Membrane Techniques for Removal Detergents and Petroleum Products from Carwash Effluents: A Review published by Ural Federal University eISSN 2411-1414 chimicatechnoacta.ru REVIEW 2023, vol. 10(1), No. 202310107 DOI: 10.15826/chimtech.2023.10.1.07 1 of 12 Membrane techniques for removal of detergents and petroleum products from carwash effluents: a review Eman S. Awad ab* , Siraj M. Abdulla c, T.M. Sabirova a , Qusay F. Alsalhy d* a: Department of Chemical Technology of Fuel and Industrial Ecology, Institute of Chemical Technol- ogy, Ural Federal University, Ekaterinburg 620002, Russia b: Environmental Research Center, University of Technology-Iraq, Baghdad 10066, Iraq c: Department of Environmental Science and Health, College of Science, Salahaddin University, Erbil 44001, Iraq d: Membrane Technology Research Unit, Department of Chemical Engineering, University of Technology-Iraq, Baghdad 10066, Iraq * Corresponding author: eman.s.awad@yandex.com (E.S.A.); qusay.f.abdulhameed@uotechnology.edu.iq (Q.F.A). This paper belongs to a Regular Issue. Abstract One of the most significant urban services is the carwash, which generates large amounts of wastewater containing a variety of pollutants, including sand, gravel, suspended solids, surfactants, oil products, diesel cleaners, etc., that may cause environmental pollution when transferred to the sew- age system without any treatment. The effective treatment is crucial to prevent environmental pollution as well as to recycle the water source. Contaminants are removed from carwash effluent using a variety of treat- ment technologies. This review focuses on identifying and comparing effi- ciency of using advanced commercial and modified membrane filtration techniques, meeting discharge standard regulations, to treat carwash im- purities, especially detergents/surfactants (anionic surfactant) and petro- leum products (oil/grease). The results of this review indicate that ultra- filtration membrane (UF) is the most common membrane filtration tech- nology for carwash wastewater treatment. Additionally, the adoption of traditional pre-treatment processes may be advantageous before utiliza- tion of membrane process for treating carwash wastewater; although con- ventional treatment processes can produce a high quality of effluent, they are less effective than membrane systems. Keywords: anionic surfactant carwash membrane filtration modified membranes water consumption wastewater Received: 04.12.22 Revised: 25.12.22 Accepted: 27.12.22 Available online: 11.01.23 Key findings ● Pollutant removal efficiency of surfactants, oil products and TSS from carwash wastewater depends on the pre-treatment method and the type of membranes used. ● The main method for obtaining new modified membrane structures is the combination of various polymers with other materials to improve the membrane performance. © 2022, the Authors. This article is published in open access under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). 1. Introduction One of the activities that consumes huge amount of water is washing cars. The amount of water consumed depends on both the geographical area and the carwash type, and 150– 600 L of water are often used to wash a car [1]. The dis- charge of the car wash station without treatment resulted in different harmful impacts on the environment because it includes various types of impurities like oils, hydrocarbons, fats, petroleum fractions, road surface pollutants, small ex- haust particles and water-soluble cleansing agent [2]. The composition of carwash wastewater varies greatly depend- ing on the washing technique, type and size of the car that is being washed [3, 4]. The proper treatment and purifica- tion of carwash wastewater is considered as a new source of water. In international practices, great attention is paid to the quality of carwash wastewater and the selection of the optimal methods for cleaning it. Recently, membrane separation processes have been effectively used to remove carwash contaminants. The manufacturing materials for the membranes are either organic (polymers) or inorganic http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2023.10.1.07 mailto:eman.s.awad@yandex.com mailto:qusay.f.abdulhameed@uotechnology.edu.iq http://creativecommons.org/licenses/by/4.0/ https://orcid.org/0000-0001-6961-8587 https://orcid.org/0000-0001-5449-9909 https://orcid.org/0000-0002-0495-1300 https://crossmark.crossref.org/dialog/?doi=https://doi.org/10.15826/chimtech.2023.10.1.05&domain=pdf&date_stamp=2022-12-22 Chimica Techno Acta 2023, vol. 10(1), No. 202310107 REVIEW 2 of 12 DOI: 10.15826/chimtech.2023.10.1.07 (ceramic, steel, aluminum, and glass). The membrane pro- cesses are able to carry out an effective treatment to de- crease the oil content, detergent and other pollutants in carwash wastewater to an acceptable level [5–10]. By con- ducting a literature survey, it no information was found about the use of modified membranes technologies for treating the contaminants present in carwash wastewater, which is one of the relevant areas of research. In this re- gard, the purpose of this literature review was to evaluate the efficiency of commercial and modified membrane filtra- tion techniques and hybrid membrane methods for remov- ing surfactants, oily products and other contaminants of carwash units with the possibility of ensuring their compli- ance with the regulations for reuse or discharge into the centralized sewer network. 