Recent Advances in Organic Pollutant Removal Technologies for High-Salinity Wastewater

Abstract

Industrial processes like farming, food processing, petroleum refinery, and leather manufacturing produce a lot of high-salinity wastewater. This wastewater presents serious environmental risks, such as soil degradation, eutrophication, and water salinization, if it is released without adequate treatment. The sources and features of high-salinity wastewater are outlined in this review, along with the main methods for removing organic pollutants, such as physicochemical, biological, and combined treatment approaches. Membrane separation, coagulation–flocculation, and advanced oxidation processes are the primary physicochemical techniques. Anaerobic and aerobic technologies are the two categories into which biological treatments fall. Physicochemical–biological combinations and the fusion of several physicochemical techniques are examples of integrated technologies. In order to achieve sustainable and effective treatment and resource recovery of high-salinity wastewater, this review compares the effectiveness and drawbacks of each method and recommends that future research concentrate on the development of salt-tolerant catalysts, anti-fouling membrane materials, halophilic microbial consortia, and optimized hybrid treatment systems.

1. Introduction

One of the main sources of pollution affecting regional water ecological security and sustainable use of water resources is the increasing discharge of high-salt wastewater brought on by the acceleration of industrialization and urbanization. Numerous industries, including petrochemical, pharmaceutical, printing and dyeing, food processing, tanning, electronic plating, and others, produce large amounts of high-salt wastewater. One of its common characteristics is the high concentration of soluble inorganic salts (e.g., SO₄²⁻, Ca²⁺, Mg²⁺, NaCl, etc.), as well as highly toxic, complex, and hard-to-degrade organic pollutants like emulsified fats and oils, surfactants, pigments, residual medications, and aromatic hydrocarbons. Wastewater is categorized as high-salt wastewater when the mass fraction of inorganic salts reaches 1–3.5% [1]. Its osmotic pressure is significantly higher than that of typical water bodies, which can coerce aquatic organisms and upset the ecosystem’s equilibrium. Furthermore, if released into the environment untreated, some high-salt wastewater will cause major environmental issues, like water mineralization, eutrophication, and soil salinization, due to its high chemical oxygen demand (COD, which can reach thousands of mg/L), significant pH fluctuations, and toxicity.

Conventional wastewater treatment methods face significant challenges in high-salt environments [2]. Since the high osmotic pressure brought on by a high salt concentration can result in microbial cell dehydration, impaired plasma membrane function, and decreased efficiency of enzymatic reactions—all of which impact the rate at which organic matter biodegrades—biological treatment, a popular low-consumption and environmentally friendly method, is frequently severely hindered in high-salt wastewater. High levels of salt also disrupt the structure of microbial populations, which leads to an imbalance in the functional division of labor and a decline in diversity. Although high-salt organic pollutants can be effectively removed using physicochemical techniques like membrane separation, redox, and electrochemical treatment, these methods have drawbacks, such as high energy consumption, significant membrane contamination, high operating costs, or difficulty handling high load fluctuations. The instability and operational complexity of the treatment system are further increased by the fact that metal ions, oil and grease, and protein pollutants frequently accompany high-salt systems. Therefore, it is imperative to create a thorough treatment pathway that has cost-controllable benefits, good salt tolerance, and adaptability to high organic loads.

Research on organic pollutant removal technology for high-salt wastewater has been expanding both domestically and internationally in recent years. Guo et al. systematically reviewed the latest advances in high-salinity wastewater treatment technologies, covering the applications and challenges of physicochemical, biological, and integrated approaches, thereby laying an important foundation in this field [3]. Membrane technology (such as reverse osmosis, nanofiltration, and electrodialysis) has been gradually applied to high-salt water reuse and concentration processes in terms of physicochemical methods; however, the anti-pollution performance of membrane materials and cleaning and regeneration issues still need to be resolved; coagulation–flocculation is a crucial pretreatment method that is frequently used to remove oil and grease, particulate matter, and part of soluble organics, which can greatly enhance the effect of the next unit of treatment; advanced oxidation, due to its strong oxidizing and mineralizing capacity, has become an efficient way to treat pollutants that are hard to break down. Aerobic granular sludge (AGS), purple photosynthetic bacteria, anaerobic granular sludge, and other organisms have demonstrated good salt tolerance and degradation performance, and biotechnology is continuously progressing in the screening and domestication of salt-tolerant bacterial strains. It is important to note that combination processes—such as coagulation + membrane, ozone + hypoxia, Fenton + MBR, electrochemical + biological methods, and other combined pathways—are increasingly being used to overcome the limitations of current technologies. By complementing one another, these processes can increase treatment stability and efficiency.

The removal of organic pollutants from high-salt wastewater is the main topic of this paper. It also thoroughly examines the common sources of high-salt wastewater, water quality features, and treatment challenges. It also discusses the current state-of-the-art physicochemical, biological, and combined technologies, their mechanisms, engineering practices, and research advancements. Finally, it compares the range of applications of each technology, its benefits and drawbacks, and the major variables influencing the analysis. We suggest the future research focus and application direction of high-efficiency catalysts, anti-pollution membrane materials, salt-resistant bacterial strains, intelligent coupling processes, etc., in conjunction with the current development trend of “resourcefulness, reduction, and harmlessness” of high-saline wastewater treatment in order to supply the theoretical underpinnings and technological tools necessary to support the industrialization and systemic integration of high-saline wastewater treatment technology. Effective catalysts, anti-pollution membrane materials, salt-resistant bacterial species, and intelligent coupling processes are the main areas of research and application.

2. Sources and Characteristics of High-Salinity Wastewater

High-salt wastewater comes from a variety of sources, and its composition varies greatly across industries, with notable variations in salt content and pollutant types (see

Table 1. Characteristics of typical high-salt wastewater from different industries.

Wastewater Type	Total Dissolved Solids (TDS)	COD Range (mg/L)	pH Range	Key Organic Pollutants
Textile	2767–11,745 mg/L	500–2000	8–10	Dyes, additives, surfactants
Tannery	1000–3500 mg/L	2000–4000	7–9	Proteins, lipids, hair and skin fragments
Pharmaceutical	18,521–52,477 mg/L	2000–6000	5–9	Drug residues, organic solvents
Petrochemical	6629–63,423 mg/L	1000–4000	6–9	Oils, benzenes
Circulating Cooling Water	>35,000 mg/L	500–1000	>9	Corrosion inhibitors, biocides
Food Processing (Seafood)	10,000–25,000 mg/L	3000–10,000	6–8	Proteins, fats, residual organic acids
Dyeing and Printing	5000–15,000 mg/L	1000–3000	9–11	Reactive dyes, surfactants
Fertilizer/Pesticide Industry	20,000–40,000 mg/L	2000–5000	4–8	Organic pesticide intermediates, phenols, acids

