Comparison of the physico-chemical properties of biochar with their utility for water remediation and fertilisation

Nguyen, Van Hien (2019). Comparison of the physico-chemical properties of biochar with their utility for water remediation and fertilisation. University of Birmingham. Ph.D.

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Three biochars (BC) were produced from Vietnamese biomass (acacia wood chip, rice husk, and bamboo) using Top Lid Up-draft Drum (TLUD) technology. The resulting biochars were characterized using a suite of state-of-the-art methods to understand their surface area, morphology, cation exchange capacity, and surface chemistry as a basis for determining their utility for application in agriculture in Vietnam. Adsorption experiments for ammonium (\(NH_4^+-N\)) and heavy metal (\(Zn^{2+}\)) in artificial aqueous solutions were conducted to assess the adsorption capacity of the various biochars. The mechanism of adsorption was assessed via the isotherm models (Langmuir, Freundlich, Temkin), the kinetic models (Lagergren-first order and pseudo-second order models) and the intraparticle diffusion model. Then, a real wastewater (landfill leachate) with various pollutants was used to test the adsorption capacity of the biochar under environmental conditions. Biochar surface areas (measured by BET) decreased in the order wood BC (479.34 \(m^2/g\)) > bamboo BC (434.53 \(m^2/g\)) > rice husk BC (3.29 \(m^2/g\)). Meanwhile, cation exchange capacity (CEC) followed the opposite trend, being rice husk BC (26.70 Cmol/kg) > bamboo BC (20.7 Cmol/kg) > wood BC (13.53 Cmol/kg) indicating a correlation between surface are and absorption capactiy. The morphology, as shown in SEM images corresponds with the area, showing a rough surface with pores for wood BC, a hollow honeycomb-like structure for bamboo BC, and smooth surface for rice husk BC. All three biochars produced were alkaline, with pH values around 10. The surface chemistry, measured by FTIR, indicated that carboxyl and hydroxyl groups or \(CO_3^{2+}\) group were observed for all three biochars, but \(PO_4^{3-}\) and \(SiO_2\) groups were only present in rice husk and wood BCs. The surface function groups played an important role for the adsorption of the biochars.

The differences in physicochemical properties resulted to various adsorption capacities among the biochars. For example, the adsorption capacity for \(NH_4^+-N\)was in the order rice husk BC > bamboo BC > wood BC, and the adsorption process was governed by surface functional groups, cation exchange, and intraparticle diffusion. In comparison, the adsorption for \(Zn^{2+}\) was in the order bamboo BC > rice husk BC ≥ wood BC, and the the organic groups (carboxyl and hydroxyl groups), and inorganic groups (\(CO_3^{2+}\), \(PO_4^{2-}\)) mainly controlled the adsorption (rather than ion exchange). There was a strong increase in adsorption for \(NH_4^+-N\)with increasing adsorbate concentrations (20-320 mg/L), while the \(Zn^{2+}\) adsorption was slowly enhanced at adsorbate concentrations higher than 60 mg/L. However, the adsorption of both the adsorbates onto the three biochar occurred via the mechanism described as multilayer formation on a heterogeneous surface.

The findings of the experiments for the wastewater (landfill leachate with concentration of \(NH_4^+-N\) up to 1790.18 mg/L) indicated that the single biochars had an excellent adsorption for \(NH_4^+-N\) with an order as for rice husk BC (44.06 ± 1.55 mg/g) > bamboo BC (40.41 ± 0.95 mg/g) ̴ wood BC (38.90 ± 1.78 mg/g). Interestingly, the binary and ternary biochars also showed a good adsorption for \(NH_4^+-N\), but not significant difference (p > 0.05) among them with the adsorption fluctuating between 39.89 and 43.10 mg/g. In addition, the ternary biochar (1:1:1) used for column test showed to be effective for \(NH_4^+-N\) removal with 43.69 ± 2.15 % removed after the leachate gone through the filter four times with flow rate 1 mL/min. However, the adsorption capacity of the single biochars was still lower than the theoretical maximum adsorption for \(NH_4^+-N\) due to the adsorption competitions of other cations (\(Ca^{2+}\), \(Mg^+\), \(Na^+\)) in the leachate. In particular, all the biochars (including binary and ternary biochars) did not adsorb \(K^+\) ions in the leachate, while \(K^+\) ions from the biochar surface were observed to exchange into the exited solvent to participate in the cation exchange process for the adsorption. Hence, the three biochars demonstrated to have good adsorption for \(NH_4^+-N\) (especially rice husk BC), while bamboo BC was identified as the best choice for \(Zn^{2+}\) removal. The information presented in this thesis will be shared with local farmers in Vietnam to help them select the most efficient biochar to use for their specific needs in water purification and/or soil fertilization utilizing existing local biomass and local production methods.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
Licence: All rights reserved
College/Faculty: Colleges (2008 onwards) > College of Life & Environmental Sciences
School or Department: School of Geography, Earth and Environmental Sciences
Funders: Other
Other Funders: Ministry of Agriculture and Rural Development (MARD), Vietnam International Education Development (VIED) - Ministry of Education and Training (MOET), EU FP7 Marie Curie Career Integration grant EcofriendlyNano
Subjects: S Agriculture > S Agriculture (General)
T Technology > TP Chemical technology


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