Sorption isotherms of NH₄⁺-N on wheat-straw biochar (W-BC), corn-straw biochar (C-BC) and peanut-shell biochar (P-BC) at different pyrolytic temperatures (Q_e: the amount of NH₄⁺-N sorbed by per unit mass of biochar at equilibrium; Ce: concentration of NH₄⁺-N in the solution at equilibrium).

<p>Bars indicate standard deviation of three replicates.</p

Sorption of NH₄⁺-N and NO₃⁻-N by W-BC500, C-BC500 and P-BC500 with different treatments in 50 mg L⁻¹ aqueous solutions.

<p>Note: Different letters indicate significant difference for the results and the adsorbed amounts of NH₄⁺-N and NO₃⁻-N were compared separately.</p><p>Sorption of NH₄⁺-N and NO₃⁻-N by W-BC500, C-BC500 and P-BC500 with different treatments in 50 mg L⁻¹ aqueous solutions.</p

Regression parameters of isotherms for expressing adsorption of solution NH₄⁺-N to W-BC, C-BC and P-BC at different pyrolytic temperatures.

<p>Regression parameters of isotherms for expressing adsorption of solution NH₄⁺-N to W-BC, C-BC and P-BC at different pyrolytic temperatures.</p

Sorption isotherms of NO₃⁻-N on wheat-straw biochar (W-BC), corn-straw biochar (C-BC) and peanut-shell biochar (P-BC) at different pyrolytic temperatures (Q_e: the amount of NO₃⁻-N sorbed by per unit mass of biochar at equilibrium; Ce: concentration of NO₃⁻-N in the solution at equilibrium).

<p>Bars indicate standard deviation of three replicates.</p

Correlations between mass of NH₄⁺-N adsorbed per mass of biochar at equilibrium (Qe) and content of C (a), content of O (b), atomic ratio O/C (c), atomic ratio H/C (d), atomic ratio (O+N)/C (e) and CEC of corn-straw biochar (f), respectively.

<p>The symbols ▪, , ▴ and ▾ represented pyrolysis temperatures at 400°C, 500°C, 600°C and 700°C, respectively.</p

Effects of Feedstock and Pyrolysis Temperature on Biochar Adsorption of Ammonium and Nitrate

<div><p>Biochar produced by pyrolysis of biomass can be used to counter nitrogen (N) pollution. The present study investigated the effects of feedstock and temperature on characteristics of biochars and their adsorption ability for ammonium N (NH₄⁺-N) and nitrate N (NO₃⁻-N). Twelve biochars were produced from wheat-straw (W-BC), corn-straw (C-BC) and peanut-shell (P-BC) at pyrolysis temperatures of 400, 500, 600 and 700°C. Biochar physical and chemical properties were determined and the biochars were used for N sorption experiments. The results showed that biochar yield and contents of N, hydrogen and oxygen decreased as pyrolysis temperature increased from 400°C to 700°C, whereas contents of ash, pH and carbon increased with greater pyrolysis temperature. All biochars could sorb substantial amounts of NH₄⁺-N, and the sorption characteristics were well fitted to the Freundlich isotherm model. The ability of biochars to adsorb NH₄⁺-N followed: C-BC>P-BC>W-BC, and the adsorption amount decreased with higher pyrolysis temperature. The ability of C-BC to sorb NH₄⁺-N was the highest because it had the largest cation exchange capacity (CEC) among all biochars (e.g., C-BC400 with a CEC of 38.3 cmol kg⁻¹ adsorbed 2.3 mg NH₄⁺-N g⁻¹ in solutions with 50 mg NH₄⁺ L⁻¹). Compared with NH₄⁺-N, none of NO₃⁻-N was adsorbed to biochars at different NO₃⁻ concentrations. Instead, some NO₃⁻-N was even released from the biochar materials. We conclude that biochars can be used under conditions where NH₄⁺-N (or NH₃) pollution is a concern, but further research is needed in terms of applying biochars to reduce NO₃⁻-N pollution.</p></div

FT-IR spectrum of wheat-straw biochar (W-BC), corn-straw biochar (C-BC) and peanut-shell biochar (P-BC) at different pyrolytic temperatures and the biochars with different treatments at 500°C (a: W-BC, b: C-BC, c: P-BC, d: W-BC500 with acid- and DI water-washed treatments, e: C-BC500 with acid- and DI water-washed treatments, f: P-BC500 with acid- and DI water-washed treatments).

<p>FT-IR spectrum of wheat-straw biochar (W-BC), corn-straw biochar (C-BC) and peanut-shell biochar (P-BC) at different pyrolytic temperatures and the biochars with different treatments at 500°C (a: W-BC, b: C-BC, c: P-BC, d: W-BC500 with acid- and DI water-washed treatments, e: C-BC500 with acid- and DI water-washed treatments, f: P-BC500 with acid- and DI water-washed treatments).</p

The yields, chemical compositions and atomic ratios of biochars produced from different feedstocks at different pyrolytic temperatures.

<p>The biochars include wheat-straw biochar (W-BC), corn-straw biochar (C-BC) and peanut-shell biochar (P-BC) as well as biochars pyrolyzed at 500°C and washed with acid (A-W-BC, A-C-BC and A-P-BC) and deionized water (W-W-BC, W-C-BC and W-P-BC).</p><p>Note: Different letters indicate significant difference for the results in the same column, excluding the biochars washed with acid and water.</p><p>The yields, chemical compositions and atomic ratios of biochars produced from different feedstocks at different pyrolytic temperatures.</p

pH values, electrical conductivity (EC), ash content, cation exchange capacity (CEC), BET surface area, pore volume and pore size of W-BC, C-BC and P-BC at different pyrolytic temperatures.

<p>Note: Different letters indicate significant difference for the results in the same column.</p><p>pH values, electrical conductivity (EC), ash content, cation exchange capacity (CEC), BET surface area, pore volume and pore size of W-BC, C-BC and P-BC at different pyrolytic temperatures.</p