). The primary sources at the moment are as follows: (1) Industrial discharge of high-salt wastewater, including wastewater from tanneries, textiles, petrochemicals, pharmaceuticals, etc. The primary components of various saline wastewaters, their salt content, and their emissions vary as a result of various industrial processes. Textile wastewater typically contains dyestuffs and inorganic metal compounds [4], which are characterized by high chromaticity, a high concentration of organics that are difficult to degrade, high pH, high salinity, high turbidity, etc. Its salt content ranges from 2767 to 11,745 mg/L and releases 100–200 L of textile wastewater for every kilogram of textile produced [5]. Tanneries must use inorganic salts to stop animal leather from decomposing; the type of salt used depends on the leather and tanning process. Tannery wastewater has a salinity of 1000–3500 mg/L and typically contains fur and animal shredded materials [6]. An average of 35–40 tons of tannery wastewater are produced for every ton of leather produced. Pharmaceutical wastewater, which makes up 3% of all industrial wastewater discharges in China, contains high concentrations of organic pollutants that are difficult to degrade, waste solvents, inorganic salts, and various types of residual drugs. The salt contents of pharmaceutical wastewater range from 18,521 to 52,477 mg/L. The salt content of petrochemical wastewater is 6629~63,423 mg/L, and the United States generates 2.23–2.86 billion cubic meters of petrochemical wastewater annually. The salt is derived from minerals and metal ions released with the extraction water, typically containing Al³⁺ and Fe³⁺ [7]. (2) Wastewater released following the use of seawater, such as industrial cooling water that has been recycled. High salinity, high hardness, and high alkalinity are characteristics of industrial circulating cooling water that can readily cause equipment scaling and corrosion [8]. This kind of wastewater also contains organic pollutants like microbiocides, corrosion inhibitors, and scale inhibitors, which make treatment even more challenging. (3) Wastewater from the food processing industry, particularly that related to the production of sauces, pickled goods, and aquatic products. This is because a lot of salt is used in soaking, pickling, rinsing, and other processes, which results in wastewater that has a lot of salts, oils, and proteins, fluctuates a lot in pollutant concentrations, and degrades poorly biochemically. “High salt concentration, heavy organic load, water quality changes” are the common characteristics of the three types of high-salt wastewater mentioned above, though they differ greatly from one another. The optimization of the current high-salt wastewater treatment process is still a hot topic in research because high-salt wastewater poses a serious environmental hazard, has a large discharge, and has an unsatisfactory organic matter disposal effect. It is also challenging to meet discharge standards for organic pollutants in wastewater.

In summary, the compound pollution characteristics of “high salt + high COD + toxicity + large fluctuation” make high-salt wastewater a significant threat to ecosystem security and water reuse. High-salt environments must be combined with various sources of wastewater quality characteristics, differentiated identification, and classification treatment because they not only cause osmotic stress to microbial cells, inhibit enzyme activity, and destroy the metabolic balance, but they also interfere with coagulation, flocculation, and membrane separation processes, affecting particle destabilization and membrane separation efficiency. Optimizing the current high-salt wastewater treatment process is still a research hotspot because the removal of organic matter from wastewater currently has an unsatisfactory effect and it is challenging to meet discharge standards for organic characteristic pollutants in wastewater.

3. Physicochemical Methods

3.1. Coagulation–Flocculation Technology

A popular pretreatment method for removing suspended solids, colloids, organics, and certain heavy metal ions from different kinds of water is coagulation–flocculation technology (Figure 1). The method is crucial for treating high-salt wastewater, even though it cannot considerably lower the salt content of wastewater on its own. Effective removal of COD, turbidity, and oil and grease from wastewater using coagulation–flocculation can help to reduce the organic loading of the subsequent biological or physicochemical treatment system, as well as to improve the overall treatment stability and efficiency. This is because colloidal particles in wastewater are more stable in high-salt environments due to electrostatic shielding, which makes direct biological treatment more challenging.

In actuality, the coagulation conditions optimization strategy is determined by the compositional features of various kinds of hypersaline wastewater. As an illustration, Mseddi et al. [9] carried out a systematic coagulation–flocculation test on wastewater from fish processing (Total dissolved solids of approximately 60 g/L; COD up to 4000 mg/L). The results demonstrated that a sensible selection of coagulant combinations could remove roughly 60% of the COD and 84% of the turbidity in the pretreatment stage, which greatly enhanced the wastewater’s biochemistry. This procedure not only lessens the organic load on the biological system that follows, but it also lowers the possibility of contamination in the membrane separation unit, highlighting the crucial role that coagulation plays in improving the effectiveness of the cascade technology that follows. Furthermore, the treatment of high-salt emulsified oil wastewater has demonstrated the great adaptability of coagulation–flocculation. Younker et al. [10] discovered that the combination of FeCl₃ and dissolved-air flotation (DAF) was effective in eliminating dispersed oil pollutants by lowering their concentration from 100 mg/L to less than the discharge standard (29 mg/L) in their investigation of offshore oil and gas extraction wastewater treatment. This study also demonstrated that pH levels have a significant impact on the coagulation effect, with pH values between 6 and 8 being beneficial for destabilizing colloidal particles and promoting floc formation, particularly in neutral to weakly alkaline conditions where it is simpler to produce large, densely structured flocs.

Engineering case studies have further demonstrated the potential of coagulation processes in the pretreatment of high-salinity wastewater. For instance, an industrial high-salinity organic wastewater treatment project employing a composite Polyaluminium chloride-polyacrylamide (PAC-PAM) coagulant combined with flotation achieved turbidity and COD removal efficiencies of 95.33% and approximately 30%, respectively, under optimized conditions, while reducing treatment time by 50%, significantly enhancing the operational stability of subsequent treatment units [11]. Another study proposed an integrated system combining simultaneous coagulation–ozonation pretreatment with electrodialysis (SC-ED), which not only improved organic matter degradation efficiency (total organic carbon removal of 32.84%) but also removed 92.97% of salts during electrodialysis, effectively mitigating membrane fouling [12]. Moreover, an enhanced Fe(II) coagulation technology based on green rust (GR) generation has demonstrated a COD removal efficiency of 53.5% in both pilot and full-scale trials treating dyeing wastewater, outperforming conventional methods and exhibiting strong pollutant adaptability and cost advantages in treating high-salinity complex wastewater [13]. These studies indicate that coagulation technology in high-salinity wastewater treatment has evolved from a single physicochemical process to a multi-unit coupled and functionally enhanced integrated system, which not only improves treatment efficiency but also lays a technical foundation for the large-scale and stable operation of complex wastewater treatment.

In conclusion, coagulation–flocculation technology plays a part in treating high-salt organic wastewater by creating favorable process conditions for further treatment in addition to the initial removal of pollutants. This technology can efficiently lower the concentration of suspended particles, oil and grease, and some organic matter by optimizing the coagulant type and operating parameters. It can also relieve the biological system’s toxicity pressure and lower the risk of membrane contamination, which is a crucial component in the development of multi-unit coupled treatment processes. Nevertheless, this approach’s capacity to eliminate dissolved organic matter is restricted (e.g., aromatic compounds), and as a result, deep purification of hard-to-degrade contaminants still requires synergistic integration with advanced oxidation or biotechnology.

3.2. Membrane Technology

Membrane technology is frequently used to treat high-salinity organic wastewater. Ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), and electrodialysis (ED) are among the commonly used membrane technologies. The performance of the various membrane separation technologies in high-salinity environments varies significantly, and

Table 2. Application of different membrane separation technologies in high-salt wastewater treatment.

