Activated Charcoal: An Adsorbent with A Difference for Waste Water Purification – An Overview

Biannual Review of Glorious Vision University Volume 2, Number 1, March, 2025 ISSN: 1595-580x Glorious Vision University Ogwa, Edo State gloriousvisionuniversityjournals.ng 271 Activated Charcoal: An Adsorbent with A Difference for Waste Water Purification – An Overview Adetuyi, Abayomi Olagundoye Department of Biological Sciences, Faculty of Basic Medical Sciences and Applied Sciences, Trinity University, Sabo, Yaba, Lagos. E-mail: [email protected] DOI: https://doi.org/10.5281/zenodo.17913192 Abstract Activated charcoal, an unnoticed porous material but unique and powerful, has been in use for centuries in addressing the menace of wastewater, characterized by odour and colour. This paper gives an overview of its potential (activated carbon/charcoal) as an adsorbent with a difference. Its preparation and properties were also highlighted in this overview. The unique pore size/ surface area per gram (500 - 1,500 m²/g) and the catenation properties of activated carbon contributed effectively to its adsorption process for efficient removal or uptake of a broad spectrum of toxic materials from gas and liquid phases than any other material available for physical adsorption. Practical applications in its absorption capacities to textile dye-liquor (water) purification, oil spillage and medicine for the removal of contaminants or toxins in waste water and patient as gastrointestinal decontaminant were discussed. and the potential to utilize its adsorption capacities in environmental remediation of sewage water recommended. Adsorption with activated charcoal, irrespective of the sources coal or agro-wastes (agricultural waste) is an excellent way to treat solid waste effluent, offering significant benefits such as affordability, profitability, ease of operation, and efficiency in providing a greener environment. Keywords: Activated charcoal, carbon, waste, wastewater, adsorption, absorption Biannual Review of Glorious Vision University Volume 2, Number 1, March, 2025 ISSN: 1595-580x Glorious Vision University Ogwa, Edo State gloriousvisionuniversityjournals.ng 272 1.0. Introduction Waste is defined, according to the Webster/Oxford Dictionary, as “unwanted or unusable materials." It is also any substance discarded after primary use that is worthless, defective, and of no use. It could be a by-product of relatively minor economic value. Table 1 depicts the United States Environmental Protection Authority [US-EPA] (2022) categorization of different types of waste. Many industrial sectors, such as the textile, paper, paint, pharmaceutical, food, leather, cosmetics, tannery, printing, and plastics industries, generated a lot of wastewaters involving dye utilizations on their products (Wong et al., 2013). The wastewaters from these sources are highly toxic and have profound negative effects on aquatic life because of the waste constituents, such as nitrates, acetic acid, surfactants, enzymes chromium compounds and metals -Cu, As, Pb, Hg, Co and many auxiliary chemicals resulting from the production reactions of those goods (Kant, 2012). In the conservation of nature for the sustenance of green environment, wastewaters are treated and among the various methods deployed are: chemical precipitation, ion exchange, coagulation and flocculation, adsorption, and membrane processes (Shafiq et al., 2018; Goher et al., 2015). The selection method to be used in the treatment system usually depends on the wastewater characteristics. Each treatment has its own constraints, not only in terms of cost but also in relation to feasibility, efficiency, practicability, reliability, environmental impact, sludge production, operation difficulty, pre-treatment requirements and the formation of chemical residues (Crini & Lichtfouse, 2019; Banerjee, 2020). Adsorption is one of the most effective processes of advanced wastewater treatment, which industries employ to reduce hazardous pollutants present in the effluents. This is a well-known and superior technique to other processes for removal of dyes from aqueous solution worldwide due to initial cost, operating conditions and simplicity of design (Fungaro & Magdalena, 2012). Most of commercial dye removal systems for industrial wastewater make use of activated carbon as an adsorbent (Hammed et al.,2009) and also as sorbent substance in a sorption Biannual Review of Glorious Vision University Volume 2, Number 1, March, 2025 ISSN: 1595-580x Glorious Vision University Ogwa, Edo State gloriousvisionuniversityjournals.ng 273 (absorption) of petroleum