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Article

Microplastics in Kuwait’s Wastewater Streams

by
Saif Uddin
1,*,
Montaha Behbehani
1,
Nazima Habibi
1,
Mohammed Faizuddin
2,
Mohammad Al-Murad
1,
Karell Martinez-Guijarro
1,
Hanan A. Al-Sarawi
3 and
Qusaie Karam
1
1
Environment and Life Sciences Research Center, Kuwait Institute for Scientific Research, Safat 13109, Kuwait
2
Gulf Geoinformation Solutions, Hamariya Free Zone, Sharjah P.O. Box 32223, United Arab Emirates
3
Environment Public Authority, Fourth Ring Rd, Shuwaikh Industrial 70050, Kuwait
*
Author to whom correspondence should be addressed.
Sustainability 2022, 14(23), 15817; https://doi.org/10.3390/su142315817
Submission received: 21 October 2022 / Revised: 20 November 2022 / Accepted: 23 November 2022 / Published: 28 November 2022
(This article belongs to the Special Issue Micro(nano)plastic Contaminants in Wastewater and Drinking Water – Occurrence, Management and Treatment Technologies)
Browse Figures
Versions Notes

Abstract

:
The wastewater stream is the most significant contributor of microplastics (MPs) to the environment. There are five wastewater treatment plants (WWTPs) in Kuwait. This baseline study provides an overview of MP removal in three major WWTPs in Kuwait that treat some 81.31% of the wastewater produced. The Sulabiya WWTP was the most efficient in MP removal, followed by the Kabd and Umm Al-Haiman WWTPs. The MP removal efficiency of plants in Kuwait is very high for Sulabiya WWTP and Kabd WWTP with an average of 2.5 MP L−1 in treated effluent comparable to the WWTPs in Australia, the United States, and Europe. The standard methodology of sample collection, preparation, and identification using microscopic examination and micro-Raman spectrometry was followed. Over 94.5 billion MPs enter the three WWTPs daily; 92.3 billion MPs are retained in sludge, while 2.2 billion are passed into the environment due to the use of treated effluent. The influent, effluent, and sludge MP inventories ranged between 119 and 230 MP L−1, 1 and 12 MP L−1, and 72 and 103 MP 10 g−1 respectively. The fiber was the dominant shape, and white, transparent, and black were prevalent colors. Currently, sludge is not used in Kuwait for any terrestrial or agricultural application; however, sludge is routinely used in many countries as a soil additive in agricultural farms. Using effluent water in irrigation leads to MP dissemination in the terrestrial environment. It is necessary to assess how far these MPs move in the soil profile and if they can contaminate the shallow aquifers. The observation of MP retention in sludge and effluent is empirical, and the use of these matrixes in agriculture is likely to raise an issue of food safety.

1. Introduction

An enormous amount of microplastics is discharged into the aquatic environment, primarily due to improperly managed plastic waste disposal [1,2,3,4,5,6,7,8,9]. Estimates suggest that between 15 and 51 trillion microplastic particles (MPs) are floating in the world’s oceans [10,11,12,13,14,15]. These MP inventories can be even higher in marginal seas and along densely populated coastlines [7,12,16]. A recent review of MPs from wastewater has even provided more staggering estimates of adding around 1.47 × 1015 MPs annually from treated effluent and 3.85 × 1016 MPs annually from the discharge of untreated effluent into the aquatic environments globally [6]. Hence, wastewater streams are expected to be a significant pathway for MPs to the aquatic environment, with microbeads from detergents, cosmetic and personal care products, and fibers of polymer from synthetic clothing entering the wastewater treatment plants (WWTPs) [17,18,19,20]. Synthetic fibers account for ~35% of MPs in the aquatic environment [21]. An experimental study on MP determination on the washing machine effluent suggested that over 1900 fibers were produced per wash from a single synthetic cloth [22], suggesting that domestic wash is one of the main contributors introducing secondary microplastics to the environment [23]. Furthermore, synthetic clothes released 124–308 mg of microfibers per kilogram of clothes washed, corresponding to 640,000–1,500,000 microfibers [24].
The importance of MPs in the aquatic environment is exacerbated by the fact that they are persistent, omnipresent, absorb hydrophobic contaminants from the water column, and toxic chemicals used in the manufacture of these plastic products can pose a risk to a variety of aquatic organisms and food chains [9,25,26,27,28,29]. The ecological concern from MPs emanates from the fact that MPs can be misidentified as prey by aquatic organisms and become toxic or even lethal when ingested [30]. The risk from MP ingestion can be both physical (blocking gills and digestive system) and/or chemical (contaminant release from MPs or acting as a carrier for metals, organic contaminants, and even microbes), and harm a variety of organisms across the trophic chain from zooplankton to mammals [31,32,33,34,35,36,37]. The report of MPs translocating in blood circulation among filter feeders is known to cause reproductive dysfunction [38]; the concern is further exacerbated by a recent report of MP/NP in human blood [39]. The indirect consequences of chronic microplastic exposure result in inflammation, malnutrition, and changes in reproductive behavior and capacities [40,41,42,43,44,45,46,47].
Microplastics have a large surface-to-volume ratio, increasing their potential for adsorbing various hydrophobic chemical contaminants from the water column. During their extended stay in the aquatic environment, MPs tend to degrade and leach out various chemical additives, such as phthalates, Bisphenol A (BPA), and polybrominated diphenyl ethers, that are commonly added to improve the properties of the plastics [48].
The WWTPs are one of the most conspicuous sources of MPs in the environment [14,49,50]. The information on MP inputs from WWTPs in the Persian Gulf region is minimal, although it has a very densely populated coastline. The average MP inventory in wastewater from Bushehr WWTP was 1.6–2.5 MP L−1. In contrast, a reasonably high inventory in sludge was observed, corresponding to 5263–6877 MP kg−1 [7]. This study was taken up to fill the data gap of MP inputs from WWTPs in the Persian Gulf and presents the first dataset on MPs in WWTPs in Kuwait and their potential release into the environment.
Sewage discharges are a significant source of coastal plastic pollution in the Persian Gulf countries [51]. Most of the Gulf countries have high capacities for wastewater treatment. However, there is no specific information on MP inventories in treated effluent used and discharged into the Gulf and in the sludge that can be used for composting and applications in greening projects. This study presents the first survey on MPs in Kuwait’s wastewater influent, effluent, and sludge.

