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ORIGINAL ARTICLE
Year : 2017  |  Volume : 4  |  Issue : 3  |  Page : 53-57

Study of electrochemical process effect on detergent removal from polluted water and fish bioassay test of the effluent


1 Department of Environmental Health Engineering, Social Determinants of Health Research Centre, Health School, Kashan University of Medical Sciences, Kashan, Iran
2 Department of Environmental Health Engineering, Health School, Kashan University of Medical Sciences, Kashan, Iran
3 Department of Epidemiology and Biostatistics, Health School, Kashan University of Medical Sciences, Kashan, Iran

Date of Web Publication6-Nov-2017

Correspondence Address:
Davarkhah Rabbani
Department of Environmental Health Engineering, Social Determinants of Health Research Centre, Health School, Kashan University of Medical Sciences, Kashan
Iran
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/iahs.iahs_10_17

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  Abstract 


Aims: Linear alkylbenzene sulfonate (LAS) is an anionic surfactant which is widely used in household and industrial detergents usage, and after use, it usually finds a way to the wastewater treatment systems. Conventional treatment is not recognized as an efficient method due to the long residence time and enlarged cost. Hence, advanced oxidation processes including electrochemical techniques are important. In this paper, electrochemical degradation of a synthetic solution of LAS with initial concentration 200 ppm has been investigated. Methods: The experiment was performed using eight stainless steel electrodes as cathode and anode with a monopolar arrangement. The effects of current intensity and density were studied as operational parameters on detergent removal efficiency. Results: The maximum removal efficiency 94% was achieved at current intensity equal to 300 mA and current density 6 mA/cm2. The energy consumption was calculated 2.7 ± 0.1 WH/g. The bioassay test showed that only under optimum conditions, 80% of fish was survived until 4 days since the end of the process and the rest were died immediately. All ten fish leaved in unpolluted were survived until 4 days monitoring. Conclusion: The results showed that, by reducing the current density, removal efficiency increases it was true for all current intensities.

Keywords: Bioassay, detergent, surfactant, water pollutants


How to cite this article:
Rabbani D, Mostafaii GR, Eskandari V, Dehghani R, Atoof F. Study of electrochemical process effect on detergent removal from polluted water and fish bioassay test of the effluent. Int Arch Health Sci 2017;4:53-7

How to cite this URL:
Rabbani D, Mostafaii GR, Eskandari V, Dehghani R, Atoof F. Study of electrochemical process effect on detergent removal from polluted water and fish bioassay test of the effluent. Int Arch Health Sci [serial online] 2017 [cited 2018 Aug 14];4:53-7. Available from: http://www.iahs.kaums.ac.ir/text.asp?2017/4/3/53/217751




