Surface modification of Trema orientalis wood biochar using natural coconut vinegar and its potential to remove aqueous calcium ions: column and batch studies

Abstract

Recent investigations have revealed the harmful health effects of elevated calcium levels in drinking water. Chemically activated biochar is the most popular option for low-cost cation adsorption. However, most of these chemicals are hardly available for rural communities, corrosive, and difficult to handle by unskilled personnel. This study aimed to determine the ability of natural coconut vinegar, a common mild acid, to activate Trema orientalis wood biochar pyrolyzed at 300ºC (BC) as a facile, safe, and low-cost approach for aqueous calcium ion (Ca 2+ ) removal. Column tests showed a two-fold increase of Ca 2+ adsorption capacity and a ten-fold increase of Ca 2+ retaining capacity of BC after activation with vinegar. The isotherm results were well correlated with the Langmuir model. The maximum Langmuir adsorption of the activated biochar (BC-A) was 9.96 mg/g. Ca 2+ amount was determined using flame photometry. EDX analysis showed that the O/C ratio of BC increased from 0.07 to 0.13 after activation. FTIR and wettability studies showed increased oxygenated functional groups on the BC-A surface. The authors suggest a possible acid-catalyzed hydration of the C-O-C bridges of the biochar, introducing new hydroxyl/carbonyl/ester/carboxylic/lactone groups to the biochar surface due to the vinegar activation, enhancing Ca 2+ adsorption through chemisorption.

Facile, green approach for aqueous methylene blue dye adsorption: Coconut vinegar treated Trema orientalis wood biochar

“…The experimental adsorption capacity could be greater due to the multilayer physical adsorption. Authors of this study have previously reported the effective use of vinegar-activated biochar in reducing water hardness [11,12]. To our knowledge, no previous studies have reported the adsorption of MB onto Trema orientalis wood biochar or any other form of vinegar-activated biochar.…”

“…Dried wood pieces were slow pyrolyzed (300。C, 2 h) under limited oxygen conditions in a household kiln. Pyrolyzed product was washed with deionized water, dried in an oven (80。C, 12 h), and ground to powder (< 0.5 mm) [12]. It was tagged as WB.…”

“…Nevertheless, these chemicals used in biochar activation are not accessible to rural communities, are unfavoured due to their corrosiveness, need skilled personnel to handle the procedures, and may even cause secondary pollution. Thus, the importance of finding natural activating agents for biochar, which are safe to handle and attainable for rural communities, was identified [11,12].…”

“…It is obtained by the fermentation of the sap of coconut blossoms, where ethanol undergoes oxidation to form acetic acid without any preservatives or chemicals. Natural coconut vinegar is ~4% acetic acid in water with an approximate pH of 2.5 [11,12]. Trema orientalis is a tropical tree with light wood, soft foliage, and a rapid growth rate which is amply available in Africa and Asia.…”

“…In addition, the low yield and high energy consumption during the process subdue the advantage of the cost-effectiveness of biochar. Considering the merits and demerits mentioned above, the pyrolysis of Trema orientalis wood was performed at 300。C in this study [12].…”