2. Materials and Methods

The samples were collected in August and December 2020 from three wastewater treatment plants (WWTPs) in Kuwait (Figure 1). The Sulabiya WWTP is state-of-the-art and the largest plant in Kuwait with a design capacity of 600,000 m3 d−1. The Sulabiya WWTP utilizes reverse osmosis (RO) and ultrafiltration (UF) membranes to treat wastewater from the very densely populated Kuwait City and Hawalli districts. The Sulabiya WWTP has a biological treatment plant (BTP) and a reclamation plant (RP). The influent from BTP goes to nine aeration tanks about 8 m deep. From these secondary clarifiers, treated water is pumped to the UF plant fitted with 8700 UF membranes, each with 10,000 transpiration tubes. The UF-purified wastewater is pumped to the RO plant that contains 21,000 membranes that filter the wastewater through three successive stages resulting in 85% of the influent being purified by RO; the remainder is rejected as brine into the sea. Unfortunately, we were not able to sample this stream.
The Umm Al-Hayman WWTP receives influent from the adjacent residential area, pumping station, and sewage pit that receives wastewater from tankers equivalent to 6000 m3 d−1. The Umm Al-Haiman WWTP uses an oxidation ditch system for secondary treatment, sand filtration, UV, and chlorination for tertiary treatment. The plant is undergoing a significant expansion and is being upgraded to treat 700,000 m3 d−1. The 20,000 m3 d−1 effluent from the Umm Al-Haiman WWTP is utilized mainly for landscape irrigation.
The Kabd WWTP treats about 270,000 m3 d−1. The plant receives the flow from the Al-Jahra pumping station that serves a wide area of Kuwait. It is a state-of-the-art computerized plant that uses Distributed Control System (DCS) technology. The biological treatment at the Kabd WWTP takes place in a vertically activated sludge process to improve the denitrification rate and saves energy, flexibility, and system reliability of treatment. Part of the tertiary treated effluent is discharged to natural bird reserves and used for landscape irrigation along highways and in major malls [52].
These three WWTPs that have been assessed represent 81.31% of the wastewater generated and treated and serve roughly 85% of the population.
An amount of 10 L of influent and effluent wastewater samples and 1 kg of sludge were collected from each site. Wastewater samples were collected using a bailer and transferred into pre-cleaned 2 L glass bottles. The sludge samples were taken with a stainless steel shovel and transferred into pre-cleaned wide-mouth glass jars. The samples were kept on ice, transported to the Kuwait Institute for Scientific Research laboratory, and stored at 4 °C until analysis.
To oxidize the organic matter in wastewater samples, 10 g of potassium hydroxide (Merck Schuchardt, Hohenbrunn, Germany) was added to each liter of the water sample and heated in an oven at 40 °C for 48 h. The digested sample was vacuum-filtered on a 0.45 µm Sterlitech Silver membrane filter (Sterlitech, Auburn, WA 98001, USA). The filter paper was put in a ZnCl2 (Merck Schuchardt, Hohenbrunn, Germany) saturated solution with a density of 2.98 g cm−3 to segregate MPs. The suspended material was transferred onto a glass coverslip. The samples on glass coverslips were stained using Nile Red (10 μg mL−1 n-hexane) by adding 1 mL of Nile Red solution and incubating for 30 min at 40 °C.
An amount of 10 g of sewage sludge was taken for MP extraction. An amount of 10 mL of 15% H2O2 was added. The samples were heated at 40 °C for 48 h to oxidize organic matter. The solution was filtered similarly to the water sample, separated on glass coverslips, and stained with Nile Red.
A multi-tier approach was adopted for MP identification. The particles on the glass coverslip were examined under a UV-stereomicroscope for the presence of any cellular structure, the consistency in diameter along the particle length with no bending or tapering, clarity, and no change in color. Cotton, cellulose, wool, paper products, black carbon, algae, chitin, wood lignin, natural waxes, and other OH-rich carbohydrates were also stained with Nile Red [53,54]. The hot needle approach [34,55,56] was used to ensure that these were not false positives. The 405 nm wavelength ultraviolet light was used for counting extracted MPs. The MP particles were classed as fibers, fragments, and films. The identified MPs were white, blue, green, black, red, and transparent in color. In addition to the physical identification, polymer characterization was carried out using micro-Raman spectroscopy (µ-RAMAN). The polymer types of the MPs were determined by matching the data in a polymer reference library. More details of the procedures employed to preclude any possible contamination and maintain the quality assurance and quality control of our analysis have been provided elsewhere [33,57,58,59]. The MPs were counted and measured at their longest dimension using ImageJ software. The shape and color of MPs were recorded.
All solutions were filtered with a 0.2 µm filter to remove MP carryover from other sources. All cleaned equipment were placed inside a laminar flow hood and covered with aluminum foil. Negative controls consisting of 10 L Millipore water were treated and analyzed simultaneously with wastewater samples.

