A mini-review on arsenic remediation techniques from water and future trends

Arsenic is ubiquitous and the 20th most abundant metalloid in Earth's crust (atomic number 33). Arsenic is a silver-grey brittle crystalline solid atomic weight (74.9 g/mole), specific gravity (5.73 g/cm³), and boiling and melting points of 614 and 817 °C, respectively. Arsenic exists in oxidation states such as −3, 0, +3, +5. It can be found in the environment as arsenious acid, arsenic acid, arsenites, arsenates, methylarsenic acid, dimethylarsinic acid, and arsine. Arsenic is mainly consumed as ions such as arsenic(III) and arsenic(V). It is widely distributed and transported primarily to the environment by water. Consumption of arsenic-contaminated surface or groundwater has severe adverse health effects on human beings. Arsenic-poisoned water from anthropogenic activities results in life-threatening complications, accumulation, and transfer in the food chain. Because of these reasons, researchers referred to arsenic contamination as a catastrophe by several authors (Jadhav et al. 2015; Da Silva et al. 2019; Rahidul Hassan 2023). Chronic arsenic poisoning occurs in Argentina, Bangladesh, Chile, China, India, Mongolia, Mexico, and Taiwan by drinking water.

To resolve the issue and problems associated with arsenic contamination, there should be proper guidelines by the authorities, reliable water sources, and satisfactory treatment technologies. Researchers have implemented various treatment methods to remove arsenic from water. The treatment method should be cost-effective, not add any secondary pollutants to the environment, and be convenient to implement on a large scale.

In this review paper, the authors discussed the advantages, disadvantages, and removal efficiency of conventional treatment approaches. In this study, the authors also discussed advanced arsenic treatment technologies' process parameters and efficiency. Furthermore, the applicability of hybrid technologies has been analyzed.

Arsenic is found in many minerals and ores and is reported to be found in more than 210 minerals. Because of its fast rate of adsorption and dissolution, arsenic is easily dissolved in groundwater and has a relatively low solid-state concentration. Arsenic in groundwater may occur due to the formation of rocks, soils, and sediments from natural or anthropogenic sources (Bhowmick et al. 2013; Ahmed et al. 2022). The major categorization of the sources of arsenic can be done as naturally occurring or geogenic type, anthropogenic or through artificial intrusions, and biogenic type. Arsenic is mainly found in sulphide minerals; two of them are pyrite and arsenopyrite. Arsenopyrite is the mineral that is most frequently discovered in a variety of forms and under anaerobic conditions. Arsenic is also found in sediments whose concentration varies with sediment depth. The eruption of volcanoes and the formation of rocks and soil are the major sources of arsenic pollution in groundwater. The second major source is human intervention type, due to intensive farming, insecticides, fertilizers, industrial activities, adverse mining, and the use of various minerals and ores. Arsenic may come from ores and minerals and can mix into groundwater through different processes. Consumption of fossil fuels as energy resources using wood preservatives, chemicals, and various disinfectants in farming is the major cause of arsenic release in groundwater from human intervention. The release of arsenic takes place in the surrounding by the volatilization of As₄O₆ due to the consumption of fossil fuels as an energy resource, whose condensation occurs in the flue system and then leaches into groundwater storages. The two ionic forms of arsenic, i.e., arsenic(III) and arsenic(V), are oxy ions. Their pH lies between 6.5 and 9.5. The toxins released by arsenic(III) are more hazardous than arsenic(V) and are also challenging to treat. Smelting and other substances containing the element may cause arsenic pollution. Specific bacteria in soils and water also increased the content of arsenic in groundwater (Chakraborti et al. 2010).

• Cancer: skin, lung, bladder, kidney, and liver cancers are just a few of the cancers associated with an elevated risk of development after prolonged exposure to high amounts of arsenic in drinking water. Long-term users of water tainted with arsenic are particularly susceptible.

• Skin lesions: thickness, discolouration, and changes in pigmentation characterizes skin lesions and can be brought on by prolonged exposure to low amounts of arsenic.

