Removal of aqueous ammonium by biochars derived from agricultural residuals at different pyrolysis temperatures

Abstract Water contamination by ammonium ions presents huge risks to the ecosystems. This work evaluated the potential of biochar as an alternative adsorbent to remove ammonium from aqueous solutions. Nine types of biochars were converted from three types of agricultural residuals at three pyrolysis temperatures. Batch sorption experiment showed that all the biochars effectively removed ammonium ions from water. The biochars produced at low pyrolysis temperatures, however, showed higher sorption of ammonium. The low-temperature biochars showed relatively fast sorption kinetics of ammonium, which reached equilibrium around 10 h. Sorption isotherms showed that the low-temperature biochars had high sorption capacities to the ammonium, and the Langmuir maximum capacities were all higher than 200 mg/g. Batch sorption experiments also showed the sorption of ammonium onto the biochar was affected by pH and temperature, but not by ionic strength. The biochar showed good sorption ability to ammonium in aqueous solutions under all of the tested conditions. Findings from this work indicated that biochar could be used as an alternative adsorbent for the treatment of ammonium in water.