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Adsorption Principle Applied for Wastewater Treatment Centering Removal of Nitrate and Phosphate-A Review

Ravina C*, Sunil Chhikara, Parveen Kumar

Department of Zoology, Baba Mastnath University, Asthal Bohar, Rohtak, India

Abstract: Development of advance water treatment technology is being the prime focus of the environmentalists and researchers. As it directly associated with the human health and cleaner ecosystem, it demands for specific methodology for the specific pollutants. Nitrate and phosphate are two most concerned contamination in the water and their removal methodology is primarily correlated with water bodies eutrophication. Adsorption has been considered as most effective principle to remove nitrate and phosphate from wastewater. This technique has proven its applicability in nitrate and phosphate removal in low cost with high efficiency. However, still there are practical challenges in applying adsorption in wastewater treatment. These challenges can only be mitigated by detailing the adsorption principle and material currently used in wastewater treatment for nitrate and phosphate removal. This review primarily illustrates the wastewater treatment in context to nitrate and phosphate removal. Surface material used in the adsorbent and the kinetics involved are the two major components that are described in this review. These parameters are required to be processed further to improve the adsorption technology applied in the nitrate and phosphate removal from wastewater.

Keywords: wastewater, wastewater treatment, nitrate removal, phosphate removal, adsorbent

Received March 25, 2022; Revised April 29, 2022; Accepted May 08, 2022

Citation: Ravina C, Sunil Chhikara, Parveen Kumar, Adsorption Principle Applied for Wastewater Treatment Centering Removal of Nitrate and Phosphate-A Review. Applied Ecology and Environmental Sciences, 10 (5). 281-291. January 2022. doi:10.12691/aees-10-5-3

1. Introduction

Water surrounds 71% of earth’s surface and constitute 65% of human bodies. Pollution of water by different sources can threat to human health and survival in longer run. Wastewater or sewage may be defined as a combination of liquid or water-carried waste sourced from residences, commercial institutions, and industrial establishments, together with ground water, surface water and storm water. It contains organic materials, inorganic chemicals and minerals, sediments, a high load of oxygen demanding wastes, pathogenic or disease-causing agents and toxic materials including metals. Wastewater can be classified into four categories (a) domestic - that refers to wastewater discharged from residences, commercial institutions, and similar facilities, (b) industrial - where wastewater is predominates by industrial waste, (c) infiltration/inflow - extraneous water that enters the sewer system through indirect and direct means such as leaking joints, cracks or porous walls (d) storm water - runoff resulting from flood due to rainfall [1]. Major sources of water pollution in shown in Figure 1. Domestic wastewater has similar characteristic universally thus the treatment of domestic water is relatively easier. However, on the other hand different industries have different characteristic of water effluent and thus it demands different treatment methods to remove these contaminants. Moreover, these industrial contaminants can be handled at early stage of the generation of wastewater at industries. It can also be treated at municipal center or completely at the industry for the reuse or discharged. Organic materials in water is another heavily contributed water pollutant came from different sources, and thus it need to treated efficiently. Before treatment. We need to estimate the level of organic contamination, COD (chemical oxygen demand) is the index that serve as indicator for organic materials in water.

Figure 1. Major sources of water pollution

The municipal water needs rigorous treatment to remove the suspended solids, oxygen demanding material, organic compounds including bacteria and inorganic materials. Treatment of water many times categorized into three levels (as shown in Figure 2):

1. Primary: this includes the processes that removes suspended particles by filtering, sedimentation, screening etc.

2. Secondary: this refers to handling the dissolved oxygen in water by oxidizing it using biologically active sludge.

3. Tertiary: This is the most advanced techniques, that targeted the removal of nitrate and other chemical using adsorption techniques.