• Effect on development: arsenic exposure during pregnancy can harm foetal development, increasing infant mortality, causing low birth weight, and causing developmental problems.

• Cardiovascular diseases: research has revealed a link between long-term exposure to arsenic and an increased risk of cardiovascular conditions such as heart disease and high blood pressure.

• Effects on the nervous system: neurological issues are linked to prolonged exposure to arsenic, such as cognitive decline and a higher chance of neurodevelopmental disorders in children.

• (i)

  Ecosystem disruption: Arsenic pollution in water bodies can cause aquatic ecosystems to become less diverse, have different species compositions, and experience disrupted food chains.

• (ii)

  Contamination of the soil: irrigation uses. When arsenic-contaminated water is used for irrigation, it can build up in the soil and harm agricultural growth. It also has the potential to infiltrate the food chain, causing concerns for human health.

• (iii)

  Arsenic can accumulate biologically in aquatic creatures. It poses a hazard to aquatic and terrestrial wildlife as it ascends the food chain since it may get to higher concentrations of predators.

• (i)

  Economic burden: treating and reducing water supply arsenic poisoning can be expensive for impacted communities, particularly in areas with scarce resources. Effective water treatment technology can be expensive to adopt.

• (ii)

  Access to safe water: arsenic contamination can make it difficult for communities to access safe drinking water, requiring them to rely on contaminated sources or pay high prices for alternate options.

• (iii)

  Affected livelihoods: farmers who rely on arsenic-contaminated water for irrigation may see a decrease in agricultural production, which could lead to financial losses. The socioeconomic difficulties experienced by impacted communities may also be made worse by the potential health effects on farmers.

There are many proposed and ready action plans to solve the water pollution problem due to arsenic. Majorly it can be categorized into two major types.

• Removal of arsenic from water so that it can be available with less or no arsenic quantity,

• Providing access to a different water source that is both sustainable and readily available (Warner et al. 2008; Masood et al. 2022).

However, each technology has pros and cons, particularly in effectiveness and price, determining the treatment technology to be adopted. Table 1 summarizes a comparative study. Other factors responsible for selecting an appropriate arsenic treatment technology include the concentration of arsenic in a particular region, the nation's development stage and solid waste management, and requirements and limitations of the water treatment technology in the area.

Iron hydroxides rapidly adsorbed the arsenic in groundwater used for agricultural purposes and became mainly unavailable to plants. In anaerobic land conditions, such as in flooded rice fields (paddy), arsenic is primarily present as arsenic(III) and is easily identified in the land pore water. It is thus more readily available to plant roots. Arsenite has a low attraction to mineral surfaces, while arsenate adsorbs readily to solid surfaces. Therefore, oxidation/precipitation technology effectively removes arsenic from water.

The main objective of oxidation is to convert the soluble arsenic(III) to arsenic(V), which is then proceeded by precipitation of arsenic(V). The oxidation of arsenic(III) into arsenic(V) is carried out by traditional chemical oxidants such as chlorine (Cl₂), chlorine dioxide (ClO₂), ozone (O₃), hydrogen peroxide (H₂O₂), chloro-amine (NH₂Cl), permanganate (⁠⁠), and ferrate (⁠⁠). Arsenite oxidation was studied with oxygen and air in groundwater samples by Kim & Nriagu (2000). The concentration of dissolved arsenic was 46–62 μg/L in the water sample. The conversion of AS(III) to AS(V) was faster with ozone than with oxygen and air. Khuntia et al. (2014) investigated the oxidation of AS(III) to AS(V) in a pilot plant by using ozone microbubbles. The oxidation rate was high in a wide pH range of 4–9. According to the study, hydroxyl radical was the dominant oxidant in acidic conditions for converting AS(III) to As(V).

