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Article

Enhancing the Performance of the Electrocoagulation−Filtration System Treating Mariculture Tailwaters by Using Alternating Pulse Current: Effects of Current Density and Current Conversion Period

by
Jianping Xu
1,2,
Tianlong Qiu
1,2,
Fudi Chen
1,2,
Ming Sun
1,2,3,
Li Zhou
1,2,
Jianming Sun
1,2,* and
Yishuai Du
1,2,*
1
CAS Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
2
Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China
3
Dalian Key Laboratory of Conservation of Fishery Resources, Liaoning Province Key Laboratory of Marine Biological Resources and Ecology, Liaoning Ocean and Fisheries Science Research Institute, Dalian 116023, China
*
Authors to whom correspondence should be addressed.
Water 2022, 14(8), 1181; https://doi.org/10.3390/w14081181
Submission received: 16 February 2022 / Revised: 29 March 2022 / Accepted: 2 April 2022 / Published: 7 April 2022
(This article belongs to the Special Issue Wastewater Treatment via the Adsorption Method)
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Abstract

:
Electrocoagulation (EC) is an environmentally friendly and effective water treatment technique. It has been recently applied in combination with a filtration process. This study investigated the effects of an alternating pulse current (APC) on the electrodes, treatment efficiency, and energy consumption of an EC−filtration system during the treatment of mariculture tailwaters, from the aspects of current density and current conversion period (CCP), to generate ideas for improving the performance of the system. Results showed that using direct current (DC) would aggravate the electrode passivation, resulting in many white insoluble substances covering the surface of the electrodes. Moreover, the electrode passivation was more intense at a higher current density and longer system operation time (SOT). Significantly, the electrode weight increased by 1546.67 ± 54.50 mg when the system was operated for 90 min under DC at a current density of 45 A/m2. Unlike DC, APC significantly alleviated electrode passivation, enhanced the treatment efficiency, and reduced energy consumption. A shorter CCP produced better results. When the CCP was 1 min, current density was 45 A/m2, and SOT was 10 min, the removal efficiency of the EC−filtration system for total suspended solids (TSS), chemical oxygen demand (CODMn), and total nitrogen (TN) was 53.55 ± 1.66%, 47.76 ± 0.18%, and 15.55 ± 0.31%, respectively, and the energy consumption was 11.88 × 10−3 kWh/m3.

Graphical Abstract

1. Introduction

Mariculture plays an extremely important role in the development of the society, providing humans with a large number of high-quality proteins [1]. However, with the rapid development of the mariculture, the arbitrary discharge of the mariculture tailwaters has brought disaster to the aquatic environment [1]. Sewage treatment is an important strategy to prevent the pollution of water resources. Filtration is the first step in most water treatment processes. The efficiency of filtration is dependent on the size of the suspended particles [2]. To enhance the efficiency of the filtration equipment and reduce the load of the subsequent treatment unit, chemical flocculants are often added before sewage filtration [2]. Compared with chemical flocculation, electrocoagulation (EC) is an emerging flocculation method that is easy to operate, has low sludge output, and causes small secondary pollution [3]. It releases flocculants by sacrificing the anode, so as to increase the particle size of the suspended solids and enhance the efficiency of the filtration equipment [3,4].
Recently, EC has been combined with filtration (EC−filtration) in different scenarios, including industrial wastewater treatment [5,6], surface water purification [7,8], and other fields. This approach has been found to effectively decrease turbidity, remove total suspended solids (TSS) [9], chemical oxygen demand (CODMn), total nitrogen (TN) [2], natural organic matter (NOM) [10], dissolved organic carbon (DOC) [11,12], and eliminate microorganisms [4,13]. However, a study by Xie et al., (2017) showed that the performance of EC−filtration technology is limited by electrode passivation [14]. The electrode passivation process is classified into two categories: anode passivation and cathode passivation [15,16]. During EC, the sacrificial anode (aluminum or iron) is oxidized and dissolved, and this process is accompanied by many side reactions, leading to the formation of a “protective layer” (aluminum oxide or iron oxide) on the surface of the anode. This layer prevents further dissolution of the anode and electron transfer, resulting in the passivation of the anode [16,17]. It has been ascertained that anode passivation in the EC−filtration system decreases flocculants, which reduces the treatment efficiency of the filtration equipment [16]. Moreover, the high concentration of hydroxide ion in the vicinity of the cathode makes the insoluble salts of calcium and magnesium attach to the cathode surface, which induces the passivation of the cathode, which affects hydrogen production and electron transfer [15,18].
Studies show that there are two main strategies to alleviate electrode passivation. The first approach is the addition of sufficient chloride ions to destroy the passivation layer on the anode surface through “pitting corrosion” [16,17]. Trompette and Vergnes (2009) explored the effects of electrolytes on aluminum electrode oxidation. It was found that chloride ions improved the corrosion of aluminum electrodes [19]. Aoudj et al., (2015) investigated the influence of chloride ions on the removal efficiency of EC for heavy metals. It was found that the addition of chloride ions alleviated electrode passivation and improved the removal efficiency of heavy metals [20]. The second approach involves the use of an alternating pulse current (APC) to alleviate electrode passivation by periodically switching between cathodes and anodes [16,21]. Eyvaz et al., (2009) compared the effects of direct current (DC) and APC in EC in the treatment of dye wastewater [22]. Results indicated that APC alleviated electrode passivation to improve the removal efficiency of dyes and reduce energy consumption. Elsewhere, Yang et al., (2015) demonstrated that an APC prevented anode passivation and promoted anode dissolution [17]. It has also been established that using APC to relieve electrode passivation is simple and easily controllable compared with the method of adding chloride ions [16,17].
APC includes two attributes: current density and current conversion period (CCP) [16]. Only studying current density or CCP cannot comprehensively explain the effect of APC on the process of EC. However, the research that combined the current density and CCP to explore the impact of APC on EC is rare. Moreover, despite some past studies that have reported the application of APC in the EC process, the conclusions obtained only involve the electrode changes or pollutant removal. In production, improving the pollutant removal efficiency of the EC−filtration system and alleviating the electrode passivation to reduce operation costs need to be considered comprehensively. In this study, the EC−filtration system was applied in the treatment of mariculture tailwaters, and the effects of APC on the electrodes, pollutants removal, and energy consumption were investigated from the aspects of current density and CCP. The findings of this study are expected to enhance the performance of the EC−filtration system and guide production.

