Preparation of activated carbon from biomass and its’ applications in water and gas purification
Due to its versatility and wide range of applications, activated carbon is widely used as contaminant removal media. Recent research have focused on enhancing the effectiveness of activated carbon by modifying their specific properties in order to enable the carbon to develop affinity for certain contaminants. In view of this, a comprehensive list of literatures on chemical, physical and biological modification techniques of activated carbon pertaining to enhancement of contaminant removal from aqueous solutions was compiled and reviewed. Acidic treatment to introduce acidic functional groups onto surface of coal based activated carbon was by far, the most studied technique. It was apparent from the literature survey that the beneficial effects of specific modification techniques on activated carbon adsorption of targeted contaminant species from aqueous solutions were profound, with some studies reported increase of contaminant uptake factors of more than 2. Concurrently, considerable decreases associated with certain contaminant uptakes can also occur depending on the technique used.
Without pure water, it is impossible to survive for any living beings. The ratio of freshwater on our planet is very poor and the demand is increasing with time for the growing population. Furthermore, water is being contaminated by industrial and agricultural activities, pharmaceuticals, technocratic civilization, pesticides, garments, global changes etc. In addition to this, environmental pollution and global warming are swelling due to the greenhouse and harmful gases generated from the dumping and burning of fossil fuel. Addressing these problems, it is necessary to find out the cost-effective and environmental friendly processes to purify the contaminated water and air. Activated carbons (ACs) are one of the best solutions for removing the pollutants from aqueous and atmosphere as it is the carbonaceous materials with a high degree of porosity, well-developed surface area, and distinguished functional groups which are required for elimination of contaminants. The preparations of activated carbon are easy and safe processes, mainly from the pyrolysis or gasification of biomass with heat and/or chemicals. The recycling and regeneration of bituminous coal based activated carbon after use are also essential for resource maintenance and environmental safety. Thus, AC can protect the ecosystem in a double direction by purifying the water and air from the pollutants.
Usually, ACs are produced from finite resources such as coal, lignite, peat, petroleum residue materials that are expensive and required intensive regeneration (Yahya et al., 2018). It is reported that the demand for AC is estimated to increase by up to 2.1 million metric tons by the year 2018 (Maneerung et al., 2016). The high demand and the necessities have led to the discovery of cheaper, environmental-friendly and sustainable resources for the production of AC like biochar from thermal treatment of biomass. The primary sources of AC are agricultural waste, sewage, municipal waste, industrial waste, forestry residue, acacia species, Imperata cylindrica(Ahmed et al., 2018a, Ahmed, Parvaz, Johari, and Rafat, 2018b; Danish and Ahmad, 2018 ). Acacia species are known as the most invasive and they have adverse effects on other trees, and thus, threatens the biodiversity seriously (Hidayat, Abu Bakar, Yang, Phusunti, and Bridgwater, 2018; Islam, Mohamad, and Azad, 2019). A total of 1350 different types of acacia trees are known to exist in the world, which can grow in any climate (Ahmed, Hidayat, et al., 2018c; Radenahmad, Rahman, Morni, and Azad, 2018; Reza et al., 2019 ). Improvements in biofuel technology have developed the new technique to manage these invasive acacia trees to convert them into biochar (Alhinai, Azad, Bakar, and Phusunti, 2018) which can produce wood based activated carbon.
The present paper reviews the efficiency of different types of activation processes of activated carbon from biomass. The adsorption capacity of contaminants and pollutants from water and air has been described elaborately to get pure water with clean air. The recycling/regeneration and handling process of Saw Dust Activated Carbon is also illustrated.
2. Preparation of activated carbon
For the preparations of shell activated carbon, two basic steps are maintained. The first one is the carbonization and the second one is the activation.