Abstract
The accumulation of heavy metals in water bodies degrades the water quality and availability. Heavy metals are toxic and can be fatal if consumed. Various techniques such as ion-exchange, precipitation and adsorption have been used to extract heavy metals in wastewater. The process of adsorption will be reviewed in this study since it uses various adsorbents from industrial waste to agricultural waste and is inexpensive. The production of adsorbents from industrial waste produces large amounts of toxins such as greenhouse gases and it is also costly to produce, thus it was suggested that adsorbents are produce using biomass, which supports both circular economy and sustainability. The most effective biomass adsorbent is activated carbon; however, it has high production costs than biochar. This study will review on synthesis of biochar, its contribution to circular economy, biochar adsorption mechanisms, heavy metals extraction techniques and peanut shells as an effective adsorbent to extract heavy metals namely, chromium, cadmium, lead, zinc and copper and as a low-cost adsorbent. Furthermore, limitations to using peanut shells derived biochar are identified. Studies were conducted using peanut shells and it was found that even using peanut shell without pyrolysis is effective to remove heavy metals. In one study raw peanut shells (non-pyrolyzed) was used to extract lead and the peanut shells dosages were at 0.5g, 1.0g and 1.5g and it was found that 74.36 %, 74.57 % and 74.05 % of lead was extracted, respectively. In other study the peanut shell were pyrolyzed to produce biochar and used to extract Cr (I II), Cu (II) and Pb (II) and it was found that it extracted 80 %, 85 % and 90 % of the metal ions, respectively. This shows that biochar adsorbs more heavy metals ions, thus it necessary to thermally degrade the biomass before usage. More literature on the usage of peanut shells to extract heavy metals in wastewater are reviewed in this article to further show that peanut shells have potential to be used as an adsorbent.