2. Materials and Methods

2.1. Experimental Set-Up

The EC−filtration water treatment system consisting of EC equipment, buffer, and microscreen drum filter (MDF) was designed. A DC regulated power supply (DP3030, Mestek Tools Co., Ltd, Shenzhen, China) was adopted to supply power to the system, which was connected with a programmable time relay (YBD-4-24, Tianlang Technology Co., Ltd, Zhongshan, China) to obtain APC and adjust the required current conversion period (CCP) [17,23]. Four aluminum plates (with the underwater length of 15 cm, width of 5 cm, and thickness of 0.3 cm) were used as electrodes, and the arrangement was monopolar in parallel connection [1]. The gap between electrodes was set to about 1.5 cm to decrease the resistance and energy consumption, as well as reduce the difficulty of construction and prevent short circuiting [2]. The total effective working area of the electrode plate was about 0.024 m2. The EC reactor and the buffer were columnar in shape, with a volume of 7.0 L and 2.0 L, respectively. The buffer was situated between the EC reactor and the MDF to improve the flocculation efficiency, and the bottom had a microporous airstone with an inlet flow of 1.0 L/min [2]. The effective filtration area of the MDF was 0.031 m2, whereas the filter pore size was 63 μm. Finally, prior to the experiment, the electrode plate was polished and soaked in 0.1 mol/L HCl solution for 5 min [24]. The structural diagram of the EC−filtration system is illustrated in Figure 1.

2.2. Experimental Water

For this experiment, the water from a culture pond of Litopenaeus vannamei was collected and subsequently filtered using sieve silk with an aperture of 120 mesh (about 125 μm) to remove shrimp shells, large particles of suspended solids, and residual feed. The salinity, pH, conductivity, TSS concentration, CODMn concentration, and TN concentration of the water used in this experiment were 15‰, 7.32, 36.35 μS/cm, 54.66 mg/L, 10.72 mg/L, and 78.46 mg/L, respectively.

2.3. Experimental Design

In this subsection, three current densities (j = 15, 30, and 45 A/m2) and four current conversion periods (T = 0, 1, 5, and 10 min) were designed. The effects of these parameters on the electrode mass, water treatment efficiency, and energy consumption of the EC−filtration system were determined. Operation parameters of the EC under different current densities and CCPs are shown in Table 1. When the CCP was 0 min, the DC was used, whereas when CCP was 1, 5, and 10 min, the APC was used. In addition, the current density was adjusted by changing the working current of the EC. The influent flow rate was maintained to 100 L/h using a liquid flowmeter. The hydraulic retention time (HRT) of the EC reactor was 4.2 min. Afterward, the concentrations of CODMn, TSS, and TN in the inlet and outlet water from the EC reactor and filtration equipment were measured to evaluate the influence of different current densities and CCPs on the ability of the EC process and filtration system to treat the water. During operation of the system, samples of the water were collected at the 10th, 30th, 60th, and 90th min, and three parallel samples were collected each time. At the end of each experiment, the electrode plate was weighed. The backwashing interval period of MDF (TMDF) and the filter residue produced by each backwashing of MDF (mMDF) was recorded. The effects of current density and CCP on the performance of the EC−filtration system were analyzed based on the change in electrode, water treatment efficiency, and energy consumption of the system.

2.4. Analysis Method

The concentrations of CODMn, TSS, TN, and Al were determined according to the standard methods of the American public health association [25,26]. At the end of the experiment, the electrode was washed with distilled water, dried at 105 °C, and then weighed using an analytical balance (BSM220.3, Shanghai Yousheng Weighing Apparatus Co., Ltd., Shanghai, China). In addition, salinity, pH, and conductivity were assessed using the YSI-556 water quality analyzer (USA). These measurements were analyzed using SPSS 19.0 with an LSD test and one-way ANOVA, and they were presented as the mean ± SE, n = 3. The level of significance was set at 0.05 for all tests.
The removal efficiency (RE, %) of the system for CODMn, TSS, and TN was calculated using Equation (1):
R E % = C 1 − C 2 C 1 × 100 %
where C1 (mg/L) and C2 (mg/L) represent the concentration of CODMn, TSS, and TN in the influent and effluent water from the EC reactor or filtration equipment, respectively.
The energy consumption (W, kWh/m3) was calculated using Equation (2):
W = U I t 1000 V
where U, I, t, and V represent voltage (V), current (A), EC reaction time (h), and wastewater treatment volume per hour (m3), respectively.
The theoretical Al concentration (CTheoretical Al, mg/L) in the EC reactor effluent was calculated using Equation (3) [12,17]:
C Theoretical   Al = 1000 I t M n F V
where I, t, M, n, F, and V represent current (A), HRT of the EC reactor (s), molecular weight (MAl = 26.98 g/mol), electron involved (n = 3), Faraday’s constant (96,485 C/mol), and effective volume of the EC reactor, respectively.
The current efficiency (Φ, %) is the ratio of the actual Al concentration (CActual Al) to the CTheoretical Al in the EC reactor effluent [12,17]:
Φ   % = C Actual   Al C Theoretical   Al × 100 %

