Reduction of Microplastic in Wastewater Via Electrocoagulation Process

In recent years, microplastic has become an emerging contaminant that has endangered the ecosystem and public health. This environmental issue has been discovered in the atmosphere, soil, and water bodies. These sources of pollutants can be either primary or secondary. The primary sources of microplastic are the clothing and cosmetic industry, plastic manufacturing plants, fishing businesses, shipping lines, sewage treatment plants, car tires and air blasting. Moreover, microplastic emission from secondary sources involves degrading large plastic particles to smaller elements under mechanical fragmentation and ultraviolet. Microplastic can be defined as plastic particles of different shapes that are less than 5mm. It can be denoted that this microplastic has been detected in the wastewater effluent and needs to be sufficiently removed from the conventional methods. Therefore, this research aims to determine the reduction rate of microplastic in wastewater via the electrocoagulation process. The wastewater effluent was taken from the wastewater treatment plant, Universiti Teknologi MARA Campus Dengkil. The characteristics of the wastewater effluent have been determined for biochemical oxygen demand (BOD), chemical oxygen demand (COD), ammonia-nitrogen, total suspended solids (TSS), turbidity and E.coli. The microplastic employed in the experiment was polystyrene (PS). A duration of 60 and 120 minutes were taken to reduce the PS. Additionally, the analysis using Fourier-transform infrared spectroscopy (FTIR) has been done to observe the chemical structure of the PS polymer. The results showed that the maximum percentage of reduction for COD was 100%, TSS with a value of 80%, ammonia-nitrogen of 98% and turbidity of 46%. Besides, the removal of PS has achieved 82% using this technique. It can be found that electrocoagulation can be a promising method for reducing the microplastic in the water environment, especially in the wastewater treatment plant.


Introduction
As stated in the United Nations Environmental Programme, microplastics (MPs) have been recognized as one of the emerging concerns.These MPs can cause significant impacts towards the loss of biodiversity, natural ecosystem degradation, and deterioration, which brings harm to human health.Based on the forecasting method on yearly data, the projected plastic production will steadily increase to 724 million metric tons in 2050 worldwide.
From the research observation, MP pollution has become a threat, especially to the aquatic environments [1].In 2016, it was estimated that over 150 million tons of plastics were found in marine water.Around 0.1% to 1.5% of this waste can be defined as microplastic because the diameter is less than 5 mm [2].Therefore, in various shapes and materials, MPs can be found from primary and secondary sources [1].Primary sources of microplastic are particles that have small sizes manufactured for commercial use like textiles, personal care products, marine activities and plastic pellets used in industries [3].Then, microplastic secondary sources formed from a larger plastic particle in the marine environment, broken down by combining ultraviolet (UV) degradation, biological processes, and mechanical stresses [2].
According to recent studies, microplastics exist in drinking water and some food products, especially salt and seafood [4].For instance, dyes and flame retardants are additives used in plastic production.These chemicals can enter the human body through bioaccumulation, mimicking cancer-like endocrine disruptors.The ingestion of microplastic by aquatic life leads to death, hepatitis, and a low growth rate [5].
Wastewater treatment plants (WWTP) can be the main source of contamination caused by microplastics.About 4 million microplastic particles are discharged from wastewater treatment plants on average daily per facility [6].Next, WWTP has been considered a pathway for microplastic to infiltrate the aquatic ecosystem.Based on Fourier-transform infrared spectroscopy (FTIR) shown, polyethene terephthalate (PET) (47%) is the highest polymer type revealed in Wuxi WWTP, followed by polystyrene (PS) (20%) [5].Other studies stated [7] that WWTP is one of the main contributors of microplastic, including domestic sewage, industrial wastewater, and some rainwater.
Moreover, the conventional wastewater treatment plant could not apprehend the emerging pollutants detected in the sewerage pipeline.Most of these hazardous materials, especially microplastics from personal care products, could not be eliminated from this method.Thus, this research paper focused on electrocoagulation (EC) treatment to reduce contaminants, especially microplastics in wastewater.This EC was selected due to the simple, rapid, cost-effective method for wastewater treatment and did not require any chemical substances [6].Supporting another study, EC uses metal electrodes to produce coagulants electrically, which makes this process uncomplicated and robust [2].

Sewage Collections
The wastewater treatment plant at Universiti Teknologi MARA (UiTM) Campus Dengkil (2.866777, 101.667377) has been selected as the case study for the sample collection.Effluent samples were collected on November 23 2022, with 20 litres at the wastewater treatment plant outlet.The initial effluent samples were tested for the standards [8] comprised of the parameters of biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), ammonia-nitrogen, temperature, and pH [9].Other tested parameters include nitrite-nitrogen, nitrate-nitrogen, turbidity, and E.-coli [9].All the samples were tested using a HORIBA probe [10] for in-situ testing and a HACH spectrophotometer [11] for laboratory testing conducted in the Environmental Laboratory, School of Civil Engineering, College of Engineering, Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia.

