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International Journal of Environment Science and Technology
Center for Environment and Energy Research and Studies (CEERS)
ISSN: 1735-1472 EISSN: 1735-2630
Vol. 8, Num. 1, 2011, pp. 107-114

International Journal of Environment Science and Technology, Vol. 8, No. 1, 2010, pp. 107-114

Survey efficiency of electrocoagulation on nitrate removal from aqueous solution

*M. Malakootian; N. Yousefi; A. Fatehizadeh

Department of Environmental Health, School of Public Health, Kerman University of Medical Sciences, Kerman, Iran

*Corresponding Author Email: m.malakootian@yahoo.com Tel.: +98 341 320 5074; Fax:+98 341 320 5105

Received 2 August 2010; revised 18 October 2010; accepted 22 November 2010; available online 1 December 2010

Code Number: st11010

ABSTRACT:

Water supply for consumption is one of the crucial objectives of water supply systems. Using of excessive fertilizer is a main source of nitrate content in water. The high amounts of nitrate in water have a determinable effect on the environment which must be removed due to drinking and industrial water standards. The purpose of this study is nitrate removal from aqueous solution by Electrocoagulation process. The applied pilot was comprised of a reservoir, electrode and power supply. In this study pH, electrical potential difference, nitrate initial concentration, total dissolved solid , kind of electrode, electrode connection methods and number of electrode were studied. Moreover, obtained optimum conditions were tested on Kerman water. The results showed that the electrocoagulation process can reach nitrate to less than standard limit. pH, electrical potential difference, total dissolved solids and number of electrodes have direct effect and initial concentration of nitrate has reverse effect on nitrate removal. This study also showed that under optimum condition, nitrate removal from Kerman water distribution system was 89.7 %. According to the results, Electrocoagulation process is suggested as an effective technique in nitrate removal.

Key words: Electrode materials; Kerman water; Monopolar; Water treatment

INTRODUCTION

Pollution of water resources by nitrate is occurred due to domestic wastewaters and unconventional consumption of fertilizers in agricultural (Horold et al., 1993; Pintar et al., 2001; Mahvi et al., 2005; Nouri et al., 2008; Atafar et al., 2010). Nitrogen containing compounds create serious problems including eutrophication, destroyed water quality and potential hazards on human and animal health when they enter to water resources (Nouri et al., 2006; Ghafari et al., 2008; Igbinosa and Okoh, 2009). Increased intake of nitrate affects health by creating of methemoglobinoma in children, hypertension, thyroid disability and carcinogenicity hazard of nitrosamine and nitrosamide (Hell et al., 1998; Luk and Au-Yeung, 2002; Vosoughifar et al., 2005; Ayyasamy et al., 2007; Ghafari et al., 2008;). The WHO guideline values are 50 mg/L as NO3 for nitrate and 3 mg/L as NO2 for nitrite, with a further provisional value of 0.2 mg/L as NO2 for nitrite based on chronic effects(Horold et al., 1993; Twort et al., 2000; Ghafari et al., 2008). The conventional methods for nitrate removal are ion exchange, biological treatment, reverse osmosis, coagulation process, activated carbon absorption, nitrification by ozonation (Lin and Wu, 1996; Bae et al., 2002; Paidar et al., 2002; Koparal and Ogutveren, 2002; Pintar et al., 2001; Aslan and Turkman, 2006; Nabi Bidhendi et al., 2006; Bandyopadhyay and Chattopadhyay, 2007; Igwe et al., 2008; Babel et al., 2009). Electrocoagulation process has been successfully employed for color, heavy metals and COD removal of industrial wastewaters (Lin and Wu, 1996; Emamjomeh and Sivakumar, 2009; Schulz et al., 2009). Electrocoagulation process has some advantages such as no need to chemical materials, no sludge production, need to small space and low investment costs (Koparal and Ogutveren, 2002; Hu et al., 2003; Kobya et al., 2006).

