Elsevier

Bioresource Technology

Volume 272, January 2019, Pages 465-472
Bioresource Technology

Adsorption characteristics of ammonium ion onto hydrous biochars in dilute aqueous solutions

https://doi.org/10.1016/j.biortech.2018.10.064Get rights and content

Highlights

  • Bamboo biochar effectively adsorbs ammonium from dilute aqueous solutions.

  • pH, ionic strength, particle size, and temperature affect ammonium adsorption.

  • Surface hydroxyl groups development on hydrous biochar surface.

  • FTIR results show changes of surface chemical groups upon ammonium adsorption.

  • Surface complexation and precipitation are major ammonium adsorption reactions.

Abstract

This research aims at studying the characteristics of ammonium adsorption onto hydrous bamboo biochar. Results showed that pH played the most important role in ammonium adsorption. High ionic strength enhanced the ammonium adsorption capacity of bamboo biochar. Ammonium adsorption was exothermic and spontaneous. FTIR results showed shift, disappearance, or appearance of specific functional groups on the bamboo biochar surface. Surface precipitation and complex formation contributed to the adsorption of ammonium onto hydrous bamboo biochar. Biochar can be an effective adsorbate for ammonium removal from water. Additionally, the formation of nitrogen containing precipitates on the biochar surface, potentially, leads to the in-situ synthesis of slow-release fertilizer.

Introduction

The International Biochar Initiative has defined biochar as a solid material obtained from thermochemical conversion of biomass in an oxygen-limited environment. As an old material, biochar has been endowed with ample of new opportunities, e.g., carbon sequestration, environmental remediation, and energy production (Lehmann, 2009). To date, biochar has received extensive attention mainly because of its potential in agronomic and environmental applications. Pyrolysis of raw biomass is a low-cost operation and can also produces many by-products, such as valuable biooil and syngas (Ahmad et al., 2014). Biochar can adsorb a wide variety of environmental pollutants because of its numeral unique physical properties such as highly porous structure and high specific surface area. Additionally, biochar has been increasingly recognized as a highly efficient and cost-effective sorbent because of its abundant multifunctional groups as well as elemental components. Biochar has been used for the removal of specific chemicals such as potassium, nitrogen and phosphorus, which ultimately can be converted to useful fertilizer products (Mohan et al., 2014).

Ammonium is an emerging contaminant. Ammonium volatilization can inhibit the photosynthesis of algae through chlorophyll fluorescence and electron transport. Excessive ammonium in fishing ponds is harmful to the respiratory metabolism of fish, which causes brain swelling via gill injury. Especially, excessive application of fertilizer also increases nitrogen flux to aquatic systems, which may deteriorate surface and ground water quality and bring about eutrophication in water bodies. Therefore, it is therefore of great importance to develop effective technology for the control of ammonium in the aquatic environment.

Efforts toward the control of ammonium flux into the environment have been focused on biological degradation (Reinhart and Basel Al-Yousfi, 1996), advanced oxidation (Murray and Parsons, 2004), and adsorption processes. Among the above methods, adsorption is a relatively simple operation, especially for dealing with solutions of dilute ammonium concentration, and thus has received most attention. Furthermore, among many ammonium adsorbents, there is recent interest on the development of black carbon adsorbent because of its porous structure, large specific surface area, thermostability, which are important properties for ammonium removal from water. Furthermore, the nutrient loaded biochar is an ideal organic fertilizer. A biochar soil management program for the recycling of agricultural wastes and energy production using renewable resources is the most innovative strategy (Lehmann et al., 2006). Currently, biochar also has been applied as a soil amendment to enhance radish yields in the presence of N fertilizer and particularly to produce significant agronomic value in a hard-setting soil (Chan et al., 2007). The great advantage of ammonium-laden biochar is that the post-adsorption product can be reused in the agriculture field as a slowly releasing fertilizer, which has been proved to increases soil fertility and crop productivity (Mohan et al., 2014). Therefore, biochar, in essence, can replace the relatively expensive traditional adsorbents such as activated carbon for ammonium adsorption and become a nitrogen fertilizer that slowly releases nitrogen nutrient to the soil matrix.

There are many studies on the adsorption of ammonium onto biochar (Yao et al., 2012, Hale et al., 2013, Hollister et al., 2013). But there is little agreement on the effect of pertinent parameters on ammonium adsorption capacity. Equally lacking is the mechanistic aspects of ammonium adsorption onto hydrous biochar. (Hale et al., 2013) reported that both unburned cacao shell and corn cob biochar effectively adsorbed ammonium-N (Hale et al., 2013), while (Hollister et al., 2013) found no adsorption of nitrogen onto biochar derived from corn (Zea mays L.) and oak (Quercus spp.). (Yao et al., 2012) reported that nine out of thirteen biochars had little adsorption capacity for nitrogen. The different results reported in the literature can be readily attributed to the use of different types of biochar studied. (Hale et al., 2013) reported that ion exchange was responsible for ammonium adsorption, while (Hollister et al., 2013) reported H-bond formation between ammonium and biochar surface contributed to ammonium adsorption. However, (Yao et al., 2011a) reported that the colloidal and nano-sized MgO particles on the biochar surface were the major binding sites.