2. Carwash units’ specifications The carwash wastewater (CWW) composition depends on the number of washed cars, the season, the type of carwash, and the parameters like detergent types and concentra- tions, and the amount of water used. The contaminants of carwash wastewater originate from detergents used in the washing process, oils and greases of the engine, organic materials, metals, residual petroleum, and particles, like carbon, dust, and salt [11, 12]. The International Car Wash Association listed the main parameters of interest to carwash operators, which include: total dissolved solids (TDS), total suspended solids (TSS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), oil and grease, detergent, zinc, lead, and trace quantities of other metals [13]. Of these constituents, the carwash operator uses the detergent only to wash off the other parameters from the car surfaces. The parameters characteristic of carwash wastewater mentioned in the literature are listed in Table 1. The concentrations of COD, oil and grease, and turbidity have a large range, as indicated in Table 1, although some parameters, such as pH, have fewer variation in the studies. According to Table 1, several studies revealed the pH of CWW were between 6.3–8.7, with the higher value rec- orded by [1]. Also, the electrical conductivity (EC) values were within 138.8–1570 μS/cm. Other CWW Constituents are present in solids that enter the vehicle from dust, mud, and silts, which also increase the turbidity of the wastewater. Van Bruggen et al. recorded the maximum value of total suspended solids (TSS) within 2458 mg/L [14], while Shete and N.P. Shinkar, recorded the high value of total dissolved solids (TDS) within 7920 mg/L [2], and the maximum value of turbidity recorded by Mirshahghassemi et al. was within 1400 NTU [15]. The chemical oxidation demand (COD) in CWW was ranged between 59–1810 mg/L. The countries such as Brazil recorded 59–85 mg/L of COD [16]; Indonesia 700 mg/L [17]; Malaysia 75.0–738 mg/L [1]; Turkey recorded 314 mg/L [18]; and India 460 mg/L [19]. The higher COD observed in Belgium was 1810 mg/L [14]. In carwash sta- tions, emulsified oil obtained from washing engine and de- tergents utilized for vehicles washes contribute to in- creased BOD levels. Based on the literature review, the bio- chemical oxygen demand (BOD5) values were 70–320 mg/L in Belgium [14] and 27–650 mg/L in South Africa [20]. Lau et al. recorded the BOD5 values in Malaysia (10.5–11.9 mg/L that are lower than the others [1]. The oil and grease which are among the CWW's most significant pollutants were stated from less than 0.1 mg/L [16] up to more than 1750 mg/L [21]. Also, Van Bruggen et al. found high level of anionic surfactant in CWW, about 15.5 mg/L [14]. Many studies in the field of treatment carwash wastewater deter- mined, total dissolved solids, total suspended solids, turbid- ity, and chemical oxygen demand (COD), but they did not measure detergents and oil products despite their great im- pact on the environment [22]. The two important parameters in carwash wastewater (detergents, and oil products) are described in the follow- ing paragraphs. 2.1. Structure characteristics and properties of the detergents in carwash technologies In car wash stations, detergents used as cleaning agents contain different types of surfactants. Surfactants are sur- face-active chemicals that reduced the surface tension and are concentrated at the interfaces between bodies or drop- lets of water or oil to act as foaming or emulsifying agents. Their chemical structure has a direct bearing on this mode of action [28]. They are long-chain molecules containing a head group that is hydrophilic (soluble in water) and a tail group that is hydrophobic (oil soluble). Table 1 The characteristics of carwash wastewater. Parameter Units Range References pH – 6.3–8.7 [1, 2, 16, 18, 19, 23, 24] Conductivity (EC) μS/cm 138.8–1570 [1, 16, 18, 19, 23] Turbidity NTU 7.7–1400 [1, 2, 15–17, 23–25] Total Suspended solids (TSS) mg/L 60–2458 [2, 14, 16, 18, 19, 26] Total Dissolved solids (TDS) mg/L 120–7920 [1, 2, 16, 23, 25] Chemical Oxygen Demand (COD) mg/L 59–1810 [1, 2, 14, 16–19, 23–27] Biochemical oxygen demand (BOD5) mg/L 10.5–650 [1, 14, 20] Oil and grease (O&G) mg/L 0.1–1750 [16, 17, 21, 24] Anionic surfactant mg/L 0.7–51 [24, 26, 27] https://doi.org/10.15826/chimtech.2023.10.1.07 Chimica Techno Acta 2023, vol. 10(1), No. 202310107 REVIEW 3 of 12 DOI: 10.15826/chimtech.2023.10.1.07 The major classification of surfactants into classes is based on the characteristics of the hydrophilic head group: anionic with a negative charge, cationic with a positive charge, non-ionic without charge, and zwit- terionic with negative and positive charges. The hy- drophobic tail group may be long chain hydrocarbons, fluorocarbons, siloxane chains, and short polymer chains [29, 30]. Among the numerous surfactant types, anionic sur- factants are particularly important because they account for 60% of all soap production worldwide [31]. Anionic surfactants are most commonly used in car washing technologies. Among the most widespread are those which have