and 10 mg/l for evaluating of process and best operating conditions that caught in first step. At the beginning of each run the solution of phosphate (900 ml) of the desired concentration was fed into the reactor and 100 ml of 1% solution of NaCl (as electrolyte) was added to it to increase the solution conductivity. Each run was timed starting with the DC power supply switching on. Fig.1. A schematic diagram of the experimental set up 3. RESULTS AND DISCUSSION This work had 3step: assess of electro coagulation for removal of phosphate with phosphate concentration based in wastewater effluent standard condition (6 mg/l), and evaluating of ph, current density and contact time for elucidating of best condition in phosphate removal and in 2th step, in best efficiencies that elucidated in first step, concentration of phosphate changed to 4 mg/l and 8 mg/l and 10 mg/l for evaluating of

5 Anal. Bioanal. Electrochem., Vol. 2, No. 3, 2010, process and best conditions that caught in first step. In 3th step, efficiency of phosphorous removal using electro-coagulation assessed First step Percentage of phosphorous removal using electro-coagulation with iron plates on synthetic wastewater that was containing phosphate in concentration of 6 mg/l was studied in first step. As seen in table 1, phosphorous removal under ph 5.5 and 40 V and 40 after electro-coagulation process was %.it must be noted that in ph 5.5 and V, after 60 of electro-coagulation process, efficiency of phosphorous removal was % too. Table.1. Result of studies with iron plates ph VOLTAGE (V) T=10 T=20 T=40 T=

6 Anal. Bioanal. Electrochem., Vol. 2, No. 3, 2010, Phosphorous removal using electro-coagulation by aluum plates on synthetic wastewater that was containing phosphate in concentration of 6 mg/l was studied in following of first step. As seen in table 2, phosphorous removal under ph 8.5 and 40 V and 40 after electro-coagulation process was %. Table.2. Result of studies with aluum plates ph VOLTAGE T=10 T=20 T=40 T=60 (V)

7 Anal. Bioanal. Electrochem., Vol. 2, No. 3, 2010, th step In 2th step, in best efficiencies that elucidated, concentration of phosphate changed to 4 mg/l and 8 mg/l and 10 mg/l for evaluating of process and best conditions that caught in first step. In best operating conditions that caught in respect with ph, efficiency of phosphorous removal with aluum plates was high in ph 8.5 and for iron plates was high in ph 5.5. For this reason, concentration of phosphate in this ph that mentioned changed. Efficiency of phosphorous removal with using electro-coagulation with iron plates has shown in table.3. As seen in this table; with decrease of phosphate concentration, efficiency of process with iron plates gives better results. Table.3. Result of studies with iron plates and ph 5.5 on synthetic wastewater Was containing phosphate phosph VOLTAGE T=10 T=20 T=40 T=60 ate (V) Efficiency of phosphorous removal with using electro-coagulation with aluum plates has shown in table 4. As seen in this table; with decrease of phosphate concentration, efficiency of process with aluum plates gives better results.

8 Anal. Bioanal. Electrochem., Vol. 2, No. 3, 2010, th step In 3th step, the optimum conditions that this work reached, on real wastewater tested. With results of 2th step and statistical analysis elucidated that efficiency of phosphorous removal with aluum plates in electro-coagulation process is higher than iron plates, so phosphorous removal using electro-coagulation in real waste water tested with aluum plates. Real wastewater was containing 5.5 mg/l phosphate. In this step, because efficiency of phosphorous removal with aluum plates was high in ph8.5, this work was on real wastewater with natural ph 6.5 and ph 8.5. Efficiency of phosphorous removal with using electro-coagulation with aluum plates in this step has shown in table.5. Table.4. Result of studies with aluum plates and ph 8.5 on synthetic wastewater Was containing phosphate phospha VOLTAGE T=10 T=20 T=40 T=60 te (V)