Figure 2. Levels of waste water treatment

The demand for advanced water purification treatments that can provide clean water in affordable, reliable, and sustainable way has been increased due to growing population, expanding economies and global warming [2]. Some of the conventional ways of water purification include screening, coagulation/flocculation, sedimentation, filtration, and disinfection. These methods are majorly focused on removing sediments, pollutants, and microorganisms. Other methods such as ion exchange, adsorption, air stripping and advanced oxidation are there, to remove chemicals, though they are not widely used [3]. The worldwide need for the clean water has given this rising field an opportunity to enhance the efficiency and affordability of water treatment. New methods include novel adsorption techniques, use of reactors and nanomaterials have been in development so that we can secure the global water supply. However, any treatment technique primarily starts with estimating the organic, inorganic and other components in the wastewater that also known as characterization of wastewater [4].

2. Discussion

2.1. Effluent Analysis

Analysis of odor and color of the sewage effluent can be done by visual inspection. TDS can be measured using portable combine electrical conductivity/TDS/temperature meter (HM Digital COM-100) after standardizing with 342 ppm sodium chloride calibration solution before starting with samples. Turbidity of the sample can be determined by using 6850 UV Spectrophotometer at 420 μm [4]. The pH of the samples can be recorded using ELICOLI 127 pH meter. TSS (total suspended solids) can be measured using JARCH DR 2000 direct reading spectrophotometer methods 8006 after estimating against deionized water as blank at a wavelength of 810 nm. Turbidity can also be used to determine the TSS [5]. Atomic absorption spectrometer is employed for the analysis of metals [6].

Moreover, total bacterial and total coliform count, samples of wastewater are standardized to obtain free metal ions and minimal interference. Later, they are introduced to digestion tubes with nitric acid until the clear solution is acquired. Eventually, they can be stored and used for further analysis of determining bacterial and coliform count by following method. The membrane filtration method includes triplicate aliquots of 100, 10, 1.0 and 0.1 ml of each water sample are filtered through 0.45-μm-pore-sized (47-mm-diameter) nitrocellulose membranes (Whatman, Maidstone UK). E. coli enumeration, the membranes are placed onto tryptone bile agar with X-glucuronide (TBX agar; Oxoid, Basingstoke, UK) and incubated at 44°C for 24 h. For Fecal coliforms enumeration, the membranes are placed onto chromogenic E. coli agar and incubated at 44°C for 24 h. Fecal enterococci enumeration, the membranes are placed onto Slanetz & Bartley Agar and incubated at 37°C for 48 h. The same water samples were also analyzed for Salmonella spp [7].

2.2. Wastewater Treatment

Conventional ways of wastewater treatment include combination of physical, chemical, and biological processes, that further be categorized based on degree of treatment comprises primary or preliminary wastewater treatment, secondary, tertiary, or advanced wastewater treatment [1].

Characterization of wastewater based on its physical and chemical properties is essential to develop for the better and advance techniques of wastewater treatment. Untreated or poorly treated water can be harmful to public health, economy, and environment. Physicochemical treatment can have a considerable influence on the biodegradation potential of organic material in wastewater [8]. The characterization includes composition of wastewater according to its origin, based on which it’s number of contaminants as well as types of pollutants fluctuate. Physicochemical characterization processes include coagulation, flocculation, and sedimentation [6]. Coagulation process is integral to neutralizing the charges (usually negative) on the colloid surfaces by adding coagulant while rapidly mixing wastewater. Ferric chloride, aluminum polychloride, ferric sulphate, aluminum sulphate, iron polychloride and sodium aluminate are the commonly used coagulants which are applied in varying doses depending on the source of wastewater, refers to domestic, agricultural, and industrial [9,10]. Flocculation involves the grouping of previously formed flocs or clumps during the slow mixing process. During the flocculation stage, a gradient is applied so that the next stage of sedimentation can be processed. Slow mixing facilitates longer contact times they either take place naturally due to inherent Brownian movement in water (perikinetic flocculation) or by forced agitation of wastewater (orthokinetic flocculation) [11,12]. The last stage of sedimentation is critical for separating liquid from eventual solids that are formed by coagulation and flocculation. Post sedimentation, varying physiochemical properties can be measured from wastewater where physical characterization, appearance/color, odor, temperature, pH, turbidity, conductivity, total dissolved solids (TDS) and total suspended solids (TSS) are taken as parameters [13].

