EFFICIENCY OF BAOBAB SHELL DERIVED ACTIVATED CARBON IN THE REMOVAL OF INORGANIC ANIONS FROM DOMESTIC WASTEWATER

The release of untreated or poorly treated domestic wastewater containing inorganic anions such as nitrate and sulphate causes major environmental and public health problems in Malawi. Conventional wastewater treatment systems have not been able to effectively remove dissolved inorganic anions; at the same time, advanced treatment technologies are expensive to implement in low resource settings. This study focused on developing a low-cost adsorbent produced from baobab fruit shells to remove inorganic anions from domestic wastewater. Phosphoric acid (H3PO4) was used for one-step chemical activation followed by carbonization at 700°C to produce activated carbon. Measured physicochemical characteristics included the carbon yield, moisture content, volatile matter, ash content, pHpzc, iodine number, pore volume and porosity of the produced adsorbent. Using batch adsorption experiments with wastewater samples obtained from the Malawi University of Science and Technology wastewater treatment facility, batch studies assessed how well the BFS-AC removed nitrate and sulphate by examining the influences of pH, adsorbent dose and contact time. The BFS-AC produced had a carbon yield of 70.3%, low moisture (1.4%), moderate ash (9.27%) and a high iodine number (922.18 mg/g) showing a good mix of porosity and capacity for adsorption. In addition, the pHpzc of the BFS-AC was 4.01, indicating that the adsorbent was acidic in nature. Evaluation revealed that the activation of baobab fruit shell for adsorption purposes would make it more efficient in the removal of nitrate and sulphate compared to raw baobab fruit shell. Furthermore, at pH 7.0, activated carbon provided the highest removal efficiencies of nitrate and sulphate as follows: removal efficiencies of 90.45% for nitrate and 88.14% for sulphate were achieved using an optimum dosage of 2.0 g of activated carbon and contact time of 90 minutes. Nitrate and sulphate were best described by pseudo-second-order models with R2 of 0.9595 for sulphate and R2 of 0.9621 for the nitrate adsorptions. This suggests that there was considerable surface interaction during adsorption process. The Freundlich isotherm provided the best fit for nitrate adsorption with the R2 value of 0.9779 which indicated that heterogeneous adsorption occurred, while the Langmuir isotherm represented the best fit for sulphate adsorption supported by high R2 value of 0.9655 indicating that monolayer-type adsorption occurred at relatively evenly-distributed active sites. The activated carbon also improved the clarity of
wastewater through substantial reduction of the electrical conductivity and total dissolved solids. Therefore, activated carbon (BFS-AC) produced from baobab fruit shell is a costeffective, sustainable and highly effective adsorbent for removing inorganic anions from domestic wastewater. This research demonstrates that locally produced agricultural residue can be used as an alternative to costly wastewater treatment systems promoting sustainable water management, pollution control, and the recovery of resources within Malawi.