Electrocoagulation Process Setup
Based on Figure 1, a schematic diagram of the electrocoagulation reactor was illustrated for this experimental study.The configuration comprised a DC power supply, a rectangular reactor, aluminium electrodes, wires connected to the DC power supply and aluminium electrodes.The rectangular reactor contains a working volume of 15 litres of the effluent sample taken from the WWTP UiTM Campus Dengkil.Polystyrene (PS) purchased from Sigma Aldrich & Co was added to the reactor with a 5.01 g/ml concentration.An electrical current of 18.75 A/m² has been supplied for detention times intervals of 60 to 120 minutes.A 500 ml was collected after 60 minutes of the experiment for parameter checking.Later, the same amount of samples was evaluated for testing after 120 minutes.

Dry weight process
After electrocoagulation (EC), polystyrene (PS) must be dried in the oven at 105 °c for 24 hours.Before that, we need to weigh polystyrene to get the initial result after EC.Then, the filter paper has been used to filter out the PS before proceeding with the drying process.As a result, we can calculate the weight loss of polystyrene.The general equation ( 1) of dry weight [12]: is stated for the initial weight of PS, while   is the wet weight of PS with aluminium.  refers to the dry weight of PS with aluminium.

Percentage Removal of Pollutants in Wastewater
According to a previous study [6], the percentage removal of microplastics can be determined by the parameters that we have tested, such as BOD, COD, TSS, ammonia-nitrogen, nitrite-nitrogen, nitratenitrogen, turbidity, pH, and E-coli.The equation (2) for the percentage removal of microplastics is as follows [12]: is stated for initial wastewater, while   is the final measurement for effluents standard [8].

Analytical Method for Microplastics
Fourier-transform infrared spectroscopy (FTIR) was done to analyze the changes in the structure of polystyrene [3].Three samples have been tested using FTIR, including the initial and the samples after electrocoagulation treatment at 60 minutes and 120 minutes.

Characteristics of Wastewater
The collected effluent sample from UiTM Campus Dengkil was characterized by the parameters mentioned in the previous section.The results showed the characteristics of effluent samples before and after the electrocoagulation treatment (refer to Table 1).All the results meet the standard requirement set by the [8].However, high pH was obtained in the EC after 120 minutes due to the interaction between the electrode and contaminants in the wastewater effluent [2].

Percentage Removal of Pollutants
Several studies found that the treatment time significantly impacts the removal of the pollutants [13].
Table 2 shows the reduction of COD, which achieved 100% based on retention time 60 and 120 minutes).The initial sample of wastewater displayed 71 mg/L before the EC process.However, after 120 minutes, the COD removal achieved the highest percentage.With higher retention time in the EC process, more hydroxyl and metal ions are produced on the electrodes.Thus, it produced a higher rate in the percentage removal of pollutants [2].It can be supported by the results, which showed that all the pollutants had a significant reduction in concentration compared to the initial sample.From the evaluation, ammonia-nitrogen exhibited the second-highest reduction percentage after the treatment (98.8%), followed by nitrate-nitrogen (87.5%) and TSS (80%).The lowest removal percentage was BOD (15.4%), and the second lowest was turbidity (46%).The performance of the BOD for both retention times of 60 and 120 minutes was insignificant as the EC runs with electric current, which will eliminate the bacteria and reduce the dissolved oxygen levels in the samples.For the turbidity parameter, more time is needed to reduce the pollutants to the appropriate level [14].However, from the overall observation, the electrocoagulation process has successfully eliminated the pollutants in the wastewater effluent and enhanced the quality before being discharged to the water bodies.Higher retention time in the EC displayed elevated removal of the pollutants and improved effluent conditions based on the standard requirements.

The dry weight of polystyrene
The results showed that over 82% of plastic polymer (polystyrene) had been removed in electrocoagulation treatment.The dry weight has been determined using an oven at 105 °c (overnight).After the dry weight process, the total polystyrene is about 0.858 g (refer to Table 3).From the analysis, EC has potentially removed a significant amount of PS in the wastewater effluent.Nevertheless, these methods could be employed in the wastewater treatment plant for the best management practices in removing emerging pollutants such as microplastics.4, with the changes detected after the electrocoagulation treatment.The EC process leads to the production of the carboxylic group of the PS.The formation of O-H represents the carboxylic group at the peak of 3299.75 cm -1 [15].The formation of C=C represents the alkane at the peak of 1631.52 cm -1 [15].These changes indicated that the chemical structure of PS was altered during the EC process [16].From the results obtained in the FTIR, there are no significant changes for both 60 minutes and 120 minutes for the EC process.

Conclusion
Based on the findings, removing microplastic (MP) in wastewater effluent using an electrocoagulation treatment showed great potential to be used for long-term sustainable practices.This method can be adopted in wastewater treatment plants as MP are small particles that can easily pass through the WWTP and enter the environment.The electrocoagulation process can significantly reduce the number of pollutants in wastewater and enhance the quality of the effluent.Furthermore, the EC process is a costeffective method and environmentally friendly, which can positively reduce the pollution in the ecosystem.Moreover, higher retention time given in the electrocoagulation process can consequentially give rise to effectiveness, which produces excellent results.

Figure 2 :
Figure 2: The Analysis of Fourier Transform Infrared (FTIR) of Polystyrene

Table 1 :
Characteristics of Wastewater Effluent Samples Before and After Treatment

Table 2 :
Percentage Removal of Pollutants in Wastewater Effluent

Table 3 :
Dry Weight Calculation

Table 4 :
Functional Group after Electrocoagulation Process