Wastewater Type	Wastewater Characteristics	Membrane Technology	Removal Performance	Reference
Fresh Olive Processing Wastewater	pH = 4.75, COD = 7250 mg/L, Cl− = 41,120 mg/L, Conductivity = 80.7 mS/cm	UF (Ultrafiltration)	COD removal rate of 66.0%	[15]
Textile Wastewater	Salinity = 60 g/L, Pressure = 600 kPa, T = 25 °C, CFV = 0.2 m/s	NF (Nanofiltration)	Organic removal up to 99.8%	[16]
Biologically Treated Textile WW	pH = 6.5–6.8, COD = 96–108 mg/L, Conductivity = 1850–2050 μs/cm	RO (Reverse Osmosis)	COD removal rate of 94.5%	[17]
Aniline Wastewater	Acid conc. = 1.25 mol/L, Base conc. = 0.85 mol/L	ED (Electrodialysis, Bipolar)	COD removal rate of 93.3%	[18]
Stable Saline Emulsion	Oil particle size = 300 nm, RO flux = 18.42 L/(m2·h)	RO (PAMAM-TMC Modified Membrane)	Oil and NaCl rejection rates above 98% and 88%, respectively	[19]
Coal Chemical Industrial Wastewater	NaCl up to 300 mM (TDS ≈ 18,000 mg/L)	RO + NF	Desalination rate > 70% for both NaCl and MgSO4	[20]

summarizes their capabilities, areas of application, and typical uses. In general, particles, microorganisms, and macromolecular organic matter in water are significantly retained by ultrafiltration and nanofiltration, despite their inability to remove inorganic ions. This makes them appropriate for the front-end pretreatment of wastewater with high salinity. Nevertheless, various forms of highly concentrated salt ions found in high-salinity wastewater can drastically alter the membrane’s characteristics during the membrane filtration process, hastening membrane contamination. High salinity makes the driving force for solutes to cross the membrane larger, and more solutes pass through the membrane into the permeate, resulting in a lower desalination rate [14]. This is because, as the salinity of the influent water increases, the osmotic pressure on the concentrate side increases, which lowers the effective filtration pressure. As a result, the implementation of appropriate pretreatment for high-salinity wastewater not only helps to delay the membrane contamination process, but also helps to improve the overall separation efficiency.

To keep dissolved macromolecular solutes in solution, ultrafiltration is a sieve pore separation technique that uses a differential pressure driving force and a molecular-level separation effect. When treating high-salt wastewater, ultrafiltration can be a crucial pretreatment to reduce organic loading and color. Garcia et al. [15] treated high-salt fresh olive processing wastewater using a novel light-modified ultrafiltration membrane. To enhance the removal of organics and preserve the maximum amount of total phenols, the ultrafiltration membranes were UV-modified in the presence of two hydrophilic substances (polyethylene glycol and alumina). A pH of 4.75, COD of 7250 mg/L, Cl concentration of 41,120 mg/L, and conductivity of 80.7 mS/cm were the raw water quality parameters. A barrel filter with a pore size of 60 μm was used to pre-filter the samples in order to prevent serious contamination of the UF membranes. At a staggered flow velocity (CFV) = 1.39 m/s, T = 25 °C, and pressure difference between the membrane’s interior and exterior ((∆P) = 200 kPa), 66.0% COD removal was accomplished. Applying the ultrafiltration process as a clean technology for the pretreatment of high-salt organic wastewater is a wise decision because it effectively reduces the color and organic loads in high-salt wastewater while allowing for the recovery of significant byproducts from the pretreatment effluent.

Although it cannot remove inorganic ions from water, nanofiltration combines the benefits of high solute retention and low energy consumption with a membrane pore size (0.5–2.0 nm) and operating pressure between reverse osmosis and ultrafiltration. In order to address the issues of either excessively high salt retention or excessively low dye retention at high salinity, Zhou et al. [16] used nanovesicles functionalized with non-reactive polymers and positively charged molecules to modify the pore size and surface charge density of thin-film composite (TFC) nanofiltration membranes through interfacial polymerization, which successfully increased the pore size and decreased the surface charge density. When dyes and salts were separated from textile wastewater using the aforementioned nanofiltration membranes, the raw water’s salinity was 60 g/L, and organic matter was removed up to 99.8% at P = 600 kPa, CFV = 0.2 m/s, and T = 25 ± 0.5 °C. It is evident that organics and salt can be successfully separated by nanofiltration membranes modified with nanovesicles. At high salinity, the modified membranes demonstrated greater separation stability than the majority of documented non-composite membranes.

One of the most important technologies for deep treatment and reusing highly salinized wastewater is reverse osmosis (RO) technology, which is a pressure-driven membrane separation process with a very high desalination capacity. Liu et al. [17] treated wastewater from textiles using reverse osmosis. The conductivity was 1850–2050 μs/cm, the COD was 96–108 mg/L, and the pH was between 6.5 and 6.8. At an initial flux of 60.0 L/m²∙h and CFV = 1.0 m/s, the COD removal rate could reach up to 9%, and it could even reach 94.5%. Reverse osmosis membranes are more effective at retaining inorganic salts than nanofiltration membranes, and the water produced can satisfy the reuse requirements of the textile and electronics industries. It should be mentioned, though, that the reverse osmosis membrane has a high sensitivity to salt and organic pollution in feed water, so it is imperative to support effective pretreatment measures.

Bipolar membrane electrodialysis (BMED) technology shows clear benefits in the resource-oriented treatment of high-salinity wastewater. This method removes organic matter and recovers acids and bases in a synergistic manner by using ion migration that is powered by an external electric field. Lv et al. used BMED to treat wastewater with a high salinity and aniline content. The feed solution had an acid concentration of 1–25 mol/L and a base concentration of 0–85 mol/L. The removal efficiency of chemical oxygen demand (COD) was 93.3% when operating at 6–8 V and 6–10 mA/cm² of current density. Furthermore, new reverse osmosis (RO) membranes have shown promise in recent research for efficiently separating wastewater that contains salt and oil. Pei et al. [19] used hyperbranched poly(amidoamine) (PAMAM) and trimesoyl chloride (TMC) to perform interfacial polymerization on a polysulfone ultrafiltration membrane surface, creating a novel kind of RO membrane. The membrane demonstrated a water flux of 18.42 L/(m²·h) and continued to function continuously for 24 h when used to treat a stable saline emulsion with oil droplets that were about 300 nm in size. It achieved rejection rates of over 98% for oil and 88% for NaCl. When compared to commercial membranes, the flux decline was only about 5%, suggesting better anti-fouling performance.

