Improvement of contaminant retention with the use of biochar in the groundwater infiltration basin of Korba (Tunisia)

The overexploitation of the Korba aquifer (Cap Bon, North Tunisia) has led to the drawing down of its static water level and the degradation of its quality due to the intrusion of saline water from the sea. To address this situation, treated wastewater is used for the artificial recharge of the aquifer through three infiltration basins.
Treated wastewater is known to carry various emerging contaminants and pharmaceuticals as they are often not retained in traditional wastewater treatment plants. To tackle this problem the use of biochars is often recommended to conduct a second stage low-cost decontamination strategy. Indeed, biochar can be produced easily at a low cost, with different agricultural residues. In this study, the impact of biochar derived from Rosemary, Bamboo, St. John's Wort, Olive, Cypress, and Palm Trees on the mobility and retention of emerging contaminants was evaluated.

The first stage of this work was to evaluate the potential retention capacity of the different biochars produced in a low-cost metallic kiln with local biomass residues. Therefore we used Methylene Blue (MB) as a proxy for organic contaminants to establish adsorption isotherms to quantify their respective specific surface area and adsorption capacities.

The adsorption isotherms at 20°C were established to evaluate their respective specific surface areas and were fitted to different adsorption models.
The surface functional groups of biochars were characterized by FTIR spectroscopy.
The analysis of the results showed that the biochar obtained from Rosemary, Bamboo, and St. John's Wort exhibited remarkable elimination and better adsorption capacity with values of 1.6g/L for Rosemary, 0.4g/L for St. John's Wort, and 0.2g/L for Bamboo. An average adsorption capacity was observed with 0.09g/L for Cypress, 0.055g/L for Olive, and low adsorption with a value of 0.03g/L for traditional Olive and Palm Trees.

The second stage was to test the dynamic retention properties of biochar on soil monolith experiments, where the MB elution curves were analyzed with and without the addition of biochar. The presence of biochar in the soil monoliths drastically reduced the retention of MB, demonstrating its efficiency as an adsorbent filter. These results underscore the strong potential of biochar in water treatment to enhance quality by reducing pollution.