a lengthy hydrophobic alkyl chain and a hy- drophilic end group that is charged with sulfonate (e.g., Linear alkylbenzene sulfonate (LAS), Secondary alkane sulfonate (SAS), a-Olefin sulfonate (AOS), and Meth- ylester sulfonate (MES)) or a sulfate charged hydrophilic end group (e.g., Alkyl sulfate (FAS or AS) and Alkylether sulfate (AES)) (Figure 1), as well as sodium, potassium, or ammonium counterions. Sodium dialkylsulfosuccin- ate, sodium dodecylsulfonate, and sodium odecylben- zenesulfonate are common surfactants. Anionic surfactants play a significant part in tech- nical applications owing to their excellent properties like superior water solubility, great cleaning efficiency, and low cost [32]. The methylene blue active substances method (MBAS) is used to determine the anionic surfac- tant content for water and wastewater. Anionic surfac- tants are the most notable of the materials exhibiting methylene blue activity, which is usually utilized in for- mulations of detergent which are strongly responsive to this approach [33]. MBAS with a high concentration of linear alkylbenzene sulfonates (LAS) may coat the oil and grease with MBAS molecules to make these droplets soluble in water. Thus, the effluent did not have lower values [34]. The anionic surfactants contained in carwash wastewater and its treatment methods are listed in Table 2. 2.2. Structure characteristics of the petroleum products in carwash wastewater Carwash wastewater can carry petroleum hydrocarbon residues, hydraulic fluids, and lubricating oils. Lubricat- ing oils are formed from a basic stock of heavier petro- leum hydrocarbons, which are generated from crude oil, together with a variety of additives to enhance their spe- cific qualities. They are mixed using base oils made of petroleum hydrocarbon, polyalphaolefins (PAO) or their mixtures in varying ratios [37]. Oil and grease that orig- inate from different types of petroleum products in car washes may be released from the vehicle surface, tires, or may be leaked out from the braking system, engine parts, and connections [38]. Oil composition is complex, typically containing aliphatic hydrocarbons (73–80%), monoaromatic hydrocarbons (11–15%), diaromatic hydro- carbons (2–5%) and polyaromatic hydrocarbons (4–8%). Also, it consists approximately of 20% of the lubrication additives, which include zinc diaryl, zinc dithiophosphate, molybdenum disulfide, metal soaps and other organome- tallic composites. Oil products in carwash wastewater are considered a serious environmental problem because they contain toxic materials (e.g. polyaromatic hydrocarbon, phenol, etc.) affecting the environment [39]. Table 3 shows oil and grease content in carwash wastewater and its treat- ment methods. Figure 1 Structural formula of common anionic surfactants. Table 2 Anionic surfactants in various carwash wastewater and the treatment methods. Anionic surfactants Initial concentration (mg/L) Final concentration (mg/L) Treatment method References Sodium dodecyl sulfate (SDS) 100 9.9–51.7 Membrane separation [14] Sodium dodecylbenzene sul- fonate (SDBS) 0.7–2.5 Not available Membrane separation [26] Sodium dodecyl benzene sul- fonate (SDBS) 0.8 0.1–0.4 Membrane separation [27] Linear alkylbenzene sulpho- nates (LAS) Not declared <0.06 Coagulation; membrane separa- tion; granular activated carbon [35] Linear alkylbenzene sulpho- nates (LAS) 2–5 Not available Coagulation; membrane separation [24] Alkylbenzene surfactant (ABS) 3–20 <0.05 Sedimentation; surface degreasing; sand filtration; ozonation; UV irra- diation, membrane separation [21] Dodecyl benzene sulfonate (DBS) 21 12 Flocculation column; flotation; sand filtration; chlorination [36] https://doi.org/10.15826/chimtech.2023.10.1.07 Chimica Techno Acta 2023, vol. 10(1), No. 202310107 REVIEW 4 of 12 DOI: 10.15826/chimtech.2023.10.1.07 Table 3 Oil and grease in various carwash wastewater and treatment techniques. 3. Legislation standards for carwash wastewater To conserve natural resources and give a high-quality wash, a new carwash technique must be used, involving water reusing. Some countries have achieved considera- ble advancements in the reuse of wastewater by estab- lishing laws and regulations, whereas the other ones still lack sufficient planning and restrictions [40]. Environ- mental legislation and regulations have been published for wastewater disposal into the public sewage system. Though many countries have their own legislations on environmental quality, the carwash sector rarely en- forces application of these laws [41]. Greywater stand- ard on carwash wastewater was created in countries like United States, Australia, and Europe. Some countries in Europe restricted consumption of fresh water for carwash, or imposed a reclamation (recycling and reuse) percentage of approximately 70–80% to meet the water quality standard [36]. The standards for the carwash wastewater discharge were included in the Standard of Sewage and Effluent Discharge. Wastewater composition standards (the standards of permissible discharges of substances into water bodies) were established in city of Yekaterinburg, Sverdlovsk region, Russia by the Regulation No. 2329 of 2021. Furthermore, Iraq established Iraqi National Standards set by the Regulation 25 of 1967 for wastewater drained to the water source or into public sewers. Malaysia also uses Standard A and Standard B Regulations 2012 based on Malaysia Sewage and Indus- trial Effluent Discharge for the effluent discharges of carwash wastewater. These legislations are applied to the carwash wastewater and are focused on suspended solids (SS), oil and grease, and chemical oxygen demand (COD), yet less attention is paid to the surfactant con- centration. The legislation standards for wastewater are summarized in Table 4. 