To enhance the treatment efficiency and system stability of high-salinity wastewater, membrane separation processes have increasingly evolved towards integrated systems in recent years, forming hybrid configurations centered on reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), electrodialysis (ED), and emerging technologies such as forward osmosis (FO) and membrane distillation (MD). These systems optimize the selectivity, energy consumption, and fouling tolerance of different membrane processes to achieve multi-objective treatment, including organic matter retention, desalination, concentration, and resource recovery [21]. For example, UF-NF or UF-RO configurations are commonly applied for combined particulate pretreatment and deep desalination of high-salinity dyeing wastewater, whereas FO-MD systems utilize low-pressure driving forces and vapor pressure gradients to realize efficient separation and energy recovery [22]. Suleman et al. [23] reported an FO-MD integrated system treating complex industrial wastewater and leachate, where FO concentrates the feed solution followed by MD purification, resulting in improved desalination efficiency and effective mitigation of pollutant permeation, thereby achieving high salinity removal with low energy consumption. Additionally, the combination of ED and NF has been applied for synergistic acid/base recovery and organic matter concentration, significantly enhancing resource recovery. Nevertheless, membrane integration systems still face challenges such as membrane fouling, inter-membrane coordination, and complex operational control. Future development should focus on synergistic membrane material design, modular system integration, and intelligent control to realize more efficient, low-energy, and sustainable treatment of high-salinity wastewater.

3.3. Advanced Oxidation Techniques

The advanced oxidation method is an effective wastewater treatment technology because it has the benefits of high oxidation efficiency and no secondary pollution. Catalytic ozonation, Fenton, electrochemical, photocatalytic, and other advanced oxidation processes use the potent oxidative property of OH- to break down organic compounds based on the kind and circumstances of OH production during the reaction process, which have been extensively employed to break down organic compounds that traditional methods are unable to destroy (

Table 3. Application of different advanced oxidation systems in high-salt wastewater treatment.

Technology Type	Organic Removal Efficiency	Actual Wastewater Type	Salinity (mg/L)	Catalyst/Core Conditions	Reference
Catalytic Ozonation (O3/Cat)	COD removal rate: 83.9%	High-salinity organic wastewater (simulated)	9110	Fe-Bi@γ-Al2O3, pH = 11, O3 flow rate = 0.2 L/min	[26]
Photo-Fenton Process	SMZ removal >80%	High-salinity agricultural wastewater	5000	Fe(III)/EDDS = 1:1, pH = 7, solar irradiation	[27]
Electrochemical Oxidation	COD removal rate: 93.7%	High-salinity petrochemical wastewater	1490	Ni-Ce/OMC/GAC particle electrode, Cl− = 6000 mg/L	[28]
Photocatalytic Oxidation	BPF removal >78%	BPF-containing brine (NaCl = 500 mM)	29,200	Porphyrin Zr-MOF (PCN-223), visible light system	[29]
Ozone Oxidation	COD removal rate ≈ 70%	High-salinity pharmaceutical wastewater	17,900	Iron-based monolithic catalytic filler	[30]
Fenton Oxidation	COD removal rate >85%	High-salinity seafood processing wastewater	25,000	Heterogeneous Fenton bed	[31]

). Different types of advanced oxidation processes (AOPs), such as catalytic ozonation, Fenton reactions, electrochemical oxidation, and photocatalysis, each offer unique advantages in treating high-salinity wastewater. They can provide higher treatment efficiencies and broader applicability, especially under saline conditions. However, translating AOPs from laboratory-scale applications in model waters to practical treatment of real high-salinity wastewater remains challenging [24]. Firstly, the high salt concentrations in such wastewater significantly affect catalyst activity, resulting in reduced reaction efficiencies [25]. For example, during Fenton and catalytic ozonation processes, salt ions may inhibit catalyst catalytic activity, thereby lowering treatment performance. Secondly, the generation and transfer of hydroxyl radicals (·OH) are suppressed in high-salinity environments, potentially slowing the oxidation reaction rates, which imposes limitations on treatment efficiency in practical applications.

For uses like disinfection and the breakdown of harmful organic pollutants, ozone oxidation has been used extensively in water treatment. However, the low ozone utilization efficiency, poor mineralization performance for organic contaminants, and the possibility of toxic disinfection by-products during the ozonation process limit its practical application. Furthermore, ozone oxidation by itself shows excellent selectivity for particular contaminants. These limitations can be partially overcome by catalytic ozonation. Catalysts facilitate the breakdown of O₃ during catalytic ozonation, producing reactive oxygen species (ROS) like hydroxyl radicals that accelerate the breakdown and mineralization of organic pollutants without producing secondary pollution. Spray coating, co-precipitation, and impregnation are common techniques for preparing catalysts [32]. Guo et al. [26] used the impregnation method to create a salt-tolerant Fe-Bi@γ-Al₂O₃ catalyst, successfully loading the active components Fe and Bi onto γ-Al₂O₃ as Fe₂O₃ and Bi₂O₃ crystals. The COD removal efficiency reached 83.9% when operating conditions were COD = 206 mg/L, TN = 4.84–7.80 mg/L, TP = 0.37–3.12 mg/L, an ozone flow rate of 0.2 L/min, a catalyst dosage of 10%, and pH = 11. Thus, the effectiveness of catalytic ozonation depends on the choice and preparation of the catalyst. In high-salinity environments, the presence of salts inhibits catalyst activity and the ozone utilization efficiency, thereby limiting the application of catalytic ozonation in treating high-salinity wastewater. Several studies have focused on addressing these challenges and improving the efficiency of catalytic ozonation. For example, fluidized bed catalytic ozonation systems enhance gas–liquid–solid contact, improving reaction kinetics and overcoming salt interference in high-salinity wastewater, thereby offering new avenues for treatment [33]. Catalyst selection and preparation are critical for catalytic ozonation technology. During prolonged operation, catalysts may become deactivated due to the formation of dense carbonaceous layers on their surfaces. Calcination regeneration can remove these carbon deposits and restore catalyst reactivity, enabling the long-term application of catalytic ozonation [34]. Furthermore, optimizing catalyst design, adjusting reaction parameters such as the pH and ozone dosage, and integrating catalytic ozonation with other advanced oxidation processes represent potential strategies to enhance treatment efficiency [35]. Future research should focus on developing salt-tolerant catalysts and non-radical catalytic systems, alongside customized catalyst design, to improve the performance of catalytic ozonation for high-salinity wastewater treatment.

The basis of Fenton oxidation is the production of highly oxidative hydroxyl radicals (•OH) by the reaction of hydrogen peroxide (H₂O₂) and iron ions (Fe²⁺) in an acidic environment. The majority of refractory organic pollutants can be quickly and non-selectively broken down by these radicals into CO₂ and H₂O. The technique has quick reaction kinetics and is easy to use. However, due to the influence of multiple factors on the optimal ratio of hydrogen peroxide to ferrous sulfate and the operation being limited to a narrow pH range, the Fenton process faces certain challenges in practical applications. Particularly in large-scale operations, catalyst recovery is difficult, and the generation of substantial amounts of ferrous sludge poses challenges for industrial implementation. To address these issues, researchers have proposed various strategies to enhance the industrial applicability of Fenton oxidation. For example, Mejri et al. [27] treated saline agricultural wastewater with 50 μg/L of imidacloprid, pymetrozine, and sulfamethoxazole using the photo-Fenton process. Even though the initial reaction rate was light-limited, more than 80% of sulfamethoxazole and pymetrozine, and more than 60% of imidacloprid were removed in 15 min at a molar ratio of Fe(III)/EDDS = 1:1 at pH = 7 and neutral pH conditions. Moreover, the photo-Fenton oxidation process demonstrates significant advantages in treating textile wastewater, particularly in color removal and COD degradation. By enhancing the reaction through irradiation, the photo-Fenton process can achieve higher removal efficiencies within shorter reaction times while also facilitating salt recovery [36]. In some studies, the integration of Fenton oxidation with membrane filtration has proven highly feasible in practical operations. For example, combining Fenton oxidation with reverse osmosis (RO) not only achieves efficient COD removal but also recovers the treated saline water for industrial reuse [37]. Nevertheless, the Fenton oxidation process still faces numerous challenges in industrial applications, especially regarding catalyst stability and sludge accumulation during the reaction. To overcome these issues, future research should focus on optimizing catalyst design, particularly developing heterogeneous catalysts that exhibit excellent efficiency and high stability over a broader pH range [38].

