Next Article in Journal
Equilibrium, Kinetic and Thermodynamic Studies for the Adsorption of Metanil Yellow Using Carbonized Pistachio Shell-Magnetic Nanoparticles
Next Article in Special Issue
Advanced Oxidation Processes for Removal of Emerging Contaminants in Water
Previous Article in Journal
Ecotoxicological and Chemical Approach to Assessing Environmental Effects from Pesticide Use in Organic and Conventional Rice Paddies
Previous Article in Special Issue
Effect of Medium Pressure Ultraviolet/Chlorine Advanced Oxidation on the Production of Disinfection by-Products from Seven Model Benzene Precursors
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Advanced Treatment of Laundry Wastewater by Electro-Hybrid Ozonation–Coagulation Process: Surfactant and Microplastic Removal and Mechanism

1
School of Environmental and Municipal Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China
2
School of Human Settlements and Civil Engineering, Xi’an Jiaotong University, Xi’an 710049, China
*
Author to whom correspondence should be addressed.
Water 2022, 14(24), 4138; https://doi.org/10.3390/w14244138
Submission received: 14 November 2022 / Revised: 6 December 2022 / Accepted: 8 December 2022 / Published: 19 December 2022
(This article belongs to the Special Issue Advanced Oxidation Processes for Emerging Contaminant Removal)

Abstract

:
Laundry wastewater is supposed to be one of the most important sources of surfactants and microplastics in the wastewater treatment plant. Consequently, the aim of the study was evaluating the performance and mechanism of the electro-hybrid ozonation–coagulation (E-HOC) process for the removal of surfactants and microplastics. In this study, the efficiency of the E-HOC process for surfactant and microplastic removal was examined at different current densities and ozone dosages. Under the optimal reaction conditions (current density 15 mA·cm−2, ozone dosage 66.2 mg·L−1), both the removal efficiency of surfactant and microplastic can reach higher than 90%. Furthermore, the mechanism of surfactant and microplastic removal was investigated by electron paramagnetic resonance (EPR) and Fourier transform infrared spectroscopy (FT-IR). The results showed that the E-HOC (carbon fiber cathode) system can produce more reactive oxygen species (ROS), which can significantly improve the removal of the contaminants. In addition, the shape, size and abundance of the microplastics were analyzed. It was found that the shape of the microplastics in laundry wastewater is mainly fiber. Microplastics less than 50 μm account for 46.9%, while only 12.4% are larger than 500 μm. The abundance of microplastics in laundry wastewater ranges between 440,000 and 1,080,000 items per 100 L. The analysis of microplastics by FT-IR showed that most of the microplastics in laundry wastewater were polyethylene, nylon and polyester. These results indicated that the E-HOC process can effectively remove surfactants and microplastics from laundry wastewater.

1. Introduction

Domestic laundry wastewater is a kind of greywater [1]. In China, the average annual water consumption of each washing machine is about 10 m3 [2]. According to statistics, the total amount of laundry wastewater discharged annually in China is about 10.71 billion tons [3]. If such a large amount of laundry wastewater is directly discharged into the environment without treatment, it will cause great burden and harm to the environment. Direct discharge of laundry wastewater may not only cause eutrophication, but also affect wastewater treatment plant performance [4]. Most of the laundry wastewater enters the wastewater treatment plant directly through the municipal wastewater plumbing, which can save water resources if it can be reused after treatment.
Domestic laundry wastewater often contains oils and fats, suspended solids, surfactants as well as microplastics, etc. [1,5]. Due to the addition of detergents, there is an increase in alkalinity and pH in laundry wastewater, which is rich in sodium, nitrogen, phosphorus and surfactants but has a low BOD [6]. Laundry wastewater has a COD, BOD and turbidity level of 375~4155 mg/L, 48~1200 mg/L and 14~400 NTU, respectively [3]. In addition, surfactants and microplastics are two typical pollutants in laundry wastewater. Surfactants will cause potential harm to the environment after entering the environment. Studies have pointed out that surfactants not only cause damage to the morphology and physiology of plants, but also cause a significant decrease in sludge dewaterability [7,8]. Microplastic is another typical pollutant. The microplastics dropped from the clothes in the laundry process is also an important pollutant. Microplastics are defined as plastic particles and fibers less than 5 mm [9,10]. The study estimated that 9.1 × 1010 microplastic items are discharged from domestic wastewater to wastewater treatment plants every day in China [11]. Studies have shown that when activated sludge is chronically exposed to microplastics, both millimeter sized microplastics and nano-sized microplastics can cause a decline in sludge dehydration capacity [12]. In addition, the presence of surfactants also enhances the migration behavior of microplastics in the environment. [13]. This may contaminate ground water, rivers and lakes, etc. There have been many studies on the removal of surfactants and microplastics, mainly divided into physicochemical (membrane filtration, adsorption and electrocoagulation) and biological (aerobic, anaerobic, biofilter and wetland). They are briefly mentioned below.
For physicochemical treatments, both ultrafiltration and microfiltration membrane processes were highly effective, removing more than 90% of NPs/MPs fragment particles. Although the membrane filtration had a high efficiency, it needed to be cleaned frequently [14]. Using micron iron oxide powder (magnetite and hematite) as an adsorbent can remove 90% of cationic surfactants within 10 min, but a large amount of adsorbents are required [15]. Furthermore, studies have shown that about 90% of the surfactant can be removed by using electrocoagulation/electroflotation [16]. Another study showed that the removal efficiencies of surfactants and microplastics are 94% and 98%, respectively, by the electrocoagulation/electroflotation process [17].
For biological treatments, the aerobic moving bed bioreactor (MBBR) can stably remove 85~96% of the surfactant after 4 months of operation [18]. Moreover, an artificial wetland to treat greywaters was developed. Their research demonstrated 77% removal of LAS after 15 days of hydraulic retention time (HRT) [19]. Meanwhile, the removal of microplastics currently mainly relies on wastewater treatment plants, and studies have shown that oxidation ditch (OD) and MBR can remove 53.6% and 82.1% of microplastics, respectively. This may be due to the improved removal of microplastics by membrane filtration in the MBR [20].
The treatment process of laundry wastewater can generally be divided into three types: physicochemical process, biological process and the combination of physicochemical and biological process [2]. Specific processes include moving bed bioreactor (MBBR) [18], membrane filtration [21,22,23,24,25], solar photo-Fenton [26], electrocoagulation, ozonation [27], membrane bioreactor (MBR) [28], UV/H2O2 [29], biological treatment combined with UV/O3 [30], etc. In these processes, the electrocoagulation process has been widely used because of its simple process, no need for manual dosing, low cost and high treatment efficiency [31]. There have been many studies on the treatment of laundry wastewater by electrocoagulation, which can effectively remove turbidity and chromaticity in water, and has a good removal efficiency on COD [16,17,32,33,34]. In addition, electrocoagulation process has a very good removal efficiency on microplastics. However, the electrocoagulation process has limited removal efficiency although it is able to remove part of the surfactant. It has been pointed out that the presence of surfactants can reduce the removal efficiency of microplastic fibers during coagulation [35]. Obviously, the single electrocoagulation process could not satisfy the treatment of all the wastewater. If it was combined with other advanced oxidation processes, the desired efficiency could be obtained. Advanced oxidation processes (AOPs) are increasingly used to remove surfactants from wastewater [36,37,38,39,40]. The combination of electrocoagulation process and electrooxidation process realizes the efficient removal of COD and TOC [41,42]. The coupling of the electrocoagulation process and ozone oxidation or electrocoagulation process in a series with ozone oxidation can achieve efficient removal of textile wastewater [43].
The research group has studied the removal mechanism of the relevant electro-hybrid ozonation–coagulation (E-HOC) process in the early stage. The research shows that the synergistic effects between ozone and coagulants (SOC) is helpful to improve the generation of hydroxyl radicals (•OH) in the reaction system [44]. In addition, the efficiency of the E-HOC process for pollutant removal was significantly improved in bipolar connection and the dual-coagulant generation mode [45]. Moreover, the E-HOC (composite anode, CA+) process achieves high efficiency and simultaneous removal of organics and ammonia in leachate. The reactive chlorine species (RCS) generated in the E-HOC system promoted the generation of hydroxyl radicals [46]. However, the efficiency and mechanism of the E-HOC process for laundry wastewater treatment are still unclear.
In this study, the removal efficiency of C-E-HOC with a carbon fiber electrode as cathode and an aluminium electrode as anode on CODcr, turbidity, LAS and microplastics in laundry wastewater was studied. The microplastics were analyzed by fluorescence microscopy for characterization, shape, size and abundance. The role of the carbon fiber electrode in the E-HOC process for production of reactive oxygen species analysis (ROS) was assessed through electron spin resonance (EPR), Fourier transform infrared spectroscopy (FT-IR) and H2O2 quantify to elucidate the mechanism of the simultaneous surfactant and microplastic removal in the C-E-HOC process.

