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Article

Development of a Concept for Closing the Water Cycle in the Surface Treatment of Ferrous and Non-Ferrous Metals

by
Jolanta Janiszewska
1,*,† and
Paulina Rajewska
1,2,†
1
Łukasiewicz Research Network—Institute for Sustainable Technologies, Pułaskiego 6/10, 26-600 Radom, Poland
2
Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Sustainability 2025, 17(5), 2212; https://doi.org/10.3390/su17052212
Submission received: 17 December 2024 / Revised: 19 February 2025 / Accepted: 26 February 2025 / Published: 4 March 2025
(This article belongs to the Section Waste and Recycling)
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Abstract

:
This study examines the treatment of industrial wastewater generated during vibro-abrasive steel and Zn-Al alloy parts machining in a Polish metal-processing plant. The machining process uses grinding fluids, which are sent for disposal after becoming saturated with contaminants, incurring high costs. A two-stage filtration process was investigated: an initial bag filtration (pore size 5 µm) followed by a low-pressure (4 bar) ultrafiltration with polyacrylonitrile membranes (30 kDa cut-off). The studies were carried out on a laboratory scale in a cross-flow system using a batch configuration. The initial filtrate flux was 0.116 mL min−1 cm−2 and 0.050 mL min−1 cm−2 for Zn-Al alloy and the steel wastewater, respectively. Key physicochemical parameters, including turbidity, COD, and TOC, were analysed for raw wastewater, feed, retentate, and permeate. Significant reductions in contaminant concentrations were achieved, with comparable total efficiencies for both the wastewaters tested. The reductions in turbidity, COD, TOC, anionic surfactants, total phosphorus and non-ionic surfactants ranged from 80% to almost 100%. A complete removal of total suspended solids was achieved. The novelty of this research lies in applying polyacrylonitrile flat-sheet membranes to treat wastewater from vibratory machining of ferrous and non-ferrous materials and recycle reclaimed water, which has not been systematically explored in previous studies. The study demonstrates the potential of low-pressure membrane filtration for wastewater recycling, offering insights into environmentally friendly and energy-efficient management of industrial wastewater.