Electrocoagulation process involves applying an electric current to sacrificial electrodes (mostly iron and aluminum) inside a reactor tank where the current generates a coagulating agent and gas bubbles (Xiong et al., 2001; Kim et al., 2002). This process has three stages: 1) coagulants formation due to anode electrical oxidation, 2) destabilizing pollutants and suspended substances and emulsion breaking and 3) combining instable particles to form floc (Xiong et al., 2001; Koparal and Ogutveren, 2002; Ramesh et al., 2007; Ghernaout et al., 2008).

Destabilization mechanisms in this process include electrical double layer compression, adsorption and charge neutralization, enmeshment in a precipitate and inter-particle bridging (Kim et al., 2002; Abdel-Ghani and Elchaghaby, 2007; Drouiche et al., 2008; Abdel-Ghani et al., 2009; Zvinowanda et al., 2009).

When iron or aluminum are used as electrode, trivalent iron or aluminum are produced which will react with hydroxyl ions and produce metal hydroxide and polyhydroxide ions (Ramesh et al., 2007). Electrocoagulation reactors could be operated by up or counter current flow or monopolar and dipolar connection (Jiang et al., 2002). The study was performed in Kerman province located in the south-eastern part of Iran with longitude 54o, 21´- 59o, 34´ and latitude of 26o, 29´ - 31o, 58´, is characterized by warm and arid climate and considerable temperature variations between day and night (Malakootian and Dowlatshahi, 2007) The aim of this study was to determine the performance of Electrocoagulation process in nitrate removal and obtain optimum conditions.

MATERIAL AND METHODS

The experimental set-up used in the study was shown in Fig.1. The dimensions of electrodes were 100× 100 × 2mm. Fat removal of electrodes surface was accomplished by acetone. A magnetic stirrer has been applied for mixing (300 rpm). In all stages of the study, the electrical potential differences and current intensities were measured by voltmeter and ohmmeter, installed on circus, respectively. The synthetic aqueous solution was prepared by potassium nitrate and deionized water. In all stages of the study, sodium chloride was added to solution due to low electrical conductivity.

In this study pH, electrical potential difference, nitrate initial concentration, total dissolved solid (TDS), kind of electrode, electrode connection methods and number of electrode were studied. Moreover, obtained optimum conditions were tested on Kerman water. For this purpose, first Kerman water quality was analyzed and the results are including pH=7.43; 1.2 g/LTDS; 75 mg/L Na; 7 mg/L K; 395 (mg/L as CaCO3) hardness and 274 (mg/L as CaCO3) alkalinity. Kerman water nitrate concentration was increased up to the value of 100mg/L by adding KNO3 (the amount that determined in groundwater of Iran).

All stages of experiment were performed at time 12, 24, 36, 48 and 60 min. Analyses were performed according to the standard methods for examination of water and wastewater (APHA, 1998).

RESULTS AND DISCUSSION

Effect of pH

pH is an effective factor on Electrocoagulation process performance (Fig. 2). The nitrate removal efficiency increases with increase of pH. This can be attributed to the reaction between metal and hydroxide ions. The results of this study have been confirmed by Malakootian and Yousefi on removal of hardness from water by electrocoagulation and Koparal on Removal of nitrate from water by electroreduction and electrocoagulation and Bazrafshan et al on removal of chromium (VI) by electrocoagulation (Koparal and Ogutveren, 2002; Mavrov et al., 2006; Bazrafshan et al., 2007; Malakootian and Yousefi, 2009). As Fig. 3 represents, with increase of the electrical potential difference, the nitrate removal efficiency increases. This is due to more flocs production in high voltage. These results also are in line with the pointed results of research in Iran and the results of Ranta Kumar et al in India in relation to removal of arsenic from water by electrocoagulation and Koparal on removal of nitrate from water by electroreduction and electrocoagulation and Lin et al in China on electrochemical removal of nitrite and ammonia for aquaculture and Hu et al in Thailand in relation to effects of co-existing anions on fluoride removal in electrocoagulation (EC) process using aluminum electrodes and Ugrulu on removal inorganic compound by electrocoagulation (Lin and Wu, 1996; Koparal and Ogutveren, 2002; Hu et al., 2003; Ratna Kumar et al., 2004; Ugurlu ,2004; Bazrafshan et al., 2008; Malakootian and Yousefi, 2009)