In chemical and biological analysis, total hardness, calcium hardness CaCO₃, magnesium hardness, nitrate (NO₃), iron (Fe), alkalinity, phosphate (PO₄), manganese (Mn), calcium (Ca2⁺), magnesium (Mg²⁺), chloride (Cl⁻), sodium (Na), sulphate (SO₄²⁻), total bacterial count, and total coliform are chosen as water pollutant components [6]. Overall performance of the physicochemical treatment process depends on several aspects and physicochemical properties of wastewater. Therefore, laboratory tests are routinely conducted to determine properties based on which the overall treatment process can be customized in terms of times, types, and dosage of chemicals.

Accumulation of nitrogen and phosphorus in the water column and bottom sediments result in eutrophication, that can further become harmful if accelerated [14]. Fertilizers, construction deposition, and leakage from septic systems can lead to eutrophication in ponds and lakes. Cultural eutrophication associated with nitrogen and phosphorus pollutants can lead to unhealthy ecosystems. In addition, eutrophication also influences species composition [15].

2.3. Adsorption Methodology

Adsorption is the most successful and cost-effective strategy for wastewater treatment. Several studies on the usage of different adsorbents for wastewater purification have been conducted in recent years. The substance that accumulates at the surface is called adsorbate and the material upon which the adsorption takes place is called an adsorbent as shown in Figure 3. Since adsorption is a significantly used technique for pollutant measures, modeling of adsorption experimental data is important to predict its mechanisms [16].

Figure 3. General representation of Adsorption phenomenon

2.4. State of the Art Development of Adsorption

Progressive developmental achievements are being reported around new strategies for wastewater treatment and fulfill the necessities for unpolluted water. However, it has been challenging to treat discharged water containing pollutants thoroughly with available method. Method selection depends on various factors like dye concentration, sewage composition, cost of the method, or the extra impurities present in wastewater. They typically include physical, chemical, and biological processes that are considered effective enough for water treatment in many ways. Treatment techniques that need high installation and running costs, increased interval, low output, and produce toxic byproducts after treatment are often less considerable for industrial application. Hence, it's crucial to seek out an alternate treatment system that may completely degrade or remove contaminant. Several techniques are reported for wastewater treatment within the literature [17,18,19]. Figure 4 shows the type of conventional and modern techniques used in water treatment. Considering all available techniques, sorption process has been considered as the best method in context to the cost and easiness to deploy. So currently, adsorption is widely used with different material to streamline the water treatment process. Another advantage of this process is noted as minimum or no byproduct pollutant formation. Variety of absorbent used as a material in the cleaning process, and they have varying capacity of adsorption.

Figure 4. Conventional and modern techniques used for wastewater treatment [17]

Recently, these materials were extensively researched and got amalgamated with other chemical material to improve the adsorption process.

2.5. Kinetic Model of Adsorption

Kinetic of adsorption is defined as the rate of uptake of sorbate at the solid solution I interface. Kinetic of adsorption is crucial parameter and it can be examined and determined using datapoints of uptake and time to create a plot, this is known as a kinetic isotherm. Here, the concentration of solute is in equilibrium with the concentration of solute at the surface of absorbent. Langmuir and Freundlich is the widely accepted equation to predict the equilibrium condition [20]. This kinetic data assist in batch adsorption to ensure optimum conditions for the experiment [21]. Moreover, comprehensive understanding and interpretation of isotherms is very crucial for the improvement of adsorption pathways. Solute uptake rate that decides the time required for completion of adsorption reaction can also be determined using adsorption rate. There are different models for adsorption and diffusion based in its type and characteristics. Adsorption reaction models are pseudo-first-order rate equation, pseudo-second-order rate equation, elovich’s equation and second order rate equation. However, adsorption diffusion models are liquid film diffusion model, intraparticle diffusion model and double exponential model (DEM) [22].