3. Results and Discussion

3.1. Effects of Current Density and CCP on Electrode Mass and Al Dissolution

The changes in electrode mass after operating the EC−filtration system for 90 min under different current densities and CCPs are shown in Figure 2. When the current density increased from 15 A/m2 to 45 A/m2 at T = 1 min, the electrode mass also increased from 122.33 ± 22.39 mg to 782.67 ± 47.4 mg. Similarly, the electrode mass increased from 202.00 ± 12.03 mg to 956.67 ± 39.36 mg when the current density increased from 15 A/m2 to 45 A/m2 at T = 5 min. Further, the electrode mass increased from 276.67 ± 48.71 mg to 1322.33 ± 73.61 mg when the current density was raised from 15 A/m2 to 45 A/m2 at T = 10 min. Likewise, the electrode mass increased from 380 ± 48.70 mg to 1546.67 ± 54.50 mg when the current density increased from 15 A/m2 to 45 A/m2 at T = 0 min (DC).
The mass of the electrode increased significantly with the rise of current density when the CCP was kept constant (p < 0.05). Müller et al., (2019) also reported that a higher current density increased the thickness of the surface layer on the electrode plate and the mass of the electrode plate [27]. Notably, the intensity of the EC reaction increased with the current density. It has been reported that vigorous EC reactions accelerated the electrode passivation [18,28]. Electrode passivation causes the electrode surface to be covered with a layer of insoluble substance, which results in the increase of electrode mass [15,16,17]. Due to electrode passivation, a lower current density is desirable to reduce the maintenance cost of the EC−filtration system. Generally, the optimum current density is 20–25 A/m2 [12,29]. Additionally, from Figure 2, it was observed that using APC with a shorter CCP resulted in a smaller mass gain of the electrode at the same current density, and the difference was significant (p < 0.05). Figure 3 depicts the electrode surface under different CCP when the current density was 45 A/m2. It can be seen that a shorter CCP was correlated with a small deposition on the electrode surface.
Table 2 represents the Al dissolution after operating the EC−filtration system for 90 min.
The study found the phenomenon that the CActual Al was higher than the CTheoretical Al, resulting in the Φ > 100%, which has been observed in the previous reports [12,15,17,23]. Two reasons have been attributed to the phenomenon: (1) the pitting corrosion of chloride ion in mariculture wastewater on the Al anode; (2) the Al cathode was corroded and dissolved [12,16,17]. The results show that, with the increase of current density, the dissolution of Al increased, but the current efficiency decreased. According to Equations (3) and (4), the dissolved amount of the Al electrodes was positively correlated with the current. However, a higher current density would aggravate the electrode passivation, resulting in a lower current efficiency [12]. Moreover, using APC could promote the dissolution of Al and improve the current efficiency. A shorter CCP produced better results. Several studies have indicated that using APC in the EC process causes the anode and cathode to switch regularly, which reduces the amount of oxide formed on the anode surface and insoluble material deposited on the cathode surface, improving the current efficiency [16,17,28,30,31]. Therefore, APC is the optimum power supply type for EC−filtration system, and CCP should be reduced appropriately to improve the performance of the system in actual production.
High current density during EC will aggravate the electrode passivation [32], which requires a shorter CCP to counter the electrode passivation [16]. Of note, lower current density accompanied by shorter CCP can better improve electrode passivation during EC, promoting the dissolution of Al and improving the current efficiency. Here, it was found that a short CCP (T = 1 min) can greatly alleviate electrode passivation; however, it cannot completely overcome the deposition of the cathode insoluble matter (Figure 3d). In another research work, short CCP has been reported as undesirable, which affects the life of the power supply [3]. From the perspective of the long-term operation of the system, it is better to supplement with physical cleaning measures to solve the problem of electrode passivation.

3.2. Effects of Current Density and CCP on TSS Removal

As shown in Figure 4, under the condition of using DC and the system operating for 10 min, when the current density raised from 15 A/m2 to 45 A/m2, the TSS concentration of the EC reactor effluent changed from 60.00 ± 1.62 mg to 77.99 ± 1.61 mg (p < 0.05), whereas the TSS concentration of the MDF effluent changed from 39.00 ± 2.13 mg to 27.00 ± 0.72 mg (p < 0.05), and the TSS removal efficiency of the EC−filtration system increased from 24.51 ± 4.12% to 47.74 ± 1.39% (p < 0.05). The results revealed that the concentration of TSS in the aquaculture wastewater increased after being treated using the EC reactor, while it decreased after filtration with MDF. During EC, metal cations were released from the anode, which formed flocculants to adsorb or flocculate TSS and dissolved pollutants in aquaculture wastewater, resulting in the addition of TSS concentration to the effluent of the EC reactor [4]. The concentration of TSS in the EC reactor effluent increased with the rise of the current density. The current density directly affects the dissolution of the metal anode, and a higher current density suggests that more metal cations can be obtained, which contributes to the removal of TSS in the EC−filtration system [29].
Moreover, under DC and current densities of 15, 30, and 45 A/m2, the SOT increased from 10 min to 90 min, and the concentration of TSS in the EC reactor effluent decreased by 4.00, 10.33, and 17.33 mg, respectively. In addition, the removal efficiency of TSS by the EC−filtration system reduced by 3.20%, 10.46%, and 16.13%, respectively. The concentration of TSS in the EC reactor effluent decreased as the SOT increased, implying that the production of flocculants decreased and the passivation of the anode was aggravated, all of which decreased the efficiency of the EC−filtration system to remove TSS [16]. Timmes et al., (2010) used EC−filtration (ultrafiltration) technology to treat seawater and obtained similar conclusions. The study also showed that, with the increase of SOT, the higher the current density was, the more the TSS removal efficiency decreased [3]. Chen et al., (2020) used EC technology (Al electrode as the anode) to remove boron from natural water. It was found that increasing the current density (from 1.8 A/m2 to 5.2 A/m2) decreased the faradaic efficiency (from 116% to 80%) [32]. This is because increasing the current density will aggravate anode passivation [16]. Therefore, using a lower current density can increase the current efficiency of the EC−filtration system and reduce energy consumption.
As depicted in Figure 4, at the current density of 45 A/m2 and the SOT of 10 min, when the CCP was 1, 5, 10, and 0 min (DC), respectively, the TSS concentration of EC reactor effluent was found to be 85.33 ± 1.08, 83.33 ± 1.68, 79.35 ± 1.24, and 77.99 ± 1.61 mg/L, the removal efficiency of the EC−filtration system for TSS was 53.55 ± 1.66%, 50.26 ± 2.19%, 48.39 ± 1.86%, and 47.74 ± 1.39%. This proved that using APC could increase the output of flocculants, alleviate anode passivation, and improve the treatment efficiency of the EC−filtration system for TSS. Significantly, a smaller CCP produces better results. Notably, when the current density was 15 A/m2, CCP exhibited no considerable effect on the removal of TSS (p > 0.05). However, as the current density increased, the treatment group with T = 1 min was significantly better compared to the treatment groups with DC and T = 10 min (p < 0.05). Within the SOT of 90 min, there was no statistical difference in TSS removal between the treatment groups with T = 1 min and T = 5 min (p > 0.05). Similarly, there was no significant difference between the treatment groups of DC and T = 10 min (p > 0.05). Ingelsson et al., (2020) proposed that longer CCPs may produce similar results as DC [16]. Based on these findings, the CCP of APC must be less than 10 min to obtain an obvious advantage compared with DC. Interestingly, it was found that T = 1 min yielded the best outcomes. Eyvaz et al., (2009) used EC technology to treat dyeing wastewater. It was observed that the treatment effect was best when the CCP was 5 min [22]. Ashraf et al., (2021) reported that APC prevented electrode passivation, and the optimal value of CCP was below 5 min [33]. In the study by Pi et al., (2014), CCP was set at 15 s during the removal of methyl orange dye, whereas it was set at 2.5 min in another study by Eyvaz (2016) during the treatment of brewery wastewater [34,35].
Table 3 presents the effect of using APC on the TMDF, mMDF, and CActual Al in MDF effluent during the EC process. Under the condition of using DC, when the current density raised from 15 A/m2 to 45 A/m2, the TMDF dropped from 25.22 min to 13.67 min, and the mMDF increased from 805.82 mg to 872.41 mg. When using APC (CCP = 1 min) and current density raised from 15 A/m2 to 45 A/m2, the TMDF decreased from 23.43 min to 11.58 min, and the mMDF increased from 830.98 mg to 946.70 mg. The results indicate that using APC and increasing current density could enhance the working efficiency of the MDF, which was associated with the increased flocculant production [3,16,33]. Of note, residual Al appeared in MDF effluent, which raised with the increase of the current density. Residual metal is an important indicator, which may cause secondary pollution [23]. In this experiment, the residual concentration of Al was relatively high (0.13~1.11 mg/L), which was mainly caused by insufficient coagulation due to the small buffer reactor of the system. The EC−filtration system is the first step in the water treatment process. Residual Al flocculants can improve the treatment efficiency of subsequent water treatment equipment, such as biofilter and air flotation separation devices [14,23]. Therefore, it is very important to investigate the role and migration of aluminum-based flocculants produced by the EC reactor in the complete water treatment process (including physical filtration, biological treatment, flotation, etc.).

