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.

Removal of ammonium from aqueous solutions using alkali-modified biochars

“…The Langmuir maximum adsorption capacities of the three biochars were 202.5, 243.3, and 217.4 mg/g for CS, PS, and CC, respectively. [17] Similar to that of the unmodified biochars, the three modified biochars also sorbed the ammonium in aqueous solutions in relatively fast ways (Figure 2). It only took 5-10 h for the adsorption kinetic curves to reach the equilibrium, which was slightly faster than that of the unmodified biochars.…”

“…The feedstock materials were grounded and then treated with 1.0 M NaOH solution at a solid-liquid ratio of 1.0 g to 2.5 mL for 2 h. This NaOH concentration was selected through a pre-experiment that showed it produced the modified biochar with higher removal of ammonium from aqueous solutions than other two NaOH concentrations ( Figure S1, Supporting Information). Each of the alkali-treated feedstock materials was oven dried and then converted into the modified biochar through slow pyrolysis at 300 °C following the procedures of Gao et al [17]. The resulting biochar samples were ground and sieved into a size range of 0.9-1.2 mm, washed with DI water, and then oven dried.…”

“…For each condition, the biochar (0.1 g) was mixed with 50 mL ammonium solutions (50 ppm) in the centrifuge tube and the mixture was shaken in the mechanical shaker (120 r/min) for 24 h. The experimental conditions were similar to that of Gao et al [17].…”

“…[10][11][12] While most of the previous studies on biochar-based sorbents mainly focus on heavy metal and organic contaminants, [3,4,13] relatively less research attention has been paid to the removal of aqueous nutrients. [14][15][16] Recently, Gao et al [17] found that biochars derived from agricultural residuals can effectively removal ammonium, a nutrient compound, from aqueous solutions. As a follow-up, this work was designed to examine the adsorption of ammonium onto modified biochars.…”

“…Because biochar surfaces are often negatively charged, [18,19] it can adsorption cations such as ammonium through electrostatic interactions. [17,20] Thus it is anticipated that alkali treatment of the biochar would increase the negative charges on its surfaces to enhance the removal of ammonium. The specific objectives of this work were to: (1) develop surface modified biochars with alkali treatment; (2) measure the sorption kinetics and isotherms of ammonium onto the modified biochars; and (3) determine the effects of temperature, pH, and ionic strength on ammonium sorption.…”