3. Results

3.1. Microplastic Concentrations

We present the first assessment of MPs in three major wastewater treatment plants in Kuwait, including their presence in influent, effluent, and sludge. All the samples were analyzed in triplicate. The numbers of MPs from wastewater influent, outfall, and sludge samples are presented in Table 1.
In total, 1522 particles from all three streams were identified as plastic. The highest concentration was in sludge, where between 72 and 103 particles were counted in each 10 g of sludge sample. The MPs in the influent were lowest in the Sulabiya WWTP (119 ± 2 − 121 ± 3 MP L−1), there were 130 ± 4 and 134 ± 5 MPsL−1 in the Kabd WWTP, and the highest number was observed in the Umm Al-Haiman WWTP at 223 ± 3 − 230 ± 4 MPs L−1 (Figure 2).
These inventories provide insight into the scale of MP pollution coming into and from the WWTPs. The Sulabiya WWTP treats an average of 450,000 m3 wastewater daily with an average of 120.5 MP L−1 in the influent, and the plant receives some 54.23 billion MPs d−1. The Kabd WWTP treats 270,000 m3 d−1 with an average of 132.5 MP L−1, and receives about 35.78 billion MPs d−1 in the influent. The Umm Al-Haiman WWTP treats about 20,000 m3 d−1 with an average of 226 MP L−1 and, thus, is likely to receive 4.52 billion MPs d−1.
There is a substantial decrease in MPs in the effluent; however, a staggering number is still likely to be added to the terrestrial and marine environment where the treated wastewater is used or discharged. To have an idea of MP discharge through treated effluent, the Kabd WWTP is likely to have 1.35 billion MPs d−1, the Sulabiya WWTP 675 million MPs d−1, and the Umm Al-Haiman WWTP 220 million MPs d−1. As per the current practice, the treated wastewater is being given to agricultural farms and used in landscaping and greening. This application is likely to result in MP addition to the soil profile. The possibility of MPs from treated effluent reaching shallow groundwater cannot be ruled out either.

