Green Adsorbents for Water Purification

*Hafsa Muzammal, Muhammad Danish Majeed, Muhammad Zaman, Muhammad Safdar, Muhammad Adnan Shahid, Zahid Maqbool and Tayyaba Majeed*

### **Abstract**

Water purification is crucial for ensuring access to safe and clean drinking water. As a sustainable and effective solution, green adsorbents have gained significant attention in recent times. These adsorbents are composed of natural or waste-based materials that are biodegradable, renewable, and abundant, making them an eco-friendly substitute for traditional adsorbents. This chapter offers a comprehensive outline of the present and prospects of green adsorbents in water purification. It encompasses a comprehensive overview of the many forms of green adsorption agents comprising natural, agriculture waste-based, & industrial waste-based adsorbents, as well as their synthesis and modification methods. Furthermore, it also explores the potential applications of green adsorbents in removing heavy metals, organic pollutants, and inorganic contaminants from water. The challenges and future directions of green adsorbent research are also discussed, including the limitations of these adsorbents and the opportunities for enhancing their performance. Overall, this chapter offers valuable insights into the potential of green adsorbents as a sustainable and eco-friendly solution for water purification.

**Keywords:** green absorbent, water purification, green treatments, natural adsorbents, agricultural adsorbents, industrial adsorbents, heavy metals, organic and inorganic solutions

#### **1. Introduction**

Water conflicts are becoming more frequent because of the rising global need for safe drinking water [1]. The primary sources of drinking water are natural waters, such as groundwater, surface water (rivers and lakes), and rainwater, although desalination of brackish and seawater is becoming more important. More than 50% of the world's population uses groundwater for drinking, which accounts for 97% of all freshwaters [2]. Groundwater is the most economically viable option in many remote and underdeveloped regions where basic water delivery systems do not exist [3]. However, inorganic contaminants such as fluoride, uranium as arsenic, and boron are regularly detected in groundwater. Humans get negative health impacts from

long-term exposure to such pollutants. For instance, chronic uranium intake from drinking water damages the kidneys, while excessive fluoride intake causes dental and skeletal fluoroscopic [4]. Inorganic pollutants are strongly influenced by geology. Therefore, creating proper and adaptable technology for local use is the most practical way to get removal of such ions, species, and toxins [5].

Adsorption, coagulation, flocculation, clarity, filtration, and disinfection are all combined in traditional water treatment techniques [6]. The main problem with conventional techniques is that they are usually inefficient at the removal of residual pollutants [5]. In comparison to traditional approaches, reverse osmosis (RO) and nanofiltration (NF) are particularly promising techniques, especially for applications involving drinking water. Because they use a variety of separation methods, NF/RO can produce high inorganic removal by processes that involve solution diffusion, size being excluded, charge repulsion, and adsorption. It is possible to choose a membrane with the proper properties for certain water quality. Bacteria, viruses, and micro-pollutants like pesticides are often present in groundwater along with inorganic contaminants, which are undesirable. Whereas elimination of micropollutants is dependent on specific properties, NF/RO can remove all those contaminants simultaneously. Additionally, NF/RO is a workable choice for rural settlements because of its modular architecture and flexible placement. However, the potential negative aspects of NF/RO, fouling of the membrane & scaling, concentrated disposal, & relatively high energy usage must all be avoided. Scaling is dependent on the likelihood of precipitate formation in each water, while fouling of membranes and scaling are inevitable throughout the separation process, they can be significantly reduced by optimizing the operating conditions. The implementation of renewable energy technology can offset high energy demand [7]. Given the high standard of water quality that NF/RO produces, using this water primarily for potable purposes is a suitable technique. Utilizing concentrates for non-potable purposes while having feed water quality permitting offers almost no opportunity for removal.

Several researchers have coupled adsorbent materials with further chemicals and substances to improve their ability to remove contaminants. Nanotechnology has recently been applied to almost every human-interest industry, especially soil and management of natural resources, particularly wastewater treatment [8]. Nonadsorbents are often more successful than traditional adsorbents at eliminating organic and inorganic pollutants from wastewater. These adsorbents are made of metallic oxide-based nanoparticles (NPs), nanotubes of carbon (CNTs), graphite, plant nanocomposites that (NCs), and other materials [9]. This study will examine the most common agricultural & non-agricultural material-based adsorbents. Their methods of removing pollutants are also discussed, along with potential modifications or treatments that could increase their effectiveness. Additionally, this evaluation outlines their chances of re-usability and safe disposal procedures [10].

#### **2. Definition and importance of water purification**

To make water safe, clean, and acceptable for use in a variety of purposes, such as drinking, irrigation, industrial processes, and recreational activities, water must first be purified. It entails the elimination of potential physical, chemical, and biological contaminants from water sources [11].

Due to the following factors, the significance of water purification cannot be overstated:

## **2.1 Keeping the public healthy**

For the maintenance of the general welfare, access to clean and safe drinking water is essential. Waterborne illnesses brought on by bacteria, viruses, protozoa, and chemical pollutants can seriously harm your health. Purifying water helps keep people and communities healthy and stops the spread of disease.

Water purification techniques like filtration, disinfection, and chemical treatment efficiently remove or reduce the concentration of disease-causing microorganisms like bacteria (like *E. coli*, Salmonella), viruses (like Hepatitis A, norovirus), and parasites (like Giardia, Cryptosporidium), thereby reducing the risk of waterborne infections.