1. Introduction

The growing demand for clean water and the need to minimise industrial environmental impacts underscore the importance of sustainable water management practices. The European Union and the European Commission emphasise the importance of water reuse and closed-loop water management in industrial sectors, particularly those with high demand for water and raw materials. The 2020 Circular Economy Action Plan sets specific goals for industrial water reuse, recognising the need to address issues related to limited resources, climate change, and pollution [1]. The Industrial Emissions Directive (IED) further enforces stringent water and pollution control standards, encouraging industries to adopt innovative wastewater treatment technologies [2]. With the increasing global water scarcity and more stringent environmental regulations, industries are pressured to adopt sustainable practices that minimise wastewater discharge and recover valuable resources, such as water, from the waste stream [3]. The efficient treatment of wastewater not only addresses environmental concerns but also presents an opportunity to recycle water within industrial processes, reducing freshwater intake and associated costs [4].
The metal industry is a significant contributor to global economic growth and one of the largest consumers of freshwater resources [5,6]. Industrial processes, such as metal finishing, electroplating, and mining, generate large volumes of wastewater, often containing hazardous pollutants, including heavy metals, oils, greases, and suspended solids [7,8]. If not properly treated, these contaminants pose severe environmental risks, such as soil and water pollution, which can harm aquatic life and human health [9]. The need for an effective removal of metals from wastewater, coupled with the potential for recovering valuable resources and reusing treated water, has driven the development of innovative treatment technologies [10]. In general, wastewater from the metal industry can be regenerated using various methods [6,11,12,13,14,15,16,17]. Conventional wastewater treatment methods, such as chemical precipitation, ion exchange, and coagulation, have been widely employed in the metal industry [18,19]. However, these methods often produce large amounts of sludge and may fail to remove trace contaminants entirely [18,20,21]. As a result, there is a growing interest in advanced treatment technologies that offer more efficient, cost-effective, and environmentally friendly solutions for water recovery [2,5,21].
Chemical precipitation is a standard method for removing metals like lead, copper, and zinc from wastewater, but it generates large amounts of sludge that require disposal [1,5,22,23,24]. It is also less effective for low metal concentrations or when complexing agents are present and is highly pH-dependent, complicating the treatment of mixed effluents [8,24]. Electrocoagulation and electrooxidation offer efficient alternatives, with electrocoagulation aggregating contaminants through sacrificial electrodes and electrooxidation degrading organic pollutants [16,21,25]. However, these methods require frequent electrode replacement and careful control of wastewater composition, raising operational costs [21]. Adsorption is effective for low metals and organic compounds concentrations, utilising materials like activated carbon and zeolites. While helpful in treating metal industry wastewater, adsorbents require regeneration or replacement after saturation, adding costs and generating waste [16,26]. Biological methods are cost-effective and environmentally friendly, but are highly sensitive to the presence of toxic heavy metals, requiring pretreatment and longer retention times [10,27,28].
Membranes are widely used in industrial wastewater treatment due to their high separation efficiency and ability to meet stringent environmental standards. In the metal industry, wastewater is characterised by its complex composition, containing not only heavy metals but also oils, greases, suspended solids, and organic compounds. As a result, the effective treatment of such wastewater presents a challenge that requires advanced membrane technologies [29,30,31].
Microfiltration and ultrafiltration are widely used as preliminary steps in treating metallurgical wastewater. Microfiltration, with pore sizes typically ranging from 0.1 to 10 micrometres, removes larger particles, including suspended solids, oils, and emulsions. Ultrafiltration, with smaller pore sizes of 0.01 to 0.1 micrometres, effectively separates colloidal particles, oils, and macromolecules. Both technologies are essential for reducing the load on downstream treatment processes, such as reverse osmosis and nanofiltration [8]. Hajer Aloulou et al. [32] focus on the development and performance evaluation of new composite membranes made from kaolin coated in sand and zeolite supports for treating industrial electroplating wastewater. The study showed excellent efficiency of turbidity (>99%), oil (>99%), COD (>96%), and heavy metals (>94%) rejection. The authors concluded that kaolin/sand composite membranes are a cost-efficient and effective solution for ultrafiltration (UF) in wastewater treatment, offering high flux performance, good antifouling properties, and low production costs. Nanofiltration (NF) membranes, with pores around 0.001 micrometres in size, are particularly effective for removing divalent and multivalent ions, such as zinc, copper, and chromium, which are commonly found in metallurgical wastewater. NF also allows the partial retention of monovalent ions, enabling a selective removal of contaminants while retaining beneficial salts required for specific industrial processes [8]. Research by Lijo Francis et al. [33] demonstrated the ability of nanostructured hollow fibre nanofiltration membranes (NHFNFMs) to achieve a high potential for metal recovery, emphasising their unique structure and properties.
