Microplastic contamination in water supply and the removal efficiencies of the treatment plants: A case of Surabaya City, Indonesia

https://doi.org/10.1016/j.jwpe.2021.102195Get rights and content

Highlights

  • The microplastic abundance in the raw water was 26.8–35 particles/L.

  • The microplastic abundance in the treated water was 8.5–12.3 particles/L.

  • Fiber was dominant (84–100%) in the raw and treated water.

  • Particles of of 351–1000 μm size were dominant (36–60%) in the raw and treated water.

  • The total microplastic removal efficiencies in SDWTPs I and II were 54 and 76%, respectively.

Abstract

Microplastics (MPs) have been recently detected in the Surabaya River, Indonesia, which is used as raw water for water supply. This condition has aroused concern about MP presence in the treated water in Surabaya drinking water treatment plants (DWTPs). This study aimed to investigate the MP abundance and characteristics of the raw and treated water and the removal efficiencies in each treatment unit in two selected Sub-DWTPs (SDWTPs) in Surabaya Water Supply Enterprise. These SDWTPs apply conventional technology comprising aeration, pre-sedimentation, coagulation, flocculation-sedimentation, filtration, and disinfection stages. The MP abundance values in the raw and treated water in SDWTPs I and II were 26.8–35 and 8.5–12.3 particles/L, respectively. The MP was dominated by 93–95% fiber in the raw water and 84–100% in the treated water. The MP dominant size in the raw and treated water was 351–1000 μm, with the percentages of 45–50 and 36–69%, respectively. The dominant polymer types of MPs in the raw water were polyethylene (PE), polypropylene (PP), and low-density polyethylene (LDPE). The total MP removal efficiencies in SDWTPs I and II were 54 and 76%, respectively.

Introduction

Microplastics (MPs) as environmental contaminants have been investigated since 1970 [1]. Recently, the occurrence of MPs in freshwater environments, including river, surface water reservoir, and groundwater, has been profoundly studied [2,3,4]. The MPs in the freshwater varied in abundance, size distribution, shape, and composition because the categories in those studies were different [5]. In regard to the MP shape, fibers were the most abundant in freshwater environments [6]. Meanwhile, the MP size of 1001–5000 μm was extensively identified in freshwater [7,8,9].

MP pollution in freshwater might lead to raw and treated water contamination because rivers are commonly used as a raw water source for drinking water treatment [5]. Pivokonsky et al. [10] studied the MP abundances in three drinking water treatment plants (DWTPs) in the Czech Republic, where surface water was used as the raw water source. The results showed that the MP abundances were 1473–3605 particles/L in the raw water and 338–628 particles/L in the treated water. Meanwhile, Wang et al. [11] investigated the abundance of MPs in an advanced DWTP in China. The abundances of MPs in the raw and treated waters were 6614 and 930 particles/L, respectively. Besides, Shen et al. [12] conducted research on the MP occurrence in drinking water from freshwater in Cangsha, China. The MP abundance in freshwater and drinking water was 2173–3998 and 338–400 particles/L, respectively. Mintenig et al. [4] performed another investigation on MP presence in raw and treated water in 5 DWTPs in Germany. The study found less MP abundance either in the raw or treated water which was 0–7 particles/L. This condition occurred because the DWTPs employed groundwater as the raw water source [13].

The DWTPs in Indonesia commonly apply conventional technology, supported by aeration, pre-sedimentation, coagulation, flocculation-sedimentation, filtration, and disinfection tanks [14]. It was proven that the MP removal could occur through the conventional technology of DWTP [13,15]. Effective removal of MP contaminant in DWTP requires an appropriate configuration of technology [10]. However, a particular technology may provide different capabilities in removing the MPs [16]. Therefore, it is essential to explore the technology's ability, either a conventional or an advanced one, in DWTP application for MP removal. This information is beneficial for determining the right technology for producing free MPs in treated water in the DWTPs.

Evidence revealed that 12 MP fragments were detected in four human placentas [17]. The MP sizes were 5–10 μm. It was presumed that MPs could enter the placentas through the gastrointestinal tract [17]. Even though the potentially toxic effects of the MPs on human health have not been clearly investigated, the MP pollution in treated water becomes concern since it is used for human consumption [2]. The ingested MPs into the human body were possibly inert hazardous material for cells and tissues because it led to inflammation and cytotoxicity (oxidative stress, the injury, and viability of cells and tissues) [18]. These potential adverse effects could be influenced by the MP characteristics (size, shape, and polymer type), MP exposure time, and the response of cells and tissues to the MPs [19]. However, thorough research on the human impacts of MPs should be performed to observe the adverse effects intensively.