2. Materials and Methods

2.1. Raw Water

Two kinds of raw waters are used in this study. One is synthetic water in the laboratory, and the other is taken from the drainage during the machine washing of household clothes (including laundry wastewater, primary rinsing water and secondary rinsing water). The raw water quality parameters were listed in Table 1 (Sodium linear alkylbenzene sulfonate (LAS) is a widely used anionic surfactant in synthetic detergents [47]). Synthetic water in the laboratory was used for the removal efficiency experiment of CODcr, turbidity and LAS, and another raw water is used for the relevant research of microplastics.

2.2. Experimental Agents

Dimethyl pyridine N-oxide (DMPO) used in EPR experiment is superior pure and purchased from Sigma Aldrich (St. Louis, MO, USA). The rest were purchased from Kermel, Tianjin, China. The potassium bromide (KBr) used in the experiment is spectral grade. Other reagents used in this study are analytical grade, such as potassium dichromate (K2Cr2O7), mercury sulfate (HgSO4), silver sulfate (Ag2SO4), concentrated sulfuric acid, potassium titanium oxalate (C4K2O9Ti·2H2O), chloroform (CHCl3), sodium hydroxide (NaOH), sodium dihydrogen phosphate monohydrate (NaH2PO4·H2O) and phenolphthalein (C20H14O4). Methylene blue is indicator level. All solutions were prepared with ultrapure water.

2.3. The E-HOC Experiment

The experiment was carried out in a cubic glass container with a reaction volume of 500 mL at room temperature. In this system, carbon fiber or stainless steel was used as the cathode and aluminium was used as the anode. The length, width and thickness of the electrodes are 7 cm, 6 cm and 0.1 cm, respectively. The effective reaction area of the electrode was 84 cm2. The reaction time was 60 min, and slow stirring was always performed at 100 rpm during the reaction. The ozone generator converts the oxygen source to ozone, which is fed through an aerated head to the reaction container. The ozone generator was purchased from Sankang, Jinan, China. The electrode was connected with a direct current (DC) power supply, which was purchased from ANNAISI, Wuxi, China. A small amount of Na2SO4 was added to the water sample before the reaction to adjust the electrical conductivity. The electrocoagulation reaction was started simultaneously with the ozonation reaction. The flocs were allowed to settle sufficiently by standing for 30 min at the end of the reaction before the assay was performed. The removal efficiencies of the E-HOC processes for CODcr, turbidity and LAS were determined at different current density or different ozone dosage.

2.4. Analytical Methods

2.4.1. Determination of Physicochemical Indexes

The COD was analyzed by fast digestion-spectrophotometry [48]. Before the determination, the interference of suspended solids in the sample should be minimized. The appropriate scale was selected according to the water quality of the water samples to be tested. The turbidity was measured by a portable turbidimeter, purchased from HANNA, Padovana, Italy. The LAS was determined by methylene blue spectrophotometry [49]. Water samples need to be pre-filtered by medium-speed qualitative paper filter to remove suspended solids in order to remove insoluble anionic surfactants in the water samples before the determination. H2O2 was determined by potassium titanate oxalate spectrophotometry. A sample was taken at 10 min (adjusted pH to 3), and 20 mL of the water sample to be measured was placed in a 25 mL colourimetric tube. Next, 1 mL of 0.05 mol/L potassium oxalate color developer was added to the water sample and subsequently diluted to the scale, shaken well and left for 8 min. The sample was poured into a 10 mm cuvette and measured with an ultraviolet spectrophotometer (UV-4802) at 385 nm wavelength.

2.4.2. Fourier Transform Infrared Spectroscopy (FT-IR) Analysis

The flocs after completion of the reaction were first frozen in the refrigerator and subsequently cold dried in a vacuum freeze dryer until the moisture completely disappeared. The sample was obtained by mixing 10 mg of the cold dried floc and 990 mg of KBr and grinding in an agate mortar. The samples were analyzed using a FT-IR spectrometer (Model Nicolet 6700, Thermo Fisher Scientific, Waltham, MA, USA) at the range from 4000 to 500 cm−1.

2.4.3. EPR Analysis

EPR experiments trap hydroxyl radicals in the reaction system at room temperature by trapping agent DMPO. Experiments were performed on a Bruker EMXmicro spectrometer (Bruker Corporation, Bremen, Germany). Water samples were filtered through a 0.45 μm filter before the determination. Next, 30 mM of the radical trapping agent DMPO were added to each 500 μL of the water sample. The instrument determined the following parameters: resonance frequency of 9.77 GHz, microwave power of 25.18 mW, modulation frequency of 100 kHz, modulation amplitude of 1.0 G, sweep width of 700 G, time constant of 81.92 ms, sweep time of 35 s, and receiver gain of 30 dB.

2.4.4. Microplastics Analysis

In all, 500 mL water samples were passed through a glass fiber filter membrane (0.7 μm. 47 mm Ø, Xingya, Shanghai, China) and the samples were filtered. The filtered filter membrane was placed in a Petri dish and wrapped in aluminium foil. Several fine holes were tied on the surface of aluminium foil with needles, and the dish was placed in an oven (60 °C) to dry for 1 h and then observed under a fluorescence microscope. The microplastics observed under the microscope were classified and counted according to shape and size.

