Innovative capacitive deionization-degaussing approach for improving adsorption/desorption for macadamia nutshell biochar

Adsorption is a well known effective technology for water treatment. Although limited capacities of adsorbents and regeneration issues are two common challenges. This study proposed and tested innovative approaches for improving adsorption/desorption of biochar made from macadamia nutshell (MBC). These approaches are capacitive deionization (CDI) and degaussing (full process detailed in methods), for the respective enhancement of adsorption and desorption of MBC. Nitrate was used as a model contaminant. It was found that CDI could extend the saturation time of MBC by increasing the bed specific throughput by 10 fold. Modeling of the breakthrough curves showed that the modified dose-response model fits well the experimental data. The regeneration of MBC with degaussing and deionized water backwash was compared with conventional tap and deionized water backwash. Degaussing increased the maximum nitrate recovery for deionized water from 50% to 73%. In comparison, the maximum nitrate recovery with tap water was 23%. The degaussing improvement of nitrate desorption holds for only the first 60 min. The obtained charge efficiency for MBC-CDI was slightly higher than literature values for the same applied voltage (78,6%). The degaussing system was also proven to be efficient with energy consumption of 43,7 J/mmol of NO3?. The possible mechanism behind degaussing improvement of nitrate desorption is the removal of the static charges on nitrate ion hydration. The regenerated MBC with degaussing and deionized water was tested with CDI for nitrate adsorption and compared to fresh MBC. The regenerated MBC-CDI exhibited better nitrate adsorption than fresh MBC for two cycles.

Automated summary

Adsorption is effective for water treatment, but limited capacities of adsorbents and regeneration issues are challenges. This study proposed innovative approaches, including capacitive deionization and degaussing, for improving the adsorption/desorption of biochar made from macadamia nutshell. The results showed that CDI extended the saturation time of MBC by 10 fold, while degaussing increased the nitrate recovery rate. The regenerated MBC-CDI exhibited better nitrate adsorption than fresh MBC for two cycles.