Biological treatment methods utilize natural biological reactions involving plants and microorganisms to remove metals from soil and groundwater. Arsenic-polluted groundwater usually contains iron and manganese, so the treatment of arsenic involves some chemical reaction which involves oxidation of Mn(II), Fe (II) and As(III). Arsenite oxidizing bacteria were isolated from activated sludge for biological oxidation of arsenite(III) by Ito et al. (2012). With an initial concentration of 1 mg/L at a hydraulic retention time of 1 h, 92% oxidation efficiency was achieved (Ito et al. 2012). Jana et al. (2015) investigated arsenic(III) oxidation using the blue-green algae Anabaena. The study showed that ∼100% conversion of As(III) to As(V) was obtained for an initial As(III) concentration of 2.5–7.5 mg/L at 30 °C for 72 h of exposure using three g/L of algal dose (Jana et al. 2015).

Before water extraction, the oxygenated water is pumped into the aquifer to reduce the arsenic concentration. Very few works have been reported in this regard. A team of European and Indian scientists has successfully implemented the process, resulting in six operating plants to supply water to the local population (Gupta et al. 2009). The treatment process does not produce any sludge, and the operational cost was 1US$ per day for making 2,000 L of potable water (Gupta et al. 2009). Halem et al. (2010) injected aerated water (∼1 m³) into the aquifer with arsenic concentration of 0.27 μmol L⁻¹ and then removed the arsenic. Brunsting & McBean (2014) performed an air sparging operation and removed around 200 μg/L of arsenic (maximum 79%).

In arsenic removal steps, coagulation and flocculation are among the most common methods ever used. Adding a coagulant, proceeded by making a floc, is a capable way to remove arsenic from groundwater. Coagulants change the surface charge properties of solids to pass the agglomeration or enmeshment of particles into a flocculated precipitate. The final result is floc or bigger particles that are filtered more quickly or settle under the influence of gravity. The destabilization of colloids by neutralizing the forces that keep them apart is the objective of coagulation. Positively charged cationic coagulants provide positive electric charges to decrease the negative charge of the colloids, and as a result, larger particles are produced due to the agglomeration of particles. Flocculation is the action of polymers to create bridges between the larger mass particles or flocs and bind the particles into the large agglomerates. In this process, generally used chemicals are aluminium salts such as aluminium sulphate [Al₂(SO₄)₃.18H₂O] and ferric salts such as ferric chloride [FeCl₃] or ferric sulphate [Fe₂(SO₄)₃.7H₂O] because of their low cost and comparative ease of handling. Ferric(III) sulphate (FS) and polyferric sulphate (PFS) performance as coagulants were compared for arsenic removal by Cui et al. 2015. Novel cellulose and chitosan-based natural biopolymer or coagulant aids with a commercial coagulant (ferric chloride FeCl₃) have been used for the removal of arsenite AS(III) from synthetic tap water (Kumar & Quaff 2019).

Based on these concepts, many researchers achieved the oxidation of arsenic(III) to arsenic(V) via photocatalytic oxidation. The process has been proven as an efficient method for arsenic treatment. The ZrO₂-Fe₃O₄ nanoparticles can efficiently oxidize As(III) to AS(V) under UV light irradiation (Sun et al. 2017; Bashir et al. 2022). It is bifunctional, with both photocatalytic oxidation and adsorption. The maximum adsorption capacity of the material was 133.48 mg/g at pH 7.0. A novel Bi₂WO₆/bentonite composite was prepared to oxidize AS(III) under sunlight (Yang et al. 2019). Photogenerated holes and superoxide radicals were the major contributors to the advanced oxidation process in the above method. A novel approach is described by Wang et al. (2021), where they have reported 2-dimensional (2D)-2D bentonite/g-C₃N₄ composite as photocatalytic material which exhibits high photocatalytic oxidation efficiency in a wide pH range from 3 to 8.5.

