Water pollution
Water pollution is a major problem affecting people across the world. Heavy metals and dyes are major pollutants that cause many problems to the health of humans and ecosystems. Several treatment technologies are available to reduce the effects of pollutants.
These problems pushing the world to have a green method that are more efficient, cost effective and environment friendly for water purification. Adsorption is regarded as a green, clean and versatile method for wastewater treatment. Cellulose based materials attained considerable attention for water purification because of its easily available, biodegradable and non-toxic nature.
Pollutants and adsorption technique
Cellulose based materials and their modified forms as adsorbents for the removal of dyes and toxic heavy metals from wastewater. The adsorption capacity of the adsorbent is enhanced by reducing the cellulosic dimension to the nanolevel.
The quality of water resources is worsening day by day due to several anthropogenic activities, increasing industrial development and unplanned expansion.
Dyes are complex organic compounds which are eliminated from various industrial sources such as textile, cosmetic, paper, leather, rubber and printing industries to color their products. Dye bearing effluent is a significant source of water pollution. Human activities have also resulted in substantial quantities of heavy metals being free into the hydrosphere causing Eco toxicological hazards due to their tendency to accumulate in vital organs and high toxicity.
Water containing dyes and heavy metals cause potential hazard to the environment and human health.
Treatment Methods:
Many treatment methods have been developed. These include chemical precipitation, ion exchange, coagulation flocculation, membrane separation, electrochemical treatment and adsorption.
Adsorption is found to be effective, cheap, simple, and relatively lower operation cost of dye removal. Different types of materials have been developed as adsorbents for effective adsorption of pollutants.
Adsorption is a fast, cheap and widely used method as it can be applied for the removal of a wide spectrum of soluble and insoluble contaminants and biological pollutants with high removal efficiency as shown in Fig. (1). Moreover, its high efficiency in pollutant removal without the production of toxic by-products makes adsorption one of the most popular methods for water refinement.
Figure 1 Most commonly based adsorbents
The process of adsorption is a mass transfer process involving the transfer of a substance from solution phase and resulting in the deposition at the surface of the other phase. The substance being adsorbed is termed the adsorbate and the adsorbing surface is called adsorbent. If the interaction between the adsorbate and the adsorbent are due to the weak van der Waal’s forces, then the process is physisorption or physical adsorption. Defiantly, if the attraction forces between the adsorbate and adsorbent are due to chemical bonding, then chemisorption. The general mechanism of adsorption involves the transfer of the contaminant from bulk solution to the outer surface of the adsorbent.
Ideal materials to be an adsorbent
The ideal materials for the adsorption of pollutants should meet several requirements
such as:
- Good mechanical and structural integrity to overcome water flow for a long time.
- High adsorption capacities with high rates.
- Have a large surface area and possess a regeneration aptitude using cost-effective approaches.
The main advantage of adsorption:
- The use of low-cost materials with satisfactory adsorption properties and environmentally-friendly nature.
- as per these requirements, nowadays researchers are switching onto green adsorbents due to their abundance, biodegradability and non-toxic nature.
Green adsorbents:
Under this term, green adsorbents include low-cost materials originated from:
- Natural sources
- Agricultural residues and wastes in particularly lignocellulosic biomass
- Low-cost sources from which activated carbon adsorbents will be produced.
These green adsorbents were found to be lower in terms of their adsorption capacity than the commercial adsorbents such as modified chitosan, activated carbons, structurally-complex inorganic composite materials etc., but their cost-potential makes them competitive. Cellulosic adsorbents have the proficiency to meet almost all the requirement for being green. With responsible and thoughtful research, development and deployment, cellulosic materials have the potential to become sustainable, green materials of choice for high end applications such as water purification
More details about green adsorbents next issue.
By
Ahmed Hasham (M.Sc. Env. Chemistry) / Ahmedhasham83@outlook.com
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References:
Grégorio Crini, Eric Lichtfouse, Green Adsorbents for Pollutant Removal: Fundamentals and Design, Volume 18 of Environmental Chemistry for a Sustainable World, Springer, 2018.