4. Membrane techniques 4.1. Commercial membrane techniques A summary of numerous studies on membrane tech- niques used for the treatment of wastewater from car washes is provided in Table 5. The UF membranes were widely used in a variety of industrial applications because of the great efficacy in removing contaminants from wastewater with higher permeation flux than that of the other membrane filtra- tion processes [42–44]. The utilization of UF membranes are the main focus of membrane research in the carwash sector [45, 46]. Different commercial and experimental membranes were applied to the carwash effluents that have a various contaminant like detergents/surfactants, oil/grease and others. Bruggen et al. investigated seven types of commercial UF membranes with carwash efflu- ents. Because of surfactants having a major role in the membrane performance, synthetic detergent solutions present in carwash effluents were employed. Three types of surfactants were utilized: sodium dodecyl sul- fate (SDS) as an anionic surfactant, cetrimide as a cati- onic surfactant, and Triton X-100® as a nonionic surfac- tant. The results showed that C100F and Ultrafilic UF possessed best performance in term of surfactant rejec- tion due to molecular weight cutoff (MWCO) of these membranes [14]. In another study, Boussu et al. showed that the desirable quality and the intended use (recycling or discharge) of the purified wastewater determine whether to use UF or NF membranes. Four typical mem- branes were used; two UF membranes and two NF mem- branes for analyzing COD and anionic, cationic and non- ionic surfactants of carwash wastewater. The authors concluded that with the proper membrane type (least membrane fouling) and process format (a hybrid pro- cess combining UF and/or a biological treatment with NF), membrane processes can be effective. UF mem- brane is the best option if the purified wastewater is used for recycling and the surfactants presence does not cause a problem [27]. In a related study, Boussu et al. investigated the application of NF membrane in the carwash sector using two different NF membranes. They revealed that the removal efficiency of NF mem- brane was 100% in terms of removing COD and surfac- tants. The membrane with the shortest MWCO, NF270, had the highest retentions, which is consistent with the results. Anionic surfactants (Sodium dodecylbenzene sulfonate (SDBS)) are better retained than other sur- factants because the negative charges of surfactant and the membrane surface are electrostatically attracted to one another [26]. Oil and grease Initial concentration (mg/L) Final concentration (mg/L) Treatment method References Oil Not declared 0.95 Coagulation; membrane separation; granular activated carbon [35] Oil 5–25 Not available Coagulation; membrane separation [24] Oil 36 2–8 Membrane separation [17] Fossil oil and grease 500–3000 4–20 Sedimentation; surface degreasing; sand filtration; ozonation; UV irradiation; membrane separation [21] https://doi.org/10.15826/chimtech.2023.10.1.07 Chimica Techno Acta 2023, vol. 10(1), No. 202310107 REVIEW 5 of 12 DOI: 10.15826/chimtech.2023.10.1.07 Table 4 The legislation standards for the carwash wastewater. Parameters Standard in Yekaterinburg, Sverdlovsk region (Regulation No. 2329 of 2021) Wastewater composition, mg/L Iraqi National Standards (Regulation No. 25 of 1967) Wastewater composition, mg/L Malaysia (Industrial Effluents) Regulations 2012 Wastewater composition, mg/L North Canalization Basin Southern Canalizat ion Basin Sewerage Basin Water Source Public Sewers Standard A Standard B Suspended solids 300 96.80 31.48 – – 50 100 BOD5 169.40 40.10 30.90 <5 <40 2 40 COD 500.00 176.90 – – <100 80 200 Petroleum products 2.21 0.60 1.30 – 10, if water drained/source water is 1:1000; 5, if water drained/source water is 1:500; 3, if water drained/source water is 1:300 1 10 Sulphates 80.10 69.00 90.44 200 <400, if the water drained/source water is 1:1000 0.5 0.5 Chlorides 53.54 72.00 139.0 200 <600, if the water drained/source water is 1:1000 – – Ammonium 25.40 3.30 8.54 1 – – – Anionic surfactant 0.80 1.60 2.17 – – – – Phosphates–P 0.24 0.24 2.45 0.13 0.98 – – Phenol 0.008 0.023 – 0.005 0.01–0.05 0,001 1 Chromium (6+) 0.0128 0.01 – 0.05 0.1 0.05 0.05 Chromium (3+) 0.0107 0.01 – 0.05 0.1 0.2 0.1 Iron 0.50 1.032 – 0.3 2 1 5 Zinc 0.05 0.051 – 0.5 2 2 2 Copper 0.0312 0.0221 – 0.05 0.2 – – Nickel 0.0099 0.0094 – 0.1 0.2 0.2 1 Aluminium 0.17 0.22 – 0.1 5 10 15 Manganese 0.20 0.10 – 0.1 0.5 0.2 1 In general, the solute rejection of membranes in- creases with decreasing membrane pore size and po- rosity. Istirokhatun et al. studied the applicability of four different commercial UF membranes with vari- ous molecular weight cut-off through filtration in a cross-flow set up [17]. In their study, PES10 had the