2.5.1. Pseudo-first-order rate Equation

The rate of adsorption procedure can be analyzed using Lagergren’s first order rate equation or pseudo-first-order reaction [22] as shown in equation (1).

and are concentration of solute adsorbed at equalibirium and temperature t.

2.5.2. Pseudo-second-order Rate Equation

Based on adsorption capacity and concentration of solution, it can also be analyzed using Ho’s second-order rate equation or Pseudo-second-order rate equation as it has been known to work successfully for adsorption of metal ions, dyes, herbicides, oils, and organic substances from aqueous solutions [22]. Equation (2) describe the pseudo second order rate equation:

Adsorption rate is majorly affected by temperature, thus thermodynamic parameter of adsorbent is essential to examine before the design. This study comes under the umbrella of adsorption thermodynamics [23]. Similar to any other chemical reaction, adsorption is also governed by change in Gibbs free energy (ΔG) which depends on change in enthalpy (ΔH) and change in entropy (ΔS) as per the equation (1).

[picture] | (1)

2.6. Surface Characteristic of Adsorbent

Selection of an appropriate adsorbent material is the most critical step for effectively removal of pollutants from wastewater/sewage. Properties that decide the selection of adsorbent material are capacity, regenerability, selectivity, compatibility, kinetics, and cost must be thoroughly analyzed. Adsorption equilibrium, mixture equilibria, isotherm equations and adsorption dynamics should also be studied for proper selection of adsorbents. Adsorbent materials can be inorganic or organic in nature. Surface characteristics of adsorbents can be studied by various methods, as infrared spectroscopy has ability to probe chemical bonds, they are widely used to model adsorption studies. FTIR (Fourier Transform Infrared) spectroscopic analysis and attenuated total reflection (ATR) are known to be used in the investigation of the adsorbent surface by determining surface complexes between inorganic ions and oxides/hydroxides surfaces [24]. Surface characteristics before and after can be determined using FTIR (Fourier Transform Infrared), since it has become a popular method for the quantitative analysis of complex mixtures, as well as the investigation of surface. FTIR is sensitive to every structural change and works on its vibrational properties [25].

Surface characterization of the adsorbent includes identification of specific surface area (SBET), pore size (ABJH) and pore volume (Vtotal). These can be characterized by using N₂ adsorption–desorption isotherms. The SBET can be calculated with the Brunauer–Emmett–Teller (BET) method while the Vtotal and ABJH can be calculated by the Barrett–Joyner–Halenda (BJH) method. The BET method is used to measure the surface area of a solid or porous adsorbent [26].

Surface properties of adsorbents like dissolution rates, catalytic activity, moisture retention, shelf life are important aspects of any adsorbent. The BJH method can be used to determine the pore size distribution of a mesoporous solid [26].

2.7. Nitrate and Phosphate Contamination

Nitrogen and phosphorus are essential for the growth of plant and thus heavily used in the fertilizer and till date there is no direct alternative [27]. Water consumed by these plants is returned to soil and underground water after the degradation of plants [28]. Demand of nitrogen and phosphorus in fertilizer and non-fertilizer is shown in Figure 3, it shows that in fertilizer the demand is significantly heavier than non-fertilizer usage. Abundance of nitrate and phosphate ions in waterbodies leads to overgrowth of algal bodies, water plants. It causes high consumption of dissolved oxygen in water as decomposition of algae require more oxygen, suffocating the other aquatic life. Moreover, some of these algae can produce toxins that are harmful if ingested by humans or animals [29]. Exposure to nitroso compounds formed by nitrates, may result in cancer, birth defects or adverse health effects [30]. In addition, lowering of plants and other organisms in waterbodies increases the carbon content of water making the pond or lake shallower [31]. Fertilizers are intended to increase the yield but excess use of it led to water & environmental pollution via contaminating by phosphorus. Increase use of phosphorous in water results into eutrophication, causing lowering the water quality & death of aquatic animals. Thus, to remove excess quantity of phosphorous, the agricultural waste or byproducts used as adsorbent for removal of phosphate from water. Metal loaded agricultural wastes were found to be effective adsorbents for removal of phosphate from aqueous solutions [32].