3.3. Effects of Current Density and CCP on CODMn Removal

As shown in Figure 5, the EC−filtration system could remove CODMn through the EC process and flocculation-filtration. Under the condition of T = 1 min and SOT of 10 min, the EC−filtration system exhibited the best removal effect on CODMn, and when the current density was 15, 30, and 45 A/m2, the removal efficiency of CODMn was 21.89 ± 0.47%, 35.07 ± 0.77%, and 47.76 ± 0.18%, respectively, and the removal efficiencies of CODMn by the EC process and flocculation-filtration were 9.20 ± 1.85% and 11.94 ± 1.23%, 14.30 ± 0.61% and 17.91 ± 0.81%, and 21.52 ± 0.47% and 22.52 ± 0.91%. This is due to anode dissolving to form flocculants during EC, while at the same time, side reactions will occur, which produce many active oxidation substances that can degrade CODMn [4,36]. The flocculants can adsorb pollutants to improve the ability of the filtration equipment to remove CODMn [3,4]. In comparison, the removal of CODMn by flocculation-filtration was more compared with that of the EC process at the current density of 15 A/m2 and 30 A/m2, and the maximum difference was approximately 5%. When the current density was 45 A/m2, the EC process and flocculation-filtration showed similar efficiency in CODMn removal. EC−filtration technology has a good treatment ability for CODMn, in which the EC process and flocculation-filtration are indispensable during the COD removal. Kamyar et al., (2018) used EC-ultrafiltration technology to treat poultry processing water and found that the EC process removed 56% of COD, while the flocculation-filtration removed 33% of COD [37]. Elsewhere, Xu et al., (2021) used EC-microfiltration technology to remove CODMn in the marine aquaculture wastewater and found that the EC process and flocculation-filtration removed equal amounts of CODMn [2]. Moreover, it was noted that the removal efficiencies of CODMn by the EC process and flocculation-filtration increased with the raise of current density. This is because that progressive raise in current density increased the concentration of active oxidation substances and flocculants [3].
As indicated in Figure 5A–C, the removal of CODMn using the EC−filtration system decreased significantly with the increase of SOT, especially when using DC (p < 0.05). When DC was used and the current density was 15 A/m2, the SOT increased from 10 min to 90 min while the CODMn removal efficiency declined by 4.97%, from 21.14 ± 1.23% to 16.17 ± 0.81%. Moreover, it decreased by 12.07% and 19.66% at current densities of 30 A/m2 and 45 A/m2, respectively. This is because a longer SOT and a higher current density will accelerate electrode passivation and reduce current efficiency [16,18]. In addition, at the current density of 15 A/m2, when T = 1, 5, and 10 min, the CODMn removal efficiency decreased by 1.87%, 3.62%, and 3.85%, respectively, after 90 min operation, which compared with that after 10 min operation of the system (Figure 5A). Similarly, at the current density of 30 A/m2 under the T = 1, 5, and 10 min (Figure 5B), the CODMn removal efficiency decreased by 7.34%, 9.58%, and 9.85%, respectively, while at the current denEC−filtrationsity of 45 A/m2, it also reduced by 5.72%, 9.93%, and 12.34%, respectively (Figure 5C). Compared with the use of DC, when using APC, the CODMn removal of the system was higher, and the difference was more significant with the increase of SOT (p < 0.05). Remarkably, the CODMn removal efficiency of the treatment group with T = 1 min was better than that of other treatment groups, and the superiority was more obvious with the increase of current density and SOT (p < 0.05). Mao et al., (2008) found that APC was more effective in increasing the amount of anode dissolved and removal efficiency of COD compared to DC [31]. APC is helpful to improve the removal efficiency of the EC−filtration system for CODMn, and the shorter the CCP, the more obvious the effect. The shorter the CCP, the stronger the penetration of the current to puncture the passive layer, which helps in generating more metal ions to form flocculants as well as reduces the deposition of insoluble substances on the electrode, thereby promoting the removal of CODMn [21,38].