  Introduction Top


Public and industrial wastewaters are a main reason of contamination of water resources. One of the major components forming the wastewater are detergents that a lot of damage caused to the environment by entrance into the water and soil.[1],[2] One of the main constituents of detergents is surfactants. Surfactants are dual nature materials that owing to their chemical characters can weaken the water surface tension and to increase its cleaning effect.[3],[4] They are composed of two parts of water solvable (hydrophilic) and water insolvable (hydrophobic).[5] Based on the character of the hydrophilic part, the surfactants can be classified in the form of cationic, anionic, nonionic, and amphoteric.[6],[7] Anionic surfactants are the largest type of surfactants used in detergent formulation.[8] Linear alkylbenzene sulfonate (LAS) is the largest type of anionic surfactants.[9] LAS has used widely in household cleaners, health and cosmetics products, and other industries [10],[11] and have highest utilization amount in the surfactant types as reported by CESIO institute.[12] Due to the high consumption of surfactants in various applications, their presence in wastewater have also increased, and after the use, they discharged into the wastewater system and from there, find their way to the treatment plants.[13],[14] Thus, the surfactant concentration in municipal and industrial wastewater effluent can be very high. For example, LAS concentration in laundry wastewater was observed to several 100 mg/L.[15] To reduce the environmental impacts, surfactants, and particularly LAS, has been intensely studied and various physical, chemical, and biological methods have been used to remove it.[16] The general technologies such as ultra-filtration and ion exchange [17] and adsorption [18],[19] have been studied for removing surfactants from wastewater. Over the years, conventional physicochemical and biological methods such as absorption, coagulation, and filtration have been used to remove various contaminants. Because these methods, especially for toxic contaminants including surfactants and high concentrations of contaminants, are not recognized very effective and moreover, are somewhat costly therefore, researches have continued to find new techniques.[20] Among these, new techniques are advanced oxidation processes (AOPs).[21] AOPs due to advantages such as high efficiency and versatility have been identified as promising alternatives. AOPs are based on the production of hydroxyl radicals, a strong oxidant.[22],[23] AOPs were first introduced in the 1980s for water purification and later have been used for the treatment of various types of sewages because strong oxidants generated in this process can easily degrade organic pollutants.[24],[25] Electrochemical methods are among of AOPs and have provided appropriate field in the environmental pollutants treatment.[26] The main advantage of this method is that it does not require chemical and electrical energy is only used to decompose pollutants.[27] In recent years, electrochemical methods such as electrooxidation, electrocoagulation, and electroflotation have attracted a lot of attention and widely been used for the treatment of sewage and water disinfection.[28] The widespread use of different types of surfactants and their entry into the environment, particularly aquatic environment, can have harmful effects on ecosystems and living organisms.[29],[30] In the past years, the electrochemical removal of surfactants from wastewater has attracted many studies and various variables have been investigated to determine the effect of the electrochemical method including the type of electrode material, current intensity, current density, voltage, pH, solution flow rate, electrical conductivity, and electrical connection of electrodes. Among them, the parameters of current intensity and current densities are the easiest parameters for controlling the electrochemical process. Also, the electrode material plays a major role in determining the mechanism of elimination of the pollutants. The electrodes such as boron-doped diamond (BDD) are expensive.[5],[31] Therefore, in this study, we tried to find the optimal conditions for LAS removal using these three variables (current density, current intensity, and electrode material). Stainless steel electrode has advantages such as cheapness, availability, and resistant to corrosion. The change in the immersion height of the electrode and the use of a relatively wide range of currents intensity are the new inventions of this study compared to the previous studies because they have fixed electrode height and examined the current density effect by change in current intensity. Hence, the way to further study in this area is still open.

To assess the toxicity effects of these pollutants on aquatic biota, physical and chemical tests alone are not enough and toxicity tests are necessary to assess the quality.[32] Toxicity tests usually are done on fish, daphnia, and algae. The purpose of this experiment was investigation of effect of electrochemical process on detergent removal from synthetic wastewater also, assessment of its effect on detergent detoxification by fish bioassay test.


  Materials and Methods Top


Apparatus

The system consists of eight stainless steel electrodes as cathodes and anodes that are connected monopolar. This arrangement reduces the energy consumption of the system due to the parallelization of the electrodes. A 2 L beaker is also used as a reactor. A simple schematic of the system can be seen in [Figure 1]. A magnetic stirrer was also used to stir the solution during the test. The samples were prepared using tap water to provide solutes needed for electrical conductivity of the solution. The tap water had chemical composition as below:
Figure 1: Schematic of experimental set-up

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Total hardness = 280 mg/L, Na = 130 mg/L, K = 5 mg/L, SO42−=201 mg/L, Cl =191 mg/L.

The electrical conductivity of the solution was measured using a METROHM 644 conductometer. Chemical experiments and bioassay test were carried out at a constant laboratory temperature (about 20°C), which was determined using a glass mercury thermometer. Hence, there was no need to control the temperature during the experiment.