products polluters of air and water by enhancing deep cleaning from oil products, without the use of chemicals to the aquatic environment. This paper share more of an overview of the uniqueness of activated carbon as its relevant to wastewater treatment, characteristics and other useful life applications. Table 1: Waste Categorizations Based on Matter Degrading feature Environmental impact Source Solid Bio-degradable Hazardous Household Liquid Non-Biodegradable Non-hazardous Industrial Air emissions Radioactive Electronic Medical Nuclear (Source: US-EPA, 2022) 2.0 Water waste Domestic wastewater, also known as municipal wastewater, is basically wastewater from residences (homes), business buildings such as hotels, and institutions (e.g., universities). Metcalf et al. (2013) defined wastewater as “water whose physical, chemical, or biological properties have been changed as a result of the introduction of certain substances that render it unsafe for some purposes, such as drinking.” Man’s daily activities are majorly water - dependent and therefore discharge ‘waste’ into water. Some of these substances include body wastes (feces and urine), hair shampoo, hair, food scraps, fat, laundry powder, and the like. Invariably, much of the water supplied ends up as wastewater, which has an impact on people’s health and the environment. In the nineteenth century, flush toilets led to an increase in the volume of waste for these agricultural lands. The discharge of waste into Biannual Review of Glorious Vision University Volume 2, Number 1, March, 2025 ISSN: 1595-580x Glorious Vision University Ogwa, Edo State gloriousvisionuniversityjournals.ng 274 watercourses led to gross pollution (destruction of biodiversity and aquatic ecosystems) and health problems for downstream users. Numerous diseases are caused by contact with or consumption of contaminated water. Recently, Nigeria experienced multiple cholera outbreaks, with significant cases reported from various states, including Lagos, around June-August 2024 (Punch, 2024). It was reported in the media then that it was due to the consumption of a contaminated local drink, KUNU/SOBO, in Lagos State. Clean water is a key factor for the economic growth of any society, and this makes water treatment or purification very important. Figure 1 shows the categorization of wastewater, majorly as greywater and blackwater. Today there have been great advances to make potable water from wastewater (Amoatey & Bani 2016). In recent times, regardless of the capacity of the receiving stream, a minimum treatment level is required before discharge permits are granted by the Environmental Protection Authority of the country (Amoatey & Bani 2016; Adu-Ahyia & Anku, 2010). There are various ways of treating these wastewaters in either a central system or in a sustainable decentralized plant, and such selections usually depend on the wastewater characteristics and the chemical composition of the waste (Shafiq et al., 2018; Goher et al., 2015). Other factors considered are feasibility, efficiency, practicability, reliability, environmental impact, sludge production, operation difficulty, and pre-treatment requirements. (Crini & Lichtfouse, 2019). All treatments focus on the reduction of biodegradable organic substances, nutrient concentration, and elimination of pathogens in the waste for a clean environment. Figure 1: Classification of Municipal Wastewater (Source: Kirmizi, 2019; Amoatey & Bani 2016) Stormwater Rainwater Gray Water Surface Runoffs Laundry Surface Washings Process Water Black Water or Sewage (Toilets) Kitchen Feces Shower and Water Basins Urine Wastewater Domestic Industrial Biannual Review of Glorious Vision University Volume 2, Number 1, March, 2025 ISSN: 1595-580x Glorious Vision University Ogwa, Edo State gloriousvisionuniversityjournals.ng 275 3.0 Adsorption and Absorption These two technical terms sound almost similar, but there is much difference between absorption and adsorption. The main difference between them is that adsorption is defined by Gabelman (2019) as “a unit operation that exploits the adhesion or attraction of solutes—atoms, molecules, or ions—from a gas, liquid, or dissolved solid in a liquid to a solid surface.” This process creates a film of the adsorbate (usually solute) on the surface of the adsorbent, which is the solid. The process is a surface phenomenon (like the settlement of dust particles on the surfaces of a table). The adsorbate does not penetrate through the material surface and into the bulk of the adsorbent. This process (adsorption) differs from absorption, in which a fluid (the absorbate) is