3.4. Effects of Current Density and CCP on TN Removal

As shown in Figure 6, the EC−filtration system removed the TN through the EC process and flocculation-filtration. When the wastewater flew through the EC reactor, some TN molecules were converted into nitrogen-containing gas, such as nitrogen (N2) due to the EC process; whereas some of the TN was adsorbed and flocculated by flocculants, it were eventually removed by filter equipment [2]. The EC process removes TN through the direct reduction of the cathode, and the efficiency of the reduction reaction is dependent on the electron transfer rate [39]. Specifically, in Figure 6A–C, under the condition of T = 1 min and SOT of 10 min, the EC−filtration system exhibited the best removal effect on TN, and when the current density was 15, 30, and 45 A/m2, the removal efficiency of TN by the EC−filtration system was 9.62 ± 0.16%, 11.51 ± 0.31%, and 15.55 ± 0.31%, respectively; among them, the TN removed by flocculation-filtration was 8.34 ± 0.18%, 9.21 ± 0.34%, and 12.60 ± 0.42%, respectively, and the TN removed by the EC process was 1.28 ± 0.03%, 2.30 ± 0.03%, and 2.95 ± 0.04%, respectively. It demonstrated that the EC−filtration system primarily relied on flocculation-filtration to remove TN in aquaculture water. In a previous study, when Al was used as the anode, the current density was 19.22 A/m2, the EC treatment time was 3.0 min, and the filtration aperture was 63 μm; the removal efficiency of TN by EC process and flocculation-filtration was about 2% and 13%, respectively [2]. Another study found that the nitrogen removal by flocculation-filtration was three times that of the EC process [39]. It was observed that the removal efficiency of TN by the two processes increased with the current density. This is because a high current density will increase the electro-reduction reactions and the output of flocculants [3,39].
Figure 6 indicates that the TN removal efficiency of the system decreased as the operation time increased, and this was most prominent when DC was used (p < 0.05). Using DC, when the current density was 15, 30, and 45 A/m2, the SOT increased from 10 min to 90 min, the removal efficiency of the EC−filtration system for TN reduced by 2.54%, 2.91%, and 3.95%, respectively. In previous reports, it was concluded that a longer SOT will lead to intense electrode passivation, hence decreasing the generation of flocculants and electron transfer [15,28]. Therefore, a longer SOT decreases the removal of TN by flocculation-filtration and electro-reduction. Compared with DC, APC is more effective in enhancing the ability of the system to remove TN (p < 0.05), which became more apparent with the increase of the current density (p < 0.05). When the current density was 45 A/m2 and SOT was 90 min, the removal efficiency of TN in the treatment group with T = 1 min was increased by 4.20% compared with the treatment group with DC, and it was 2.56% and 3.18% when the current density was 15 A/m2 and 30 A/m2, respectively. Karamati-Niaragh et al., (2018) used EC technology to remove nitrogen. It was found that when the current density was 60 A/m2 and 90 A/m2, the nitrogen removal efficiency of the system using APC was about 2% and 8% higher than the system using DC, respectively [40]. Noticeably, the treatment groups with T = 1 min and T = 5 min were significantly better, relative to the treatment groups with T = 10 min (p < 0.05). Moreover, when the current density was 45 A/m2, the removal efficiency of TN of the treatment group with T = 1 min was markedly higher than that of the treatment group with T = 5 min (p < 0.05), while at the current density of 15 A/m2 and 30 A/m2, the treatment group with T = 1 min was more superior compared to the treatment group with T = 5 min after system operating for 60 min (p < 0.05). Using APC can improve the ability of the EC−filtration system to remove TN, and a shorter CCP will produce better results.

3.5. Effects of Current Density and CCP on Energy Consumption

The effects of current density and APC on energy consumption are outlined in Table 4. The findings revealed that the longer the SOT, the higher the energy consumption, which was most notable when using DC. In addition, when using DC and the current density was 15, 30, and 45 A/m2, the SOT increased from 10 min to 90 min, and the energy consumption of EC increased by 2.37%, 3.38%, and 4.59%, respectively. The additional energy consumption during EC increased with the current density and SOT. It has been found that a higher current density and longer SOT will accelerate the electrode passivation [3,16]. During EC, the electrode passivation will form an insulation layer on the surface of the electrode, which induces a significant increase in passive over potential, resulting in higher power consumption [3]. The study has suggested that a shorter CCP can reduce the additional energy consumption of EC, whereas the greater the current density and the longer the SOT, the more prominent the role of CCP. At the current density of 45 A/m2, when the CCP was 1, 5, and 10 min, the SOT increased from 10 min to 90 min, while the energy consumption of EC also increased by 0.33%, 0.93%, and 1.83%, respectively. Compared with the use of DC, using APC can reduce the energy consumption of EC, and the shorter the CCP, the smaller the energy consumption [21]. Mao et al., (2008) utilized the EC to remove COD in graywater. It was found that using APC saved up to 30% of the energy consumed [31]. Bian et al., (2019) used EC to treat oily bilge water and found that the extra energy consumption increased by 258% after the electrode worked for 24 h when using DC, while it increased by only 19% using APC [15]. Eyvaz et al., (2009) and Vasudevan et al., (2011) also demonstrated that using APC during EC can enhance the removal of pollutants as well as reduce energy consumption [22,30]. During the operation of the EC−filtration system, an APC with a smaller CCP and lower current density is recommended to reduce the energy consumption.

4. Conclusions

In this paper, the EC−filtration system was used for the pretreatment of mariculture tailwaters. From the aspects of current density and CCP, the effects of APC on the electrode, treatment efficiency, and energy consumption of EC−filtration system were examined. The following conclusions were obtained.
Compared with the use of DC, using APC could suppress the electrode passivation, improve the current efficiency, increase the removal efficiency of TSS, CODMn, and TN by the EC−filtration system, and reduce the energy consumed. With the increase of current density and SOT, the positive effect of APC was more obvious.
A higher current density is conducive to the removal of TSS, CODMn, and TN, but it will accelerate the electrode passivation and reduce the current efficiency, increasing additional energy consumption. Therefore, in actual production, the number or working area of the electrodes should be increased appropriately, so that the current density can be reduced without changing the working current of EC, which can ensure the removal of pollutants and alleviate the passivation of the electrodes.
CCP is an important parameter of APC. Significantly, the shorter the CCP of APC, the better the results. Compared with DC, APC had significant advantages when the CCP was less than 10 min.
The longer the operation time of the EC−filtration system, the more serious the electrode passivation, the higher the energy consumption, and the more unfavorable it is for TSS, CODMn, and TN removal. To operate the system for a long period with lower maintenance costs, an APC with a smaller CCP and lower current density is suggested.

Author Contributions

Conceptualization, J.S.; data curation, J.X.; formal analysis, J.X.; investigation, J.X.; project administration, J.S.; resources, M.S. and L.Z.; writing—original draft, J.X.; writing—review and editing, J.X., T.Q., F.C. and Y.D. All authors have read and agreed to the published version of the manuscript.