For the bioassay test, black molly fish was used. Suitable conditions for keeping this fish are temperature = 20°C–26°C, pH = 7.5–8, and DO = min 3 mg/L. The minimum dissolved oxygen in the samples that measured using an oxygen sensor (AL20OXi AQUALYTIC) was 4.8 mg/L. Hence, there was no need to aeration of samples during the test.

The absorbance of solutions was measured by a spectrophotometer (DR/2010; HACH Co.).

pH was measured by a pH meter model 262 TS technology and current intensity by a digital multimeter model ECS820B SOAR respectively.

Experimental procedure

  • Step a: At first, 2 L tap water was taken from urban network, and with the addition of LAS, the synthetic wastewater with certain concentration (200 mg/L) was prepared. The polluted water was poured in an electrolytic cell (a 2 L beaker) and using stainless steel electrodes (15 cm length, 3 cm width, and 1 mm thickness) electrochemical process was applied on it. In this run, 3 cm height of electrodes was submerged in the solution. The electrochemical process was done without, any changes in pH (about 7–8), temperature (about 20°C) and electroconductivity (2200 μs/cm), it was done by the aforementioned electrodes at the current intensity of 200 mA for 1 h. Then, a sample was taken to determine the concentration of LAS residue. The LAS residue was measured using methylene blue active substance on the basis of the 5540°C method in the 22nd edition of standard methods for the examination of water and wastewater book. Finally, transferring the rest of cell content to another vessel, a total of 10 fish were leaved in it. The experiments were repeated four times for good accuracy.
  • Step b: Such as step a but with current intensity of 200, 300, 400, 500, 600, 700, 800, and 900 mA, the experiments were done
  • Step c: At this stage, the submerged height of electrodes was increased to 6 cm and the steps a and b were repeated
  • Step d: This stage is similar to the step c with the exception of 9 cm submerged electrodes height.


The energy consumption was calculated by the following formula for each run.



Which, U is voltage, I is current intensity, t is period of process time, V is volume of sample, C0 is initial concentration of LAS, and C is final concentration of LAS.

Black molly fish (Poecilia sphenops) was applied to the bioassay test on treated and untreated synthetic wastewater samples. Ten fish 5 ± 1 cm length, 2 ± 1 g weight were leaved in each of them. The fish survival status was monitored up to 96 h. The number of dead and live fish at the end of each 24 h was recorded. Findings were analyzed by Chi-square and ANOVA test by SPSS statistical software version 16.


  Results Top


In this study, the effect of electrochemical process to remove LAS from synthetic wastewater was investigated and bioassay test was used for its detoxification confirmation.

[Table 1] shows the remained LAS concentrations besides, energy consumptions according to electrical current intensity and electrode immersion heights. It is noticeable that the initial concentration in all runs was 200 mgL−1. It can be concluded that the optimum electrical current and electrode height are 300 mAmp and 9 cm, respectively. In this condition, the energy consumption was calculated 2.7 WH/g removed LAS.
Table 1: Remained linear alkyl benzene sulfonate and energy consumption in different electrical current intensities and electrode immersion heights

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In [Figure 2], the LAS removal efficiency in terms of current intensity for different electrode submersion heights has been shown. As can be seen with increasing height of electrode immersion, LAS removal efficiency was increased. Obviously, the optimum current intensity and electrode height were 300 mA and 9 cm, respectively. In this condition, the maximum removal efficiency of LAS was 94%, which the LAS concentration was reduced from 200 to 12 mg/L.
Figure 2: The linear alkylbenzene sulfonate removal efficiency in terms of current intensity for different electrode submersion heights

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[Figure 3] shows the LAS removal efficiency versus current density; it can be concluded that the best efficiency is obtainable in 6 mA/cm 2.
Figure 3: The linear alkylbenzene sulfonate removal efficiency versus current density

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ANOVA test on chemical results to compare optimal conditions with other conditions showed a significant difference between them (P< 0.05).