Nitrate is a crucial nutrient for the plant growth and so routinely used in the fertilizers to increase the crop production. Increased concentrations of nitrate led to eutrophication in water bodies. Here, different adsorbents applied for the nitrate removal. However, choice of the adsorbents generally depends on NO₃ concentrations, presence of other competing ions, pH of water, and other physiological factors [33].

Figure 5. Global demand of nitrogen and phosphorus in fertilizer and non-fertilizer usage

To remove nitrates and phosphates from aqueous solutions, several adsorption processes are utilised. These adsorption techniques involve electrostatic attraction, ion exchange, surface complexation, ligand exchange, hydrogen bonding, physisorption, chemisorption and precipitation. In addition to these, methodologies, other adsorbents including modified nano adsorbents, chitosan hydrogel beads, modified steel slag, amine cross-linked biosorbent (ACB), magnetic amine-cross linked biopolymer-based corn stalk, magnetic Co₃O₄/Fe₃O₄ doped polyaniline nanocomposite, activated carbon magnetic nanoparticles, zeolites, hollow fiber membrane contactors, local clay and raw aluminosilicate (RAS) are used for removal of nitrates [30,34]. In the case of phosphates removal, calcium silicate hydrate (CSH) adsorbents, biochar adsorbents, zeolites and clay adsorbents, iron oxide adsorbents, novel miscellaneous adsorbents are commonly used as adsorbents. Similarly, co-removal of nitrates and phosphates is performed by chitosan/Al₂O₃/Fe₃O₄ composite nanofibrous adsorbents, novel zirconium-based graphene oxide (GO) modified with strontium nanoparticles (MGO-Sr) and zeolite (Z-Fe/Ni) were reported useful [34,35,36]. Recently, magnetic nanoparticles are being used to remove the phosphate from wastewater due to its useful adsorption properties [37]. List of various material used as adsorbent is mentioned in supplementary Table S1 and Table S2.

One important nanomaterial used in adsorption of nitrates and phosphates is MgAl-augmented double-layered hydroxide (biochar-MgAl-LDH) nanocomposite. According to a study, it enhances removal of nitrate and phosphate from wastewater because of its higher selectivity and adsorption affinity towards these ions. This adsorption is explained by pseudo-first-order model. The better performance of this nanocomposite is due to synergetic influence of the MgAl-LDH incorporation into the biochar [38]. Nanoparticles have several advantages over other material used in water cleaning. These materials are high surface/volume ratio that allows for higher adsorption. This further also speedup the process of treatment with greater efficiency. Graphene, MXene, MoS₂, g-C₃N₄, h-BN and black phosphorus that are 2D nanomaterials have all these above attributes and contribute for higher efficiency in water treatment [39]. In addition, nanocomposites which is mixture of compounds (two or more) to enhance the properties in order to bring the larger change in adsorption characteristics. These materials have even higher surface/volume ratio than nanomaterials and made the final compounds with better matrix properties. Carbon nanotubes were also used for adsorption for the organic waste in water. Here, the researchers are trying to modify the surface of carbon nanotube to improve the adsorption rate. Magnetic nanocomposite also falls under the nano particles umbrella, made of Fe2O3 where coating can be done by Ag, TiO2, CNT, GO, Pd, and SiO2.