One popular electrochemical water treatment method is electrochemical oxidation (EO), in which organic contaminants are either directly oxidized at the anode or indirectly broken down by hydroxyl radicals generated on the electrode surface. Due to its eco-friendly, effective, and user-friendly features, EO has gained more and more attention since the turn of the twenty-first century. Zhang et al. developed a Ni₀ [19]/Ce_0.2/granular activated carbon (GAC)/ordered mesoporous carbon (OMC) particle electrode with a 1:1 Ni/Ce ratio. The dispersion of metal species and catalytic activity were improved by the synergistic effects of Ni, Ce, and OMC. The Ni₀/Ce₀/Ce enabled quick oxygen storage and release through Ce³⁺/Ce⁴⁺ transitions, which helped to generate •OH through O₃ activation, while the ₂/OMC structure encouraged the reduction of O₂ to H₂O₂. The COD removal efficiency reached 93.7% under ideal conditions, which included COD = 770–800 mg/L, pH = 7–8, Cl⁻ concentration = 6000 mg/L, electrode spacing = 2.5 cm, current density = 27.6 mA/cm², particle electrode dosage = 5 g, and reaction time = 60 min. Saline wastewater’s high conductivity eliminates the need for extra electrolytes, preventing secondary pollution and enabling the removal of deep organic pollutants using EO. Electrochemical oxidation technology has been successfully applied at an industrial scale in various sectors. For example, a coal chemical plant employing an electrochemical flow oxidation system achieved COD and color removal efficiencies ranging from 55.3% to 93.6% and over 90%, respectively, at current densities between 10 and 20 mA/cm² [39]. Additionally, Ti/SnO₂ + Sb₂O₃/β-PbO₂ electrodes exhibit excellent electrocatalytic activity under high COD and salinity conditions, with a long service life of up to two years [40]. These findings underscore the critical importance of selecting appropriate electrode materials for high-salinity wastewater treatment. Optimizing electrode material selection and reaction parameters, such as current density and reaction time, can enhance treatment performance while reducing energy consumption and material costs, thereby facilitating large-scale applications. Nevertheless, electrode durability, fouling accumulation during operation, and the long-term stability and efficiency of the system remain key bottlenecks limiting widespread adoption [41]. In certain industrial applications, such as petrochemical and steel industries, energy efficiency issues of electrochemical oxidation systems are particularly prominent, necessitating further pilot-scale testing and process optimization for large-scale engineering deployment.

In photocatalytic degradation, semiconductor catalysts are activated by high-energy UV or visible light (e.g., G/TiO₂), which, when photon energy reaches or surpasses the bandgap energy, produce reactive oxygen species. Because of their high oxidative reactivity, these ROS can completely mineralize organic pollutants or break them down into smaller, less harmful molecules. Thus, photocatalysis has attracted a lot of interest due to its potential for degrading organic pollutants in wastewater. Wang et al. [20] employed a visible-light-driven system to degrade bisphenol F (BPF) in saline water (BPF = 15 mg/L and NaCl = 500 mM) using a zirconium-based porphyrinic metal–organic framework (MOF), PCN-223. The PCN-223/visible-light system demonstrated exceptional degradation performance while demonstrating robust resistance to interference from coexisting anions and organic matter. At a MOF dosage of 0–2 g/L, the catalyst demonstrated good stability in saline conditions, removing over 78% of the BPF after eight cycles. Additionally, the photocatalytic system maintained its efficacy in five distinct water matrices and over a broad pH range. Coexisting anions improved photoinduced electron transfer in visible light and provided a novel method for the removal of organic pollutants in complex saline environments by promoting ionic bonding and increasing electron conductivity. Beyond research on catalytic materials, various advanced photocatalytic systems have been continuously proposed. For instance, a ZnO/ZnS/Ag ternary nanocomposite achieved efficient degradation of methylene blue through bandgap engineering and suppression of charge carrier recombination [42]. In the context of green and low-carbon technologies, the P25/TiO₂ coupled with a sunlight-driven UV/P25/O₂ system demonstrated effective degradation of ethylene glycol wastewater under natural light, exhibiting excellent onsite adaptability and catalyst stability [43]. With the increasing challenge of high-salinity wastewater discharge, photocatalytic oxidation technology is gradually transitioning from laboratory studies to engineering applications. Pilot-scale treatment of high-salinity textile wastewater using a UV/O₃ high-pressure synergistic system has been reported, where ultraviolet irradiation combined with pressurization enhanced ozone mass transfer rates and free radical generation, significantly improving COD and color removal efficiencies [44]. Overall, current photocatalytic technologies are evolving towards higher selectivity, strong salt tolerance, and engineering feasibility. Despite challenges such as energy consumption, reactor design, and catalyst longevity, their industrial potential for high-salinity organic wastewater treatment is progressively emerging.

In recent years, research efforts have increasingly focused on enhancing the applicability of advanced oxidation processes (AOPs) in high-salinity wastewater treatment. For example, the development of salt-tolerant catalysts and membrane materials, as well as the optimization of operating conditions to improve the ·OH generation efficiency, have emerged as prominent research directions. In addition, integrating AOPs with other wastewater treatment technologies, such as membrane separation, has shown considerable promise. Such hybrid systems can complement each other and overcome the limitations of single technologies in high-salinity environments, thereby achieving more efficient treatment performance. Nevertheless, the application of AOPs in high-salinity wastewater treatment still faces challenges related to high energy consumption and operational costs, which hinder large-scale deployment. Therefore, future studies should focus on reducing operating costs, improving the economic feasibility of the technology, and achieving a balance between treatment efficiency and sustainability.

4. Biological Methods

4.1. Aerobic Biotechnology

Because of its dense structure, good sedimentation, and salt tolerance of dominant bacterial groups, aerobic granular sludge (AGS) has gradually shown its potential for use in high-salt wastewater treatment, despite the fact that high-salt environments present a challenge to conventional aerobic systems (Figure 2). Its capabilities include biosorption, nitrogen and phosphorus removal, and organic matter degradation, all of which offer a viable route for the effective biological treatment of high-salt wastewater. Corsino et al. [45] looked into the viability of treating canned fish wastewater by simultaneously nitrifying and denitrifying aerobic granular sludge. Both processes were successful when the mass concentration of NaCl was 50 g/L and the effluent’s total nitrogen content was less than 10 mg/L. The nitrification system failed when the salinity exceeded 50 g NaCl/L. The organic carbon removal efficiencies were up to 90% under all of these conditions, which is consistent with the previous periods. The sludge retention time was 45–50 days. In contrast, organic removal was influenced by the organic loading rate (OLR) rather than salinity. The influent flow rate and OLR were cut in half when the reaction cycle length was doubled to distinguish between the effects of high salinity and OLR. More than 95% of particulate organic matter could be eliminated by aerobic granular sludge, and both COD and BOD removal rates were higher than 90%.