highest rejection for all pollutants, which is evident in the fact that this membrane has the smallest MWCO. The UF membranes have within 90–95%, 78–100%, and 100% rejection for COD, oil and grease, and tur- bidity, respectively [17]. The concentration of COD can indicate contaminants outside of the vehicle such as various composting dust, bird droppings, or fallen fruit. Detergents, too, can con- tribute to increased levels of COD in effluents and were identified as COD in many studies [1], [18]. Lau et al. ex- amined the treatment of carwash effluents by using three various types of commercial polymeric membranes UF and NF; their characteristics summarized in Table 5. During filtration in a lab-scale cross-flow unit, it was de- termined that the COD removal depend on the membrane characteristics and the best removal (91.5%) was gained by the NF270 [1]. In a similar study, Uçar [18] filtered carwash wastewater by four UF membranes of varying MWCO and one NF membrane. The COD measurements were made to specify the detergent in this study. The re- sults showed the COD removal efficiency corresponding to 97% for NF membrane, which is more than that for the UF membrane. Furthermore, these studies empha- size the importance of pre-treatment when using mem- branes for treatment of carwash wastewater. 4.2. Modified membrane techniques Membranes are generally prepared from ceramic and polymeric materials. Although the cost of manufacturing ceramic membrane is high, it can be minimized by using locally sourced precursors like pore-formers, clay, and plasticizer. Zrelli et al. prepared a ceramic membrane from clay and 22% oasis waste by using semidry-press- ing process; the membrane was sintered at 800 °C and molded at 8 bars. This ceramic membrane was used to treat carwash wastewater which was collected from five car washing units located in Tunisia. The characteristics of the used carwash wastewater in this study were total solid (1115 mg/L), oil content (137 mg/L), pH = 7.5, and conductivity (915 μs/cm). https://doi.org/10.15826/chimtech.2023.10.1.07 Chimica Techno Acta 2023, vol. 10(1), No. 202310107 REVIEW 6 of 12 DOI: 10.15826/chimtech.2023.10.1.07 Table 5 Carwash wastewater treatment techniques with various commercial membranes. Membrane Characteristics Influent characteristics Effluent characteristics References MWCO (kDa) Material UF C100F 100 Cellulose Synthetic solutions: Nonionic surfactant 100 mg/L; Anionic surfactant 100 mg/L; Cationic surfactant 100 mg/L; Nonionic surfactant 55.9– 94.6 mg/L; Anionic surfactant 48.3– 90.1 mg/L; Cationic surfactant 5.2–83.3 mg/L [14] P150F 150 Polyethersulfone PES 20 Polyethersulfone PES 10 10 Polyethersulfone HFM 116 100 PVDF HFM 180 250 PVDF Ultrafilic UF 100 Polyacrylonitrile UF UF P150F 150 Polyethersulfone COD 208–316 mg/L; Nonionic surfactant 26–39 mg/L; anionic surfactant 0–0.8 mg/L; cationic surfactant 4.3–7.9 mg/L COD 192 mg/L; Nonionic surfactant 23 mg/L; anionic surfactant 0; cationic surfactant 7.3 mg/L [27] Ultrafilic 100 Polyacrylonitrile COD ND; Nonionic surfactant 24 mg/L; anionic surfactant 0 mg/L; cationic surfactant 3.9 mg/L NF NFPES10 1.2 Polyethersulfone COD 106 mg/L; Nonionic surfactant 21 mg/L; anionic surfactant 0.4 mg/L; cationic surfactant 0.9 mg/L NF270 0.17 Polyamide COD 10 mg/L; Nonionic surfactant 1 mg/L; anionic surfactant 0.1 mg/L; cationic surfactant 0.2 mg/L NF NF270 0.17 Polyamide SS 60–140 mg/L; COD 208–382 mg/L; Nonionic surfactant 32–51 mg/L; Anionic surfactant 0.7–2.5 mg/L; Cationic surfactant 1.7–3.7 mg/L COD 33–100 mg/L [26] NFPES10 1.2 Polyethersulfone UF PES10 10 Poly (Ether) Sulfone COD 700 mg/L; O&G 36 mg/L; Turbidity 186.6 NTU COD 33.3–40 mg/L; Turbidity 0.22–0.25 NTU; O&G 0–2 mg/L [17] PS25 25 Polysulfone COD 40–70 mg/L; Turbidity 0.24–0.57 NTU; O&G 2–8 mg/L PS50 50 Polysulfone PS100 100 Polysulfone UF GE 1 Composite polyamide pH 7.3; COD 314 mg /L; EC 729 μS/cm; PO43–P 9.05 mg/L pH 7.34–7.59 COD 64.5–85.5 mg/L; EC 523–629 μs/cm; PO43–P < 1 mg/L [18] PT 5 Polyethersulfone PW 10 Polyethersulfone MW 50 PAN/Ultrafilic NF NF270 0.2–0.4 pH 7.61; COD 8.1 mg/L; EC 391 μs/cm; PO43–P < 0.05 mg/L UF PVDF100 100 Polyvinylidene difluoride COD 75.0– 738.0 mg/L; Turbidity 34.7– 86.0 NTU; TDS 89.2–151.8 mg/L; EC 138.8–260.7 μS/m COD 56.11–82.41 mg/L; Turbidity 92.37– 96.85 NTU; TDS 13.59–16.56 mg/L; EC 16.9–19.6 μS/m [1] PES30 30 Polyethersulfone COD 54.85–83.89 mg/L; turbidity 97.27–97.34 NTU; TDS 17.61–31.45 mg/L; EC 23.57–35.44 μS/m NF NF270 0.3 Polyamide COD 70.9–91.49 mg/L; turbidity 94.42–98.75 NTU; TDS 59.99–61.53 mg/L; EC 61.92–63.62 μS/m https://doi.org/10.15826/chimtech.2023.10.1.07 Chimica Techno Acta 2023, vol. 10(1), No. 202310107 REVIEW 7 of 12 DOI: 10.15826/chimtech.2023.10.1.07 To reduce the fouling and increase the treatment effi- ciency, the authors used sedimentation for 1 hour and filtration as a pretreatment of the carwash wastewater samples, and then treated them with a dead-end filtra- tion unit. The authors examined the effect of percentage of oasis waste on open and closed porosity at a molding pressure (8 bars) and sintering temperature (800 °C), as shown in Figure 2. The concepts of open and closed po- rosity are used to describe different types of porous ma- terials. The volume of fluid that the continuous fluid phase occupies in