3.2. Characteristics of Microplastics

Wastewater effluents and sludge samples were classified based on their type, size, and color. Based on the color, the MPs were dominantly white and transparent (colorless), followed by black, blue, green, and red (Figure 3).
Most of the adult male population wears a white robe and headscarf, and a significant number of females wear a black cloak. Sometimes, especially in the winter, the males wear red and white headscarves. The MPs’ colors provide evidence that laundry wash can be the dominant source of MP input.
The MPs were classed into fibers, fragments, and films in wastewater and sludge based on the shape. (Figure 4). The percentage of fiber in the influent of the Kabd, Umm Al-Haiman, and Sulabiya WWTPs were 78%, 84%, and 79%, respectively. The fragments were less abundant in shape, contributing 20%, 13%, and 17% in the influent of the Kabd, Umm Al-Haiman, and Sulabiya WWTPs, respectively. Films contributed only 2%, 3%, and 4% in the Kabd, Umm Al-Haiman, and Sulabiya WWTPs, respectively. The dominant shape in effluents across the water treatment plants was fiber, constituting 73 to 100%, whereas the fragments were only 0–27%. There were no films in the treated effluent waste. The fibers were the dominant shape in the sludge samples, constituting 64–69%; followed by fragments varying between 25–29%; and films were the least present shape, constituting 5–7%.
The MPs retrieved from the WWTPs have been divided into four arbitrary size classes, <63 µm, 63–150 µm, 150–333 µm, and >333 µm (Figure 5), to have an idea of the dominant size class within the WWTPs. In the influent samples across the WWTPs, the maximum number of particles were between 63 and 333 µm in size. The <63 µm particle size was highest at 13% in the Sulabiya WWTP and lowest at 5% in the Umm Al-Haiman WWTP. The particles >333 µm were highest in the influent of the Kabd WWTP, followed by the Umm Al-Haiman WWTP and the Sulabiya WWTP corresponding to 20, 10, and 5%, respectively, of the total MPs identified. The <63 µm MPs were restricted to the Kabd WWTP and Sulabiya the WWTP, with the percentages being 1–3%. The maximum number of MPs in sludge were in the size range of 64–333 µm. The particles in the >333 µm size in sludge ranged between 13 and 32%, with the lowest presence in the Sulabiya WWTP and the highest in the Kabd WWTP. The particle size of MP is very important as smaller MPs have much higher potential to impact organisms and the ecosystem [60]. The presence of <63 µm particle size in the effluent was highest in the Sulabiya WWTP, where 100% of the particles were <63 µm, followed by 87% in the Umm Al-Haiman and 80% in the Kabd WWTP. The 63–150 µm particles in effluent were 20% in the Kabd WWTP and 13% in the Umm Al-Haiman WWTP.
The smaller MPs were dominant in the effluent in all the WWTPs. raising a concern about the use of effluent water. The use of effluent in Kuwait is both as supply to farms and usage in landscaping. The use of effluent water in agriculture and aquaculture might pose a significant risk [33,61,62]. The smaller MPs, which have a very large surface-to-volume ratio [63], can possibly act as vectors for contaminants and even penetrate shallow aquifers. The relative importance of contaminant exposure mediated by MPs compared to other exposure pathways remains largely unknown today [64].

3.3. Microplastic Polymer Identification

The polymeric characterization was carried out using micro-Raman Spectrometry using a 532 nm excitation laser and a charge-coupled detector to measure the spectra of each MP. The 15 s integration time window and a grating of 900 gr/mm in 100 to 4000 cm−1 wavelength range was used for polyethylene, and 800–1600 cm−1 for polyamide and polypropylene. In the 75 particles subjected to micro-Raman, the most dominant polymers were nylon (PA), polypropylene (PP), and polyethylene (PE). The highest dominance was of PA (~55%), followed by PP (~30%) and PE (~15%). There was also a fragment of PVC in the sludge sample.