2.8. Nitrate and Phosphate Removal Mechanism

2.8.1. Electrostatic Attraction

Electrostatic attraction refers to the electrostatic force of long-range interaction regulated between the electrostatic adsorption in aqueous solution with differently charged particles or uncharged particles. The protonated surface of the nitrate and phosphate adsorbents are electrostatically attracted with negatively charged nitrate ion (NO₃−) and phosphate ions (H₂PO₄⁻, HPO₄²⁻, PO₄³⁻) [30,40].

2.8.2. Ion Exchange

Ion exchange is exchange of ions between a solution and solid adsorbents. The ion exchanging adsorbent can be a cation exchanger or an anion exchanger. Different functional groups linked to the surface of the adsorbents, such as amine groups (primary, secondary, and tertiary), quaternary ammonium functional groups, and chloride ions, can play a role in nitrate and phosphate adsorption via the ion-exchange process. The primary amino groups available in chitosan resin is reported to have hydrophilic characteristics and removes the nitrate and phosphate. The amine group in amine-functionalized epichlorohydrin-grafted cellulose is used as the anion-exchanger to remove H2PO4− ion at pH 4.5 [30]. A molecular simulation study is reported for ion exchange using rho zeolite-like metal–organic framework (ZMOF). The non-framework Na+ ions in rho-ZMOF exchange with Pb2+ ions in PbCl2 solution [35].

2.8.3. Surface Complexation

There are two surface complexation mechanisms: inner-sphere and outer-sphere complexation. Electron transfer is carried out between complexes that do not undergo substitution, and no bonds are broken or generated because of the electron transfer in the outer-sphere complexation process. Mechanism of inner-sphere complexation electron transfer takes place between complexes through a bridging ligand, and at least one of the complexes must be responsible for bridge formation. Amongst which La (OH)₃ and MgO modified complexation are found to be successful in removal of phosphates [41,42].

2.8.4. Ligand Exchange

Ligands are ions or neutral compounds that contain electron pairs that can be donated to a metal atom to create a coordinate covalent connection. Ligand exchange reaction between OH and phosphate ions can result in removal of phosphates [31,36]. A study shows Zr (IV) cations were used to successfully remove phosphate ions [36].

2.8.5. Physisorption and Chemisorption

Chemisorption is when a functional group of an organic chemical interacts with a reactive surface on the adsorbents through the formation of strong chemical bonds, principally covalent bonds. Whereas physisorption is adsorption by van der Waals force, which is a weak intermolecular attraction that takes place below the critical temperature of the adsorbate and results in the development of a monolayer or multilayer. Magnetic Co3O4/Fe3O4 doped polyaniline nanocomposite and activated carbon-Fe₃O₄ magnetic nanoparticles adsorbates are known to adsorb nitrate ions [30].

2.8.6. Other Adsorbents

As per earlier study, MgO-biochar (wood waste biochar loaded with magnesium oxides) and MG@La (nanosized lanthanum hydrous doped on magnetic graphene nanocomposite) showed maximum capacity for adsorption of nitrate and phosphate. These adsorbents are believed to show 50-60% removal efficiency after 5-6 cycles [30].

2.9. Recovery Methods

The method commonly used for recovery of nitrate and phosphate after adsorption is the elution. In which different concentrations of HCl, H₂SO₄, NaOH, NaCl-NaOH binary solution, NaCl and Na₂CO₃ are used as nitrate and phosphate leaching agents from adsorbents [30]. Recovery performance of different techniques reported recently for nitrate removal. Rezaei Kalantary et al. showed a method using synthetic activated carbon magnetic nanoparticle that has desorption efficiency of 98.9% that stands out as best. This method used Fe₃O₄ which is coated on activated carbon [43]. Another method that reported significantly higher recovery of 90% was demonstrated by Wei et al. using Commer. 201X7 adsorbent in effluent buffer of 5% NaCl [44]. Other than these two methods and adsorbents, MAB-CS (magnetic amine-crosslinked biopolymer-based corn stalk) in 0.1% HCL effluent also showed recovery of 78.67% [45]. Chitosan hydrogel beads was also used as adsorbent in nitrate removal process and reported as 75% recovery [46].

