Peanut Shell-Derived Biochar as a Low-Cost Adsorbent to Extract Cadmium, Chromium, Lead, Copper, and Zinc (Heavy Metals) from Wastewater: Circular Economy Approach

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 shell-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) were used to extract lead and the peanut shells' dosages were at 0.5 g, 1.0 g, and 1.5 g and it was found that 74.36%, 74.57%, and 74.05% of lead was extracted, respectively. In other study, the peanut shells 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 metal ions; thus, it is 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.

Adsorptive removal of heavy metals from wastewater using Cobalt-diphenylamine (Co-DPA) complex

“…Usually, heavy metal ions can be adsorbed on the surface of the adsorbent via intermolecular interactions. The amputation of heavy metals from numerous sources of wastewater has reportedly been accomplished using commercial activated carbon [ 15 , 29 , 30 ], zeolites, and biomass-derived adsorbents like peanut shells [ 31 – 33 ], banana peel [ 34 , 35 ], dry tree leaves [ 36 ], rice husk [ 37 ], tea and coffee waste [ 38 ], coconut shell powder [ 39 ], papaya seed [ 40 ], and eggshell [ 41 ]. Nevertheless, some problems, including the need for a prolonged reaction time, excessive calcination temperature, inadequate stability, short reusability, a low surface area, etc.…”

Hydrothermal liquefaction for biochar production from finger millet waste: its valorisation, process optimization, and characterization

“…The increased HHV could be attributed to the release of ionic substances into the biochar and enhanced carbon content in biochar. 48,49 Fig. 4 Numerical optimization is a process of making compromises between responses, to achieve a common target.…”

“…The increased HHV could be attributed to the release of ionic substances into the biochar and enhanced carbon content in biochar. 48,49…”

Biochar Production and Demineralization Characteristics of Food Waste for Fuel Conversion

“…The HHV increased at 400 °C because this temperature triggered the pyrolysis reaction; subse- In all temperature ranges, the HHV of food waste-based biochar increased after demineralization (Figure 1), while the chlorine concentration decreased after demineralization. HHV increases with temperature and residence time because ionic substances are released inside the biochar, and there is an increase in carbon content [33,34]. The HHV increased at 400 • C because this temperature triggered the pyrolysis reaction; subsequently, it slightly decreased at 500 • C [31].…”