Despite its advantages, NF faces limitations such as fouling from metal precipitates and organic matter, which necessitate pretreatment steps to enhance its long-term performance [33].
Reverse osmosis is a pressure-driven membrane technology capable of producing high-purity water by rejecting almost all dissolved salts, heavy metals, and organic contaminants. Its application in the metallurgical industry includes treating process water and achieving compliance with stringent discharge standards [8,34]. RO is frequently used as the final treatment stage in zero-liquid discharge (ZLD) systems, ensuring the complete removal of pollutants. A study by Roxanne Engstler and co-authors [34] confirms the feasibility of recycling the RO concentrate back into the plating process, providing a novel approach to achieving circularity in electroplating operations. This study explores reverse osmosis (RO) for recovering and recycling chromium and other components from electroplating rinse water, addressing the significant volumes of wastewater generated in the industry. The process achieved excellent rejections, with >99.9% for chromium, 99.6% for sulphate, and 93.8% for boric acid. The investigation highlights the potential of RO to align electroplating practices with sustainability goals, such as those outlined in the European Green Deal, by reducing the environmental and economic costs of rinse water disposal.
Membrane technologies are becoming increasingly popular in treating wastewater from the metallurgical industry for several important reasons. First, they are characterised by a high degree of separation and effective removal of contaminants such as heavy metals, oils, and greases. They produce treated water that meets regulatory standards and is safe for discharge or reuse [8,29,30,31,32,33,34]. Second, membrane processes often require fewer chemicals than traditional treatment methods, leading to lower operating costs and a minimised environmental impact [30]. In addition, they enable the recovery of valuable materials from wastewater; for example, metals can be recovered and recycled, contributing to resource efficiency in line with the principles of the circular economy [3,4,5,30]. Finally, the modular nature of membrane systems allows for easy scalability and adaptation to variable flow rates and contaminant loads [35]. This flexibility is essential in the metallurgical industry, where wastewater characteristics vary significantly between processes. Together, these factors make membrane technologies an attractive choice for wastewater treatment in this industrial sector, promoting efficiency, sustainability, and compliance with environmental regulations.
In the literature, there are reports on removing or recovering heavy metals from wastewater/spent baths used in the metallurgical industry. Still, information on the recovery of baths from the vibro-abrasive processing of metal parts [5,6,7,8,9,10,36] is absent. Vibro-abrasive machining is utilised as a finalisation process, serving to eliminate burrs along edges or to refine surfaces [37]. This technique is employed within enclosed containers, housing a blend of workpieces and a working medium consisting of appropriately chosen abrasive or polishing elements and a machining fluid. Vibrational motions within the machine’s enclosed container induce the movement of abrasive shapes and processed components relative to each other. This dynamic interaction results in the abrasion of surface irregularities facilitated by the materials within the container. Vibro-abrasive machining finds extensive application across diverse industries, particularly for refining small components with intricate geometries [37,38,39].
There is a significant body of literature exploring the influence of various parameters on the vibro-abrasive process, such as vibration frequency, abrasive media composition, and processing time, as well as their impact on the final surface quality, dimensional accuracy, and overall efficiency of treated components [40,41,42]. These studies provide valuable insights into optimising the process to achieve desired surface finishing and component durability outcomes. However, despite the extensive research into the operational aspects and outcomes of vibro-abrasive machining, there remains a critical gap in the literature regarding the water recovery aspects of the process.
Specifically, no studies have investigated the feasibility of regenerating the vibro-abrasive bath, which contains a mixture of machining fluids, debris, and residual abrasive particles. This gap is significant, as the inability to renew or recycle the bath results in frequent disposal and replenishment, leading to increased operating costs, higher consumption of resources, and a more significant environmental impact. Addressing this gap is crucial for advancing the sustainability of vibro-abrasive machining, aligning with broader industry goals of water reuse and resource recovery and reducing manufacturing processes’ environmental footprint. This study explores the application of membrane filtration to enable closed-water circulation in the processing of metal and non-metallic materials. It evaluates the effectiveness of membrane treatment in purifying wastewater produced during the vibro-abrasive machining of steel and Zn-Al alloys, focusing on the physicochemical properties of the recovered water and its suitability for reuse within the same industrial processes. The findings contribute to efforts to reduce freshwater consumption and improve wastewater management. Aligning with EU circular economy goals, the study highlights the potential of membrane technology to enhance the sustainability and efficiency of industrial operations. However, further research and practical implementation are necessary to realise its full benefits.

