Potential of Biochar as Cost Effective Adsorbent in Removal of Heavy Metals Ions from Aqueous Phase: A Mini Review

Today, environmental pollution has become one of the most global problem. Out of which water pollution is also a big concern because of rapid industrialisation and urbanisation. Approximately 1 billion people of the world do not get safe water and about 2 million losses their life every year due to polluted water (Gleick et al., 2003). Moreover World Health Organisation (WHO) specified that climate change will increase this problem of potable water for the half of the global people (World Health Organization). According to United Nation scheme world would have shortage of 40% water next 15 years. Polluted water is also very hazardous for water bodies as every year it causes death of 1 million marine, according to UNESCO (WWAP 2015). Water pollution is caused by various pollutants such as organic, inorganic which are added by the industries. Among them heavy metal ions are the greatest threats to the environment, a living organism because these cannot be biodegraded and they are highly venomous nature (Shannon et al., 2008; Range et al., 2012). There are various natural and anthropogenic sources of heavy metals in aqueous solution, as shown in Figure 1. Discarding of heavy metals increased water pollution day by day throughout the world. The existence of heavy metals ion in the water sources (river, ponds, lakes and sea) caused serious threat to both flora and fauna. They are not contaminated surface but also caused the contamination of ground water (via leakage or rain) (Keiluwei et al., 2009). So earth water consist different hazardous heavy metals. Therefore to reduced the risk of heavy metals, its essential to remediate heavy metals from the aqueous solution. To remediate heavy numerous technologies such ion exchange, reverse osmosis, membrane filtetration, coagulation flotation and adsorption. Amongst these techniques adsorption is optimize techniques due to low cost, easy operation and high efficiency (Kumar et al., 2011). The utilization of low cost adsorbent such as biochar is the innovative method to remediate heavy metals from the aqueous solution. Biochar is a black carbon produced by thermal decomposition (pyrolysis) of biomass, which consist high amount of carbon in the absent of oxygen or oxygen deficient environment. Biochars playing a numerous function due to which researcher attracted towards utilization of biochars as less expensive adsorbent for the remediation of heavy metals. Biochars mainly removed Potential of Biochar as Cost Effective Adsorbent in Removal of Heavy Metals Ions from Aqueous Phase: A Mini Review


Introduction
Today, environmental pollution has become one of the most global problem. Out of which water pollution is also a big concern because of rapid industrialisation and urbanisation. Approximately 1 billion people of the world do not get safe water and about 2 million losses their life every year due to polluted water (Gleick et al., 2003). Moreover World Health Organisation (WHO) specified that climate change will increase this problem of potable water for the half of the global people (World Health Organization). According to United Nation scheme world would have shortage of 40% water next 15 years. Polluted water is also very hazardous for water bodies as every year it causes death of 1 million marine, according to UNESCO (WWAP 2015).
Water pollution is caused by various pollutants such as organic, inorganic which are added by the industries. Among them heavy metal ions are the greatest threats to the environment, a living organism because these cannot be biodegraded and they are highly venomous nature (Shannon et al., 2008;Range et al., 2012). There are various natural and anthropogenic sources of heavy metals in aqueous solution, as shown in Figure 1. Discarding of heavy metals increased water pollution day by day throughout the world. The existence of heavy metals ion in the water sources (river, ponds, lakes and sea) caused serious threat to both flora and fauna. They are not contaminated surface but also caused the contamination of ground water (via leakage or rain) (Keiluwei et al., 2009). So earth water consist different hazardous heavy metals. Therefore to reduced the risk of heavy metals, its essential to remediate heavy metals from the aqueous solution. To remediate heavy numerous technologies such ion exchange, reverse osmosis, membrane filtetration, coagulation flotation and adsorption. Amongst these techniques adsorption is optimize techniques due to low cost, easy operation and high efficiency (Kumar et al., 2011). The utilization of low cost adsorbent such as biochar is the innovative method to remediate heavy metals from the aqueous solution. Biochar is a black carbon produced by thermal decomposition (pyrolysis) of biomass, which consist high amount of carbon in the absent of oxygen or oxygen deficient environment. Biochars playing a numerous function due to which researcher attracted towards utilization of biochars as less expensive adsorbent for the remediation of heavy metals. Biochars mainly removed heavy metals from the water by physiochemical interaction (Kołodyn et al., 2012;Hollister et al., 2013).
Figute 1: Sources of heavy metals contaminate in water.

Mechanism
Heavy metals can be removed from the water by different mechanism for example complexation, electrostatic interaction, physical sorption and precipitation. Due to surface heterogeneity biochars shows higher sorption capacity for removal of heavy metal as activated carbon. In literature number of biochars given which have higher surface area as well as perfectly distributed pore network together with mesopores (2-50nm), macropores (>50nm) and micropores (<2nm) (Mukherjee et al., 2011). Biochars shows higher affinity towards heavy metal due to higher pore volume and surface the reason behind this the metallic ion may be sorbed physically on the surface of biochar and retained inside the pore . There are number of biocahs which carry negative charge and have ability to adsorbed positively charged metal by electrostatic interaction. Biochars carried functional group and specific ligands may be attracting with many metals to form complexes otherwise their solid minerals phase precipitated (Cao et al., 2009;Inyang et al., 2012;Kim et al., 2013).

Application of Biochar for Water Treatment
Biochars possess high porous volume, greater surface area, efficiently remove contaminant from the water and functional group with unique characteristics. On the basis of the literature survey about 45% biochars utilized to remove heavy metals from the aqueous solution. In the current world the contamination of aqueous solution with heavy metals has been become a big issue. Therefore today researcher attracted towards the utilization of biochar to remediate heavy metals from aqueous solution. Examples of the most toxic heavy metals are arsenic (As), zinc (Zn), mercury (Hg), nickel (Ni), cadmium (Cd), (Cr), copper (Cu), lead (Pb), uranium (U), chromium and aluminum (Al) Sun et al., 2011;Hollister et al., 2013).

Literature Survey
Year of Publication

Concluding Remarks
Adsorption is the best techniques for the elimination of heavy metals from contaminated water due to its low cost, easy to operate and environmentally friendly. Recently, an urgent need has arisen to develop efficient, economically and green adsorbent for the elimination of arsenic ion. Therefore, biochar as an adsorbent are considered the promising adsorbents owing to their unique characteristics like greater surface area, highly porous structure and better functionality. This review focussed on systematically development of different biochar for heavy metals ions removals. Adsorption data is best fitted in pseudo second order kinetic model and Langmuir and Freundlich isotherm model. By critically analyzing biochar give information about the further research in the field of nanoadsorbents. In nutshell, this review discussed the recent progress and better understanding of biochar to remediate heavy metals ions efficiently.