Funding

The work was funded by the National Key R and D Program of China, grant numbers 2019YFD0900502, the Science and Technology Major Project of Guangxi, grant numbers AA17204094-3, the Key Research and Development Program of Shandong Province, grant numbers 2019GHY112004, and the China Postdoctoral Science Foundation, grant numbers 2021M693212. The APC was funded by 2019YFD0900502.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The authors thank the Dalian Huixin Titanium Equipment Development Co., Ltd. for supporting this study. The authors also thank Home for Researchers (www.home-for-researchers.com, accessed on 16 November 2021) for editing the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Igwegbe, C.A.; Onukwuli, O.D.; Ighalo, J.O.; Umembamalu, C.J. Electrocoagulation-flocculation of aquaculture effluent using hybrid iron and aluminium electrodes: A comparative study. Chem. Eng. J. Adv. 2021, 6, 100107. [Google Scholar] [CrossRef]
  2. Xu, J.P.; Du, Y.S.; Qiu, T.L.; Zhou, L.; Li, Y.; Chen, F.D.; Sun, J.M. Application of hybrid electrocoagulation-filtration methods in the pretreatment of marine aquaculture wastewater. Water Sci. Technol. 2021, 83, 1315–1326. [Google Scholar] [CrossRef] [PubMed]
  3. Moussa, D.T.; El-Naas, M.H.; Nasser, M.; Al-Marri, M.J. A comprehensive review of electrocoagulation for water treatment: Potentials and challenges. J. Environ. Manag. 2017, 186, 24–41. [Google Scholar] [CrossRef] [PubMed]
  4. Heffron, J.; McDermid, B.; Maher, E.; McNamara, P.J.; Mayer, B.K. Mechanisms of virus mitigation and suitability of bacteriophages as surrogates in drinking water treatment by iron electrocoagulation. Water Res. 2019, 163, 114877. [Google Scholar] [CrossRef]
  5. García-Morales, M.A.; Juárez, J.C.G.; Martínez-Gallegos, S.; Roa-Morales, G.; Peralta, E.; del Campo López, E.M.; Barrera-Díaz, C.; Miranda, V.M.; Blancas, T.T. Pretreatment of real wastewater from the chocolate manufacturing industry through an integrated process of electrocoagulation and sand filtration. Int. J. Photoenergy 2018, 2018, 2146751. [Google Scholar] [CrossRef] [Green Version]
  6. Khorram, A.G.; Fallah, N. Comparison of electrocoagulation and photocatalytic process for treatment of industrial dyeing wastewater: Energy consumption analysis. Environ. Prog. Sustain. Energy 2020, 39, 13288. [Google Scholar] [CrossRef]
  7. Vepsäläinen, M.; Pulliainen, M.; Sillanpää, M. Effect of electrochemical cell structure on natural organic matter (NOM) removal from surface water through electrocoagulation (EC). Sep. Purif. Technol. 2012, 99, 20–27. [Google Scholar] [CrossRef]
  8. Zhao, S.; Huang, G.; Cheng, G.; Wang, Y.; Fu, H. Hardness, COD and turbidity removals from produced water by electrocoagulation pretreatment prior to reverse osmosis membranes. Desalination 2014, 344, 454–462. [Google Scholar] [CrossRef]
  9. Singh, H.; Mishra, B.K. Assessment of kinetics behavior of electrocoagulation process for the removal of suspended solids and metals from synthetic water. Environ. Eng. Res. 2017, 22, 150–153. [Google Scholar] [CrossRef]
  10. Chellam, S.; Sari, M.A. Aluminum electrocoagulation as pretreatment during microfiltration of surface water containing NOM: A review of fouling, NOM, DBP, and virus control. J. Hazard. Mater. 2016, 304, 490–501. [Google Scholar] [CrossRef] [Green Version]
  11. Jiang, J.Q.; Graham, N.; André, C.; Kelsall, G.H.; Brandon, N. Laboratory study of electro-coagulation-flotation for water treatment. Water Res. 2002, 36, 4064–4078. [Google Scholar] [CrossRef]
  12. Jiang, J.Q.; Graham, N.J.D.; André, C.M.; Kelsall, G.H.; Brandon, N.P.; Chipps, M.J. Comparative performance of an electrocoagulation/flotation system with chemical coagulation/dissolved air flotation: A pilot-scale trial. Water Sci. Technol. Water Supply 2002, 2, 289–297. [Google Scholar] [CrossRef]
  13. Sari, M.A.; Chellam, S. Electrocoagulation process considerations during advanced pretreatment for brackish inland surface water desalination: Nanofilter fouling control and permeate water quality. Desalination 2017, 410, 66–76. [Google Scholar] [CrossRef]
  14. Xie, S.; Yuan, S.; Liao, P.; Tong, M.; Gan, Y.; Wang, Y. Iron-anode enhanced sand filter for arsenic removal from tube well water. Environ. Sci. Technol. 2017, 51, 889–896. [Google Scholar] [CrossRef]
  15. Bian, Y.; Ge, Z.; Albano, C.; Lobo, F.L.; Ren, Z.J. Oily bilge water treatment using DC/AC powered electrocoagulation. Environ. Sci. Water Res. Technol. 2019, 5, 1654–1660. [Google Scholar] [CrossRef]
  16. Ingelsson, M.; Yasri, N.; Roberts, E.P. Electrode Passivation, Faradaic Efficiency, and Performance Enhancement Strategies in Electrocoagulation-A Review. Water Res. 2020, 187, 116433. [Google Scholar] [CrossRef]
  17. Yang, Z.H.; Xu, H.Y.; Zeng, G.M.; Luo, Y.L.; Yang, X.; Huang, J.; Wang, L.K.; Song, P.P. The behavior of dissolution/passivation and the transformation of passive films during electrocoagulation: Influences of initial pH, Cr (VI) concentration, and alternating pulsed current. Electrochim. Acta 2015, 153, 149–158. [Google Scholar] [CrossRef]
  18. Gabrielli, C.; Maurin, G.; Francy-Chausson, H.; Thery, P.; Tran, T.T.M.; Tlili, M. Electrochemical water softening: Principle and application. Desalination 2016, 201, 150–163. [Google Scholar] [CrossRef]
  19. Trompette, J.L.; Vergnes, H. On the crucial influence of some supporting electrolytes during electrocoagulation in the presence of aluminum electrodes. J. Hazard. Mater. 2009, 163, 1282–1288. [Google Scholar] [CrossRef] [Green Version]
  20. Aoudj, S.; Khelifa, A.; Drouiche, N.; Belkada, R.; Miroud, D. Simultaneous removal of chromium (VI) and fluoride by electrocoagulation–electroflotation: Application of a hybrid Fe-Al anode. Chem. Eng. J. 2015, 267, 153–162. [Google Scholar] [CrossRef]
  21. Zhou, R.; Liu, F.; Wei, N.; Yang, C.; Yang, J.; Wu, Y.; Li, Y.; Xu, K.Q.; Chen, X.C.; Zhang, C.P. Comparison of Cr (VI) removal by direct and pulse current electrocoagulation: Implications for energy consumption optimization, sludge reduction and floc magnetism. J. Water Process Eng. 2020, 37, 101387. [Google Scholar] [CrossRef]