3. Results and Discussion

3.1. Removal Performance

The E-HOC process at the different current densities or different ozone dosages for the removal efficiency of CODcr (a1, b1), turbidity (a2, b2), as well as LAS (a3, b3) in laundry wastewater is shown in Figure 1. According to Figure 1, the E-HOC process resulted in a superior CODcr removal efficiency compared with the electrocoagulation (EC) and ozonation processes. The use of the EC process or ozonation process as the separate treatment process faces important practical limitations. Neither the electrocoagulation process nor the ozonation process can effectively remove CODcr, turbidity and LAS. Obviously, a single treatment process cannot meet the treatment standards [50]. By contrast, the E-HOC process can remove CODcr, turbidity and LAS efficiently. Our previous study found that Al-based coagulants can not only enhance·OH generation during ozonation, but also the addition of ozone promotes the conversion of the Al salt coagulant hydrolysis form to the higher polymerized Al species. Consequently, there are synergistic effects between ozone and coagulants (SOC) in the E-HOC process. [44]. In addition, contrasting Figure 1a2 with Figure 1b2, it can be seen that the removal of turbidity was mainly dependent on the EC process. This is similar to the previous research results. EC has an outstanding efficiency on removing turbidity in the water samples [51,52,53,54].
However, the EC process is less effective for the removal of LAS than the ozonation process. Contrasting Figure 1a3 with Figure 1b3, it can be seen that the ozonation process can remove LAS from laundry wastewater with high efficiency. There are two ways for ozone to oxidize organic compounds in laundry wastewater: (i) direct reaction between ozone and organic molecules or (ii) indirect reaction by attack of free radical species produced by ozone decomposition. Studies have shown that ozone has the highest contribution rate in the process of removing surfactant. The radical reaction plays a dominant role in the oxidation of surfactant [55]. In addition, studies have shown that the presence of low concentrations of surfactants can contribute to the ozone dissolution and indirect generation of hydroxyl radicals in the ozone process [56]. Therefore, the removal of LAS mainly depends on the ozonation process.
Ultimately, the optimal reaction conditions of the E-HOC process in three laundry wastewaters were obtained ((washing wastewater, 15 mA·cm−2, 66.2 mg·L−1) (primary rinsing water, 10 mA·cm−2, 36.6 mg·L−1) (secondary rinsing water, 10 mA·cm−2, 36.6 mg·L−1)). Under the optimal reaction conditions, the removal rates of CODcr, turbidity and LAS in washing wastewater are 93.9%, 99.7% and 99.9%, respectively. The pollutants in laundry wastewater are mainly long-chain alkanes, aromatic compounds, esters and ethers. Long-chain alkanes are firstly decomposed into short-chain alkanes. These substances subsequently further decomposed into small molecule alkanes as well as small molecule organic acids. Finally, long-chain alkanes, alkenes, ethers and esters have been completely degraded [57,58].

3.2. Microplastic Analysis

3.2.1. Microplastics Removal Performance

The removal efficiency of the EC and E-HOC processes for microplastics from three laundry wastewaters are shown in Figure 2. According to Figure 2, both E-HOC and EC had a significant efficiency in removing the microplastics. In addition, a slightly lower microplastics removal efficiency for the E-HOC process can be seen compared to the EC process at the same reaction conditions. This is probably due to the addition of ozone. Ozone causes the large flocs formed in the EC process to be broken into small flocs, resulting in part in the microplastics falling off the flocs and returning back to the water sample. Compared with the EC process, the flocs produced by E-HOC process are looser and smaller in particle size.
The process of EC can produce aluminium salt coagulant in situ at the Al electrode, which synergistically removes microplastics from water bodies through a variety of mechanisms including charge neutralization, adsorptive bridging and sweep flocculation [59]. There have been many previous studies that have shown that EC has excellent removal efficiency for microplastics. The removal efficiency can reach 96.5% for microplastics under the reaction conditions with a current density of 2.88 mA·cm−2 and an initial pH of 4 for the real wastewater samples [60]. In addition, the aluminium anode is superior to the iron anode in removing microplastics. When the pH is within the range from 3 to 10, the removal efficiency of EC for microplastics can reach more than 82%, and when the pH is 7.2, the maximum removal efficiency for microplastics can reach 98.4% [61]. A considerable number of studies have proved that the removal efficiency of microplastics by the EC process can reach more than 90% [17,62,63].

3.2.2. Shape and Size Analysis

Microplastics are divided into fibers, particles, fragments and films based on the shape [64,65,66,67]. Before collecting laundry wastewater, wash the washing machine twice without adding clothes to reduce interference. The shape of the microplastics observed under the fluorescence microscope is shown in Figure 3. As shown in Figure 3, fiber-shaped microplastics account for the vast majority of them. Clothing releases a large number of microplastic fibers during its washing, and laundry wastewater is an important source of microplastic fibers in wastewater treatment plants and the environment [68].
To further study the characteristics of microplastics in laundry wastewater, the shape and size distribution of the microplastics is shown in Figure 4. As shown in Figure 4, 73.8% of the microplastics detected in laundry wastewater were fibers. According to the microplastics size, it was divided into four ranges: less than 50 μm, more than 50 μm and less than 200 μm, more than 200 μm and less than 500 μm, more than 500 μm. According to Figure 4, 46.9% of the microplastics were less than 50 μm, Only 12.4% of the microplastics were larger than 500 μm. The microplastics were available in sizes ranging from 6.1 μm to 4000 μm. A study found that the average length of the microplastics found in household laundry wastewater was 2258.59 μm [69]. In addition, only 7% of the microplastics fibers were longer than 500 μm, 40% were between 100 and 500 μm and 53% were between 50 and 100 μm [70]. In household laundry wastewater, the study found that 48.64% of the released microfibers were shorter than 5 μm in length, and only 11.49% of the microfibers were longer than 500 μm [71]. This is similar to our findings.

3.2.3. Quantitative Analysis

Due to the consideration of the factor that the amount of water in laundry wastewater is large, even low concentration of microplastics have many microplastics discharged to the environment. As shown in Figure 5, overall, the amount of microplastics in the washing wastewater was the largest, followed by the primary rinsing wastewater and finally the secondary rinsing wastewater. In terms of the overall quantity, sample 1 released 44 × 104 items of microplastics per 100 L of water, and sample 4 released 108 × 104 items of microplastics per 100 L of water. This can be caused by many factors including the fabric, the textile process as well as the thickness of the clothing. Studies have confirmed that the interlacing coefficient of textiles affects the number of particles in wastewater. The results show that the higher the yarn’s density/cm in the fabric, the lower the fiber content in the wastewater [72]. One study has shown that more than 150,000 fibers are released per 1 kg of laundry wash [11]. Cleaning PET knitted fibers in the washing machine releases 4489.93 fibers/L or 368,094.07 fibers per kilogram [73].
It can be seen that the quantity of microplastics is easily affected by many factors, but considering that the total amount of microplastics discharged into the environment is still large, its potential harm to the environment cannot be ignored. We can think of a front-end design to remove microplastics before they enter the wastewater treatment plant or the environment.

3.2.4. FT-IR Analysis of Microplastics

The FT-IR spectra of the microplastics detected from the different stages of laundry wastewater are shown in Figure 6. According to Figure 6, the kinds of microplastics in laundry wastewater at the different stages did not change obviously. Comparing with FT-IR spectra of standards [74], it is found that the microplastics in laundry wastewater are mainly polyethylene (PE), nylon (Polyamide, PA) and polyester (PET). The peaks of PE, PA and PET are 2914 and 2850 cm−1, 1650 and 1540 cm−1, 1700 and 1060 cm−1, respectively. These are the plastic polymers commonly used in textiles [69]. PE may also come from personal care products such as toothpaste and facial cleanser [75]. This is similar to the composition of microplastic fibers in wastewater treatment plants [76].

