# The Removal of Crystal Violet from Textile Wastewater Using Palm Kernel Shell-Derived Biochar
## 1 Introduction  
Wastewater from paper, textile, cosmetics, food processing, and plastic producing industries contain various kinds of organic and harmful substances such as dyes [1]. Dyes such as crystal violet (CV) are composed of many functional groups that are stable and difficult to decompose because of their aromatic nature [2, 3]. CV is used for making black and blue inks in ball-point pens and in printer ink jet manufacturing industrials [4]. Color paints, pharmaceuticals, leather, detergents, fertilizers, varnish, and waxes are also manufactured from CV [5, 6, 7]. However, CV, similar to most dyes, is a toxic carcinogenic with a recalcitrant classification because of its non-biodegradability, persistence in various environments, and poor microbial metabolization [7, 8, 9]. Furthermore, CV causes undesirable colorations of water bodies, resulting in low light penetration for photosynthetic activities, which affects aquatic life such as the growth of tumors in fish [10, 11]. Consequently, the removal ofCV from wastewater before discharge must be implemented for the survival of both humans and aquatic organisms.  
Recently, many technologies such as ion exchange [12], ozonation [12], coagulation [13], membrane filtration [14; 15; 16], catalytic degradation [17; 18], precipitation [19], electrochemical treatment [20], and adsorption [21; 22; 23; 24; 25] have been investigated for the removal of dyes in wastewater. However, most of these treatments methods are expensive and require large amounts of energy [26]. Therefore, adsorption has been considered attractive due to its ease of operation and high effectiveness [27]. Adsorption should involve the use of low-cost, environmental friendly, and high-capacity adsorbents [28].  
Biochar is a product of the biomass pyrolytic process with high-compact structure and dense surface functional groups that are responsible for its high adsorption capacity and surface reactivity [29; 30]. Unlike highly efficient commercial activated carbon used in wastewater treatment, biochar has low economic viability. Therefore, new raw materials must be explored [31]. Many researchers have focused on the use of agricultural byproducts for the production of biochar because they are readily available, recyclable, less expensive, and easy to handle [32; 33; 34; 35; 36; 37]. Biochar has been prepared from materials such as cabbage waste [38], mango leaves [39], woody trees [40], sugarcane [41], mushrooms [42], rice bran [43], corncobs [44], peanut shells [45], date seeds [46], pine sawdust [47], coir pith [48], and dew melon peel [49] and has demonstrated a high adsorption capacity for the removal of contaminants.  
Palm oil mills processing involve the production of mesocarp fiber and kernel shells [50]. The palm kernel shell (PKS) discarded as waste is chemically stable, insoluble, rich in functional groups [51], and a good candidate for the production of biochar [52; 53]. Additionally, we know of no works on the use of biochar prepared from PKS (BC-PKS) for the removal of CV dye.  
Therefore, this study explored to examine the applicability of BC-PKS for the removal of CV from textile wastewater. Additionally, kinetics, equilibrium, and thermodynamic studies were conducted under batch experiment conditions. Finally, the effect of solution pH and competitive cations on adsorption efficiency was also examined.