To assess the electrolysis detoxification of LAS biological test carried out on samples using molly fish (P. sphenops). Ten fish were leaved in each 2 L beaker full of the treated solution than the fish vital status every hour up to 96 h from the beginning. In parallel, this test was done on contaminated water without electrochemical process and raw water as control groups. All fish leaved in uncontaminated water survived for 4 days while all in untreated contaminated samples died in early minutes. Only under the optimum electrochemical process condition, eight fish were survived until 4 days since the end of the process [Figure 4] and the statistical analysis showed a meaningful difference between optimum condition and the others for fish survival (P< 0.05).
Figure 4: Number of live fishes in different current intensity

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  Discussion Top


The aim of this article was investigation of effect of electrochemical process on LAS removal from synthetic wastewater and fish bioassay test to assessment of the process capability for detoxification of detergent. A review of several studies on the removal of LAS from real and synthetic effluents shows that with increasing the current density, the LAS removal efficiency was increased. For example, Koparal et al.[1] showed that, in the range of 10–15 mA/cm 2, a uniform increase in the efficiency of LAS removal was observed. Similar results were obtained in the study of Lissenset al.,[31] Konget al.,[33] and Önderet al.[26] These researchers used BDD, Ti, and cast iron electrodes in their tests, respectively. However, the Panizza et al.[5] showed that, at a current density of 25–75 mA/cm 2, the removal efficiency decreased by increasing the current density, which is more consistent with our results. Therefore, it can be concluded that, at lower current densities, the higher removal efficiency and at the higher current densities, the lower removal efficiency are achieved. Hence, there is an optimal current density, in which the removal efficiency can be the highest. Of course, according to the study of Önder et al.,[26] the type of electrode also plays an important role in this current density position as with low oxygen evolution potential electrodes, lower current density is preferred and with high oxygen evolution potential electrodes, higher current density is more important. The reason for reducing the removal efficiency in the 300–700 mA range is due to the side reactions in the reactor that compete with LAS removal reaction. The most important of these reactions is the release of oxygen in the anode based on the following reaction:



Furthermore, due to the presence of oxidable anions such as chloride in solution (following reaction), the removal efficiency increases in high current intensities as shown in [Figure 2] at current intensities higher than 700 mA. Because the molecule of chlorine is a strong oxidizing agent in the chemical oxidation of LAS.



We applied bioassay test for assessment of the effectiveness of electrochemical process on LAS detoxification. Results showed all fish leaved in uncontaminated water survived for 4 days whereas all in untreated contaminated samples died in early minutes that is due to the high toxicity of LAS for fishes at concentrations higher than 12 ppm.

Only under optimum conditions, 80% of fish was survived until 4 days since the end of the process. From the standpoint of bioassay test, the difference between optimum and the other conditions was significant, so it can be concluded that the electrochemical process under optimum condition has a good capability to reduce the LAS toxicity as well as detergent removal.


  Conclusion Top


From the results of this experiment, it can be deduced that both the surface area of the electrode and the current intensity are effective in determining the removal efficiency. Therefore, based on the findings of optimal conditions, the design of large-scale batch electrochemical reactors is easy. Because the use of expensive electrodes such as BDD in the large scale is not economical and due to the ease and simplicity of the reactor used in the test, the importance of this study is further enhanced. The results of this study can solve the environmental problems of plants such as detergent manufacturers, laundries, and carwashes that are exposed to high concentrations of surfactants in their wastewater. The authors recommend that the effect of the surface area of the electrode and the current intensities above 1000 mA that are not addressed in this study be examined in more detail.

Acknowledgment

The authors are grateful to the deputy of research and technology of Kashan University of medical sciences for financial support. We are also thank full from Ali Azari, PhD student of environmental health engineering, school of public health, Tehran University of medical sciences, for his considerable help in review of this paper.

Financial support and sponsorship

This work was supported by Kashan University of Medical Sciences in Kashan. This paper is extracted from the results of research project No. 9522, which was conducted at Kashan University of medical sciences.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

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