Charcoal Residue from Cashew Nutshells as a Bioadsorbent in Fixed Bed Column for Produced Water

Abstract

One of the produced water treatment methods is adsorption, however, the use of commercial activated carbon as an adsorbent, in industrial scale, makes the process expensive. An alternative for replacing commercial activated carbon is the use of bioadsorbents, which have been gaining emphasis in recent decades, high performance, and low production costs. The objective of this work is to develop an efficient and low cost bioadsorbent by reusing the charcoal from the cashew nutshell (Anarcadium accidentale L.) for the removal of metal ions (Cu²⁺, Pb²⁺ and Cr³⁺), oil and grease content (OGC). The bioadsorbent was pretreated with NaOH and characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), point of zero charge (pHpzc) and Boehm titration. The adsorption tests involved adsorption kinetics and equilibrium experiments in a batch system using metallic solution and in a fixed bed column using multi-element metallic and semi-synthetic OGC solution. The characterization results revealed the presence of hydroxyl, carboxyl and carbonyl groups, as well as an irregular and heterogeneous structure, which are favorable characteristics for the adsorption process. The bioadsorbent was able to remove 98.9; 90.9, 77.1 and 100% for Cu²⁺, Pb²⁺, Cr³⁺ and OGC, respectively, in a fixed bed adsorption column. It is concluded that bioadsorbent developed has high potential for removing metals and OGC, in addition to being an abundant product in nature, renewable, biodegradable and its reuse contributes to reduce environmental pollution, waste production and improves the local circular economy through the recovery of the by-product.