3.3. Mechanism Analysis

3.3.1. Reactive Oxygen Species Analysis

The production of •OH in the reaction system was compared by EPR when the cathode was a carbon fiber electrode and a stainless steel electrode, respectively (Figure 7). According to Figure 7, there were four peaks centered at 3500 G in the EPR spectrum with a peak height ratio close to 1:2:2:1, which was a typical DMPO-•OH profile [77,78]. •OH was detected in both laundry wastewater and ultrapure water, but it was not obviously detected in ultrapure water by the carbon fiber cathode system. Compared with Figure 7a,b, the EPR peak of •OH generated by the carbon fiber cathode system is higher than that of the stainless steel cathode system, which is because the carbon fiber cathode will generate H2O2 in the system (Equation (1)) [79], and H2O2 will further react and convert into •OH. This indicates that more •OH is produced in the carbon fiber cathode system than in the stainless steel cathode system. Previous studies of our group have shown that •O2 can also be produced in the reaction system [44,45], which can be further converted to •OH in the system (Equations (2) and (3)) [80,81]. The change of pH in the system before and after the reaction was measured. The carbon fiber system changed from 8.3 to 8.9, and the stainless steel system changed from 8.26 to 8.78.
O 2 + 2 H + + 2 e H 2 O 2 ,
O 2 + H + H 2 O 2 + O 2 ,
O 2 + H 2 O 2 + H + O 2 + O H + H 2 O ,
To further verify the ability of the carbon fiber cathode system to produce H2O2, the concentration of H2O2 in the reaction system at different current densities or under different reaction conditions was determined in the washing wastewater. There are two groups of reactions. One is to keep the ozone dosage constant, only changing the current density, while the other is to keep the current density constant, only changing the ozone dosage.
Figure 8 shows the ability of the carbon fiber cathode and the stainless steel cathode to produce H2O2 under different current densities or different ozone dosages by using titanium salt photometry. According to Figure 8, under different reaction conditions, the carbon fiber cathode had a stronger ability to produce H2O2 in the reaction system than the stainless steel cathode. The best reaction conditions were further demonstrated by the fact that the carbon fiber electrode has the highest capacity to produce H2O2 in the reaction system with a current density of 15 mA·cm−2 or ozone dosage of 66.2 mg·L−1. Under the optimal reaction conditions (current density of 15 mA·cm−2, ozone dosage of 66.2 mg·L−1), the carbon fiber system produced H2O2 at a concentration 32.2% higher than that of the stainless steel system. This also verifies the result that the peak height of the carbon fiber cathode system is higher than the stainless steel cathode system in EPR experiments.
Based on the previous research, •OH, H2O2 and •O2 were generated in the E-HOC process. The •OH quenching experiences indicated that •OH accounted for approximately 90% contribution for the E-HOC process, which indicated •OH played a dominant role in pollutant removal [45].

3.3.2. FT-IR Analysis of Flocs

In order to further define the characteristics of the E-HOC process with the carbon fiber electrode as the cathode, the functional group changes of the flocs after the reaction of the contrasting carbon fiber system with the stainless steel system were determined. As shown in Figure 9, the peak around 1630 cm−1 is mainly caused by the stretching vibration of the -C=C- or O-H bending of the absorbed water molecules [82,83,84,85]. The peak around 3400 cm−1 results from the stretching of the O-H bond of the hydroxyl group [86]. The peak around 1400 cm−1 may be due to the formation of the H bond with the aluminium hydroxide precipitates [87].
Comparing the FT-IR spectra of the flocs between the carbon fiber cathode system and the stainless steel cathode system, the peaks of both basically coincided, but the peaks in the carbon fiber cathode system was a little lower than that in the stainless steel cathode system. In a previous study, the O3 addition during the EC process decreased the peak intensity of hydroxyl groups on the surface of the aluminium salt coagulants generated in situ at the anode, indicating that there is an interaction between the surface hydroxyl groups and O3, and that there is a complexation between the coagulant and the surface hydroxyl groups of organics in the system [88]. Since the carbon fiber cathode system showed higher removal efficiency for the contaminants than the stainless steel cathode system with a large consumption of reactive oxygen species, the intensity of the peaks would be lower than that of the stainless steel cathode system.

4. Discussion

The removal efficiency of CODcr, turbidity and LAS in the C-E-HOC process is higher than that in the traditional electrocoagulation process and the ozonation process. The optimal reaction conditions of C-E-HOC for washing wastewater are a current density of 15 mA·cm−2 and an ozone dosage of 66.2 mg·L−1. The removal efficiency of microplastics by the C-E-HOC process is slightly lower than that by the EC process because ozone aeration causes the large flocs to break down, causing a portion of the microplastics to fall off from the flocs. In addition, 73.8% of the microplastics were shaped as fibers, and nearly half of the microplastics were less than 50 μm in size. In the process of household laundry, 440,000 to 1,080,000 microplastics will be released to the environment for per 100 L of water. According to FT-IR analysis, the microplastics in laundry wastewater are mainly polyethylene, nylon and polyester. By comparing the E-HOC processes of different types of cathodes, the C-E-HOC process generated more •OH during the reaction compared with SS-E-HOC. In addition, more H2O2 could be generated from the carbon fiber cathode in the system, and H2O2 would be further converted to •OH.