2. Materials and Methods

2.1. The Examined Wastewater

The study was conducted on actual industrial wastewater generated by a large Polish company representing the ferrous and non-ferrous metals industry (producing parts for various industrial sectors, including automotive and energy). The study focused on wastewater, the disposal of which is associated with the highest cost to the company; the wastewater is generated during vibro-abrasive machining of parts made of steel and Zn-Al alloy. This machining is carried out in a closed system using resin or ceramic mouldings (Figure 1). The installation has a capacity of 1000 L and is filled with an aqueous solution of commercially available grinding fluids (2–5% KFL and 1–2% FC 430 for Zn-Al parts; 2–5% ZF 322 for steel parts). The grinding fluid is periodically cleaned by adding a coagulant and centrifuging the sediment. The operating time of one liquid portion in such a system is approximately three weeks for Zn-Al alloy parts and six days for steel parts. After this time, the used fluid is sent for disposal, which involves significant costs for the company. Such wastewater, saturated with pollutants, that can no longer be purified by centrifugation was subjected to the presented procedure.

2.2. Membrane Filtration

To remove suspended and settled solid particles from the examined wastewater, filtration through a bag filter with a pore diameter of 5 µm was first used. The resulting filtrate was the feed to the membrane filtration process.
The membrane experiments were conducted on a laboratory scale using a Sterlitech (Auburn, WA, USA) system. The setup included a membrane module mounted in a hydraulic press, a 19 L conical feed tank, a thermostatic control system, and a high-pressure pump (Figure 2). Polyacrylonitrile flat-sheet membranes (Sterlitech, Auburn, WA, USA) were used, recommended among others for the treatment of wastewater containing an oily phase. The molecular weight cut-off of the membrane was 30 kDa, and the effective surface area was 1.4 × 10⁻2 m2. The filtration was performed using a cross-flow system in a batch configuration. Initial membrane resistance was assessed using deionised water as the feed before ultrafiltration (UF) (Figure 3). The experiments were carried out at an operating pressure of 4 bar, with a constant feed temperature of 25 ± 1 °C. The initial volume of wastewater subjected to membrane filtration was 8 L (two portions of averaged wastewater from Zn-Al alloy and steel, respectively, were tested). The concentrate flow rate ranged between 0.22 and 0.23 m3/h. The permeate was collected in a graduated cylinder for flux measurement and representative samples (n = 3) of both the filtrate and concentrate (Figure 4) were taken after the process for subsequent physicochemical analyses.

2.3. Analytical Methods

Water recovery efficiency in wastewater treatment from the vibro-abrasive machining of Zn-Al alloys and steel parts was assessed using a multiparameter physical and chemical analysis of raw wastewater, feed, retentate, and permeate samples (n = 3). Dry residue was determined at 105 °C with a laboratory moisture analyser (MAC 50/1, Radwag, Radom, Poland), while turbidity was measured using a portable turbidity meter 2100Q IS (Hach Lange, Berlin, Germany). Conductivity changes were investigated using a SevenMulti conductivity meter and an InLab 731 conductivity probe (Mettler Toledo, Columbus, OH, USA). The concentrations of TOC, phosphorus, nitrogen, organic acids, and surfactants, as well as TSS and COD, were determined using a DR 6000 spectrophotometer (Hach Lange, Berlin, Germany). Chemical analyses relied on cuvette tests (Hach Lange, Berlin, Germany, Table 1). TSS was determined using a 25 mL cuvette and measured at a wavelength of 810 nm. The examined wastewater samples were diluted to the required level, if necessary.
The permeate flux was calculated with the following equation:
J A = V A × t
where
  • JA is the permeate flux (at constant temperature and pressure; mL (min × cm2)−1);
  • V is the volume of filtrate (mL);
  • A is the effective area of flat sheet membrane (cm2);
  • t is the sampling time (min).
The rejection coefficient (R) for each parameter was calculated to assess the purification efficiency:
R = 1 − x p x n × 100 %
where
  • R—the rejection coefficient (%);
  • xp and xn—the values of the tested parameter in the permeate and the feed respectively (%, µS·cm−1, NTU or mg L−1, depending on the determined parameter).
This comprehensive analysis allows the assessment of whether the polymeric filtration membranes and low-pressure filtration conditions allow the purification of the wastewater generated during the vibro-abrasive machining of Zn-Al alloy and steel components to a level that will enable their reuse in the original process.