relation to the entire volume of porous material is referred to as the open porosity. In contrast, closed porosity is the percentage of the total volume in which fluids are present but cannot flow effectively [47]. The membranes had stronger hydrophilic characteristics with increased concentration of oasis waste. When the concentration of oasis waste was between 8–15% for the fabricated ceramic membrane, a sharp increase of the open porosity 26.12–40.05% and a slight variation of the closed porosity were detected, and above this concentra- tion, no effect was observed on the open porosity, while the closed porosity increased. Furthermore, the evolu- tion of permeate flux and oil rejection were compared for oily wastewater with 125 mg/l oil concentration and carwash wastewater for the prepared ceramic mem- brane, as shown in Figure 3. The authors concluded that the permeate flux decreases with the time increase, and the flux evolution of the carwash wastewater was about 5% lower than that of the oily wastewater. Also, the oil rejection of carwash wastewater was about 93% which complies with the Tunisian standard of wastewater. These outcomes are a result of using detergents composed of surfactants in the carwash units, which interact with the membrane surface to give reduced. These detergents flux reduction and improved the oil rejection [47]. Polymeric modified membranes have been employed for solving issues relating to water treatment or water re- use due to their exceptional efficiency, cost-effectiveness, clean technology, and environmental friendliness by effi- ciently eliminating oil and grease, detergents, and highly hazardous surfactants from carwash effluents [46, 48]. Figure 2 Open and closed porosity evolution with percentage of oasis waste [47]. There are few studies on the use of modified mem- branes for the treatment of carwash wastewater. Kame- lian et al. prepared 10 types of acrylonitrile-butadiene- styrene (ABS) membranes with thickness ranged be- tween 82.4–113.9 µm. The impact of solvent-nonsolvent types, ABS and additive concentrations (polyethylene glycol (PEG)) on the structures and wastewater treat- ment of carwash was assessed. The 1-methyl-2-pyrroli- done (NMP) and Dimethyl acetamide (DMAc) were uti- lized as solvents, and water and heptane (C7) were used as antisolvents. The authors clarified through the cross- sectional images that the membranes made by using the NMP/C7 pair (e.g. M2) have a denser structure in com- parison with the membranes prepared using the NMP/water pair (e.g. M9) which have a fingerlike struc- ture as shown in Figure 4, because NMP has low solubil- ity in heptane (C7); meanwhile, NMP has a large cross- affinity with water. Also, the membranes prepared by using 20 wt.% ABS have denser and thinner structures in comparison with the membranes prepared by using lower concentration, 17 wt.%, of ABS because the high concentration of ABS increase the casting solution vis- cosity, cause slow demixing in the coagulation bath, and thus reduce the nuclei growth rate in the structure through phase inversion. The surface SEM images (Fig- ure 5) of M1, M2 and M3 proves the porosity reduction with 0, 6, 10 wt.% PEG addition, respectively. Also, the authors concluded that the membrane structure, which was prepared using NMP/water pair, was negatively im- pacted by the AN migration to the water coagulation bath through the precipitation process. Furthermore, similar performance of the membranes prepared with NMP and DMAc as solvent results in similar impact on the membrane structure. The authors revealed that the porous membranes fabricated with similar concentra- tions in the water coagulation bath have lower rejection percentages of COD, TDS, and turbidity, and more stable flux. Additionally, it was shown through the study of the effectiveness of membranes prepared with various ABS concentrations that increasing the ABS concentration raises rejection rates while lowering stable flux. Figure 3 The permeate flux and oil rejection with time [47]. https://doi.org/10.15826/chimtech.2023.10.1.07 Chimica Techno Acta 2023, vol. 10(1), No. 202310107 REVIEW 8 of 12 DOI: 10.15826/chimtech.2023.10.1.07 Figure 4 The cross-sectional SEM images of prepared membranes. Figure 5 The surface SEM images of some prepared membranes. Also, increasing the PEG concentration caused an in- crease in rejection rates and a decrease in stable flux at a constant ABS concentration. All these results are con- sistent with the cross sectional and surface SEM images of the membranes. Moreover, to study the migration ef- fect from ABS to water, the authors used the Fourier transform infrared (FTIR) spectra, which focused on the characteristic peak of AN. The intensity changes as the coagulation bath changes, which means the AN migra- tion from ABS to water occurred [25]. Kiran et al. fabricated two membranes, Cellulose ac- etate (CA) and polyethersulfone (PES), by using hydro- philic polymer sulfonated polyether ether ketone (SPEEK) and nanoclay bentonite, and compared their performance with the commercial polyethersulfone (PES) membrane in the removal of carwash effluent. The authors concluded based on the surface SEM images that the membranes CA/SPEEK/bentonite and PES/ SPEEK/bentonite have loose porous structures with clear bigger