Author Contributions

Methodology, J.L. and X.J.; formal analysis, J.L.; investigation, J.L. and Y.W.; data curation, J.L.; writing—original draft preparation, J.L.; writing—review and editing, X.J. and J.L.; project administration, P.J.; funding acquisition, P.J. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (No. 52230001, 52070151, 52170052), the Key Research and Development Project of Shaanxi Province (No. 2021ZDLSF05-06), Technology Innovation Leading Program of Shaanxi (No. 2020CGXNG-021).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data will be made available on request.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Deshayes, S.; Eudes, V.; Bigourie, M.; Droguet, C.; Moilleron, R. Alkylphenol and phthalate contamination of all sources of greywater from French households. Sci. Total Environ. 2017, 599, 883–890. [Google Scholar] [CrossRef] [PubMed]
  2. Ho, K.C.; Teow, Y.H.; Sum, J.Y.; Ng, Z.J.; Mohammad, A.W. Water pathways through the ages: Integrated laundry wastewater treatment for pollution prevention. Sci. Total Environ. 2021, 760. [Google Scholar] [CrossRef] [PubMed]
  3. Manouchehri, M.; Kargari, A. Water recovery from laundry wastewater by the cross flow microfiltration process: A strategy for water recycling in residential buildings. J. Clean. Prod. 2017, 168, 227–238. [Google Scholar] [CrossRef]
  4. Santiago, D.E.; Hernández Rodriguez, M.J.; Pulido-Melian, E. Laundry Wastewater Treatment: Review and Life Cycle Assessment. J. Environ. Eng. 2021, 147, 143966. [Google Scholar] [CrossRef]
  5. Cesa, F.S.; Turra, A.; Baruque-Ramos, J. Synthetic fibers as microplastics in the marine environment: A review from textile perspective with a focus on domestic washings. Sci. Total Environ. 2017, 598, 1116–1129. [Google Scholar] [CrossRef]
  6. Shi, K.-W.; Wang, C.-W.; Jiang, S.C. Quantitative microbial risk assessment of Greywater on-site reuse. Sci. Total Environ. 2018, 635, 1507–1519. [Google Scholar] [CrossRef]
  7. Nicolotti, G.; Rettori, A.; Paoletti, E.; Gullino, M.L. Morphological and physiological damage by surfactant-polluted seaspray on Pinus pinea and Pinus halepensis. Environ. Monit. Assess. 2005, 105, 175–191. [Google Scholar] [CrossRef]
  8. Wang, L.-F.; Wang, L.-L.; Li, W.-W.; He, D.-Q.; Jiang, H.; Ye, X.-D.; Yuan, H.-P.; Zhu, N.-W.; Yu, H.-Q. Surfactant-mediated settleability and dewaterability of activated sludge. Chem. Eng. Sci. 2014, 116, 228–234. [Google Scholar] [CrossRef]
  9. Sun, J.; Zhu, Z.R.; Li, W.H.; Yan, X.; Wang, L.K.; Zhang, L.; Jin, J.; Dai, X.; Ni, B.J. Revisiting Microplastics in Landfill Leachate: Unnoticed Tiny Microplastics and Their Fate in Treatment Works. Water Res. 2021, 190, 116784. [Google Scholar] [CrossRef]
  10. Li, J.Y.; Liu, H.H.; Chen, J.P. Microplastics in freshwater systems: A review on occurrence, environmental effects, and methods for microplastics detection. Water Res. 2018, 137, 362–374. [Google Scholar] [CrossRef]
  11. Tang, N.; Liu, X.N.; Xing, W. Microplastics in wastewater treatment plants of Wuhan, Central China: Abundance, removal, and potential source in household wastewater. Sci. Total Environ. 2020, 745, 141026. [Google Scholar] [CrossRef] [PubMed]
  12. Xu, J.; Wang, X.; Zhang, Z.; Yan, Z.; Zhang, Y. Effects of chronic exposure to different sizes and polymers of microplastics on the characteristics of activated sludge. Sci. Total Environ. 2021, 783, 146954. [Google Scholar] [CrossRef] [PubMed]
  13. Jiang, Y.J.; Zhou, S.; Fei, J.; Qin, Z.; Yin, X.; Sun, H.; Sun, Y. Transport of different microplastics in porous media: Effect of the adhesion of surfactants on microplastics. Water Res. 2022, 215, 118262. [Google Scholar] [CrossRef] [PubMed]
  14. Pramanik, B.K.; Pramanik, S.K.; Monira, S. Understanding the fragmentation of microplastics into nano-plastics and removal of nano/microplastics from wastewater using membrane, air flotation and nano-ferrofluid processes. Chemosphere 2021, 282. [Google Scholar] [CrossRef]
  15. Borghi, C.C.; Fabbri, M.; Fiorini, M.; Mancini, M.; Ribani, P.L. Magnetic removal of surfactants from wastewater using micrometric iron oxide powders. Sep. Purif. Technol. 2011, 83, 180–188. [Google Scholar] [CrossRef]
  16. Dimoglo, A.; Sevim-Elibol, P.; Dinc, O.; Gökmen, K.; Erdoğan, H. Electrocoagulation/electroflotation as a combined process for the laundry wastewater purification and reuse. J. Water Process Eng. 2019, 31, 100877. [Google Scholar] [CrossRef]
  17. Akarsu, C.; Deniz, F. Electrocoagulation/Electroflotation Process for Removal of Organics and Microplastics in Laundry Wastewater. Clean-Soil Air Water 2021, 49, 2000146. [Google Scholar] [CrossRef]
  18. Bering, S.; Mazur, J.; Tarnowski, K.; Janus, M.; Mozia, S.; Morawski, A.W. The application of moving bed bio-reactor (MBBR) in commercial laundry waste water treatment. Sci. Total Environ. 2018, 627, 1638–1643. [Google Scholar] [CrossRef]
  19. Perez-Lopez, M.E.; Arreola-Ortiz, A.E.; Malagon Zamora, P. Evaluation of detergent removal in artificial wetlands (biofilters). Ecol. Eng. 2018, 122, 135–142. [Google Scholar] [CrossRef]
  20. Lv, X.; Dong, Q.; Zuo, Z.; Liu, Y.; Huang, X.; Wu, W.M. Microplastics in a municipal wastewater treatment plant: Fate, dynamic distribution, removal efficiencies, and control strategies. J. Clean. Prod. 2019, 225, 579–586. [Google Scholar] [CrossRef]
  21. Bilad, M.R.; Nawi, N.I.M.; Subramaniam, D.D.; Shamsuddin, N.; Khan, A.L.; Jaafar, J.; Nandiyanto, A.B.D. Low-pressure submerged membrane filtration for potential reuse of detergent and water from laundry wastewater. J. Water Process Eng. 2020, 36, 101264. [Google Scholar] [CrossRef]
  22. Kogut, I.; Szwast, M.; Hussy, S.; Polakb, D.; Gerhardtsa, A.; Piątkiewiczd, W. Evaluation of wastewater reuse in commercial laundries: A pilot field study. Desalination Water Treat. 2021, 214, 39–48. [Google Scholar] [CrossRef]
  23. Park, C.; Kim, S. Fouling behavior and cleaning strategies of ceramic ultrafiltration membranes for the treatment and reuse of laundry wastewater. J. Water Process Eng. 2022, 48, 102840. [Google Scholar]
  24. Sumisha, A.; Arthanareeswaran, G.; Thuyavan, Y.L.; Ismail, A.F.; Chakraborty, S. Treatment of laundry wastewater using polyethersulfone/polyvinylpyrollidone ultrafiltration membranes. Ecotoxicol. Environ. Saf. 2015, 121, 174–179. [Google Scholar] [CrossRef] [PubMed]
  25. Szwast, M.; Polak, D. New membranes for industrial laundry wastewater treatment. Przem. Chem. 2018, 97, 439–441. [Google Scholar]
