**10. Removal of organic pollutants (e.g., dyes, pesticides, pharmaceuticals)**

Utilizing green adsorbents to remove organic pollutants from water, such as dyes, pesticides, and medicines, is a successful method of water filtration. Green adsorbents, made from natural resources, provide a long-term and sustainable option for

the elimination of harmful organic pollutants [37]. The elimination of organic pollutants by various commonly used green adsorbents is described below.

#### **10.1 Biomass-derived activated carbon**

For the elimination of organic pollutants, activated carbon is frequently made from biomass sources such as agricultural waste, wood, and coconut shells. It has a huge surface area and a highly porous structure, which allows for the physical adsorption of organic molecules. Van der Waals forces or hydrophobic interactions can be used to bind organic molecules to the surface of activated carbon because of the porous structure [38].

#### **10.2 Plant-based materials**

A variety of plant-based materials, such as leaves, sawdust, or agricultural leftovers, can be used as green adsorbents to remove organic pollutants. These substances frequently have functional groups that can interact with organic molecules and porous structures. For example, lignocellulosic materials may attract organic contaminants through hydrophobic interactions and physical adsorption.

#### **10.3 Minerals in clay**

For the elimination of organic pollutants, clay minerals such as montmorillonite and bentonite have been employed as green adsorbents. The layered structure of these minerals has a large specific surface area. Cation exchange, Van der Waals forces, or hydrophobic interactions are a few of the processes by which organic contaminants might be absorbed onto the clay mineral surfaces or inter-layer spaces [39].

#### **10.4 Membrane processes**

Membrane filtration methods like reverse osmosis (RO), nanofiltration (NF), or ultrafiltration (UF) may effectively eliminate organic contaminants from water. These methods make use of semi-permeable membranes, which let water through while filtering out dissolved organic molecules based on their size and charge. Membrane procedures can be used with other treatment techniques to increase the removal efficiency of tiny organic molecules, which they are particularly good at eliminating.

#### **10.5 Biological treatment**

Techniques for biological treatment use microorganisms' capacity to break down organic contaminants. Microbial activity is used in processes like activated sludge, sequencing batch reactors (SBRs), and created wetlands to break down organic chemicals into simpler, less dangerous molecules. Biodegradable organic pollutants benefit most from biological treatment [40].

#### **10.6 Chemical coagulation/flocculation**

Chemical coagulation and flocculation is the process of adding coagulants or flocculants to water to aggregate and destabilize organic contaminants into bigger particles that may then be separated by sedimentation or filtering. Polymers are

frequently employed as flocculants, while common coagulants include aluminum or iron salts. Certain organic contaminants, particularly those with larger molecular sizes, can be effectively removed with this technique [41].

#### **10.7 Photocatalysis**

To produce reactive species that can break down organic contaminants, photocatalysis uses photocatalysts like titanium dioxide (TiO2) which are activated by ultraviolet (UV) light. The photocatalyst, when exposed to radiation, generates electron-hole pairs that start oxidation processes, breaking down organic materials into inert byproducts.

#### **10.8 Electrochemical techniques**

The elimination of organic contaminants can be accomplished using electrochemical techniques such as electrooxidation and electrocoagulation [42]. These techniques use electrodes and electric currents to trigger chemical processes that decompose or remove organic pollutants. For a variety of organic contaminants, electrochemical approaches work well and can be combined with other treatment methods.

The characteristics of the organic contaminants, the water quality metrics, the treatment objectives, economic considerations, and regulatory requirements all play a role in determining which approach is most appropriate. In some instances, a combination of various procedures may be used to accomplish the best organic pollution removal and ensure the safety of the water [43].

### **11. Removal of inorganic contaminants (e.g., fluoride, nitrate, sulfate)**

To ensure that water is safe to drink, inorganic pollutants like fluoride, nitrate, and sulfate must be removed. These inorganic pollutants can be effectively removed using a variety of techniques. Here are some methods for getting rid of them:

#### **11.1 Ion exchange**

Ion exchange is a common technique for clearing out inorganic impurities from water. A solid resin and the water exchange ions in this process. Anion exchange resins, which selectively absorb fluoride ions and release other ions (such as chloride) in exchange, are used to remove fluoride from water. Similarly, nitrate and sulfate ions can be eliminated using cation exchange resins.

#### **11.2 Reverse osmosis (RO)**

Reverse osmosis is a membrane-based filtering method that can successfully rid water of inorganic impurities. It functions by exerting pressure on the water and forcing it through a semi-permeable membrane that picks out specific ions, such as fluoride, nitrate, and sulfate, and removes them from the solution. Reverse osmosis is frequently employed in water treatment systems and is capable of removing a variety of inorganic impurities [44].

#### *Green Adsorbents for Water Purification DOI: http://dx.doi.org/10.5772/intechopen.112652*

Adsorption is a procedure used to draw out and remove impurities from water using solid adsorbents. For the filtration of inorganic pollutants, a variety of adsorbents, including e.g., clay, zeolites, biochar, activated carbon, activated alumina, and zeolites, can be used. These adsorbents may selectively absorb and remove fluoride, nitrate, and sulfate due to their high surface area and affinity for ions.

#### **11.3 Precipitation**

Precipitation is the addition of chemicals that combine with the inorganic pollutants to create insoluble compounds that may then be removed using sedimentation or filtration. For instance, fluoride ions can be precipitated as calcium fluoride using calcium hydroxide (lime). Like how calcium or magnesium compounds can be used to precipitate sulfate ions, biological denitrification is one method that can be used to remove nitrate.

#### **11.4 Ion-selective membranes**

Ion-selective membranes are used in the electrochemical process of electrodialysis for dropping inorganic impurities from water. It entails applying an electric field across the membranes, which allows the flow of ions to be selectively allowed based on their charge. Fluoride, nitrate, and sulfate ions can all be successfully removed from water using electrodialysis [45].