On the other hand, phosphate removal recovery has been reported relatively higher than nitrate. Application of several adsorbents has made the recovery to 100%. Zeolite beads (ZB) modified with lanthanum (La) has been demonstrated 100% recovery for phosphate removal in 1M NaOH buffer effluent [47]. Other technique where a unique adsorbent meat and bone meal (MBM) incineration ash used in the phosphate removal also showed 100% recovery [48]. Cellulose grafted epichlorohydrin functionalized polyethylenimine (Cell-g-E/PEI) used in the phosphate removal reported by Anirudhan et. al. that showed 99.6% phosphate removal recovery using effluent buffer of 0.1 M Na₂CO₃ [49]. These three methods mentioned above have 100 or close to 100% phosphate recovery. Absorbent pure-CSH with 0.1 M H₂SO4 was used by Lee et al. that reported 98.9% recovery and showed high potential in phosphate removal [50].

2.10. Techno-economic Analysis

There are number of water purification techniques, but adsorption is the foremost simplest, effective and economical method for wastewater purification. The removal efficiency of adsorption can range up to 99.9%. Adsorption is a well-developed process for re-moving dyes from wastewater because of its simplicity and cost-effectiveness compared with the opposite approaches. Preferably, an adsorbent should be supplied with enough binding sites which will perform appropriate adsorption for pollutants [51]. Adsorption has low installation expense, high performance, and easy operational design. Among all the new innovations identified in water purification processes, nanotechnology and metal-organic frameworks adsorbents are the most attractive for elimination of emerging contaminants [52].

Tertiary treatment is the most critical and efficient techniques used for wastewater treatment. Here, the equipment size is dependent on the maximum flow rate we want to achieve in the process. Mass energy balance can give the capacity of the design. Cost indices and scaling factors are two verticals that are used to calculate the cost of equipment. CEPCI (chemical engineering plant cost index) is used to find the cost for the given equipment based on available data. However, the other parameter, scaling factor calculating the cost of equipment from other similar equipment and scaling factor associate with it by below equation.

A: Equipment which cost need to be estimated

B: Equipment which cost is known

XA: Capacity of equipment A

XB: Capacity of equipment B

α: Scaling factorBottom of Form

3. Conclusion

Classification and characterization of wastewater effluent is essential to understand the basic principle required for the removal of various pollutants. Wastewater treatment methodology depends on the physical and chemical properties of these materials. Coagulation, flocculation, and sedimentation are three most widely used methods for characterization of wastewater. The characterization further indicated that nitrogen and phosphorus are abundantly present in the wastewater due to high usage of these material in fertilizers. These fertilizers are used by plant and organism for their growth. However, these are released back to the underground water and soil after the decomposition of plants and organism. Demand for the technologies to remove these two materials from water is of great importance for the cleaner environment. Adsorption is the well accepted techniques used for the removal of pollutants from wastewater. Thus, due to its high efficiency and low cost it is also used for nitrate and phosphate removal. However, examining the adsorption kinetics and thermodynamics is critical to design more effective and economical adsorbent material for nitrate and phosphate material. These adsorbents possess variety of characteristics that vary with the materials. These characteristics govern the selection of the absorbent. Various adsorbents have been used to remove nitrogen from wastewater that includes soil, smectite, kaolinite, ceramicite, aluminium oxide, activated carbons, graphene oxide, diatomite and zeolite. Metal oxides are having specific affinity for phosphorus and thus sed in adsorbent material. However, their adsorption rate is not significant, and, in many cases, they are not effective for commercial purpose. Alumina is the cheapest material used in adsorption for phosphate removal. Nanoparticle materials are recently being popularly used in the adsorbent due to their distinctive adsorption characteristics.

Acknowledgements

Authors acknowledge Growdea Technologies Pvt Ltd, Gurugram, India for their support.

References

Table S1. Nitrate adsorbents

Table S2. Phosphate adsorbents

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