Effect of nitrate initial concentrations

With increase nitrate initial concentration, the nitrate removal efficiency decreases (Fig. 4). Also, with increase nitrate initial concentration, the requirement time for achieves the desired amount of nitrate remaining increases. The results of this study have been confirmed by the results of the Bazrafshan et al study in Iran and Drouiche et al in Algeria on electrocoagulation treatment of chemical mechanical polishing wastewater : removal of fluoride sludge characteristics operation cost and Koparal on removal of nitrate from water by electroreduction and electrocoagulation, Kashefialasl et al in Iran on treatment of dye solution containing colored index acid yellow 36 by electrocoagulation using iron electrodes and Lin et al in China for electrochemical removal of nitrite and ammonia for aquaculture (Lin and Wu, 1996; Koparal and Ogutveren, 2002; Kashefialasl et al., 2006; Bazrafshan et al., 2008; Drouiche et al., 2008;).Fig. 5 showed that with increase of the concentration of TDS, the nitrate removal efficiency increases. It's referred to this fact that with increase of the TDS (electrical conductivity), the electrical current and floc production increases and subsequent nitrate removal efficiency increases. The results of this study by Lin and wu study in China was consistent(Lin and Wu, 1996).

Effect of electrode number

Fig. 6 showed that with increases in electrode number, the nitrate removal efficiency increases. It can be due to more consumption of energy and then production more flocs in shorter time. This results has been also confirmed by Lin in China (Lin and Wu, 1996).

Effect of electrodes connection methods

According to Fig. 7, the nitrate removal efficiency with monopolar connection was higher than the bipolar electrodes connection method. It can be due to more consumption of electric energy in the monopolar connection and more production of flocs in shorter time. But more energy consumption will be followed.

Effect of electrode kind

Fig. 8 showed that iron electrodes have more efficiency in nitrate removal than aluminum electrodes.

It can refer to high density of iron hydroxide ions than aluminum and this has also been conflicted by Rahmani in his study in Iran about removal of water turbidity by the electrocoagulation method (Rahmani, 2008). It should be mentioned that using Iron electrodes has limits due to the production of color(Kawamura, 2000).

Effect of electrocoagulation process on Kerman water

Fig. 9 showed the results of nitrate removal from Kerman water distribution system in experiment optimum conditions (pH=7.43, electrical potential difference 40V, TDS=1.27g/L, iron electrodes, bipolar connection method and four electrode pairs) that the amount of nitrate was increased to 100 mg/L as NO3. Due to no need to chemical material before and after electrocoagulation process, the water pH didn't change and the pH of water distribution system was surveyed in the experiment stage of Kerman water distribution system. Moreover, due to the amount of TDS were relatively sufficient to experiment and with increases of TDS, the amount of its will be higher than drinking water standard (TDS standard is 1500 mg/L), in this regard, the amount os TDS was not changed in Kerman water distribution system. In addition, the bipolar connection was used because of the bipolar connection has less energy consumption to reach the standard limit than monopolar connection.The results showed that pH, electrical potential difference, TDS and number of electrodes have direct effect and initial nitrate concentration has reverse effect on efficiency of nitrate removal. The effectiveness of this process with study optimum conditions (pH=7.34, electrical potential difference 40V, initial concentration of nitrate 100 mg/ L, TDS=1.27g/L, iron electrode and 4 pairs of electrodes) on nitrate removal from the Kerman water distribution system showed that the nitrate removal efficiency was 89.7%. Therefore, this process is suggested as an efficient alternative technique on nitrate removal from aqueous solution.

ACKNOWLEDGEMENTS

The authors would like to thank Environmental Health Research Committee of Kerman University of Medical Sciences for approving this research. Special thanks also to Mr. Moosazadeh and Fatehizadeh due to their close cooperation

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