In the electrocoagulation (EC) method, direct current is applied, resulting in the dissolution of sacrificial anodes and, consequently, in situ production of coagulants in the solution for the degradation of the target compound (Xu et al. 2018). While the anode generates metal cations, hydrogen gas generation occurs at the cathode surface along with the simultaneous release of hydroxyl radical. The anodic dissolution of Fe or Al electrode leads to the formation of ferric or aluminium ions depending on the pH of the solution, which in turn form monomeric species and polymeric hydroxyl metallic complexes, causing coagulation (Daniel & Prabhakara Rao 2012). Furthermore, iron/aluminium oxides such as hydrous ferric oxide, Al(OH)₃, amorphous Fe(OH)₃, lepidocrocite (γ-FeOOH) goethite (α-FeOOH) are known to strongly adsorb arsenic ions in the bulk solution (Daniel & Prabhakara Rao 2012). Thus, complex surface adsorption and compound formation are responsible for the removal of As by iron species. Precipitation at the As–Fe phase surface can also occur on the surface of aggregated iron hydroxides. Other possible mechanisms include the enmeshment of pollutants in the interior of developing particles and colloidal arsenic oxyanions coagulation or blockage enabled by electrochemistry. Oxidation of AS(III) to AS(V) and, subsequently, its surface complexation with iron hydroxides is suggested as one of the main mechanisms of AS(III) removal by the EC process equipped with a Fe electrode.

The combined effects of anions on arsenic removal using aerated EC reactor with 3D Al electrodes in groundwater were studied by Goren & Kobya (2021). They have reported 98.6% arsenic removal efficiency with 0.411 kWh m⁻³ consumptions of energy and 0.0124 kg m⁻³ electrode. Implementing iron electrocoagulation (FeEC) removes arsenic effectively and simultaneously generates hydroxyl radical (Bandaru et al. 2020). The above-said process was successfully implemented with only 19 s of retention time to remove dissolved arsenic from contaminated groundwater in rural California.

Phytoremediation is a plant-based, environmental-friendly technology for the remediation of arsenic-polluted sites, using plants and microbes to clean up polluted air, soil and water with very little nutrient input (Manoj et al. 2020). This method is environmentally sustainable and easy to manage. Phytoremediation employs plants with extensive root systems, high tolerance, rapid growth with high biomass production, adaptability, and the ability to absorb and remove arsenic from contaminated soil. The phytoremediation method is categorized as phytoextraction, phytostabilization, phytofiltration, and phytovolatilization, according to the metal uptake and transport routes (Dalcorso et al. 2019; Souri et al. 2022).

The metal removal process has various steps, including uptake, translocation, accumulation, distribution, exclusion, and osmoregulation. The metals are extracted and moved towards the roots surface. Further, root uptake of the metals is based on the selectively permeable identification of heavy metals by binding metal ions to the root cells and transporting them to the aerial part (Suman et al. 2018). Plant vascular system with some transporter protein performs metal ion transportation. Direct A of metal from wastewater occurs in the aquatic system, leading to aerial metal accumulation. Lemna valdiviana was used by De Souza et al. (2019) which was effective under pH conditions between 6.3 and 7.0, phosphorus (P-PO₄) concentration of 0.0488 mmol L⁻¹, and nitrogen in the form of 7.9 mmol L⁻¹ nitrate. Under the above-mentioned condition, the plants showed 82% removal of arsenic from aqueous media and could accumulate 1,190 mg kg⁻¹ As (in dry weight) from the aqueous media and reduce 82% of its initial concentration.