3. Results and Discussion

The characteristics of the wastewater, from which the company could no longer centrifuge the contaminants and which constituted raw wastewater subjected to testing, are presented in Table 2. The wastewater generated after the vibro-abrasive processing of steel elements is characterised by a significantly higher pollutant load. All the tested physicochemical parameters had higher values. The most significant differences occurred for the total phosphorus content, where 92.2-fold higher amounts were determined for steel wastewater than for Zn-Al wastewater.
The use of only bag filtration (pore diameter 5 µm) resulted in a reduction of turbidity and suspended solids concentration by 93.5% and 94.8%, respectively, in the case of Zn-Al alloy parts, and by 97.5% and 98.4% in the case of steel parts, respectively (Figure 5). The remaining parameters tested were reduced by 0.9–96.7%. For several parameters tested (total nitrogen content, conductivity, total phosphorus content, anionic surfactants concentration, COD), a significantly greater (from 2.1 to 4.5-fold) decline was noted in Zn-Al wastewater than in steel wastewater. The most significant difference (50.5-fold) was observed in the case of organic acid content reduction (65.5% for Zn-Al wastewater and 1.3% for steel wastewater). Despite achieving significant reduction rates for most of the tested physicochemical parameters after filtration through the bag filter, neither wastewater met the conditions for reuse in vibro-abrasive processing or discharge to the sewer system.
Considering the need to minimise the industry’s energy consumption and, consequently, reduce the process’s operating costs, the investigation focused on determining the filtration efficiency for a transmembrane pressure of 4 bar. The use of low pressure is a compromise between filtration flow rate—directly proportional to the transmembrane pressure—and energy consumption. However, it should be remembered that conducting the process under the conditions of low transmembrane pressure promotes exposure to undesirable fouling. The deposition of a filter cake can be minimised by increasing the pressure and, thus, the feed flow and shear forces acting on the membrane surface. The accumulated filter cake can be removed by cyclic chemical membrane cleaning (clean-in-place, CIP) or counter-current flushing. In the context of this research, no attempt was made to remove fouling by washing the membrane due to the scale of the process, batch configuration, and the equipment used (the lack of additional installation elements for the backflush).
Due to the lack of publications on the subject, our work (at the current stage) was focused on confirming the possibility of treating wastewater from vibro-abrasive surface processing of ferrous and non-ferrous metals in the low-pressure ultrafiltration process using polymer membranes, as well as examining the effectiveness of this process.
The efficiency of the membrane filtration process was tested by determining the permeate flux through the membrane (Figure 6). A higher (approx. twice as high) filtration flux was achieved for the Zn-Al alloy wastewater. The main reason for this difference may be the higher pollutant load (Table 2) of the steel wastewater. Higher filtration fluxes corresponded to higher retention rates for some of the components and physicochemical parameters tested (Figure 7).
The rejection coefficient values indicate a similar degree of treatment efficiency for Zn-Al and steel wastewater. The data shows that the UF step completely removed total suspended solids (TSS) in both cases. This is significant because TSS is a critical parameter that directly impacts the clarity and quality of wastewater. The high values of rejection coefficients (above 80%) of turbidity, COD, TOC and anionic surfactants, total phosphorus, and non-ionic surfactants were achieved. The high removal efficiency for these compounds reflects the potential of UF technology to significantly reduce the organic load, improving water quality for reuse or safe disposal. The efficient removal of phosphorus via UF is a positive outcome, especially when dealing with wastewater from industrial sources, which often contains high levels of this component. Despite the overall high performance of the UF process, the study also reveals that some parameters were removed to a lesser extent. The wastewaters were purified of nitrogen compounds to only a minor extent (below 20% in both streams, Zn-Al and steel). It is necessary to extend the scope of the study to include long-term cyclic processes and to check whether the concentration of nitrogen compounds will increase with each subsequent cycle. At the current research stage, the nitrogen concentrations determined in the permeate are entirely acceptable to the company for reuse in vibro-abrasive processing.
Surfactants are often difficult to remove using conventional purification methods. Therefore, their high removal efficiency by UF indicates the suitability of this method for complex wastewater treatment. The retention factors for surfactants obtained are proportional to the determined concentration of these groups of components. In the Zn-Al alloy wastewater, 314 mg L−1 of anionic, 119 mg L−1 of non-ionic and 0.51 mg L−1 of cationic surfactants were measured, which corresponded to the retention factors of 96.9%, 82.3%, and 48.9%, respectively, after a two-stage purification (Table 3). For the steel wastewater, these concentrations were 1085 mg L−1 of anionic, 377 mg L−1 of non-ionic, and 5.04 mg L−1 of cationic surfactants, which corresponded to the following retention factors: 97.4%, 73.2%, and 39.5%. Such a relationship is caused by the aggregation of surfactant particles (forming micelles) to sizes exceeding the membrane pore size (>30 kDa) after reaching the critical micelle concentration.
Surfactants present in wastewater also affect the structure of the polymer (the membrane, as well as the bag filter), influencing their transport and separation properties. These properties may even improve at low surfactant concentrations due to hydrophilisation of the membrane surface covered with surfactant monomers. With increasing surfactant concentration, the dominant phenomenon is membrane fouling (blocking pores and forming a gel layer on its surface). The surface and pores of the membrane can also be blocked by other wastewater contaminants, including other organic compounds, as well as nitrogen and phosphorus compounds. The consequence of fouling is a reduction in the size of the membrane pores and, thus, a more significant transmembrane pressure and retention of contaminants. The cross-flow system of the filtrate in relation to the feed used reduces the negative effects of concentration polarisation and membrane fouling. However, at the next stage of our investigation, it is necessary to select the conditions for membrane regeneration.
The absolute values of the examined physicochemical parameters for the permeates obtained after ultrafiltration, as well as the total retention factors calculated for the entire two-stage purification process, are presented in Table 3. The results indicate that the degrees of purification of both the wastewaters tested using the two-stage method proposed in this work are comparable. The greatest differences in the total retention factors occurred in the case of total nitrogen content and cationic surfactants. In both cases, these components’ slightly larger amounts (2.6-fold and 1.8-fold, respectively) were removed from the Zn-Al wastewater. However, due to significant differences in the pollutant load in the wastewater received from the company, the absolute values of the physicochemical parameters are higher for the steel wastewater.
The research results indicate that the use of a polymer ultrafiltration membrane and low transmembrane pressure (4 bar), preceded by filtration through a bag filter (pore diameter 5 um), is sufficient to remove all suspension and reduce turbidity by >99.9% for both the tested wastewaters. These parameters are crucial to the possibility of reusing the recovered water in the primary vibro-abrasive treatment process. Due to its nature, fine solid particles suspended in the grinding fluid solution (surfactants) constitute the main contaminant of the tested wastewater. Complete removal of suspension was a necessary condition specified by the company for the possibility of introducing the recovered water into a closed circuit in the vibro-abrasive treatment process. Achieving this goal allowed the proposal of a concept for closing the water circuit in the vibroabrasive machining of Zn-Al alloy and steel (Figure 8). The cleaning process produces a retentate stream, which is characterised by a significantly smaller volume in relation to the feed. Therefore, its disposal requires significantly lower financial outlays. The presented research can be continued to extend the retentate value chain, e.g., to develop a method for recovering metals from it or to increase water recovery by subjecting the retentate to for example, flotation and re-ultrafiltration processes. The proposed method of purifying the tested wastewater may become a significant element in implementing the circular economy concept into the metal and non-metal surface treatment industries. The simple technological structure (pre-treatment and single-stage filtration) and low-pressure conditions (relatively low investment and operating costs) indicate the high implementation potential of this method. The lack of the need to use high-pressure processes not only brings direct economic and environmental benefits but also reduces the amount of added surfactants, which were only partially removed in the low-pressure process. Saving raw materials is another element of the circular economy, enabled by implementing the proposed solution to industrial production.