AGS is a smaller footprint than the conventional activated sludge process and is denser and more compact than aerobic granular sludge (AGS). Hou et al. [46] analyzed the performance and microbial characterization of AGS in different salinities and alternate salinities. In addition to improving the COD removal efficiency, alternating salinity also produced a high concentration of particulate biomass with good settling ability, because the alternating salinity improved the salt tolerance of the sludge and the growth of salt-tolerant bacterial strains. In Jiang et al., the granular sludge method was used for pharmaceutical wastewater treatment, and after a 90-day incubation, both high-salt synthetic wastewater and dilute pharmaceutical wastewater could form granular sludge and could achieve an effluent bCOD (biodegradable chemical oxygen demand) <1 mgL⁻¹, with an average TN removal of 70.3%, but high-salt pharmaceutical wastewater could not form granular sludge because of the high concentration of inhibitory organisms that inhibited the secretion of EPS. Zhao et al. [47] SBR-treated saline wastewater at 2.0 wt% salinity. The SBR system inoculated with activated sludge removed up to 95% of COD, BOD, ammonia nitrogen, and total phosphorus; the dominant genus was Candida spp. Candidate_division_TM7, which provided a model and theoretical basis for the treatment of high-salt synthetic wastewater with granular sludge. In Woolard et al. [48], synthetic high-salt organic wastewater inoculated with salt-tolerant bacteria was treated with the SBBR process, with the influent COD, BOD, ammonia nitrogen, and total phosphorus removed. Under an influent COD of 290 mg-L⁻¹, salinity of 150 g L⁻¹, and hydraulic retention time of 24 h, the COD removal rate was 99.0%, and the results showed that salt-tolerant bacteria were important in the treatment of synthetic high-salt organic wastewater. The results showed that salt-tolerant bacteria were better suited to treat sewage than adapted bacteria.

In practical engineering applications, significant progress has been made in treating the large volumes of high-salinity, oil-containing wastewater generated during offshore oil production using a combined aerobic biological treatment and ceramic membrane filtration process, namely, the flat-sheet ceramic membrane bioreactor (C–MBR) system [49]. Pilot-scale results showed that, when treating high-salinity oily wastewater with a sequential batch reactor (SBR) coupled with C–MBR, COD and ammonia nitrogen removal efficiencies reached 93% and 98.9%, respectively. Microbial community analysis indicated that the symbiosis of Marinobacterium, Marinobacter, and Nitrosomonas likely contributed positively to the nitrogen removal efficiency. Moreover, the process demonstrated notable advantages in reducing membrane fouling and enhancing treatment efficiency, offering an economically viable solution with a unit treatment cost of only USD 0.21/m³. In another case, a pilot-scale biological wastewater treatment system developed for high-salinity wastewater in a chemical industrial park also achieved promising results [50]. Under a salinity of 3%, COD, ammonia nitrogen, and total phosphorus removal efficiencies were 72.15%, 95.40%, and 64.32%, respectively. The adaptation and performance of halotolerant bacteria provided strong support for high-salinity wastewater treatment. However, when salinity exceeded 3%, the nitrification process was significantly inhibited, accompanied by a decline in the nitrification gene abundance, indicating the impact of salinity on system stability. By optimizing the hydrolysis tank design and cultivating halotolerant microbial consortia, the system was able to effectively mitigate salinity inhibition within a certain range.

Overall, although aerobic biotechnology holds great promise for the treatment of high-salinity wastewater, challenges remain in terms of treatment capacity, system stability, and cost-effectiveness in practical engineering applications. The development of more efficient aerobic granular sludge systems, the cultivation of highly salt-tolerant microbial consortia, and the optimization of membrane technology and reactor design will be key directions for enhancing treatment performance in the future. By integrating advanced microbial and membrane technologies, it is possible to significantly improve treatment efficiency, reduce energy consumption, and promote the widespread industrial application of these processes.

4.2. Anaerobic Biotechnology

Traditional anaerobic treatment of organic wastewater with high salinity is ineffective due to the inhibitory effect of salt, and high concentrations of Na+ or chloride are generally thought to be one of the most important factors inhibiting anaerobic wastewater treatment because they strongly inhibit methane production when the concentration of Na⁺ exceeds 10 g·L⁻¹. As a result, many researchers have been able to cultivate microorganisms and improve their salt tolerance by gradually increasing the wastewater’s salinity (

Table 4. Anaerobic technology for the treatment of saline organic wastewater.

Wastewater Type	Process Type	Salinity (g/L)	COD Removal Rate (%)	Reference
Canned Fish Wastewater	SBR + Anaerobic Granular Sludge (AGS)	20	80–90	[52]
Tannery Wastewater	Upflow Anaerobic Sludge Bed (UASB)	71	78	[53]
Phenol-containing Wastewater	UASB	≤26	47	[54]
Synthetic High-Salinity Wastewater	Halanaerobium lacusrosei Reactor	30	84	[55]
Heparin Sodium Pharmaceutical Wastewater	Spiral Symmetry Stream Anaerobic Bioreactor (SSSAB)	35.7	82	[56]
High-Salinity Domestic Wastewater	Purple Phototrophic Bacteria (under seawater conditions)	Seawater	86	[57]
Simulated High-Salinity Wastewater	UASB + Magnetite Conductive Material	23.4	78.2	[58]

). Because anaerobic processes use less energy without aeration and can generate energy in the form of fuel alcohols or methane, they have better application prospects than aerobic processes [51].

Carrera et al. [52] examined how aerobic granular sludge (AGS) developed and remained stable in two sequencing batch reactors (SBRs) that treated wastewater from fish canning. Their results demonstrated that adding an anaerobic feeding/reaction phase greatly increased the organic matter removal efficiency (80–90%), which was previously only 75–85% under fully aerobic conditions. Lefebvre et al. [53], after 307 days of acclimation, treated tannery wastewater using an upflow anaerobic sludge blanket (UASB) reactor and obtained a COD removal efficiency of 78%. The system functioned with total dissolved solids (TDS) concentration of 71 g·L⁻¹ and an organic loading rate (OLR) of 0.5 kg COD·m⁻³·d⁻¹. Even though anaerobic treatment shows a lot of promise in treating high-strength wastewater, one significant drawback is the lengthy acclimation times. In the same way, Sierra et al. [54] used a UASB reactor to treat phenolic wastewater. Microbial communities in UASB reactors are extremely volatile and sensitive to salinity fluctuations, as evidenced by the system’s collapse after 379 days of operation when the salinity surpassed 26 g Na⁺·L⁻¹. This demonstrates how unreliable UASB systems are when used on saline household wastewater.