Due to its low cost, great efficiency, and ease of usage, the adsorption process is seen to be one of the most promising methods (Ahmad et al. 2023; Franco et al. 2023a, 2023b; Georgin et al. 2023; Manzar et al. 2023). Recently, several researchers have concentrated on developing novel materials based on alumina, activated carbon, iron oxides, zeolites, clays, etc., on adsorbing arsenic from water (Ahmaruzzaman 2022; Jain 2022; Aljohani et al. 2023). A zeolite-reduced graphene oxide (ZrGO)-based composite was synthesized to remove arsenic from water with a maximum adsorption capacity of 49.23 μg/g with an initial arsenic concentration of 100 μg/L (Soni & Shukla 2019; Jain 2022; Aljohani et al. 2023). Halloysite-CeO_x (x = 1.5–2.0) was used by Song et al. (2020) for the adsorption of arsenic with an adsorption efficiency of 91.4% even after three generation cycles. The synergistic and antagonistic effect of haematite + Mn oxide and ferrihydrite + Mn oxide on arsenic was investigated by Zheng et al. (2020). CuO nanoparticles with a surface area of 85 m²/g were applied for the adsorption of AS(III) and AS(V) between pH 6 and 10 (Martinson & Reddy 2009). There have been a number of iron-based materials used as adsorbents for the removal of arsenic, including iron-based nanoparticles, zero-valent iron (ZVI), iron-based layered double hydroxides (LDHs), iron-doped polymer/biomass materials, iron-doped activated carbon, iron-containing combined metal oxides and iron-doped inorganic minerals (Hao et al. 2018a; Ahmaruzzaman 2022). Table 2 describes the adsorption techniques and related adsorbents for removing AS(V) from water.

These adsorption techniques use different adsorbents to absorb the arsenic ions on their surfaces or within their porous structures to remove AS(V) from water. The specific surface area, pore structure, surface functional groups, and the desired operating conditions all play a role in the adsorbent selection process. The adsorbents can also be changed to improve their AS(V) removal selectivity and adsorption capabilities.

Ion exchange is a physicochemical process in exchanging an ion present in the solid phase for an ion in the solution. This method mainly reduces water hardness and extracts contaminants such as arsenate, selenite, nitrate, and chromate anions in contaminated water. Natural and synthetic resins are commonly used materials for ion exchange. The solid resin is an elastic three-dimensional hydrocarbon network of many ionizable groups electrostatically bound to the resin. These groups are exchanged for ions of the same charge in solution with a stronger exchange attraction (i.e., selectivity) for the resin. Typically, strong-base anion exchange resins are usually used for the removal of arsenic where the oxy-anionic species of Arsenic(V) (such as ⁠, ⁠, and ⁠) are effectively exchanged with the anionically charged functional group of the resin, thus forms effluents with a low concentration of Arsenic(V). Strong-base anion resins over a more extensive pH range are more effective than weak-base resins. The already-used exhausted resin with high arsenic concentration needs further treatment before disposal or reuse.

A novel amine-doped acrylic fibre was applied to remove AS(V) from water by ion exchange method (Lee et al. 2017). N-methyl-D-glucamine functionalized resins were the membrane for removing boron and arsenic from saline geothermal water through an adsorption-membrane filtration hybrid process (Çermikli et al. 2020). Ion exchange technology is ineffective for the free AS(III) species in water and is only effective for AS(V) elimination. Moreover, developing ion exchange resin and high-tech water purification systems is usually expensive. The adsorption capacity was limited because of the interference from competitive Adsorption of other co-existing anions. The adsorbent regeneration process also created a sludge disposal problem.

Membranes are generally artificial materials with billions of pores or microscopic holes that act as a selective barrier; the membrane structure allows some components to go through, while others are not allowed or rejected. The movement of molecules across the membrane needs a driving force, such as the pressure difference between the two sides. This technology can reduce arsenic compositions to less than 50 μg/L and sometimes to less than 10 μg/L. It creates large residual volumes and is costlier than other arsenic treatment technologies. Researchers have studied different types of pressure-driven membranes, such as microfiltration, ultra-filtration, nanofiltration and reverse osmosis, to remove arsenic from polluted groundwater. In recent years, membrane techniques, including nanofiltration and reverse osmosis, have been increasingly reported for arsenic removal from water. Such methods have the advantages of high-removal efficiency, easy operation and minimum toxic sludge generated during the process.

