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

Abstract

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.

Substitution of peat moss with softwood biochar for soil-free marigold growth

“…Compared to peat, the longer decomposition half-life of high-temperature BCs such as the one in this study, and the potential of nutrient ions to bind to BC (Gai et al, 2014;Lehmann and Joseph, 2015;Yao et al, 2012) and re-solubilize when applied to soils (Joseph et al, 2013;Yao et al, 2013) raises the possibility of re-using BC-based substrates as fertilizers.…”

Recovery of nutrients from biogas digestate with biochar and clinoptilolite

“…Similarly, Gai et al (2014) reported a decrease in biochar's ability to remove ammonium after being washed in deionised water. Wang et al (2015) found that the ammonium adsorption capacity of biochar did not change after activation with H2O2 unless the pH of activated biochar was adjusted from 3.7 to 7.…”

“…Biochar has been suggested as a sorbent for ammonium (TaghizadehToosi et al, 2012a;Hale et al, 2013;Gai et al, 2014;Carey et al, 2015;Cui et al, 2016), orthophosphate (Hollister et al, 2013;Sarkhot et al, 2013;Xu et al, 2014) and organic contaminants (Ahmad et al, 2014;Mohan et al, 2014;Wang et al, 2015b) removal from various wastewaters. Chemical activation of biochar has been shown to increase the oxygen-containing functional groups (Xue et al, 2012;Wang et al, 2015a) which affects the cation sorption on biochar, and orthophosphate removal due to cation bridge bonding (Lin et al, 2012;Qian et al, 2013).…”

“…Cation U-BC DW-BC H 2 SO 4 -BC NaOH-BC H 2 O 2 -BC exchange was used as one possible mechanism to explain ammonium removal (Sarkhot et al, 2013;Gai et al, 2014;Cui et al, 2016). Sarkhot et al (2013) observed the release of Ca + ions and Cui et al (2016) reported that Mg 2+ and Ca 2+ were released into the liquid solutions whereas NH4 + was removed, therefore concluding that these cations play an important role in the sorption of ammonium.…”

“…Several studies have suggested that pyrolysis temperature is an important parameter affecting biochar properties (Ahmad et al, 2014;Lehmann & Joseph, 2015). Increasing pyrolysis temperatures results in the removal of oxygen-containing functional groups and produces high aromaticity and low polarity biochars, which may negatively affect ammonium sorption to biochar (Gai et al, 2014). Newly produced biochars are also known to have a low ability to adsorb cations due to the presence of fewer oxygen-containing functional groups (Cheng et al, 2014).…”