  26. Esteban Garcia, A.B.; Szymanski, K.; Mozia, S.; Sánchez Pérez, J.A. Treatment of laundry wastewater by solar photo-Fenton process at pilot plant scale. Environ. Sci. Pollut. Res. 2021, 28, 8576–8584. [Google Scholar] [CrossRef]
  27. Joseph, C.G.; Farm, Y.Y.; Taufiq-Yap, Y.H.; Pang, C.K.; Nga, J.L.; Puma, G.L. Ozonation treatment processes for the remediation of detergent wastewater: A comprehensive review. J. Environ. Chem. Eng. 2021, 9, 106099. [Google Scholar] [CrossRef]
  28. Bering, S.; Mazur, J.; Tarnowski, K.; Dąbkowska, N.; Janus, M.; Mozia, S.; Morawski, A.W. Removal of organic pollutants and surfactants from laundry wastewater in membrane bioreactor (MBR). Desalination Water Treat. 2018, 134, 281–288. [Google Scholar] [CrossRef]
  29. Zotesso, J.P.; Cossich, E.S.; Janeiro, V.; Tavares, C.R.G. Treatment of hospital laundry wastewater by UV/H2O2 process. Environ. Sci. Pollut. Res. 2017, 24, 6278–6287. [Google Scholar] [CrossRef]
  30. Benis, K.Z.; Behnami, A.; Aghayani, E.; Farabi, S.; Pourakbar, M. Water recovery and on-site reuse of laundry wastewater by a facile and cost-effective system: Combined biological and advanced oxidation process. Sci. Total Environ. 2021, 789, 148068. [Google Scholar] [CrossRef]
  31. 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]
  32. Ramcharan, T.; Bissessur, A. Treatment of laundry wastewater by biological and electrocoagulation methods. Water Sci. Technol. 2017, 75, 84–93. [Google Scholar] [CrossRef] [PubMed]
  33. Pratiwi, N.I.; Mukimin, A.; Zen, N.; Septarina, I. Integration of electrocoagulation, adsorption and wetland technology for jewelry industry wastewater treatment. Sep. Purif. Technol. 2021, 279, 119690. [Google Scholar] [CrossRef]
  34. Medrano-Hurtado, Z.Y.; Medina-Aguirre, J.C.; Marcelo-Medrano, H.; Castillón-Barraza, A.; Zamora-Alarcón, R.; Casillas-Lamadrid, M.E.; Jumilla-Corral, A.A.; Mayorga-Ortiz, P. Domestic wastewater treatment by electrocoagulation system using photovoltaic solar energy. Rev. Mex. Ing. Quim. 2022, 21, IA2809. [Google Scholar] [CrossRef]
  35. Li, J.; Dagnew, M.; Ray, M.B. Effect of coagulation on microfibers in laundry wastewater. Environ. Res. 2022, 212, 113401. [Google Scholar] [CrossRef]
  36. Da Silva, S.W.; Klauck, C.R.; Siqueira, M.A.; Bernardes, A.M. Degradation of the commercial surfactant nonylphenol ethoxylate by advanced oxidation processes. J. Hazard. Mater. 2015, 282, 241–248. [Google Scholar] [CrossRef]
  37. Mondal, B.; Adak, A.; Datta, P. Anionic surfactant degradation by UV-H2O2 advanced oxidation process and optimization of process parameters. J. Indian Chem. Soc. 2020, 97, 1328–1335. [Google Scholar]
  38. Rios, F.; Olak-Kucharczyk, M.; Gmurek, M.; Ledakowicz, S. Removal efficiency of anionic surfactants from water during UVC photolysis and advanced oxidation process in H2O2/UVC system. Arch. Environ. Prot. 2017, 43, 20–26. [Google Scholar] [CrossRef] [Green Version]
  39. Bai, X.; Wang, Y.; Zheng, X.; Zhu, K.; Long, A.; Wu, X.; Zhang, H. Remediation of phenanthrene contaminated soil by coupling soil washing with Tween 80, oxidation using the UV/S2O82- process and recycling of the surfactant. Chem. Eng. J. 2019, 369, 1014–1023. [Google Scholar] [CrossRef]
  40. Wang, X.-J.; Song, Y.; Mai, J.-S. Combined Fenton oxidation and aerobic biological processes for treating a surfactant wastewater containing abundant sulfate. J. Hazard. Mater. 2008, 160, 344–348. [Google Scholar] [CrossRef]
  41. Linares Hernandez, I.; Barrera Diaz, C.; Valdes Cerecero, M.; Almazan Sanchez, P.T.; Castaneda Juarez, M.; Lugo Lugo, V. Soft drink wastewater treatment by electrocoagulation-electrooxidation processes. Environ. Technol. 2017, 38, 433–442. [Google Scholar] [CrossRef] [PubMed]
  42. Nayir, T.Y.; Kara, S. Container washing wastewater treatment by combined electrocoagulation-electrooxidation. Sep. Sci. Technol. 2018, 53, 1592–1603. [Google Scholar] [CrossRef]
  43. Bilinska, L.; Blus, K.; Gmurek, M.; Ledakowicz, S. Coupling of electrocoagulation and ozone treatment for textile wastewater reuse. Chem. Eng. J. 2019, 358, 992–1001. [Google Scholar] [CrossRef]
  44. Jin, X.; Xie, X.; Liu, Y.; Wang, Y.; Wang, R.; Jin, P.; Yang, C.; Shi, X.; Wang, X.C.; Xu, H. The role of synergistic effects between ozone and coagulants (SOC) in the electro-hybrid ozonation-coagulation process. Water Res. 2020, 177, 115800. [Google Scholar] [CrossRef] [PubMed]
  45. Jin, X.; Xie, X.; Zhang, S.; Yang, C.; Xu, L.; Shi, X.; Jin, P.; Wang, X.C. Insights into the electro-hybrid ozonation-coagulation process-Significance of connection configurations and electrode types. Water Res. 2021, 204, 117600. [Google Scholar] [CrossRef] [PubMed]
  46. Yang, C.; Jin, X.; Guo, K.; Diao, Y.; Jin, P. Simultaneous removal of organics and ammonia using a novel composite magnetic anode in the electro-hybrid ozonation-coagulation (E-HOC) process toward leachate treatment. J. Hazard. Mater. 2022, 439, 129664. [Google Scholar] [CrossRef] [PubMed]
  47. Ramcharan, T.; Bissessur, A. Analysis of Linear Alkylbenzene Sulfonate in Laundry Wastewater by HPLC-UV and UV-Vis Spectrophotometry. J. Surfactants Deterg. 2016, 19, 209–218. [Google Scholar] [CrossRef]
  48. Zhou, Z.Q.; Yu, T.; Dong, H.L.; Huang, L.; Chu, R.K.; Tolic, N.; Wang, X.; Zeng, Q. Chemical oxygen demand (COD) removal from bio-treated coking wastewater by hydroxyl radicals produced from a reduced clay mineral. Appl. Clay Sci. 2019, 180, 105199. [Google Scholar] [CrossRef]
  49. Hu, N.; Li, Y.F.; Yang, C.Y.; Wu, Z.; Liu, W. In-Situ activated nanoparticle as an efficient and recyclable foam stabilizer for enhancing foam separation of LAS. J. Hazard. Mater. 2019, 379, 120843. [Google Scholar] [CrossRef]
  50. Kumar, S.; Mostafazadeh, A.K.; Kumar, L.R.; Tyagi, R.D.; Drogui, P.; Brien, E. Advancements in laundry wastewater treatment for reuse: A review. J. Environ. Sci. Health Part A-Toxic/Hazard. Subst. Environ. Eng. 2022, 57, 927–946. [Google Scholar] [CrossRef]
  51. Rookesh, T.; Samaei, M.R.; Yousefinejad, S.; Hashemi, H.; Derakhshan, Z.; Abbasi, F.; Jalili, M.; Giannakis, S.; Bilal, M. Investigating the Electrocoagulation Treatment of Landfill Leachate by Iron/Graphite Electrodes: Process Parameters and Efficacy Assessment. Water 2022, 14, 205. [Google Scholar] [CrossRef]
  52. Rodriguez, A.Z.; Wang, H.; Hu, L.; Zhang, Y.; Xu, P. Treatment of Produced Water in the Permian Basin for Hydraulic Fracturing: Comparison of Different Coagulation Processes and Innovative Filter Media. Water 2020, 12, 770. [Google Scholar] [CrossRef] [Green Version]