Various researchers combined reverse osmosis membrane with pre-oxidation for arsenic removal (Moreira et al. 2021; Shakoor et al. 2022). A strong-base anionic (SBA) resin was used by Chen et al. (2020) for the simultaneous removal of arsenic, nitrate, antimony, uranium and vanadium with a >99% rejection rate. The main disadvantages of these processes are that the initial investment and running costs are relatively high; high pressure is usually needed to force the contaminated water through the membranes. Moreover, the discharge of the concentrate, membrane fouling, and flux decline are generally inevitable in the membrane process. The electrodialysis could remove arsenic and other contaminants, but the cathode deposited large amounts of insoluble coagulants.

Due to recent scientific and technological improvements, arsenic remediation is implemented with a better understanding of complex chemical mechanisms. Because of the demerits of single operating processes summarized in Table 1, some advanced hybrid and integrated methods are listed in Table 3. These technologies include a combination of treatment processes like adsorption and photocatalytic oxidation, adsorption and membrane/ultra-filtration, adsorption and coagulation, adsorption and ion exchange. Hybrid and integrated technologies are beneficial in several ways, such as

• High removal efficiency

• Less sludge generation

• Efficient without controlling pH.

The successful application of arsenic removal techniques depends on many factors, including scalability, material regeneration and reusability, matrix compatibility and stability, treatment of high arsenic concentrations, monitoring and control, long-term performance and maintenance, affordability in resource-constrained environments, and environmental impact. By addressing these obstacles and constraints, we may create solutions to arsenic pollution in water that are efficient, long-lasting, and economical (Asere et al. 2019; Kumarathilaka et al. 2019; Du et al. 2020; Kobya et al. 2020; Pandi et al. 2020; Bundschuh et al. 2021; Ahmed et al. 2022). Details of limitations and challenges in removing arsenic are discussed in the following.

• (a)

  Competing with common anions: It can be challenging to remove arsenic selectively when common anions are frequently present in larger amounts in natural waters or wastewater. Arsenic removal can be challenging since these frequent anions might compete with it for adsorption.

• (b)

  A variation on oxidation state: Arsenic may occur in various oxidation states, such as AS(III) and AS(V), each with unique physical and chemical characteristics. Numerous strategies must be developed to address the various oxidation states to effectively remove all arsenic forms.

• (c)

  pH dependence: Most materials for selective arsenic removal operate at their best within a narrow pH range, usually between 6 and 8. The complete range of natural fluids may not fall within this pH range, and changes in pH can affect how well arsenic is removed.

• (d)

  Limitations of redox potential: Redox potential of water plays a significant role in eliminating arsenic. The behaviour of selective arsenic removal materials under various redox potential situations has unfortunately not been well studied. Further research utilizing actual polluted water is required to overcome it.

• (e)

  Thiol-based methods: Thiol-based removal techniques can target specific species of arsenic. Further research is needed on their effectiveness in the presence of phosphate interference and their compatibility with other components or processes.

• (f)

  Microbial techniques: Although there are microbial techniques for removing arsenic, their influence on phosphate removal has not been thoroughly investigated. In order to solve problems with common ion interference, future research should concentrate on assessing the viability of integrating chemical and microbiological techniques.

• (g)

  Economic viability: One important factor to consider is the economic viability of selective arsenic removal techniques. The cost of the removal process as a whole is greatly influenced by elements including raw material availability, pre-adjustment needs, waste disposal, regeneration capacity, and energy usage.

• (h)

  Scalability: While experiments in the laboratory using prepared arsenic solutions have demonstrated selective arsenic removal strategies to be effective, their applicability to large-scale water treatment systems in the real world presents difficulties. More investigation and testing are required to confirm the efficacy and viability on a broader scale.

• (i)

  Regeneration and reusability: After attaining their adsorption capability, certain arsenic removal materials may need to be recycled or disposed of. If regeneration is necessary, it should be done quickly and affordably. Additionally, the material's capacity and effectiveness may alter following regeneration, decreasing its potential for repeated use.

• (j)

  Matrix compatibility: Hydrated granular or amorphous Fe(III) or other metal ions must be successfully deposited in a suitable matrix for selective removal of arsenic. Finding an appropriate matrix that combines stability, durability, and effective arsenic removal might be difficult.