4. Conclusions

This study investigated the treatment of industrial wastewater generated during vibro-abrasive machining processes in the metal and non-ferrous metal industries, with particular emphasis on steel and Zn-Al alloys. These processes produce wastewater with high concentrations of suspended solids, organic compounds and other pollutants, which results in significant disposal costs.
A two-stage purification process was developed and tested to address these challenges: prefiltration through a 5 µm bag filter and subsequent low-pressure ultrafiltration using flat polyacrylonitrile membranes with a molecular weight cut-off of 30 kDa. The process reduced turbidity, COD, TOC, anionic surfactants, total phosphorus and non-ionic surfactants by 80% to almost 100%. A complete removal of total suspended solids was achieved, allowing for the potential reuse of the recovered water in vibro-abrasive processes.
This method shows a significant potential for broader applications. By adapting the treatment process to different industrial sectors, such as other metalworking or automotive industries, similar benefits in terms of wastewater reuse and cost reduction can be achieved. Moreover, taking into account the significant advantage of membrane techniques, which is the scalability of the process by multiplying the number of membrane modules, as well as the relatively simple technological structure and operation at low pressure, this approach can be scaled to more extensive industrial operations, providing an economically viable and environmentally friendly solution for wastewater treatment. The proposed method complies with the principles of the circular economy by reducing water consumption, enabling the recycling of grinding fluids, and rationalising energy consumption (low-pressure conditions). Its implementation, however, still requires further research involving a grander scale of the process (minimum quarter-technical), the implementation of long-term studies, and the selection of conditions for periodic membrane cleaning (fouling removal).
It should be emphasised that the literature offers no reports on the possibilities of treating wastewater from the vibratory machining of ferrous and non-ferrous materials and recycling the reclaimed water. This study, therefore, makes a significant contribution in providing a framework for sustainable water reuse that can bring significant benefits to metalworking and related industries, contributing to global efforts to protect water resources and the natural environment.