pores, owing to the incompatibility between inorganic bentonite and an organic polymer; thus, de- mixing the casting dope solution improves the pore for- mation. Additionally, the bigger surface area and the smaller size of nanoclay bentonite cause it to disperse in both the top and bottom layers of the membrane surface. The membranes' cross-sectional images revealed a thin skin layer and finely interconnected porous structure that were responsible for the improved permeation rate brought on by the addition of both bentonite and SPEEK to the casting dope solution. A higher flux was observed for CA/SPEEK/bentonite membrane (52.3 L/m2h) com- pared with that of the commercial PES membrane (41.5 L/m2h); this might be caused by more solutes being absorbed onto the membrane surface. Also, the higher rejection, 60% COD and 82% turbidity, was gained for the CA/SPEEK/bentonite membrane. In this study, fou- rier transform infrared (FTIR) spectra (Figure 6) re- vealed that the wavenumbers 1030–1060 cm–1 and 550 cm–1 in membranes correspond to alcohols (CH2OH) and disulfide, respectively, which showed that the pollutant was adsorbed on the surface of the membrane. Yet, the commercial PES membrane displayed a higher adsorp- tion intensity with carwash effluent, which may be re- lated to its hydrophobic properties [23]. 5. Hybrid-membrane techniques Numerous studies were published on using integrated membrane techniques either alone or in combination with conventional methods such us mechanical separa- tion, flotation, chemical coagulation, etc. Figure 6 Fourier transform infrared (FTIR) spectra of mem- branes. Reproduced from ref. [23] © 2015 Elsevier Inc. https://doi.org/10.15826/chimtech.2023.10.1.07 Chimica Techno Acta 2023, vol. 10(1), No. 202310107 REVIEW 9 of 12 DOI: 10.15826/chimtech.2023.10.1.07 Establishing an effective pre-treatment is crucial to ensuring that the membranes operate consistently and to improving the wastewater quality based on its nature and the discharge standard regulation. In the study of Nagamani et al. the authors used a combined pre-treatment consisting of utilizing a coarse filter (20 μm PP cartridge), an MF ceramic membrane (3 μm kaolin), and ultimately an NF membrane (500 Da Pol- yamide Membrane) to ensure that the filtrate is of suf- ficient quality to be recycled and used again. Deter- gents, oil, grease, and other contaminants may be in- dicated by the COD concentration. They found that the concentrations of COD post 20 μm cartridge filtration has a minimum change <2%, which means that the particle sizes were less than 20 μm, and the removal efficiency of COD was 99% after filtration by course filter, MF and NF membrane [19]. In another study, Moazzem et al. achieved high removal efficiency of turbidity 99.9%, suspended solids 100%, and COD 96% from carwash wastewater by using two types of membranes, including ceramic UF membrane and re- verse osmosis (RO) with pretreatment as coagulation flocculation process and sand filtration [22]. Also, Tan and Tang clarified that it is preferable to utilize pre- treatment before UF membrane to prevent more con- taminants from adsorbing in pores. It was shown that using chemical coagulation as pretreatment by adding KMnO4 to the coagulant PAC can improve efficiency of the coagulation and help to reduce the blockage of the two types of PS UF membranes with MWCO (6 and 20 kDa) which were used [24]. In a similar study, Tang et al. separated carwash wastewater by using two sorts of PS hollow fiber UF membranes (6 and 20 kDa) with enhanced coagulation and granular activated carbon (GAC), resulting in good removal levels of oil, COD, BOD, and LAS. The GAC tank following the UF membrane can efficiently adsorb LAS, odor, and color. A schematic diagram of the apparatus is presented in Figure 7. AFM analysis was conducted on the mem- brane (Figure 8), and it was concluded that the LAS existence in carwash wastewater might loosen the gel layer and improve the membrane flux [35]. Moreover, Shete et al. checked the feasibility for obtaining refuse-free water by using sedimentation and induced air flotation as a pretreatment, and then cross-flow UF and reverse osmosis. The removal effi- ciency values for the total dissolved solids (TDS), total suspended solids (TSS), oil and grease, and COD by UF were 81%, 82%, 74%, and 67%, respectively (the ef- fluent poses can be safely discharged into any local water bodies, including rivers), and by RO these val- ues were 91%, 82%, 90%, and 81%, respectively (it is safe to reuse the effluent for any productive activity, such as car washing or landscape gardening). It was possible to obtain a sufficient quantity of water with high purity from carwash effluent using these proce- dures [2]. Table 6 provides a summary of several stud- ies on hybrid-membrane techniques that were con- ducted for the treatment of wastewater from car washes. In the study by Jiku et al., coagulation-flotation was utilized as a pre-treatment before hollow fiber ultrafil- tration membrane for oil removing from car washing wastewater. The oil content in car washing effluents ranged from 5.2 to 13.47 mg/L. According to the their results, the combined processes may remove more than 40% of the oil content, more than doubling the oil re- moval rate of the traditional coagulation and flotation method [49]. 