dissolved by or permeates a liquid or solid (the absorbent). It is a bulk phenomenon—similar to dyeing of fabric (Figure 2)—and adsorption often precedes absorption. There is another technical word called sorption, which encompasses both adsorption and absorption, which is usually effective in many unit operations, such as in dyeing fabrics. Desorption is the reverse of sorption. It is a physical process where adsorbed atoms or molecules are released from the surface into the surrounding vacuum or fluid. This occurs when a molecule gains enough energy to overcome the activation barrier and the binding energy that keeps it attached to the surface (Negm et al., 2017; Abesekara et al., 2020). Among all the various treatments available for wastewater purification, adsorption using activated carbon is very popular. Though the high cost of the raw material (coal-based activated carbon) is the major challenge (Research & Market, 2018), this has necessitated researchers to adjust the adsorption method by substituting the utilization of commercial adsorbent for agricultural waste (Alalwan et al., 2020; Yunus et al., 2019; Saxena et al., 2017; Negm et al., 2017). In the treatment process (adsorption), adsorption requires surface energy, just like surface tension. Bonding (or force of attachment—ionic, covalent, or metallic) is involved, and the exact nature of the bonding depends on the details of the species of the adsorbate and adsorbent involved. Generally, the adsorption process, which is determined during the isotherm and kinetic study, is classified as physisorption (a characteristic of weak van der Waals forces) or chemisorption Biannual Review of Glorious Vision University Volume 2, Number 1, March, 2025 ISSN: 1595-580x Glorious Vision University Ogwa, Edo State gloriousvisionuniversityjournals.ng 276 (characteristic of covalent bonding) (Abesekara et al., 2020; Ayob et al., 2021). It may also occur due to electrostatic attraction. The nature of the adsorption can affect the structure of the adsorbed species, and full details of the determinations of these kinetics and thermokinetics of the interactions are found in the literature (Sims et al., 2019; Milan, 2014; Mathew et al., 2016; Kwon et al., 2011). Figure 2: Graphic Representations of Adsorption and Absorption 4.0 Adsorbents Adsorbents are substances that trap or adsorb another substance. They are usually in the form of spherical pellets, rods, moldings, or monoliths with a hydrodynamic radius between 0.25 and 5 mm. They have high abrasion resistance, high thermal stability, and small pore diameters—for a higher exposed surface area and high capacity for adsorption (Gabelman, 2019). The industrial adsorbents currently and previously used are: • Oxygen-containing compounds are typically hydrophilic and polar, including materials such as silica gel, limestone (calcium carbonate), and zeolites. Biannual Review of Glorious Vision University Volume 2, Number 1, March, 2025 ISSN: 1595-580x Glorious Vision University Ogwa, Edo State gloriousvisionuniversityjournals.ng 277 • Carbon-based compounds are typically hydrophobic (water-resistant) and non-polar, including materials such as activated carbon and graphite. • Polymer-based compounds are polar or non-polar, depending on the functional groups in the polymer matrix. • Agro-industrial waste materials, granular or powdered activated carbon (AC), and modified AC (Shahrakia et al., 2021). Activated carbon (AC) is a popular adsorbent due to its high adsorption capacity owing to its porous structure and surface chemical groups. Its high surface area is due to the development of mainly microporous and mesoporous materials of different sizes and shapes. The presence of different pore size distributions influences the performance properties of the AC. Macro-pores have little contribution to the development of surface area. 5.0 Activated Carbon / Charcoal Activated carbon (also known as activated charcoal) is a highly porous, amorphous solid consisting of microcrystallites with a graphite lattice, usually prepared in small pellets or a powder. It is nonpolar and cheap and reacts with oxygen at moderate temperatures (over 300 °C). It is a highly effective and versatile adsorbent widely used in various applications, from water purification to air filtration and medical treatments (David, 2016). The uniqueness in the property of activated carbon or charcoal is due to the unique attributes of carbon atoms that form the major composition of the material. Carbon has a capacity of being able to bond together to form very long, durable chains with or without branches