Author Contributions

Conceptualization, J.J. and P.R.; methodology, J.J. and P.R.; software, J.J. and P.R.; validation, J.J. and P.R.; formal analysis, J.J. and P.R.; investigation, J.J. and P.R.; resources, J.J. and P.R.; data curation, J.J. and P.R.; writing—original draft preparation, J.J. and P.R.; writing—review and editing, J.J. and P.R.; visualisation, J.J. and P.R.; supervision, J.J. and P.R.; project administration, J.J. and P.R.; funding acquisition, J.J. and P.R. All authors have read and agreed to the published version of the manuscript.

Funding

This research was financed by the Ministry of Science and Higher Education of Poland under the 2025 subvention for Łukasiewicz Research Network—Institute for Sustainable Technologies.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. The installation diagram for vibro-abrasive machining of steel and Zn-Al alloy parts.
Figure 1. The installation diagram for vibro-abrasive machining of steel and Zn-Al alloy parts.
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Figure 2. A schematic diagram of the laboratory membrane filtration system used.
Figure 2. A schematic diagram of the laboratory membrane filtration system used.
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Figure 3. The characteristics of the membrane used for the treatment of tested wastewater.
Figure 3. The characteristics of the membrane used for the treatment of tested wastewater.
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Figure 4. A photo of samples (Zn-Al alloy; wastewater after filtration through a 5 µm filter bag is the feed).
Figure 4. A photo of samples (Zn-Al alloy; wastewater after filtration through a 5 µm filter bag is the feed).
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Figure 5. The reduction (%) of the tested physicochemical parameters after filtration on a bag filter (pore diameter 5 µm).
Figure 5. The reduction (%) of the tested physicochemical parameters after filtration on a bag filter (pore diameter 5 µm).
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Figure 6. Changes in the permeate flux during the membrane filtration process of (a) Zn-Al alloy wastewater and (b) steel wastewater.
Figure 6. Changes in the permeate flux during the membrane filtration process of (a) Zn-Al alloy wastewater and (b) steel wastewater.
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Figure 7. A comparison of rejection coefficients for the determined physicochemical parameters of (a,b) Zn-Al wastewater and (c,d) steel wastewater obtained in the UF process (relative to the feed).
Figure 7. A comparison of rejection coefficients for the determined physicochemical parameters of (a,b) Zn-Al wastewater and (c,d) steel wastewater obtained in the UF process (relative to the feed).
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Figure 8. Schematic diagram of the concept of closing the water circuit in the vibro-abrasive treatment of Zn-Al alloy and steel.
Figure 8. Schematic diagram of the concept of closing the water circuit in the vibro-abrasive treatment of Zn-Al alloy and steel.
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Table 1. The characteristics of the methods used to determine total phosphorus, total nitrogen, chemical oxygen demand, total organic carbon, surfactants (anionic, cationic and non-ionic), and organic acids.
Table 1. The characteristics of the methods used to determine total phosphorus, total nitrogen, chemical oxygen demand, total organic carbon, surfactants (anionic, cationic and non-ionic), and organic acids.
Parameter/AnalyteNumber of Cuvette TestApplied Method
Number of NormName of Norm/Method
∑P (as PO43−)LCK 350