  53. Llanos, J.; Cotillas, S.; Canizares, P.; Rodrigo, M.A. Effect of bipolar electrode material on the reclamation of urban wastewater by an integrated electrodisinfection/electrocoagulation process. Water Res. 2014, 53, 329–338. [Google Scholar] [CrossRef] [PubMed]
  54. Khor, C.M.; Wang, J.; Li, M.; Oettel, B.A.; Kaner, R.B.; Jassby, D.; Hoek, E.M. Performance, Energy and Cost of Produced Water Treatment by Chemical and Electrochemical Coagulation. Water 2020, 12, 3426. [Google Scholar] [CrossRef]
  55. Rivera-Utrilla, J.; Bautista-Toledo, M.I.; Sanchez-Polo, M.; Méndez-Díaz, J.D. Removal of surfactant dodecylbenzenesulfonate by consecutive use of ozonation and biodegradation. Eng. Life Sci. 2012, 12, 113–116. [Google Scholar] [CrossRef]
  56. Chu, W.; Chan, K.H.; Graham, N.J.D. Enhancement of ozone oxidation and its associated processes in the presence of surfactant: Degradation of atrazine. Chemosphere 2006, 64, 931–936. [Google Scholar] [CrossRef]
  57. Ma, Y. Study on Treatment and Reuse of Laundry Wastewater by Electrocoagulation-Ozone. Master’s Thesis, Jiangsu University, Zhenjiang, China, 2020. (In Chinese). [Google Scholar]
  58. Motteran, F.; Nascimento, R.F.; Nadai, B.M.; Titato, G.M.; dos Santos Neto, Á.J.; Silva, E.L.; Varesche, M.B.A. Identification of Anionic and Nonionic Surfactant and Recalcitrants Compounds in Commercial Laundry Wastewater by GC-MS Analysis after Anaerobic Fluidized Bed Reactor Treatment. Water Air Soil Pollut. 2019, 230, 301. [Google Scholar] [CrossRef]
  59. Tang, W.H.; Li, H.; Fei, L.Y.; Wei, B.; Zhou, T.; Zhang, H. The removal of microplastics from water by coagulation: A comprehensive review. Sci. Total Environ. 2022, 851, 158224. [Google Scholar] [CrossRef]
  60. Elkhatib, D.; Oyanedel-Craver, V.; Carissimi, E. Electrocoagulation applied for the removal of microplastics from wastewater treatment facilities. Sep. Purif. Technol. 2021, 276, 118877. [Google Scholar] [CrossRef]
  61. Shen, M.C.; Zhang, Y.X.; Almatrafi, E.; Hu, T.; Zhou, C.; Song, B.; Zeng, Z.; Zeng, G. Efficient removal of microplastics from wastewater by an electrocoagulation process. Chem. Eng. J. 2022, 428, 131161. [Google Scholar] [CrossRef]
  62. Xu, R.Y.; Yang, Z.N.; Niu, Y.X.; Xu, D.; Wang, J.; Han, J.; Wang, H. Removal of microplastics and attached heavy metals from secondary effluent of wastewater treatment plant using interpenetrating bipolar plate electrocoagulation. Sep. Purif. Technol. 2022, 290, 120905. [Google Scholar] [CrossRef]
  63. Perren, W.; Wojtasik, A.; Cai, Q. Removal of Microbeads from Wastewater Using Electrocoagulation. Acs Omega 2018, 3, 3357–3364. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  64. Qiao, R.X.; Deng, Y.F.; Zhang, S.H.; Wolosker, M.B.; Zhu, Q.; Ren, H.; Zhang, Y. Accumulation of different shapes of microplastics initiates intestinal injury and gut microbiota dysbiosis in the gut of zebrafish. Chemosphere 2019, 236, 124334. [Google Scholar] [CrossRef] [PubMed]
  65. Choi, D.; Hwang, J.; Bang, J.; Han, S.; Kim, T.; Oh, Y.; Hwang, Y.; Choi, J.; Hong, J. In Vitro toxicity from a physical perspective of polyethylene microplastics based on statistical curvature change analysis. Sci. Total Environ. 2021, 752, 142242. [Google Scholar] [CrossRef]
  66. Chia, R.W.; Lee, J.Y.; Kim, H.; Jang, J. Microplastic pollution in soil and groundwater: A review. Environ. Chem. Lett. 2021, 19, 4211–4224. [Google Scholar] [CrossRef]
  67. Ding, J.F.; Li, J.X.; Sun, C.J.; Jiang, F.; Ju, P.; Qu, L.; Zheng, Y.; He, C. Detection of microplastics in local marine organisms using a multi-technology system. Anal. Methods 2019, 11, 78–87. [Google Scholar] [CrossRef]
  68. Tian, Y.; Chen, Z.; Zhang, J.; Wang, Z.; Zhu, Y.; Wang, P.; Zhang, T.; Pu, J.; Sun, H.; Wang, L. An innovative evaluation method based on polymer mass detection to evaluate the contribution of microfibers from laundry process to municipal wastewater. J. Hazard. Mater. 2021, 407, 124861. [Google Scholar] [CrossRef]
  69. Praveena, S.M.; Asmawi, M.S.; Chyi, J.L.Y. Microplastic emissions from household washing machines: Preliminary findings from Greater Kuala Lumpur (Malaysia). Environ. Sci. Pollut. Res. 2021, 28, 18518–18522. [Google Scholar] [CrossRef]
  70. Galvao, A.; Aleixo, M.; De Pablo, H.; Lopes, C.; Raimundo, J. Microplastics in wastewater: Microfiber emissions from common household laundry. Environ. Sci. Pollut. Res. 2020, 27, 26643–26649. [Google Scholar] [CrossRef]
  71. Sudheshna, A.A.; Srivastava, M.; Prakash, C. Characterization of microfibers emission from textile washing from a domestic environment. Sci. Total Environ. 2022, 852, 158511. [Google Scholar] [CrossRef]
  72. Berruezo, M.; Bonet-Aracil, M.; Montava, I.; Bou-Belda, E.; Díaz-García, P.; Gisbert-Payá, J. Preliminary study of weave pattern influence on microplastics from fabric laundering. Text. Res. J. 2021, 91, 1037–1045. [Google Scholar] [CrossRef]
  73. Ozkan, I.; Gundogdu, S. Investigation on the microfiber release under controlled washings from the knitted fabrics produced by recycled and virgin polyester yarns. J. Text. Inst. 2021, 112, 264–272. [Google Scholar] [CrossRef]
  74. Prajapati, S.; Beal, M.; Maley, J.; Brinkmann, M. Qualitative and quantitative analysis of microplastics and microfiber contamination in effluents of the City of Saskatoon wastewater treatment plant. Environ. Sci. Pollut. Res. 2021, 28, 32545–32553. [Google Scholar] [CrossRef] [PubMed]
  75. Ziajahromi, S.; Neale, P.A.; Rintoul, L.; Leusch, F.D. Wastewater treatment plants as a pathway for microplastics: Development of a new approach to sample wastewater-based microplastics. Water Res. 2017, 112, 93–99. [Google Scholar] [CrossRef]
  76. Hongprasith, N.; Kittimethawong, C.; Lertluksanaporn, R.; Eamchotchawalit, T.; Kittipongvises, S.; Lohwacharin, J. IR microspectroscopic identification of microplastics in municipal wastewater treatment plants. Environ. Sci. Pollut. Res. 2020, 27, 18557–18564. [Google Scholar] [CrossRef]
  77. Fontmorin, J.M.; Castillo, R.C.B.; Tang, W.Z.; Sillanpää, M. Stability of 5,5-dimethyl-1-pyrroline-N-oxide as a spin-trap for quantification of hydroxyl radicals in processes based on Fenton reaction. Water Res. 2016, 99, 24–32. [Google Scholar] [CrossRef]
  78. Xu, L.; Yang, L.; Bai, X.; Du, X.; Wang, Y.; Jin, P. Persulfate activation towards organic decomposition and Cr(VI) reduction achieved by a novel CQDs-TiO2-x/rGO nanocomposite. Chem. Eng. J. 2019, 373, 238–250. [Google Scholar] [CrossRef]