or rings of various sizes and often contains thousands of carbon atoms, called catenation (Figure 3). Chain Ring Branched chain Biannual Review of Glorious Vision University Volume 2, Number 1, March, 2025 ISSN: 1595-580x Glorious Vision University Ogwa, Edo State gloriousvisionuniversityjournals.ng 278 Figure 3: The Power of Carbon – Catenation Again, carbon is the only chemical element that has a major field of chemistry devoted to the study of its compounds, called organic chemistry. Over 95% of millions of chemical compounds are carbon compounds, and most organic compounds come from living things or things that were once living, such as crude oil and coal. Life chemistry is carbon chemistry, and what makes carbon suitable for life also makes it suitable for many industrial processes. All these set activated carbon/charcoal apart from other adsorbents. Table 2 shows the chemical and physical parameters of activated charcoal that significantly influence its performance as an adsorbent over others in adsorbing various contaminants. A teaspoon of activated carbon has more surface area (500 - 1,500 m²/g) than a football field (4,050 - 10,800 m²) (Nowicki, 2016). Several factors can influence its adsorptive capacity, such as temperature, pore size, particle size, surface area, solubility and toxic ionization stage, the pH, the presence of inorganic salts, and the gastric contents (Bonilla-Velez & Marin-Cuero, 2017). Table 2: The Chemical and Physical Parameters of Activated Charcoal Parameters Qualities Chemical Composition -majorly carbon (usually >85-90%), - coconut shells, fruits wood Surface area -high surface area, Brunauer-Emmett-Teller (BET) 500 - 1,500 m²/g. Porous structure / Pore Size -highly porous structure <2nm ->50nm ϴ Chemical Reactivity -Highly modifiable for functional group addition pH range & Density -pH:6-10; 0.2-0.5g/cm3 Moisture & Thermal stability -M.C: < below 5% ; stable up to 600 -1,000°C Regenerability -easily reuseable - thermal regeneration method Biocompatibility -Highly biocompatible & non-toxic for medical use Applications -highly versatile (-across various industries) Cost-Effectiveness - relatively cost-effective, widely available & ease of preparation Biannual Review of Glorious Vision University Volume 2, Number 1, March, 2025 ISSN: 1595-580x Glorious Vision University Ogwa, Edo State gloriousvisionuniversityjournals.ng 279 6.0. Activated Carbon Preparation Method Activated carbon is a mixture of particles that are insoluble and are manufactured from numerous/diverse carbonaceous materials, including coal (bituminous, subbituminous, and lignite), peat, wood, or nutshells (e.g., coconut). Research has shown that coconut shell (CS) and coal give ideal adsorption efficiency, and they are commonly used in industrial manufacturing to make commercial AC (Ayob et al., 2021). The manufacturing process consists of two phases: carbonization and activation (Figure 4). The carbonization process includes drying and then heating to separate by-products, including tars and other hydrocarbons, from the raw material, as well as to drive off any gases generated. The process is completed by heating the material over 400 °C (750 °F) in an oxygen-free atmosphere that cannot support combustion (Mohammad-Khah & Ansari, 2009). Cx(H2O)y → C(s) + yH2O ……….Carbonization C(s)+ 2H2O → CO2 + 2H2 ……….Steam activation (DH =+75 KJ) C(s)+CO2 → 2CO ……………..Activation by CO2 ( DH = +159 KJ) Figure 4: Flow chart of preparation of Activated Charcoal (Source: Sunmit-Dhawane, 2024) Biannual Review of Glorious Vision University Volume 2, Number 1, March, 2025 ISSN: 1595-580x Glorious Vision University Ogwa, Edo State gloriousvisionuniversityjournals.ng 286 Kwon S., Fan M., Herbert F.M., Armistead D, Kathryn G.R, Berchtold A. & Manvendra K.D., (2011). Coal Gasification and Its Applications Chapter 10 - CO2 Sorption, 293-339. Metcalf, E., Tchobanoglous, G., Franklin, B. & Stensel, H.D. (2013). Wastewater Engineering: Treatment and Reuse. 4th Ed, McGraw-Hill, New York. Mathew, B.B., Jaishankar, M., Biju, V. G. & Beeregowda K.N. (2016). Role of bioadsorbents in reducing toxic metals. Journal Toxicology, 12, 1–13. Milan, K. (2014). Adsorption, chemisorption, and catalysis. Chemical Papers. 68. Mohammad-Khah, A. & Ansari, R. 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Basic Appl. Sci. 9: 127-177 Yunus, Z. M., Gopalakrishnan Y., Adel A.G., Othman N., Hamdan R., & Nurun R. (2020). Advanced methods for activated carbon from agriculture wastes; A comprehensive review. International Journal of Environmental Analytical Chemistry. DOI: 10.1080/03067319.2020.1717477