6. Limitations This review studied the membrane filtration techniques and their effectiveness in eliminating various contami- nants from carwash wastewater, including surfactants, oil products, dissolved and suspended particles. The ma- jor restriction of membrane filtration for the treatment of carwash is the rapid membrane flux reduction during the operation; therefore, the selection of the suitable membrane or modification of the structure of membrane might be necessary. Figure 7 Schematic diagram of system setup. Figure 8 AFM analysis on UF membrane: (a) new UF mem- brane, (b) membrane contaminated with oil and (c) membrane contaminated with oil and LAS. Reproduced from ref. [35] © IWA Publishing 2007. https://doi.org/10.15826/chimtech.2023.10.1.07 Chimica Techno Acta 2023, vol. 10(1), No. 202310107 REVIEW 10 of 12 DOI: 10.15826/chimtech.2023.10.1.07 Table 6 Carwash wastewater treatment methods based on Hybrid-Membrane techniques. Pretreatment Membrane Characteristics Influent characteristics Effluent characteristics Ref. MWCO (kDa) Pore size, μm Material Coarse filter PP Ceramic-MF – 3 kaolin pH 6.4; EC 680 μS/cm; COD 460 mg/l; TS 1280 mg /L After MF+NF pH 7.73; EC 226 μS/cm; COD 4 mg/l [19] NF 0.5 – Polyamide Coagulation- flocculation, sand filtration Ceramic-UF – 0.02 Zirconia oxide pH 4.66–6.42; EC 404–509 μs/cm; Turbidity 522–763 NTU UF pH 5.32; EC 273–298 μs/cm; Turbidity 1.84–0.86 NTU [22] RO – – – After UF+RO pH 5.32; EC 7.6–14.6 μs/cm; Turbidity 0.86–0.16 NTU Enhanced coagulation UF 6 20 – Polysulfone pH 6.5–8; Turbidity 70 NTU; COD 100–160 mg/L; Oil 5–25 mg/L; LAS 2–5 mg/L Not declared [24] Enhanced coagulation UF 6 20 – Polysulfone Not declared COD 33.4 mg/L, BOD 4.8 mg/L, Turbidity 0.42 NTU, LAS 0.06 mg/L, oil 0.95 mg/L, SS 1 mg/l DS 115 mg/l [35] Granular activated carbon (GAC) Sedimentation & Induced air flotation UF – – – pH 8.5; Turbidity 7.7 NTU; TDS 7920 mg/l; TSS 1134 mg/l; COD 288 mg/l; O&G 34.19 mg/l UF pH 7.26; Turbidity 1.20 NTU; TDS 791.5 mg/l; TSS 124 mg/l; COD 83 mg/l; O&G 3.11 mg/l [2] RO – – – After UF+RO pH 6.38; Turbidity 0.0 NTU; TDS 140 mg/l; TSS 10 mg/l; COD 12.8 mg/l; O&G 0.31mg/l Coagulation - Flotation Hollow fiber UF – – – pH 6.9–7.6; Oil and grease 5– 13.4 mg/L; Turbidity 362–450 NTU Oil and grease >2.1– 5.4 mg/L [49] 7. Conclusion and future prospects According to the reviewed studies into the membrane fil- tration systems and hybrid membrane technologies, tra- ditional filtration methods such as mechanical separa- tion, coagulation-flocculation process, air flotation, etc., are the most interesting choices for treating carwash wastewater and getting rid of various contaminants that pose a serious threat to the environment. Moreover, these methods cost effective and can produce high-qual- ity filtering. The concentrations of surfactants and oily products were also found to be reduced based on the treatment type and the membrane technology employed. The main approach to obtaining new modified mem- brane structures is a combination of various polymers and other materials in the manufacturing technology, which allows to improve the removal efficiency and other performance properties of membranes. This study allows giving some suggestions for the fu- ture works in the carwash sector. Firstly, it is necessary to conduct more studies on using the modified mem- branes to treat wastewater for car washes, to consider the cost and the main characteristics, and then to apply the membranes on field-scale to obtain an efficient wastewater treatment. Also, developing good and cost- efficient membrane filtration techniques and using them in the car washing will reduce the cost of using munici- pal water through recycling. ● Supplementary materials No supplementary materials are available. ● Funding This research had no external funding. https://doi.org/10.15826/chimtech.2023.10.1.07 Chimica Techno Acta 2023, vol. 10(1), No. 202310107 REVIEW 11 of 12 DOI: 10.15826/chimtech.2023.10.1.07 ● Acknowledgments None. ● Author contributions Conceptualization: E.S.A., S.M.A., T.M.S., Q.F.A. Data curation: E.S.A., Q.F.A. Formal Analysis: E.S.A., S.M.A., T.M.S., Q.F.A. Funding acquisition: E.S.A., T.M.S., Q.F.A. Investigation: E.S.A., S.M.A. Methodology: E.S.A. Project administration: T.M.S., Q.F.A. Resources: E.S.A., S.M.A., T.M.S., Q.F.A. Software: E.S.A., S.M.A. Supervision: T.M.S., Q.F.A. Validation: E.S.A., S.M.A., T.M.S., Q.F.A. Visualization: E.S.A. Writing – original draft: E.S.A. Writing – review & editing: T.M.S., Q.F.A. ● Conflict of interest The authors declare no conflict of interest. ● Additional information Author IDs: Eman S. Awad, Scopus ID 56921998200; T.M. Sabirova, Scopus ID 6602344446; Qusay F. Alsalhy, Scopus ID 50861207300. Websites: Ural Federal University, https://urfu.ru/en; University of Technology-Iraq, https://uotechnol- ogy.edu.iq; College of Science, Salahaddin University, https://colleges.su.edu.krd/science. References 1. Lau WJ, Ismail AF, Firdaus S. Car wash industry in Malaysia: Treatment of car wash effluent using ultrafiltration and nanofiltration membranes. Sep Purif Technol. 2013;104:26–31. doi:10.1016/j.seppur.2012.11.012 2. Shete BS, Shinkar NP. Use of membrane to treat car wash wastewater. 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