  79. Wang, H.J.; Yuan, S.; Zhan, J.H.; Wang, Y.; Yu, G.; Deng, S.; Huang, J.; Wang, B. Mechanisms of enhanced total organic carbon elimination from oxalic acid solutions by electro-peroxone process. Water Res. 2015, 80, 20–29. [Google Scholar] [CrossRef] [Green Version]
  80. Li, M.; Xia, J.; Tian, R.; Wang, J.; Fan, J.; Du, J.; Long, S.; Song, X.; Foley, J.W.; Peng, X. Near-Infrared Light-Initiated Molecular Superoxide Radical Generator: Rejuvenating Photodynamic Therapy against Hypoxic Tumors. J. Am. Chem. Soc. 2018, 140, 14851–14859. [Google Scholar] [CrossRef]
  81. Malik, R.; Tomer, V.K.; Joshi, N.; Dankwort, T.; Lin, L.; Kienle, L. Au-TiO2-Loaded Cubic gC3N4 Nanohybrids for Photocatalytic and Volatile Organic Amine Sensing Applications. ACS Appl. Mater. Interfaces 2018, 10, 34087–34097. [Google Scholar] [CrossRef]
  82. Zhou, R.; Liu, F.Y.; Du, X.Y.; Zhang, C.; Yang, C.; Offiong, N.A.; Bi, Y.; Zeng, W.; Ren, H. Removal of metronidazole from wastewater by electrocoagulation with chloride ions electrolyte: The role of reactive chlorine species and process optimization. Sep. Purif. Technol. 2022, 290, 120799. [Google Scholar] [CrossRef]
  83. Karatas, O.; Gengec, N.A.; Gengec, E.; Khataee, A.; Kobya, M. High-performance carbon black electrode for oxygen reduction reaction and oxidation of atrazine by electro-Fenton process. Chemosphere 2022, 287, 132370. [Google Scholar] [CrossRef]
  84. Qiu, R.L.; Zhang, D.D.; Diao, Z.H.; Huang, X.; He, C.; Morel, J.L.; Xiong, Y. Visible light induced photocatalytic reduction of Cr(VI) over polymer-sensitized TiO2 and its synergism with phenol oxidation. Water Res. 2012, 46, 2299–2306. [Google Scholar] [CrossRef] [PubMed]
  85. Gomes, A.J.G.; Atambo, D.O.; Das, K.K.; Cocke, D.L.; Das, K.P. Electrochemical remediation of chicken processing plant wastewater. J. Environ. Chem. Eng. 2018, 6, 6028–6036. [Google Scholar] [CrossRef]
  86. Asfaha, Y.G.; Zewge, F.; Yohannes, T.; Kebede, S. Application of hybrid electrocoagulation and electrooxidation process for treatment of wastewater from the cotton textile industry. Chemosphere 2022, 302. [Google Scholar] [CrossRef]
  87. Kumari, S.; Kumar, R.N. River water treatment using electrocoagulation for removal of acetaminophen and natural organic matter. Chemosphere 2021, 273, 128571. [Google Scholar] [CrossRef]
  88. Jin, X.; Liu, Y.; Wang, Y.; Zhang, S.; Zhang, W.; Jin, P.; Xu, L.; Shi, X.; Wang, X.C.; Lv, S. Towards a comparison between the hybrid ozonation-coagulation (HOC) process using Al- and Fe-based coagulants: Performance and mechanism. Chemosphere 2020, 253, 126625. [Google Scholar] [CrossRef]
Figure 1. The E-HOC process at different current densities (a1,a2,a3) or different ozone dosages (b1,b2,b3) for the removal efficiency of CODcr (a1,b1), turbidity (a2,b2), LAS (a3,b3).
Figure 1. The E-HOC process at different current densities (a1,a2,a3) or different ozone dosages (b1,b2,b3) for the removal efficiency of CODcr (a1,b1), turbidity (a2,b2), LAS (a3,b3).
Water 14 04138 g001
Figure 2. The EC and E-HOC processes on the removal efficiency of microplastics from three laundry wastewaters.
Figure 2. The EC and E-HOC processes on the removal efficiency of microplastics from three laundry wastewaters.
Water 14 04138 g002
Figure 3. Microplastics observed by fluorescence microscopy.
Figure 3. Microplastics observed by fluorescence microscopy.
Water 14 04138 g003
Figure 4. Shape (a) and size (b) distribution of microplastics.
Figure 4. Shape (a) and size (b) distribution of microplastics.
Water 14 04138 g004
Figure 5. Total drainage microplastics emissions in different stages.
Figure 5. Total drainage microplastics emissions in different stages.
Water 14 04138 g005
Figure 6. FT-IR spectra of microplastics from laundry wastewater.
Figure 6. FT-IR spectra of microplastics from laundry wastewater.
Water 14 04138 g006
Figure 7. EPR spectra detected in the E-HOC processes. Reaction conditions: current density 15 mA·cm−2, ozone dosage 66.2 mg·L−1. Samples for EPR test were taken at the 10th min during the reactions. Experimental condition: raw water (laundry wastewater (a,b), ultrapure water (c,d)), cathode (carbon fiber (a,c), stainless steel (b,d)).
Figure 7. EPR spectra detected in the E-HOC processes. Reaction conditions: current density 15 mA·cm−2, ozone dosage 66.2 mg·L−1. Samples for EPR test were taken at the 10th min during the reactions. Experimental condition: raw water (laundry wastewater (a,b), ultrapure water (c,d)), cathode (carbon fiber (a,c), stainless steel (b,d)).
Water 14 04138 g007
Figure 8. Concentration of H2O2 under different cathode electrodes (a) at different ozone dosages (0, 22.9, 36.6, 66.2 and 74.7 mg·L−1) (b) at different current densities (0, 5, 10, 15 and 20 mA·cm−2).
Figure 8. Concentration of H2O2 under different cathode electrodes (a) at different ozone dosages (0, 22.9, 36.6, 66.2 and 74.7 mg·L−1) (b) at different current densities (0, 5, 10, 15 and 20 mA·cm−2).
Water 14 04138 g008
Figure 9. FT-IR spectra of flocs in the reaction system of washing wastewater treatment by E-HOC process under different cathode electrode conditions.
Figure 9. FT-IR spectra of flocs in the reaction system of washing wastewater treatment by E-HOC process under different cathode electrode conditions.
Water 14 04138 g009
Table 1. Raw water quality parameters.
Table 1. Raw water quality parameters.
Raw WaterCODcr (mg/L)Turbidity (NTU)LAS (mg/L)
synthetic wastewater800 ± 5090 ± 20100 ± 20
laundry wastewater800 ± 10097.5 ± 17.5800 ± 50
primary rinsing water140 ± 4022.5 ± 7.515.5 ± 4.5
secondary rinsing water80 ± 2010.5 ± 4.58 ± 2
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Luo, J.; Jin, X.; Wang, Y.; Jin, P. Advanced Treatment of Laundry Wastewater by Electro-Hybrid Ozonation–Coagulation Process: Surfactant and Microplastic Removal and Mechanism. Water 2022, 14, 4138. https://doi.org/10.3390/w14244138

AMA Style

Luo J, Jin X, Wang Y, Jin P. Advanced Treatment of Laundry Wastewater by Electro-Hybrid Ozonation–Coagulation Process: Surfactant and Microplastic Removal and Mechanism. Water. 2022; 14(24):4138. https://doi.org/10.3390/w14244138

Chicago/Turabian Style

Luo, Jiahao, Xin Jin, Yadong Wang, and Pengkang Jin. 2022. "Advanced Treatment of Laundry Wastewater by Electro-Hybrid Ozonation–Coagulation Process: Surfactant and Microplastic Removal and Mechanism" Water 14, no. 24: 4138. https://doi.org/10.3390/w14244138

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop