Performance Evaluation of Non Rotating and Rotating Anode Reactor in Electro Coagulation Process

Electro coagulation process using various deigns and configurations have been tested from time to time and found to impart major role in the process. Mostly non rotating configurations were used in the available literature. The usage of rotating electrode reactors has come to light and found out to be effective configuration. The effect of rotating and non rotating reactor configurations along with other affecting parameters likes current density, detention time and energy consumption were investigated. Set of experiments were conducted using simulated sample prepared by dissolving basic red dye in tap water to carry out the performance evaluation of the two type of reactors configuration. A comparative study between the two configurations was made to investigate their effectiveness in term of COD removal efficiency and economics of treatment. The results show that rotating reactor configuration have consumed 15-17% less energy for maximum COD removal of 96.40% and thus have better removal efficiency and lower specific energy consumption than non rotating reactor configuration.


INTRODUCTION
The major challenge standing in front of the modern world is demand, supply and availability of clean water for domestic and industrial use [1]. Due to large quantity and diverse nature of industrial wastewater, the issue of its treatment remains a major environmental concern. So, the gap in demand and supply has made it compulsory to reuse the treated wastewater.
The textile wastewater from dyeing and finishing process has been a serious environmental concern for decades. The textile wastewater contains high color, varying pH, high COD concentration, high turbidity, suspended particles and low biodegradability [2]- [5] which makes it difficult to use conventional technologies available. A host of modern era imparted the use of very promising technique based on electrochemical technology like electro coagulation, electro flotation [6] etc. EC has been a very complex process involving various multitude mechanisms operating simultaneously to treat wastewater.
A wide variety of opinions exist in literature for key mechanism and reactor configurations. A systematic and holistic approach is required to understand EC and its controlling parameters [1]. Over the broad range of time period over which this technology is used it is surprising the available literature does not reveal any systematic approach to EC reactor design, configuration and operation [7].
EC treatment of textile wastewater has been conducted on a laboratory scale and good removal of COD, color, turbidity, and dissolved solids at various operating parameters have been obtained [8]- [11]. And, the process has been found to be very efficient in COD removal and decoloration with low energy consumption [12].
The commonly explored variables for laboratory studies include wastewater characteristics such as pH & conductivity, and process variables such as current density, detention time, electrode material etc. Meanwhile, an important design variable not fully investigated in previous researches is the reactor configurations i.e. rotating and non rotating reactor configuration.
Since the rotating and non rotating reactor configuration has not been compared in detail for the process, it is the purpose of this study to compare the treatment of textile wastewater by both the configurations. The two performance criteria which are of primordial importance are COD and energy consumption in both the configurations is used for the comparison. Further goal of this study is to select the reactor configuration with highest removals and minimum energy consumption for the same to provide a solid universal and scientific understanding for future design.

Reactor Design: The Contrast
Since EC is an enigmatic technology. Despite being widely used for decades, there appears to be no real consensus on the most appropriate approach for any given application, little in way of systematic reactor design rules, and almost nothing in way of generic a priori modeling approach [7]. The EC reactor for present study was designed considering the intersection of three more fundamental technologies -electrochemistry, coagulation and flotation that governs the process. All three of them were given due consideration in the design of reactor [7]. In this investigation, a 3D perforated cylindrical aluminum anode and cathode was used for treatment of synthetic textile wastewater with EC. The reactor was made of Plexiglas having conical structure at the bottom to effectively collect and enhance the settling of the sludge produced at the time of EC. The anode was made of hollow Al cylinder having pores at regular distance in order to enhance the turbulence in the reactor. The effective area of the electrode was 284.52 cm 2 . The cathode was an aluminum rod with 7 mm inner diameter, 1.2 cm outer diameter and 14 cm height. The aluminum rod and perforated aluminum cylinder were isolated by perforated epoxy resin. The inter-electrode distance was fixed at 2 cm. The experimental system used is represented in Figure I.

The Analysis
As shown by many investigators that aluminium was used as electrode material for treatment of textile wastewater [13]. The synthetic textile wastewater was prepared in laboratory. The wastewater was prepared by using tap water. The pH was adjusted using NaOH and H 2 SO 4 /HCl when required. The conductivity of the wastewater was adjusted using NaCl. The required currents were applied by a DC power supply (Kusam Meco, Model: KM-PS-305-DII). The analytical determination of the Color and COD removal was investigated with the standard procedure (5220 D. Closed Reflux, Calorimetric Method) using an UV Spectrophotometer (Shimadzu, Model: UV-1800) [14]. The pH and conductivity were measured by pH meter (Hanna, Model: HI 98128) and conductivity meter (Lutron, Model: CD-4302). The COD and Color removal efficiency (RE%) were calculated using the following equations: Where; Co and C are the concentration of COD before and after treatment, respectively, in ppm or mg/L.
Where; Ao and A are the absorbance of dye before and after treatment, respectively. The specific electrical energy consumption per mg COD removed (E COD ) were calculated as follows: Where, V is voltage, I is current, t is time (usually taken as 60 min for specific energy consumption, C 0 and C are the initial and final COD concentrations.

Effect of Detention Time
There is a significant effect of detention time on treatment efficiency in an electrochemical technique [15]. It was observed that increase in detention time had resulted in increase in COD removal efficiency, when other affecting parameters were kept constant. This effect can be explained by the Faraday's law, according to which an increase in detention time will lead more The mechanism of COD re aggregation. The optimum COD of) depend on detention time. As when the detention time was ch mA/cm 2 , the COD removal was in that for shorter detention time of Therefore, the COD removal w rotating reactor configuration, th rotation of the anode increases t time for the pollutant to get trea COD removal achieved was 96.4 The detention time was furthe decreases to 64.98% and 75.91% to the fact that for increased deten simultaneously aluminum hyd hydroxides does not found pollu efficiency remains nearly constan While for quicker detention tim was observed to be 46.48% a respectively. It was due to the destabilize all colloidal and finely

Effect of Current Density
Previously, it was shown that electro coagulation process [18]to the electrolytic cell to the surfa influences the COD removal and very important parameter that . This coincide f 20 min, the time was not sufficient to complet as better at 30 min of detention time. Wherea he optimum detention time was found to be 2 the turbulence inside the reactor. This shortens ated as the mixing inside the rector increases. T 40% for 6mA/cm 2 . er increased to 40 and 50 min, the COD remo for non rotating and rotating reactor configuratio ntion time, the pollutant in wastewater goes on d droxides generation increases. This increase utants for removal, so beyond optimal point, C nt [17]. me i.e. 10 min, the COD removal efficiency wa and 69.40% for non rotating and rotating c fact that the metal ion (Al 3+ ) dosage was not y suspended particles [15]. current density can influence the treatment effi [21]. The current density is defined as the ratio of ace area of the electrode. It was observed that c d increased current density increases the COD affects the electro coagulation process becau While for quicker detention time i.e. 10 min, the COD removal efficiency was not good. It was observed to be 46.48% and 69.40% for non rotating and rotating configurations respectively. It was due to the fact that the metal ion (Al 3+ ) dosage was not sufficient to destabilize all colloidal and finely suspended particles [15]. determines both coagulant dosag solution mixing and mass transfe parameter that affecting the system separation mode [22].
In case of non rotating and rotat was observed at 8 mA/cm 2 and configuration 50% of removal eff to rotating reactor configuration efficiency decreases.
The COD removal efficiency configuration over non rotating re As the current density decrease However, the cost of the proces electrode and electrical energy. A one may use an optimum value [23].

Energy Consumption
In electro coagulation techniqu applied voltage, current and d combination of applied voltage, t current directly affects metal ion supplied it will be wasted in heat Thus, energy consumed for unit Reactor Configuration.
For all experiments in continuo time, after pseudo steady state w mg of COD) in each experiment w Specific energy consumed for un find out the energy efficiency of t ge and bubble generation rates and strongly in er at the electrodes. So current density is the ke m's response time and also influencing the domi ting reactor configuration, maximum COD remo d 6 mA/cm 2 as shown in fig. III. In case of ficiency was achieved at higher current density i n. As the current density was increased further values showed the better performance of ro eactor configuration. ed, the time needed to achieve similar efficienc ss is required to determine by the consumption As the increase in current density augment the cos of current density for efficient treatment and m ue of treatment, total electrical energy consume detention. Many researchers have shown th time and current assure high treatment efficiency n generation, consequently treatment but if too h ting up of system i.e. efficiency of system will d COD removal was calculated for Non Rotating ous flow reactor, energy consumed for 60 minut was calculated. Energy consumed for unit remov was calculated and reported here as specific ener nit COD removal was analyzed with correspon the system.  As shown in fig. IV; the energy time varies from 0.037 to 0.083 reactor configuration it varies fro was approximately 50% less than As the detention time was incre V, the energy consumption for n J/mg but for rotating reactor conf Further, increasing the detentio for both non rotating and rotat decreases due to the fact that now So, the energy consumed for ma 17% less for the similar results in 4. CONCLUSION It was observed that in compari process. The rotating reactor con efficiency than non rotating rea consumption decreases to 17-58% offers better energy efficiency. rotating reactor configurations ha