3.4. Microplastics in Wastewater Streams from Other Studies

The data show a substantial decrease in the number of MPs after treatment. In the treated effluents, the average inventory of MP is 2.5 MPs L−1 for the Kabd and Sulabiya WWTPs that, combined, treat 820,000 m3 of water. However, considering the fact that an enormous quantity of treated effluent comes out of these plants, an average of 2.245 million MPs enter Kuwait’s environment daily through effluent application in agriculture and greening projects. Similar observations of very high releases into the aquatic environment are known (Table 2) [6,7,8,19,65]. This is the first estimate from Kuwait and highlights the need for further detailed assessment. The mean MPs L−1 from the WWTPs in Kuwait are compared to those reported elsewhere. Generally, Australian WWTPs could be described as more efficient with MP concentrations of <2 MPs L−1 [23,65]. A survey of 17 WWTPs in North America found an average MP concentration of 0.05 MPs L−1 [17], whereas another study from the USA found MP concentrations in the range of 0.5–5.9 MPs L−1 [66]. Similarly, European WWTPs have a relatively wide range of MP concentrations with considerably lower values of <1 (e.g., 0.005 MPs L−1 from Finnish WWTPs [67]) and the highest reported concentrations in the range of 100 MPs L−1 (i.e., 91 MPs L−1 Dutch WWTPs [68]. Further studies are needed to follow each step of the treatment process, but the results reported here show that despite 95–99% of MPs captured into the sludge a significant concentration enters the environment due to the usage of the effluent stream.
The predominance of fibers in the outflow fractions is consistent with other studies [17,65,66,67]. This is not surprising given that WWTP water originates from households and, thus, the presence and abundance of fibers is indicative of laundry and textile washing [69].
Table
Table 2. Microplastic concentration in different wastewater matrixes.
Table 2. Microplastic concentration in different wastewater matrixes.
LocPlantMatrixConcentrationReferences
KuwaitKabd WWTP—treating approximately 270,000 m3 d−1Influent130 ± 4–134 ± 5 MP/LThis Study
Effluent5 ± 1 MP/L
Sludge72 ± 3–81 ± 4 MP/g
Umm Al-Haiman WWTP treats about 20,000 m3 d−1Influent223 ± 4–230 ± 3 MP/L
Effluent11 ± 2–12 ± 3 MP/L
Sludge87 ± 5–99 ± 6 MP/g
Sulabiya WWTP treats about 450,000 m3 d−1Influent119 ± 2–121 ± 3 MP/L
Effluent1 ± 1–2 ± 1 MP/L
Sludge98 ± 5–103 ± 6 MP/g
Sydney, AustraliaWWTP—A: Serving >1,000,000 inhabitants; receiving 308 million liters influent per dayEffluent post
Primary Wastewater
Treatment		12 particles total (10 PET and 2 PE). 1.5 MP/L making a total discharge of 4.6 × 108 MP/day discharged to the ocean via a deep pipeline[70]
WWTP—B: Secondary treatment of 17 million liters
wastewater		Effluent post
Secondary Treatment		0.48 MP/L; likely to discharge 8.16 × 106 MP/day from a cliff into the ocean.
WWTP—CPrimary81 MP identified;
2.2 MP/L
Tertiary
(13 × 106 L d−1)		59 MP identified; 0.28 MP/L
3.6 × 106 MP/day discharged
RO
(40 × 106 L d−1)		42 MP identified;
0.21 MP/L, 1.0 × 107 MP/day discharged
British Colombia, CanadaMajor WWTP, VancouverInfluent31.1 ± 6.7 MP/L[71]
Primary Effluent2.6 ± 1.4 MP/L
Secondary Effluent0.5 ± 0.2 MP/L
Primary Sludge14.9 ± 6.3 MP/g
Secondary Sludge4.4 ± 2.8 MP/g
China6031 WWTP, ChinaEstimates from Effluent disposalAverage microbeads discharge 170.5 × 1012 MP/year; 249.5 t y−1[72]
28 WWTPsSludge22.7 ± 12.1 × 103 MP/kg dw[73]
Denmark (10 largest WWTPs managing 26% of Denmark’s wastewater)
WWTP1Influent10,044 MP/L, 181 µg/L[74]
Effluent127 MP/L, 3.6 µg/L
WWTP2Influent8762 MP/L, 407 µg/L
Effluent447 MP/L, 11.9 µg/L
WWTP3Influent6830 MP/L, 268 µg/L
Effluent42 MP/L, 0.6 µg/L
WWTP4Influent6021 MP/L, 193 µg/L
Effluent29 MP/L, 0.5 µg/L
WWTP5Influent18,285 MP/L, 482 µg/L
Effluent214 MP/L, 5.4 µg/L
WWTP6Influent4994 MP/L, 1189 µg/L
Effluent182 MP/L, 11.6 µg/L
WWTP7Influent2223 MP/L, 212 µg/L
Effluent35 MP/L, 0.7 µg/L
WWTP8Influent8149 MP/L, 407 µg/L
Effluent19 MP/L, 1.4 µg/L
WWTP9Influent7601 MP/L, 118 µg/L
Effluent43 MP/L, 4.8 µg/L
WWTP10Influent5362 MP/L, 61 µg/L
Effluent65 MP/L, 3.8 µg/L
Mikkeli, FinlandKenkaveronniemi WWTP, treating 10,000 m3/dayInfluent57.6 ± 12.4 MP/L[69]
Effluent1.0 ± 0.4 MP/L
Pilot membrane bioreactor, Mikkeli WWTP 3 m3/dayPermeate0.4 ± 0.1 MP/L
MBR Sludge27.3 ± 4.7 MP/g dw
Kenkaveronniemi WWTPActivated Sludge23.0 ± 4.2 MP/g dw
Digested Sludge170.9 ± 28.7 MP/g dw
Helsinki, FinlandViikinmaki WWTPInfluent180 MP/L (textile fibers); 430 MP/L (synthetic particles[67]
Marine Sediment1.7 ± 1.0 MP/Kg (fibers), 1220 ± 160 MP/kg black carbon, 7.2 ± 4.9 MP/kg synthetic particles; 70 ± 20 MP/kg ring-shaped
Suomenoja WWTPEffluent4.9 ± 1.4 MP/L (fibers)
8.6 ± 2.5 MP/L (synthetic fibers)
Marine Sediment4.7 ± 3.5 MP/Kg (fibers), 1060 ± 471 MP/kg black carbon, 10 ± 14 MP/kg synthetic particles; 3.8 ± 2.3 MP/kg ring-shaped
Helsinki archipelagoSeawater0.01–0.24 MP/L (fibers)
0.5–9.4 MP/L (particles)
Viikinmaki Discharge site0.06 MP/L (fibers)
2.4 MP/L (particles)
Suomenoja Discharge site0.17 MP/L (fibers)
3.1 MP/L (particles)
Vanhakaupunki Bay0.65 MP/L (fibers)
0.5 MP/L (particles)
Viikinmaki WWTP: discharges an average of 270,000 m3 treated water into the Gulf of FinlandInfluent380 ± 52.2–686.7 ± 155.0 MP/L[75]
Post Pre-treatment9.9 ± 1.0–14.2 ± 4.0 MP/L
After AS1.0 ± 0.6–2.0 ± 0.2 MP/L
Effluent0.7 ± 0.6–3.5 ± 1.3 MP/L
Reject water12,866.7 ± 275.4 MP/L; 12.9 ± 0.3 MP/g
2.74 × 106 L/day
Recess + Raw Sludge63,611.1 ± 3543.7 MP/L
76.3 ± 4.3 MP/g; 2.92 × 106 L/day
Dry Sludge186.7 ± 26.0 MP/g; 1.84 × 105 L/day
FranceSeine-Centre WWTPInfluent293,000 MP/m3[76]
Settled wastewater90,000 MP/m3
Effluent35,000 MP/m3
GermanyJade Bight, Wilhelmshaven WWTPEffluent32.7 ± 16.7 MP/L (granular)
23.7 ± 1.1 MP/L (fragments)		[77]
12 WWTPs in SaxonyWastewater Effluent10 MP m−3 (Oldenburg); 80 MP m−3 (Neuharlingersiel); 700 MP m−3 (Essen); 9000 MP m−3 in Holdorf[78]
Sludge1000 MP kg−1 Dw in Oldenbury to 24,000 MP kg−1 dw in Scharrel
India Influent17.88 MP/L[79]
Effluent2.75 MP/L
IranBandar Abbas WWTPEffluent2.02 MP/L[7]
Sludge6070 MP kg−1 dw
ItalyNorthern Italy WWTPInfluent2.0 ± 0.3 MP/L[80]
Settler0.6 ± 0.2 MP/L
Effluent0.3 ± 0.1 MP/L
Sludge59.5 MP/gram
NetherlandsWestpoort WWTPInfluent910 MP/L[81]
Effluent39 MP/L
Amsterdam West WWTPEffluent60 ± 45 MP/L
Amstelveen WWTPInfluent73 ± 13 MP/L
Effluent65 ± 67 MP/L
Blaricum WWTPInfluent238 ± 289 MP/L
Effluent81 ± 56 MP/L
Horstermeer WWTPInfluent91 ± 116 MP/L
Effluent56 ± 43 MP/L
Houtrust WWTPEffluent55 ± 15 MP/L
Heenvliet WWTPInfluent68 ± 27 MP/L
Effluent58 ± 29 MP/L
MBR, Heenvliet WWTPEffluent51 ± 14 MP/L
Heenvliet WWTPSludge660 ± 410 MP/kg ww
Westpoort WWTPSludge510 MP/kg ww
Amsterdam West WWTPSludge760 MP/kg ww
ScotlandGlasgow WWTP producing 260,954 m3 treated water per dayInfluent (coarse screening)15.70 ± 5.23 MP/L
4097 ± 1365 million MP/day		[82]
Effluent (grit and grease)8.70 ± 1.56 MP/L
2270 ± 406 million MP/day
Primary effluent3.40 ± 0.28 MP/L
887 ± 74 million MP/day
Final effluent0.25 ± 0.04 MP/L
65 ± 11 million MP/day
Spain Influent4.40 MP/L[83]
Effluent0.92–1.08 MP/L
Effluent12.8 MP/L[84]
Effluent0.44 MP/L[85]
Effluent0.31 MP/L[86]
CadizInfluent574.92 (274.7–1567.5 MP/L)[87]
Effluent41.77 (7.15–131.55 MP/L)
Influent645–1567 MP/L[88]
Effluent16.4–13.35 MP/L
Sludge112 MP/g[85]
Sludge165 MP/g[84]
Sludge50.1 MP/g[89]
SwedenLangeviksverket WWTPInfluent15.1 ± 0.89 × 103 MP/m3[90]
Effluent8.25 ± 0.85 MP/m3
Sludge720 ± 112 MP/kg ww
16.7 ± 1.96 × 103 MP/kg dw
Thailand Influent12.2 MP/L[91]
Effluent2.0 MP/L
Sludge103.4 MP/kg dw
TurkiyeW1–W2Influent1.5–3.1 MP/L[92,93]
Effluent4.11–7.00 MP/L
Influent23.44–26.56 MP/L
Effluent0.6–1.6 MP/L
United Kingdom Influent7011 (955–17,214 MP/L)[94]
Effluent15.7 (2–54 MP/L)
Sludge301–10,380 MP/g
United States of AmericaDetroit, Michigan WWTPInfluent797.8 MP/L[95]
Effluent5.88 MP/L
Northfield, Minnesota
WWTP		Influent367 M/L
Effluent6.2 MP/L
Northfield Pilot AnMBRInfluent367 MP/L
Effluent0.53 MP/L
Northern California SFB1Effluent0.195 MP/L; 456,691 MP/day[96]
Northern California SFB2Effluent0.064 MP/L; 2,045,092 MP/day
Northern California SFB3Effluent0.092 MP/L; 4,134,574 MP/day
Northern California SFB4Effluent0.127 MP/L; 9,625,335 MP/day
Northern California SFB5Effluent0.072 MP/L; 8,086,115 MP/day
Northern California SFB6Effluent0.071 MP/L; 12,433,886 MP/day
Northern California SFB7Effluent0.022 MP/L; 4,105,857 MP/day
Northern California SFB8Effluent0.047 MP/L; 14,916,649 MP/day
Western New York LE1Effluent0.01 MP/L; 64,487 MP/day
Western New York LE2Effluent0.009 MP/L; 101,365 MP/day
Western New York LE3Effluent0.047 MP/L; 1,237,402 MP/day
Eastern New York, LCEffluent0.004 MP/L; 52,773 MP/day
Central New York FL1Effluent0.008 MP/L; 118,706 MP/day
Central New York FL2Effluent0.019 MP/L; 4,078,889 MP/day
Northern Ohio LE4Effluent0.042 MP/L; 4,769,334 MP/day
Eastern Wisconsin LM1Effluent0.0007 MP/L; 2,251,990 MP/day
Eastern Wisconsin LM2Effluent0.017 MP/L; 6,055,005 MP/day
Los Angeles, WRP1Effluent0.082 MP/m3[97]
Los Angeles, WRP2Effluent0.039 MP/m3
Los Angeles, WRP3Effluent0.018 MP/m3
Los Angeles, WRP4Effluent0.022 MP/m3
Los Angeles, WRP5Effluent0.136 MP/m3
Los Angeles, WRP6Effluent0.020 MP/m3
Los Angeles, WRP7Effluent0.005 MP/m3
East Bay Main Wastewater Treatment Plant, San Francisco Bay 0.09 MP/gallon[98]
Modified after Uddin et al. [6].

4. Discussion

This study presents the baseline of the microplastics in the waste streams in Kuwait. Although we were not able to cover all the five plants in this screening, the three plants covered represent 81.3% of total wastewater treated. In spite of the 99% retention of MPs in sludge, an average of 2.245 billion MPs enter the environment daily from the usage of effluent from these three WWTPs. However, the fate of the brine discharge from the Sulabiya WWTP is likely to add an exorbitant number of MPs to the environment. A more detailed long-term assessment should be taken up, and the numbers in the irrigated area and in shallow groundwater are to be looked at in the future. The highest number of MPs were in the size fraction of 63 and 333 µm. The likely source of these fibers is laundry wash. It is quite likely that the WWTPs are not very efficient in capturing the ultrafine MPs and they might remain buoyant for a longer time. The higher concentration of <63 µm MPs in the Sulabiya WWTP might be the result of its membrane filtration. The dominance of nylon (PA) and white and transparent fibers likely come from clothing. Most men wear a white cloak and the presence of black can also be traced as coming from clothing, as women in the country often wear black cloaks. The MPs in the treated effluent in Kuwait are similar to those reported in Australia, Europe, and North America. It is obvious that WWTPs are very effective in capturing MPs. The average MP removal efficiency of WWTPs in Kuwait is ~98%, which is a significant reduction. Since sludge is not used in Kuwait, the sludge-bound MPs remain trapped in the matrix. However, in countries like Spain, Ireland, and Norway, 50–80% of sludge generated is used in agriculture, raising an environmental concern; thus, the question remains, are MPs contaminating soil profiles?