Several anaerobic bioreactor-based synergistic approaches have been investigated to get around these restrictions. Kapdan et al. [55] used the halophilic bacterium Halanaerobium lacusrosei to treat wastewater that had a COD of 1900 mg·L⁻¹ and a salinity of 30 g·L⁻¹. A 94% COD removal efficiency was attained at a hydraulic retention time (HRT) of 19 h. COD removal stayed high at 84% even after the COD rose to about 3400 mg·L⁻¹ and HRT was prolonged to 30 h. Song et al. [56] used a spiral symmetry stream anaerobic bioreactor (SSSAB) to treat pharmaceutical wastewater containing heparin sodium. This bioreactor demonstrated exceptional resistance to organic loading shocks. The system demonstrated its suitability for high-salinity organic wastewater with an 82% COD removal efficiency under conditions of COD = 8731 mg·L⁻¹ and salinity = 3.57 wt%. Hulsen et al. [57] used purple phototrophic bacteria with a biomass yield of 0–8 g COD/g COD fed to treat saline household wastewater. This demonstrated purple phototrophs’ ability to quickly adapt to saline environments, including those with seawater and NaCl. By adding magnetite to a UASB reactor, which encouraged direct interspecies electron transfer (DIET), Chen et al. [58] improved the anaerobic digestion of saline organic wastewater, increasing COD removal by 15–2% and methane production by 47–4%. These results show that conductive materials have a promising role in enhancing the anaerobic treatment of wastewater with high salinity.

In recent years, efforts to advance engineering-scale applications have continued to progress. For example, anaerobic membrane distillation bioreactors (AnMDBRs) have demonstrated high COD removal efficiencies (>97%) and substantial methane production (267 mL/g COD at influent salinity ≤1.0%) in the treatment of saline organic wastewater, while simultaneously achieving seawater desalination and energy recovery [59]. In the oil and gas industry, laboratory-scale systems for high-salinity produced water have achieved 93% COD and 89% TOC (Total Organic Carbon) removal, along with methane recovery of 33.9 mmol/g carbon, indicating considerable potential for resource recovery in arid regions [60]. Long-term operational data also show that the combination of UASB systems with subsequent aerobic treatment can achieve stable COD removal of 93.05% and color removal of 86.41% over 12 years of industrial textile wastewater treatment, meeting discharge standards and demonstrating the feasibility of combining anaerobic and other processes for the large-scale treatment of high-salinity wastewater [61].

In summary, anaerobic biological technologies for high-salinity organic wastewater treatment have evolved diversely from conventional UASB systems to novel integrated reactors such as anaerobic membrane distillation bioreactors (AnMDBRs). These technologies have demonstrated COD removal efficiencies of 70–97% and effective methane recovery in pilot- and engineering-scale applications involving seafood processing wastewater, produced water from oil extraction, and textile wastewater. Their advantages include low energy consumption, energy recovery, and high tolerance to organic loading. However, challenges remain in terms of long salt adaptation periods, microbial stability, and by-product management. Future research should focus on constructing robust halotolerant microbial consortia, strengthening reactor processes, enabling synergistic desalination and resource recovery, and developing comprehensive multi-source high-salinity wastewater databases and operational control models.

5. Combined Processes

It is frequently challenging to use physical–chemical or biological technologies alone to achieve the best treatment effect because of the high-salt environment’s inhibitory effect. In order to overcome the treatment bottleneck and accomplish deep purification, it is now crucial to combine the water quality features of high-salt wastewater and organically combine various processes (Figure 3). Organic pollutants frequently exhibit low biochemistry in high-salinity environments, which restricts the use of biological techniques. Catalytic ozonation as a pretreatment for biological methods has emerged as a successful tactic to get around this bottleneck. In catalytic ozonation, the reaction pathways of O₃ can be classified into two main types. First, O₃ can directly oxidize organic pollutants on the catalyst surface, degrading them into small molecules or ultimately mineralizing them to CO₂. Second, O₃ can be decomposed in the presence of the catalyst to generate highly reactive species such as ·OH, which possess stronger oxidation potential and can further attack organic pollutants, thereby achieving deep degradation. An et al. [30] treated high-salinity pharmaceutical wastewater using a combined catalytic ozonation–anoxic process and examined the impact of catalytic ozonation on the wastewater’s biochemistry. It was shown to significantly improve the biochemistry by reducing COD from 163.5 to 118.2 mg/L on average, removing NH₄⁺-N by an average of 70.3%, and increasing BOD₅/COD from 0.065 to 0.165. After 588 days of reactor operation, it was discovered that the catalytic ozonation–anoxia process significantly decreased effluent COD and NH₄⁺-N concentrations. The catalytic ozonation process is well suited to the anoxic process because it can break down large molecular pollutants into smaller ones like acetic and oxalic acids, which are readily broken down by microorganisms. In addition to promoting the use of catalytic ozonation–anoxic processes in high-salinity practical wastewater treatment, the enormous potential of iron-based monolithic catalyst packing was fully demonstrated.

The deep integration of advanced oxidation and high-efficiency membrane separation technology has also drawn the attention of researchers based on improved biochemistry. Li et al. [31] developed an efficient photosynthetic bacteria (PSB)–GO (two-dimensional graphene oxide)/PVDF (polyvinylidene fluoride) membrane photobioreactor (MPBR) coupled with a heterogeneous Fenton-fluidized-bed process, and successfully applied it to the treatment of refractory high-salinity seafood processing wastewater. The flux recovery of GO/PVDF membranes was as high as 94% because of the notable decrease in hydrophobic proteins in extracellular polymers (EPSs), which also demonstrated improved hydrophilicity and a 4–4-fold higher permeability when compared to PVDF membranes. With an average biological yield of up to 105 mg/L-d and an average removal of COD and NH₄⁺N of about 95 and 98%, respectively, the GO/PVDF membrane MPBR offers a more appealing option for the deep treatment of high-salinity practical seafood processing wastewater, confirming the potential of the MBR process in conjunction with new materials for the efficient treatment and beneficial reuse of high-salinity organic wastewater that is difficult to degrade. Police et al. [62] combined a membrane bioreactor (MBR) with an ozonation process to achieve chemical–biological degradation of naphthenic acids in a high-salinity environment. In this system, the ozonation unit was installed in the recirculating water of the bioreactor, with the recirculation flow rate set at three times the influent flow rate. Comparison of the combined system with a single ozonation step after the MBR revealed that the introduction of ozone had no adverse effects on the biological or filtration processes. To investigate the effect of catalytic ozonation on the biodegradability of high-salinity wastewater, Guo et al. [63] integrated catalytic ozonation with a biological contact oxidation process and subjected the bioreactor to shock loading with high-salinity wastewater. The influent BOD₅/COD (B/C) ratio was 0.12; after two cycles (20 days) of treatment with wastewater containing 30% high salinity, four parallel reactors achieved COD removal efficiencies of 78%, 84%, 86%, and 91%, respectively. When the reaction time was 40 min, the B/C value increased to 0.91, indicating a significant improvement in wastewater biodegradability. Scanning electron microscopy (SEM) observations revealed abundant fungi and filamentous microorganisms on the sludge surface. Under high-salinity shock loading, the microbial community underwent substantial changes, with Proteobacteria and Bacteroidetes becoming the dominant phyla, confirming that catalytic ozonation effectively promoted microbial community shifts and enhanced wastewater biodegradability.