• (k)

  Matrix stability: To stop absorbed arsenic from seeping back into the water, the stability of the matrix employed for arsenic removal is essential. Variables, including pH, redox potential, and the inclusion of additional chemicals or pollutants, can impact the stability of the matrix.

• (l)

  High arsenic concentration treatment: Some areas may have water sources with incredibly high arsenic concentrations, necessitating more sophisticated and specialized treatment techniques. In such circumstances, the above-indicated selective arsenic removal approaches might not be enough, necessitating additional methods.

• (m)

  Monitoring and control: Continuous monitoring and control are required to maintain the efficacy of the arsenic removal process.

• (n)

  Long-term performance and maintenance: Considering the selective arsenic removal techniques' long-term performance and maintenance needs is crucial. Elements including material deterioration, fouling, and the requirement for frequent maintenance might impact the sustainability and dependability of the treatment system.

• (o)

  Affordability in resource-limited settings: In areas with limited infrastructure and financial resources, the cost of arsenic removal technology becomes a severe problem. Implementing and sustaining efficient arsenic removal procedures in these circumstances may call for creative and affordable fixes.

• (p)

  Environmental impact: Carefully consider how arsenic removal techniques may affect the ecosystem. The treatment process's sustainability, possible arsenic leaching, and waste disposal should all be considered.

The removal of arsenic from water is problematic for various reasons, including competition with other common anions, changes in oxidation states, dependence on pH, redox potential limitations, phosphate interference, and more research and development. Selective arsenic removal methods must be economically viable to be used. Arsenic removal strategies should also consider the environment's impact, scalability, regeneration and reusability, matrix compatibility and stability, treatment of high arsenic concentrations, monitoring and control, long-term performance and maintenance. This in-depth analysis of arsenic removal technology can be a manual for applying remediation techniques in a real-world setting. The authors found several conclusions from this study, as listed in the following:

• Due to the tremendous harm that arsenic pollution does to people, it must be adequately addressed.

• The paper emphasizes the difficulty in choosing the optimum method for arsenic remediation as each treatment technique has disadvantages and advantages. As a result, hybrid treatment systems are urgently needed, with photocatalysis-adsorption being a popular hybrid method. In Table 2, the article also summarizes hybrid approaches, their operational characteristics, and removal efficiency.

• Hybrid technologies must also offer flexibility, simplicity of handling, and little maintenance needs. They must also be sustainable and favourable to the environment. Underprivileged populations would significantly benefit from creating a low-cost, effective hybrid arsenic removal system since it would guarantee access to clean drinking water.

• The limits of current arsenic removal technology require further study and development. Innovative solutions and technique optimization are needed to address the complexity of phosphate interference, changes in oxidation states, and competition from common anions.

• Hybrid treatment methods, such as the photocatalysis-adsorption method, might potentially overcome the limitations of selective arsenic removal. These methods incorporate many strategies to increase removal efficacy and raise the remediation of arsenic's overall effectiveness. Future research should focus on scaling up and optimizing these hybrid technologies for real-world applications.

• Strategies for removing arsenic should prioritize sustainability and the environment. The treatment procedure must not have adverse environmental effects, which includes preventing arsenic from seeping back into the environment and disposing of waste products properly. Long-term success and preserving ecosystems and public health depend on removal techniques' life cycle and sustainability.

• The high cost of arsenic removal methods remains one of the bottlenecks, especially in environments with limited resources. Developing affordable and appropriate solutions for use in places with limited infrastructure and financial resources is essential. To make arsenic remediation accessible and sustainable for all communities, this calls for integrating creative strategies and alliances.

In conclusion, a multifaceted strategy is needed to meet the challenges posed by the removal of arsenic from water. We may strive towards successful and broad deployment of arsenic remediation techniques, enabling access to safe and clean drinking water for all people by considering the numerous obstacles, including hybrid treatment systems, encouraging sustainability, and prioritizing cost.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.