LCK 348		EN ISO 6878 [43]Determination of phosphorus. Ammonium molybdate spectrometric method
∑NLCK 338EN ISO 11905-1 [44]Determination of nitrogen. Method using oxidative digestion with peroxodisulphate
CODLCK 514
LCK 914		ISO 6060 [45]Determination of chemical oxygen demand. Dichromate spectrometric method.
TOCLCK 387EN 1484 [46]Guidelines for the determination of total organic carbon (TOC) and dissolved organic carbon (DOC)
Anionic SurfactantsLCK 432ISO 7875-1 [47]Determination of anionic surfactants. Methylene Blue (MBA) method.
Cationic surfactantsLCK 331N/ADetermination of cationic surfactants. Bromophenol Blue method.
Nonionic SurfactantsLCK 333N/ADetermination of nonionic surfactants. TBPE (tetrabromophenolphthalein ethyl ester) method.
Organic AcidsLCK 365N/ADetermination of organic acids. Esterification spectrometric method
Table 2. The physicochemical parameters of the examined wastewater were collected directly from the production line.
Table 2. The physicochemical parameters of the examined wastewater were collected directly from the production line.
Parameter/AnalyteUnitDetermined Value/Concentration
(±SD; n = 3)
Zn-Al WastewaterSteel Wastewater
Dry residue %0.70 ± 0.02 3.50 ± 0.05
ConductivitymS·cm−12.610 ± 0.0025.940 ± 0.002
TurbidityNTU2640 ± 885098 ± 2
TSSg·L−12.510 ± 0.0014.950 ± 0.004
CODg·L−110.7 ± 0.143.0 ± 0.2
TOCg·L−113.6 ± 0.437.9 ± 0.3
Organic acidsg·L−11.06 ± 0.012.53 ± 0.03
∑P (as PO43−)mg·L−15.8 ± 0.1535.0 ± 6.0
∑Nmg·L−191 ± 11160 ± 27
Anionic surfactantsmg·L−1314 ± 141085 ± 25
Cationic surfactantsmg·L−10.51 ± 0.015.04 ± 0.14
Non-ionic surfactantsmg·L−1119 ± 2377 ± 8
Table 3. The physicochemical properties of permeates obtained after UF and the total reduction of the tested physicochemical parameters after two-stage filtration (bag filter and UF).
Table 3. The physicochemical properties of permeates obtained after UF and the total reduction of the tested physicochemical parameters after two-stage filtration (bag filter and UF).
Parameter/AnalyteUnitZn-Al WastewaterSteel Wastewater
Determined Value in Permeate
(±SD; n = 3)		Total Rejection CoefficientDetermined Value in Permeate
(±SD; n = 3)		Total Rejection Coefficient
Dry residue%0.18 ± 0.0173.8%0.98 ± 0.0272.1%
ConductivityµS·cm−11663 ± 136.2%4352 ± 226.8%
TurbidityNTU0.25 ± 0.09100% (99.99%)4.30 ± 0.1699.9%
TSSmg·L−10 ± 0100%0 ± 0100%
CODmg·L−1355 ± 996.7%2170 ± 5295.0%
TOCmg·L−126.7 ± 1.699.8%163.0 ± 4.699.6%
Organic acidsmg·L−1143 ± 386.5%1017 ± 4059.8%
∑P (as PO43−)mg·L−10.12 ± 0.0198.0%105.5 ± 1.580.3%
∑Nmg·L−149.8 ± 1.045.0%960.0 ± 9.217.3%
Anionic surfactantsmg·L−110.5 ± 0.996.6%22.2 ± 2.998.0%
Cationic surfactantsmg·L−10.16 ± 0.0169.0%3.12 ± 0.1038.0%
Non-ionic surfactantsmg·L−118.4 ± 1.184.6%88.3 ± 2.276.6%
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Janiszewska, J.; Rajewska, P. Development of a Concept for Closing the Water Cycle in the Surface Treatment of Ferrous and Non-Ferrous Metals. Sustainability 2025, 17, 2212. https://doi.org/10.3390/su17052212

AMA Style

Janiszewska J, Rajewska P. Development of a Concept for Closing the Water Cycle in the Surface Treatment of Ferrous and Non-Ferrous Metals. Sustainability. 2025; 17(5):2212. https://doi.org/10.3390/su17052212

Chicago/Turabian Style

Janiszewska, Jolanta, and Paulina Rajewska. 2025. "Development of a Concept for Closing the Water Cycle in the Surface Treatment of Ferrous and Non-Ferrous Metals" Sustainability 17, no. 5: 2212. https://doi.org/10.3390/su17052212

APA Style

Janiszewska, J., & Rajewska, P. (2025). Development of a Concept for Closing the Water Cycle in the Surface Treatment of Ferrous and Non-Ferrous Metals. Sustainability, 17(5), 2212. https://doi.org/10.3390/su17052212

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