Physicochemical–physicochemical combined processes can also significantly enhance the removal performance of high-salinity organic wastewater. Because of the intricacy of saline matrices, these systems frequently need dilution or desalination procedures beforehand to improve the removal of organic pollutants. Chai et al. [64] created a system that combined electro-Fenton and electro-adsorption, and under ideal circumstances (applied voltage = 1 point 5 V, initial pH = 4, electrode spacing = 1 cm, flow rate = 40 mL/min, and H₂O₂ concentration = 50 mM) it performed remarkably well. The removal efficiencies for COD, total nitrogen (TN), and salinity after actual wastewater was treated using the integrated system were 96.5%, 98.2%, and 46.2%, respectively. According to mechanistic analysis, electro-adsorption mainly helped to remove salt, but the combined effects of Fenton oxidation, electron transfer, and active chlorine reactions improved the breakdown of organic matter. With an estimated operating cost of just USD 1.18/m³, the system showed excellent economic feasibility and provided a low-cost, high-efficiency solution for organic wastewater with high salinity. Zhang et al. [65] went on to create a hybrid electrochemical system that used Ni₀ to combine electrocatalytic oxidation and ozonation. A Ce₀. ₂/ordered mesoporous carbon (OMC) composite electrode was used to treat wastewater with amicarbazone that is high in salinity. The removal rate of amicarbazone reached 99.7% with a mineralization efficiency of 75.7% when the following parameters were met: pH = 2, ozone flow rate = 0.1 L/min, current = 10 mA, and particle electrode dosage of 5 g per 150 mL. After several cycles, the composite electrode maintained its high pollutant removal efficiency, indicating strong operational stability and potential for real-world uses.

In addition, coupling thermally driven brine desalination technologies with membrane separation or advanced oxidation processes offers a feasible pathway for the deep treatment of high-salinity organic wastewater. Embedding photocatalytic functionality into solar interfacial evaporators enables high evaporation rates (≈1.95 kg·m⁻²·h⁻¹) under solar irradiation while simultaneously degrading organic contaminants, making it suitable for off-grid or solar-rich scenarios [66]. In membrane distillation (MD) systems, the incorporation of thermally activated H₂O₂ as a pre-oxidation step can modify pollutant–membrane interactions (via the extended Derjaguin–Landau–Verwey–Overbeek, XDLVO, mechanism), thereby mitigating membrane fouling, enhancing flux, and improving ion rejection, with promising scalability [67]. Overall, coupling thermally driven brine desalination with membrane separation or advanced oxidation processes can synergistically achieve efficient desalination and organic pollutant degradation. However, large-scale implementation still requires addressing challenges such as energy integration, salt crystallization control, and by-product suppression, which may be overcome through pilot-scale demonstrations and modular system design to accelerate practical deployment.

Building on the aforementioned unit process combinations, various pilot- and engineering-scale integrated systems have recently demonstrated their feasibility and advantages in treating high-salinity wastewater. For example, electrocoagulation–microfiltration (EC–MF) pretreatment coupled with membrane distillation (MD) has efficiently removed suspended solids (TSS) and scaling potential (>95%) from produced water (PW) desalination, achieving a 99% salt rejection and a maximum flux of 66 L·m⁻²·h⁻¹. The vapor heat consumption was as low as 2.7 GOR, with potential for further energy reduction via waste heat integration [68]. An array air microbubble plasma system combined with a persulfate/ferrous catalyst achieved complete removal of dye organics under 300 L and 3% NaCl conditions, with an energy efficiency of 18.36 g·kWh⁻¹, demonstrating scalability for advanced oxidation in high-salinity wastewater treatment [69]. In biological treatment, a continuous-flow biofilm photobioreactor based on the halotolerant Dunaliella salina coupled with a membrane bioreactor (MBR) maintained stable algal–bacterial communities and achieved COD, total nitrogen (TN), and phosphate (PO₄³⁻-P) removal efficiencies of 84.3%, 81.6%, and 91.0%, respectively, during 40 days of continuous operation, showing promise for simultaneous nitrogen and phosphorus removal from high-salinity wastewater [70]. These engineering cases indicate that the organic integration of physicochemical, oxidative, and biological processes can overcome performance bottlenecks of individual technologies in high-salinity environments, while achieving a balance between stability, energy consumption, and cost-effectiveness, thus providing a solid technical foundation for the large-scale, advanced treatment of high-salinity wastewater.

6. Conclusions

Because of its high osmotic pressure, toxicity, and complex composition, high-salt organic wastewater significantly reduces the stability and efficiency of conventional treatment methods. The current state of the art in organic removal technologies for high-salt wastewater is systematically reviewed in this paper, along with the development and use of physicochemical, biological, and combined processes. Membrane technology uses less energy than other physicochemical techniques, but it has drawbacks like membrane pollution, which makes it a promising option for treating high-salt, oily wastewater. The organic load in water can be decreased by using coagulation–flocculation technology as a pretreatment step. The benefits of advanced oxidation technology, which include low energy consumption, low cost, easy operation, high oxidation efficiency, strong mineralization effect, and no secondary pollution, have made it a popular physical–chemical technology direction. Biotechnology is environmentally benign and conserves resources. Because it does not need aeration and generates energy in the form of methane and other compounds, anaerobic biotechnology holds greater promise than aerobic biotechnology. The interactions between various target pollutant types, salts, and particular pollutants in activated sludge, as well as the fact that it is sensitive to variables like pH and temperature, require further study. By combining any two technologies, combination treatment technology can partially mitigate the shortcomings of each process when applied separately. High-salt wastewater combination technology will become the primary treatment method with the implementation of the requirements of complete zero discharge of wastewater. Therefore, it is advised that, in accordance with the characteristics of wastewater generated by various industries, a highly efficient and energy-saving combination of processes be explored in order to improve the efficiency of the treatment of organic matter in high-salt wastewater. Although various technologies have demonstrated good performance under specific conditions, they generally face limitations such as high energy consumption, high operational costs, susceptibility to contamination, and sensitivity to fluctuations in water quality. Future research should focus on the design of salt-tolerant catalysts, the development of highly anti-fouling and selective membrane materials, and the construction of efficient and stable salt-tolerant microbial communities. Furthermore, intelligent and modular hybrid systems combining biological, physicochemical, and thermal desalination technologies will become the key path for achieving efficient removal, organic matter energy recovery, and resource recycling. During large-scale application, challenges such as long microbial acclimatization periods, membrane fouling, catalyst deactivation, and high energy consumption need to be addressed through material innovation, process optimization, and energy integration. To promote commercialization, it is essential to enhance system standardization, conduct multi-scale demonstration validation, and integrate life-cycle economic evaluations. Moreover, leveraging policy support and emission standards will be crucial in driving the industrialization process.