The Surabaya River is used as a raw water source for drinking water treatment in Surabaya City, which serves 92.5% of the population, from a total of three million [20]. There are two main DWTPs in Surabaya City, namely Ngagel and Karangpilang. Each of the Ngagel and Karangpilang DWTPs has three Sub-DWTPs (SDWTPs). The total water treatment capacities of Ngagel and Karangpilang DWTPs were 4550 and 5950 L/s, respectively [14]. Among these SDWTPs, only 1 SDWTP in Ngagel DWTP uses advanced treatment technology [21]. Unfortunately, no study has been conducted concerning the MP abundance and removal in the DWTP and water supply systems in this country. Very few MP studies had been carried out in the Surabaya River [22,23,24]. Lestari and Trihadiningrum [22] studied that the Surabaya River had been impacted by MPs due to improper solid waste management. Firdaus et al. [23] investigated the MP pollution in the sediment of Jagir Estuary, Surabaya. Meanwhile, Lestari et al. [24] studied the MP distribution in the Surabaya River water. The MPs in the sediment of Jagir Estuary ranged from 92 to 590 particles/kg dry weight (DW) sediment, with 1001–5000 μm MP size range (68%), the fiber (57%), and the polyester (PES) (56.7%) as the dominant MPs [23]. The MP presence in the Jagir Estuary were most probably due to the plastic waste generation in the settlements around the study site [23]. Lestari et al. [24] revealed that the MP abundance in the Surabaya River varied from 1.47–43.11 particles/m3. The MPs were dominated by the MP size of 1001–5000 μm (43.1–93.2%), with film shape (45.8–92.9%), and low-density polyethylene (LDPE) polymer type (44–68%).

The MP presence in the Surabaya River raised concern since this might lead to water supply contamination. Based on the abovementioned consideration, the study of MP occurrence in the treated water and effluent of each treatment unit in DWTP was important for a better understanding the MP contamination and removal in DWTPs. However, there were insufficient data of MP abundance and characteristics in Indonesian DWTPs. This study was focused on the presence of MP in the raw water, effluent water of each treatment unit, and treated water in the two SDWTPs in Surabaya City. The data could provide a new insight to improve the DWTP performance in reducing MP contaminants.

Section snippets

Sampling sites and water sample collection

The sampling sites were two conventional SDWTPs, namely SDWTPs I and II, in the Water Supply Enterprise of Surabaya City, which used the Surabaya River as raw water source (Fig. 1). The water treatment capacities of SDWTPs I and II were 1450 and 2000 L/s, respectively. Water treatment technologies that were applied in both SDWTPs were aeration, pre-sedimentation, coagulation, flocculation-sedimentation, filtration, disinfection, as shown in Fig. 2.

Water samples were collected at raw water

Microplastic content in the raw and treated water

This study revealed that the MPs were found in all samples from SDWTPs I and II. The content of MPs in raw and treated water varied in terms of size, shape, and color. Table 1 shows the average abundances of the MPs in the raw and treated water samples of SDWTPs I and II.

The abundance values in Table 1 were classified into MP size, shape, and color. Data in Table 1 present that the total MP abundance values in SDWTPs I and II were 26.8–35 particles/L in the raw water, and 8.5–12.3 in the

Practical application to the current water treatment

Currently, the MP contamination has attracted utmost attention, especially in relation to the human consumption. This study was the first investigation of MP contamination in drinking water supply in Surabaya City. The conventional technologies of DWTPs in this study represented the current technology applied in the most Indonesian DWTPs. The conventional technologies are not originally employed to remove the emerging MP pollutant. It was proven from the previous study in the Czech Republic,

Conclusion

The MP has contaminated the water supply in two SDWTPs in Surabaya City. The MP abundances in the raw and treated water in SDWTPs I and II were 26.8–35 and 8.5–12.3 particles/L, respectively. The existing conventional DWTPs have minimized the MP contamination in water supply from 54% to 76%. Previous study in other country proved that conventional technology could achieve up to 70% MP removal efficiency. Application of GAC filtration and ozone could enhance the MP removal efficiency up to

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors are grateful for Laboratory Research Grant 2020 No. 910/PKS/ITS/2020 from the Directorate of Research and Public Service of Institut Teknologi Sepuluh Nopember. We also acknowledge the Surabaya Water Supply Enterprise for the research permit.

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