The present study is to assess the role of pH, as a maser variable, and other pertinent parameters such as ionic strength and temperature on ammonium adsorption onto hydrous biochar exemplified by bamboo biochar. How to describe the surface acidity of biochar with respect to ammonium adsorption in lieu of its highly heterogeneous and complex nature? What role the ash composition of biochar plays in ammonium adsorption? In order to answer the above equations, this present study aimed at 1) quantifying the surface acidity of biochar, 2) investigating the effect of parameters, such as pH, particle size, ionic strength, and temperature, on the adsorption of ammonium onto hydrous bamboo biochar, and 3) gaining insight into the adsorption mechanism of ammonium onto hydrous bamboo biochar.

Section snippets

Chemicals and biochar preparation

Ammonium chloride and sodium chloride were purchased from Fisher Scientific™. Bamboo-derived biochar was purchased from Lewis Chemical Company, Rome, GA, USA and ground into different particle sizes with mortar and pestle in nitrogen-filling chamber. According to the manufacturer, the biochar was prepared by low-temperature pyrolysis at 370 °C of bamboo in the absence of air. The biochar was ground and sieved into different size classes then stored in clean glass bottles with lids until use.

Ash content and ash element composition

The

Ash content and element composition

Table 1 shows that the ash content of the bamboo biochar was 5.80 and 5.22% on a wet and dry basis, respectively. The difference was attributed to its moisture content of 9.95%. The bamboo biochar used in this study had a relatively higher ash content than samples reported by Liu et al. (2014). As indicated above, a higher ash content of the bamboo biochar may be derived from its low pyrolysis temperature of about 370 °C.

To some extent, the ash content can be determined for the mineral-rich

Conclusion

Ammonium ions can be effectively absorbed on the bamboo biochar surface at the maximum adsorptive capacity of 6.38 mM-g−1. Solution pH plays a major role on ammonium adsorption. Particle size of biochar in the range of 88–917 µm, did not have significant influence on ammonium adsorption. Interestingly, higher ionic strength enhanced the adsorption of ammonium, which indicated the possible contribution of physical reaction, i.e., electrostatic force, specific chemical bonds, and surface

Acknowledgements

This work was provided by US NSF IOA grand number 1632899 to CPH.

References (48)

  • S.E. Hale et al.

    The sorption and desorption of phosphate-P, ammonium-N and nitrate-N in cacao shell and corn cob biochars

    Chemosphere

    (2013)
  • M. Jia et al.

    Effects of pH and metal ions on oxytetracycline sorption to maize-straw-derived biochar

    Bioresour. Technol.

    (2013)
  • S. Kizito et al.

    Evaluation of slow pyrolyzed wood and rice husks biochar for adsorption of ammonium nitrogen from piggery manure anaerobic digestate slurry

    Sci. Total Environ.

    (2015)
  • J. Li et al.

    The role of ash content on bisphenol A sorption to biochars derived from different agricultural wastes

    Chemosphere

    (2017)
  • J. Liu et al.

    Effect of pH, ionic strength, and temperature on the phosphate adsorption onto lanthanum-doped activated carbon fiber

    J. Colloid Interface Sci.

    (2011)
  • Z. Liu et al.

    Combustion characteristics of bamboo-biochars

    Bioresour. Technol.

    (2014)
  • Z. Liu et al.

    Removal of lead from water using biochars prepared from hydrothermal liquefaction of biomass

    J. Hazard. Mater.

    (2009)
  • D. Mohan et al.

    Sorption of arsenic, cadmium, and lead by chars produced from fast pyrolysis of wood and bark during bio-oil production

    J. Colloid Interface Sci.

    (2007)
  • D. Mohan et al.

    Organic and inorganic contaminants removal from water with biochar, a renewable, low cost and sustainable adsorbent – a critical review

    Bioresour. Technol.

    (2014)
  • A. Mukherjee et al.

    Surface chemistry variations among a series of laboratory-produced biochars

    Geoderma

    (2011)
  • C.A. Mullen et al.

    Bio-oil and bio-char production from corn cobs and stover by fast pyrolysis

    Biomass Bioenergy

    (2010)
  • C. Namasivayam et al.

    Removal of Congo Red from water by adsorption onto activated carbon prepared from coir pith, an agricultural solid waste

    Dyes Pigm.

    (2002)
  • S. Netpradit et al.

    Adsorption of three azo reactive dyes by metal hydroxide sludge: effect of temperature, pH, and electrolytes

    J. Colloid Interface Sci.

    (2004)
  • G. Newcombe et al.

    Adsorption of NOM onto activated carbon: electrostatic and non-electrostatic effects

    Carbon

    (1997)
  • Cited by (84)

    View all citing articles on Scopus
    View full text