  22. Eyvaz, M.; Kirlaroglu, M.; Aktas, T.S.; Yuksel, E. The effects of alternating current electrocoagulation on dye removal from aqueous solutions. Chem. Eng. J. 2009, 153, 16–22. [Google Scholar] [CrossRef]
  23. Xu, J.; Qiu, T.; Chen, F.; Zhou, L.; Sun, J.; Du, Y. Construction and application of an electrocoagulation and filtration linkage control system in a recirculating aquaculture system. J. Water Process Eng. 2021, 44, 102379. [Google Scholar] [CrossRef]
  24. Hu, C.; Sun, J.; Wang, S.; Liu, R.; Liu, H.; Qu, J. Enhanced efficiency in HA removal by electrocoagulation through optimizing flocs properties: Role of current density and pH. Sep. Purif. Technol. 2017, 175, 248–254. [Google Scholar] [CrossRef]
  25. APHA. Standard Methods for the Examination of Water and Wastewater. American Public Health Association; American Water Works Association; Water Environment Federation: Washington, DC, USA, 1998. [Google Scholar]
  26. Zhen, Z.; Yao, J.; Pang, Z.; Bo, L. Optimization of electrocoagulation process to eliminate CODMn in micro-polluted surface water using response surface method. J. Dispers. Sci. Technol. 2016, 37, 743–751. [Google Scholar] [CrossRef]
  27. Müller, S.; Behrends, T.; van Genuchten, C.M. Sustaining efficient production of aqueous iron during repeated operation of Fe(0)-electrocoagulation. Water Res. 2019, 155, 455–464. [Google Scholar] [CrossRef]
  28. Eyvaz, M.; Gürbulak, E.; Kara, S.; Yüksel, E. Preventing of cathode passivation/deposition in electrochemical treatment methods–a case study on winery wastewater with electrocoagulation. In Modern Electrochemical Methods in Nano, Surface and Corrosion Science; IntechOpen: London, UK, 2014; Volume 1. [Google Scholar] [CrossRef] [Green Version]
  29. Hakizimana, J.N.; Gourich, B.; Chafi, M.; Stiriba, Y.; Vial, C.; Drogui, P.; Naja, J. Electrocoagulation process in water treatment: A review of electrocoagulation modeling approaches. Desalination 2017, 404, 1–21. [Google Scholar] [CrossRef]
  30. Vasudevan, S.; Kannan, B.S.; Lakshmi, J.; Mohanraj, S.; Sozhan, G. Effects of alternating and direct current in electrocoagulation process on the removal of fluoride from water. J. Chem. Technol. Biotechnol. 2011, 86, 428–436. [Google Scholar] [CrossRef]
  31. Mao, X.; Hong, S.; Zhu, H.; Lin, H.; Wei, L.; Gan, F. Alternating pulse current in electrocoagulation for wastewater treatment to prevent the passivation of al electrode. J. Wuhan Univ. Technol.-Mater Sci. Ed. 2008, 23, 239–241. [Google Scholar] [CrossRef]
  32. Chen, M.; Dollar, O.; Shafer-Peltier, K.E.; Randtke, S.; Peltier, E. Boron removal by electrocoagulation: Removal mechanism, adsorption models and factors influencing removal. Water Res. 2020, 170, 115362. [Google Scholar] [CrossRef]
  33. Ashraf, S.N.; Rajapakse, J.; Dawes, L.A.; Millar, G.J. Impact of turbidity, hydraulic retention time, and polarity reversal upon iron electrode based electrocoagulation pre-treatment of coal seam gas associated water. Environ. Technol. Innov. 2021, 23, 101622. [Google Scholar] [CrossRef]
  34. Pi, K.W.; Xiao, Q.; Zhang, H.Q.; Xia, M.; Gerson, A.R. Decolorization of synthetic methyl orange wastewater by electrocoagulation with periodic reversal of electrodes and optimization by RSM. Process Saf. Environ. Prot. 2014, 92, 796–806. [Google Scholar] [CrossRef]
  35. Eyvaz, M. Treatment of brewery wastewater with electrocoagulation: Improving the process performance by using alternating pulse current. Int. J. Electrochem. Sci. 2016, 11, 4988–5008. [Google Scholar] [CrossRef]
  36. Govindan, K.; Angelin, A.; Rangarajan, M. Critical evaluation of mechanism responsible for biomass abatement during electrochemical coagulation (EC) process: A critical review. J. Environ. Manag. 2018, 227, 335–353. [Google Scholar] [CrossRef]
  37. Kamyar, S.; John, A.; Yu-Hsuan, C.; Siavash, D.; Mohanad, K.; Ranil, W.S. Electrocoagulation followed by ultrafiltration for treating poultry processing wastewater. J. Environ. Chem. Eng. 2018, 6, 4937–4944. [Google Scholar] [CrossRef]
  38. Xu, L.; Huang, Q.; Xu, X.; Cao, G.; He, C.; Wang, Y.; Yang, M. Simultaneous removal of Zn2+ and Mn2+ ions from synthetic and real smelting wastewater using electrocoagulation process: Influence of pulse current parameters and anions. Sep. Purif. Technol. 2017, 188, 316–328. [Google Scholar] [CrossRef]
  39. Govindan, K.; Noel, M.; Mohan, R. Removal of nitrate ion from water by electrochemical approaches. J. Water Process Eng. 2015, 6, 58–63. [Google Scholar] [CrossRef]
  40. Karamati-Niaragh, E.; Moghaddam, M.; Emamjomeh, M.M.; Nazlabadi, E. Evaluation of direct and alternating current on nitrate removal using a continuous electrocoagulation process: Economical and environmental approaches through RSM. J. Environ. Manag. 2018, 230, 245–254. [Google Scholar] [CrossRef]
Water 14 01181 g001 550
Figure 1. The structural diagram of the EC−filtration system: (1) water storage tank, (2) water pump, (3) liquid flowmeter, (4) DC power supply, (5) programmable time relay, (6) electrodes, (7) EC reactor, (8) valve, (9) air pump, (10) airstone, (11) drain valve, (12) buffer, (13) liquid level, and (14) microscreen drum filter.
Figure 1. The structural diagram of the EC−filtration system: (1) water storage tank, (2) water pump, (3) liquid flowmeter, (4) DC power supply, (5) programmable time relay, (6) electrodes, (7) EC reactor, (8) valve, (9) air pump, (10) airstone, (11) drain valve, (12) buffer, (13) liquid level, and (14) microscreen drum filter.
Water 14 01181 g001
Water 14 01181 g002 550
Figure 2. Changes in electrode mass after operating the EC−filtration system for 90 min under different current densities and CCPs. (In the same CCP group, different lowercase letters on some values indicate significant differences (p < 0.05). At the same current density across different CCPs, different uppercase letters on some values indicate significant differences (p < 0.05)).
Figure 2. Changes in electrode mass after operating the EC−filtration system for 90 min under different current densities and CCPs. (In the same CCP group, different lowercase letters on some values indicate significant differences (p < 0.05). At the same current density across different CCPs, different uppercase letters on some values indicate significant differences (p < 0.05)).