5. Conclusions

This study establishes the baseline of MPs in the wastewater influent, effluent, and sludge in three wastewater treatment plants in Kuwait that treat over 81% of the total wastewater generated in the country. The influent stream receives about 94.5 billion MPs daily. The treatment at the WWTPs results in ~98% retention of MPs in sludge. About 2.245 billion MPs pass into the effluent, while 92.3 billion MPs are retained in sludge. The efficiency of MP removal in Kuwait is comparable to WWTPs in Australia, North America, and Europe. Since the bulk of the MPs are retained in sludge, the use of sludge in agriculture raises the concern whether it will contaminate the soil profile due to the downward movement of MPs in soil. The joint program between the International Atomic Energy Agency and the Food and Agricultural Organization has launched a coordinated research project to address this issue of the contamination of agricultural soils by sludge application. It is also important to explore if this downward movement of MPs in agricultural soils can lead to the contamination of shallow aquifers.

Author Contributions

Conceptualization, S.U. and M.B.; methodology, S.U.; software, N.H.; validation, S.U., M.B. and N.H.; formal analysis, M.B.; investigation, S.U., N.H. and M.F.; resources, K.M.-G. and H.A.A.-S.; data curation, M.F.; writing—original draft preparation, S.U.; writing—review and editing, S.U., M.B. and N.H.; visualization, N.H.; supervision, M.A.-M.; project administration, S.U. and M.B.; Sampling, S.U. and Q.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Location map of the wastewater treatment plants from where the samples were collected.
Figure 1. Location map of the wastewater treatment plants from where the samples were collected.
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Figure 2. Number of microplastic particles in a wastewater stream in the three investigated wastewater treatment plants.
Figure 2. Number of microplastic particles in a wastewater stream in the three investigated wastewater treatment plants.
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Figure 3. The color of different microplastic particles identified during microscopic examination.
Figure 3. The color of different microplastic particles identified during microscopic examination.
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Figure 4. The shape of microplastics in the influent, effluent, and sludge samples retrieved from the three wastewater treatment plants.
Figure 4. The shape of microplastics in the influent, effluent, and sludge samples retrieved from the three wastewater treatment plants.
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Figure 5. Size distribution of microplastic particles in influent, sludge, and effluent.
Figure 5. Size distribution of microplastic particles in influent, sludge, and effluent.
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Table
Table 1. Microplastics in wastewater streams.
Table 1. Microplastics in wastewater streams.
Sampling DateInfluent (MPs L−1)Effluent (MPs L−1)Sludge (MPs 10 g−1)
Kabd10 August 2020130 ± 4 5 ± 172 ± 3
1 December 2020134 ± 55 ± 181 ± 4
Umm Al-Haiman11 August 2020230 ± 312 ± 199 ± 6
2 December 2020223 ± 411 ± 287 ± 5
Sulabiya12 August 2020119 ± 21 ± 198 ± 5
3 December 2020121 ± 32 ± 1103 ± 6
Blank NIL
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Uddin, S.; Behbehani, M.; Habibi, N.; Faizuddin, M.; Al-Murad, M.; Martinez-Guijarro, K.; Al-Sarawi, H.A.; Karam, Q. Microplastics in Kuwait’s Wastewater Streams. Sustainability 2022, 14, 15817. https://doi.org/10.3390/su142315817

AMA Style

Uddin S, Behbehani M, Habibi N, Faizuddin M, Al-Murad M, Martinez-Guijarro K, Al-Sarawi HA, Karam Q. Microplastics in Kuwait’s Wastewater Streams. Sustainability. 2022; 14(23):15817. https://doi.org/10.3390/su142315817

Chicago/Turabian Style

Uddin, Saif, Montaha Behbehani, Nazima Habibi, Mohammed Faizuddin, Mohammad Al-Murad, Karell Martinez-Guijarro, Hanan A. Al-Sarawi, and Qusaie Karam. 2022. "Microplastics in Kuwait’s Wastewater Streams" Sustainability 14, no. 23: 15817. https://doi.org/10.3390/su142315817

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