Getting rid of chemical pollutants Chemical contaminants such as heavy metals, pesticides, drugs, industrial chemicals, and organic molecules can all be found in water sources. These contaminants can be eliminated or reduced using purification techniques such e.g., clay, zeolites, biochar, activated carbon adsorption, oxidation, and ion exchange, protecting the environment and public health [12].

### **2.2 Enhancing flavor and odor**

Water purification techniques can make it taste and smell better by removing or cutting down on contaminants that cause unpleasant tastes, odors, or discoloration. This improves the drinking experience overall and encourages taking in enough water to be hydrated.

#### **2.3 Environmental protection**

Water pollution can disrupt the ecological balance, degrade aquatic habitats, destroy aquatic species, and harm aquatic ecosystems. Excess nutrients, pollutants, and poisons, as well as other contaminants that might harm aquatic environments, can be eliminated by water filtration, protecting ecosystem health and biodiversity.

#### **2.4 Supporting industrial and agricultural processes**

Industrial processes and irrigation in agriculture both require water. Purification ensures that the water used in these industries follows quality requirements, preventing damage to machinery, maintaining product quality, and reducing the effects of pollution discharge on the environment.

#### **2.5 Response to emergencies and disasters**

Access to clean water becomes vital in times of emergency, such as during natural disasters or epidemics. To provide impacted communities with safe drinking water, avert further health emergencies, and ensure survival and well-being in difficult circumstances, water purification technologies and techniques are essential.

Overall, water purification is essential for maintaining ecosystems, promoting sustainable water usage, safeguarding public health, and facilitating a variety of human endeavors.

#### **3. Overview of green adsorbents**

This term refers to low-cost materials that come from (i) agricultural commodities as well as materials (fruits, vegetables, and foods); (ii) farming and waste material residues; and (iii) low-cost substances from that the most complicated adsorption agents will be manufactured (specifically, activated carbons produced after pyrolysis from plant sources). Whereas these "green adsorbents" are expected to have lesser adsorption capabilities than the super-adsorbents mentioned in the scientific literature (complex materials such as modified chitosan, activated carbon, highly complex inorganic material composites, and so on), they remain relevant due to their low cost. In this study, two major types of environmental pollutants were used: colors and heavy metals, as well as a few others: medicines, pesticides, and phenols. Despite their little studies, several contaminants were discovered in wastewater [12].

Green adsorbents are derived from a number of different sources, such as minerals from clay, natural polymers, organic substances, agricultural sources and by-products, agricultural residue and waste, and agricultural waste pyrolysis. Heavy metals must be removed from the aqueous phase, green adsorbents made from diverse agricultural waste products, by-products, and residues are becoming more and more popular today. Numerous agricultural by-products and residues, including rice bran, wheat bran, cottonseed hulls, maize corn cobs, dal husk, mango peel, sugar beet pulp, grape bagasse, and others, have been investigated as adsorbents. These agricultural by-products have the benefits of being affordable, widely accessible, and easily regenerated. They also have a high absorption capacity. They also have a high ability for adsorption as well as selective heavy metal adsorption [13].

#### **4. Types of green adsorbents for water purification**

Adsorbents are often divided into two categories: natural and synthetic, depending on where they were created. Minerals, charcoal, ores, clay, and zeolites are examples of natural adsorbents. While synthetic adsorbents are made from waste materials such as waste sludge, trash from agriculture, and industrial waste [14].

**Figure 1** explain the flow chart of adsorbents for removal of pollutants. Its further divided in to five types include activated carbon adsorbents, non-conventional low-cost adsorbents, nanomaterial adsorbents, composite and nanocomposites adsorbents, and miscellaneous adsorbents. Activated Carbon adsorbents are further divided into two types including commercial activated carbon and AC prepared from water materials. Nano-conventional Low -cost Adsorbents are further divided into waste materials from Agriculture and industry, Natural Materials, and Bioadsorbents. Nanomaterial Adsorbents are further divided into nanoparticles, nanotubes, nanowires, and nanorods. Waste materials from Agriculture further explain the agricultural solid waste and Industrial by-products. Natural materials are further divided into clays and zeolites and siliceous materials. Bio adsorbents further explain the Biomass and Biopolymers & Peal. Industrial by-products are divided into Metal hydroxide sludge, Fly Ash, Red Mud, Bio Solids, and waste slurry.

Chemicals coagulation, which precipitating, the decomposition of separation of membranes, sludge activation, flocculation, and ion exchange are just a few of the processes used for removing pollutants from contaminated water [15]. The demand for rapid and simple processes for removing harmful dyes and chemicals from dirty water is continually increasing. Utilizing green adsorption for water filtration is much

**Figure 1.**

*Adsorbents for removal of pollutants.*

more advantageous than utilizing conventional methods due to its ease of use, low price, high effectiveness, and environmental friendliness [16].

Natural green adsorbents such as orange peel, peel from bananas, husks of rice, bagasse from sugar cane, tea waste, avocado peel, Hami melons peel, the peel of dragon fruit peels, and other peels have been utilized to recover ions of heavy metals & organic dyes from contaminated water [17]. One of the most common applications for fruit peel debris is water treatment. Using solid waste as green adsorbents, harmful compounds such as metals, pigments, and pesticide can be eliminated from contaminated water [18].