Water 14 01181 g002
Water 14 01181 g003 550
Figure 3. The surface of the electrodes after operating the EC−filtration system for 90 min under different CCPs at j = 45 A/m2, (a) DC, (b) T = 10 min, (c) T = 5 min, (d) T = 1 min).
Figure 3. The surface of the electrodes after operating the EC−filtration system for 90 min under different CCPs at j = 45 A/m2, (a) DC, (b) T = 10 min, (c) T = 5 min, (d) T = 1 min).
Water 14 01181 g003
Water 14 01181 g004 550
Figure 4. Effects of current density and CCP on the removal of TSS by the EC−filtration system ((A) j = 15 A/m2, (B) j = 30 A/m2, (C) j = 45 A/m2). In the same CCP, different lowercase letters on the RE(EC−filtration system) indicate significant differences (p < 0.05). At the same operation time across different CCPs, different uppercase letters on the RE(EC−filtration system) indicate significant differences (p < 0.05).
Figure 4. Effects of current density and CCP on the removal of TSS by the EC−filtration system ((A) j = 15 A/m2, (B) j = 30 A/m2, (C) j = 45 A/m2). In the same CCP, different lowercase letters on the RE(EC−filtration system) indicate significant differences (p < 0.05). At the same operation time across different CCPs, different uppercase letters on the RE(EC−filtration system) indicate significant differences (p < 0.05).
Water 14 01181 g004
Water 14 01181 g005 550
Figure 5. Effects of current density and CCP on the removal of CODMn by the EC−filtration system: (A) j = 15 A/m2, (B) j = 30 A/m2, (C) j = 45 A/m2. In the same CCP, different lowercase letters on the RE(Total) indicate significant differences (p < 0.05). At the same operation time across different CCPs, different uppercase letters on the RE(Total) indicate significant differences (p < 0.05).
Figure 5. Effects of current density and CCP on the removal of CODMn by the EC−filtration system: (A) j = 15 A/m2, (B) j = 30 A/m2, (C) j = 45 A/m2. In the same CCP, different lowercase letters on the RE(Total) indicate significant differences (p < 0.05). At the same operation time across different CCPs, different uppercase letters on the RE(Total) indicate significant differences (p < 0.05).
Water 14 01181 g005
Water 14 01181 g006 550
Figure 6. Effects of current density and CCP on the removal of TN by the EC−filtration system: (A) j = 15 A/m2, (B) j = 30 A/m2, (C) j = 45 A/m2. In the same CCP, different lowercase letters on the RE(Total) indicate significant differences (p < 0.05). At the same current density across different CCPs, different uppercase letters on the RE(Total) indicate significant differences (p < 0.05).
Figure 6. Effects of current density and CCP on the removal of TN by the EC−filtration system: (A) j = 15 A/m2, (B) j = 30 A/m2, (C) j = 45 A/m2. In the same CCP, different lowercase letters on the RE(Total) indicate significant differences (p < 0.05). At the same current density across different CCPs, different uppercase letters on the RE(Total) indicate significant differences (p < 0.05).
Water 14 01181 g006
Table
Table 1. Operating parameters of the EC reactor system.
Table 1. Operating parameters of the EC reactor system.
Current TypeCCP (min)j = 15 A/m2j = 30 A/m2j = 45 A/m2
U (V)I (A)U (V)I (A)U (V)I (A)
DC00.940.361.030.711.201.08
APC10.940.361.010.711.101.08
50.940.361.010.711.131.08
100.940.361.020.711.151.08
Table
Table 2. Effects of the current density and CCP on Al dissolution after operating the EC−filtration system for 90 min.
Table 2. Effects of the current density and CCP on Al dissolution after operating the EC−filtration system for 90 min.
Current TypeCCP (min)j = 15 A/m2j = 30 A/m2j = 45 A/m2
CTheoretical Al (mg/L)CActual Al (mg/L)Φ (%)CTheoretical Al (mg/L)CActual Al (mg/L)Φ (%)CTheoretical Al (mg/L)CActual Al (mg/L)Φ (%)
DC01.211.541272.382.931233.634.21116
APC11.211.771462.383.421443.635.15142
51.211.691402.383.271373.634.83133
101.211.601322.383.071293.634.50124
Table
Table 3. Effects of APC on the TMDF, mMDF, and CActual Al in MDF effluent.
Table 3. Effects of APC on the TMDF, mMDF, and CActual Al in MDF effluent.
Current Typej = 15 A/m2j = 30 A/m2j = 45 A/m2
TMDF (min)mMDF (mg)CActual Al (mg/L)TMDF (min)mMDF (mg)CActual Al (mg/L)TMDF (min)mMDF (mg)CActual Al (mg/L)
DC25.22805.820.1319.56832.380.8513.67872.411.02
APC (CCP = 1 min)23.43830.980.2216.15912.170.7811.58946.701.11
Table
Table 4. Effects of current density and CCP on energy consumption.
Table 4. Effects of current density and CCP on energy consumption.
Current TypeCCP (min)Energy Consumption (kWh/m3)
j = 15 A/m2j = 30 A/m2j = 45 A/m2
SOT = 10 minSOT = 90 minSOT = 10 minSOT = 90 minSOT = 10 minSOT = 90 min
DC03.38 × 10−33.46 × 10−37.10 × 10−37.34 × 10−311.99 × 10−312.54 × 10−3
APC13.38 × 10−33.38 × 10−37.07 × 10−37.07 × 10−311.88 × 10−311.92 × 10−3
53.38 × 10−33.38 × 10−37.07 × 10−37.10 × 10−311.88 × 10−311.99 × 10−3
103.38 × 10−33.42 × 10−37.10 × 10−37.17 × 10−311.99 × 10−312.21 × 10−3
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Xu, J.; Qiu, T.; Chen, F.; Sun, M.; Zhou, L.; Sun, J.; Du, Y. Enhancing the Performance of the Electrocoagulation−Filtration System Treating Mariculture Tailwaters by Using Alternating Pulse Current: Effects of Current Density and Current Conversion Period. Water 2022, 14, 1181. https://doi.org/10.3390/w14081181

AMA Style

Xu J, Qiu T, Chen F, Sun M, Zhou L, Sun J, Du Y. Enhancing the Performance of the Electrocoagulation−Filtration System Treating Mariculture Tailwaters by Using Alternating Pulse Current: Effects of Current Density and Current Conversion Period. Water. 2022; 14(8):1181. https://doi.org/10.3390/w14081181

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Xu, Jianping, Tianlong Qiu, Fudi Chen, Ming Sun, Li Zhou, Jianming Sun, and Yishuai Du. 2022. "Enhancing the Performance of the Electrocoagulation−Filtration System Treating Mariculture Tailwaters by Using Alternating Pulse Current: Effects of Current Density and Current Conversion Period" Water 14, no. 8: 1181. https://doi.org/10.3390/w14081181

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