9 Anal. Bioanal. Electrochem., Vol. 2, No. 3, 2010, Table.5. Result of studies with aluum plates on real wastewater was containing 6 mg/l phosphate ph VOLTAGE (V) T=10 T=20 T=40 T=60 Real As seen in table.5, efficiency of phosphorous removal using electro-coagulation with aluum plates on real wastewater is % in 40 V and after 10 of starting process and in ph 8.5, efficiency is % in V and after 10 of starting process Statistical analysis Statistical method used in this study is analysis of variance with repeated measurements. Whole tests were performed with significance level of 0.05[p<0.05]. In this study, time variable had a significant effect on removal process [p<0.0005] when iron plates were used. In Fig. 2, diagram of phosphate removal is shown along with the time. Also the voltage and ph have a significant effect on phosphate removal (p). Maximum of the phosphorous removal was seen in voltage 40 and ph 5.5 which corresponding means are and , respectively.

10 Anal. Bioanal. Electrochem., Vol. 2, No. 3, 2010, Fig. 2. Diagram of phosphate removal using iron electrodes along with the time Difference of each mean with other level of corresponding variable is statistically significant [p< and p<0.0005]. Using aluum plate, it was shown that time variable has a significant effect on the removal process [p<0.0005]. Diagram of time effect for aluum plate is shown in the Fig. 3. The ph and voltage have a significant effect on phosphorous removal too. Fig. 3. Diagram of phosphate removal using aluum electrodes along with the time

11 Anal. Bioanal. Electrochem., Vol. 2, No. 3, 2010, The maximum of phosphorous removal in this plate was seen in voltage 40 and ph 8.5 which mean removal is and , respectively. Finally, results show that mean removal using aluum plates is higher than iron plates. This difference is statistically significant [p<0.0005]. In the next step, it was illustrated that phosphate variable had a significance effect on removal percentage [p=0.007] when phosphate added to reactor. The maximum removal using iron plates achieved in phosphate concentration of 4 mg/l which mean difference of this phosphate level with the other levels was significant [p= 0.03 and p= 0.008]. Along with the time, removal percentage increased in phosphate concentrations of 4 mg/l, 8 mg/l, and 10 mg/l; this process is shown in Fig. 4. However, removal percentage in phosphate concentration of 4 mg/l is higher than other concentrations. Fig. 4. Removal percentage of phosphate concentration using iron electrodes along with the time When aluum plates were used, the maximum removal was observed in the concentration of 4 mg/l. Mean difference of the phosphate level with the other levels are significant [p= 0.02 and p= 0.01]. Removal percentage of phosphate concentration with aluum plates is shown in Fig. 5. Removal percentage increased along with the time in concentrations of 4 mg/l, 8 mg/l, and 10 mg/l.

12 Anal. Bioanal. Electrochem., Vol. 2, No. 3, 2010, Fig. 5. Removal percentage of phosphate concentration using aluum electrodes along with the time 4. CONCLUSION In this work, electro-coagulation process was used for removal of phosphate from wastewater effluent. Result obtained from experiments on synthetic waste water showed that the most effective phosphate removal by AL/AL plates is % in ph 8.5 and voltage 40 and 40 after starting process and for IR/IR plates is % in ph 5.5 and voltage 40 and 40 after starting process. Result obtained from 2th step revealed that the removal efficiency was high whenever concentration of phosphate decreased and efficiency of removal with AL/AL plates is higher than IR/IR plates. In 3th step, efficiency of phosphorous removal using electro-coagulation assessed and efficiency of this step with aluum plates on real wastewater under different conditions is %. According to these results, it can be concluded that electro-coagulation process for phosphorous removal using aluum plates is better than iron plates and is able to operate for phosphate removal with high efficiency from wastewater effluent. REFERENCES [1] Wastewater Engineering, G. Tchobanoglous, F. L. Burton, McGraw-Hill, (1991). [2] G. Kiely, Environmental Engineering, McGraw-Hill, New York (1997). [3] G. K. Morse, S.W. Brett, J. A. Guy, J. N. Lester, Sci. Tot. Environ. 212 (1998) 69.

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