Thesis
Efficient utilisation of biochar for water remediation and soil amendment - towards a circular economy
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2026
- Thesis identifier
- T17579
- Person Identifier (Local)
- 202189988
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- In recent years, an increasing volume of work has been conducted on the use of modified biochar for the recovery of phosphorus (P) from aqueous systems, with potential applications in the treatment of waterbodies with excessive plant and algal growth due to detrimentally high nutrient levels. Considering biochar's suitability for use in soil systems, the opportunity exists to create a circular economy framework by utilising biochar for the recovery of aqueous P with subsequent recycling back to soil. However, further clarification is needed in the literature regarding the optimal process for producing functionalised biochar for the discussed purpose, with an enhanced understanding of biochar’s aqueous P-recovery mechanisms and resilience to environmental factors required before implementing the process in real systems. This thesis presents the optimisation of Ca-biochar (calcium salt functionalised biochar) production for aqueous P-removal using a design of experiments (DoE) methodology to understand the effect of two key functionalisation parameters (pyrolysis temperature and chemical loading ratio (CLR)) on the physicochemical properties and aqueous P-removal of biochars. Aqueous P-removal mechanisms are discussed, and the performance of Ca-biochars in conditions reflective of real wastewaters is presented, alongside pot trials demonstrating the suitability of P-charged biochar as a soil amendment. Biochar functionalised using calcium chloride demonstrated a superior P-removal capacity compared to biochar functionalised using magnesium chloride. Pre-pyrolysis particle size control and activation were found to increase uptake of calcium salt, and subsequently the aqueous P-removal of biochar samples, compared to post-pyrolysis particle size control or activation. Optimal P-removal was achieved when impregnating particle-size-controlled wood flakes pre-pyrolysis with CaCl2. A DoE methodology successfully determining the relationship between functionalisation conditions (pyrolysis temperature and CLR) and key physicochemical characteristics (yield, surface area, average pore volume, and mass ratio of Cl:Ca) of biochar is presented. A mechanism for the transformation of CaCl2 to CaCO3 during pyrolysis is proposed. Aqueous P-removal by Ca-biochars synthesised in this work was found to occur via a dual mechanism of bulk precipitation and adsorption. The Ca-biochar samples produced demonstrated excellent total P-removal, achieving up to 97% removal in a 20 mgP/L solution and 79 % in a 200 mgP/L solution. Adsorption alone was able to remove up to 43.7 % of P in a 20 mgP/L solution, with regression analysis successfully determining a quadratic relationship between P-adsorption and functionalisation conditions. Biochars' P-adsorption was shown to be subject to synergistic effects of functionalisation conditions, with optimal CLR increasing with rising pyrolysis temperature. The Ca-biochar samples displayed excellent resilience to changes in pH and the presence of coexisting ions. However, the samples experienced a significant decrease in P-recovery at low initial concentrations, removing up to 27% of P from a 1 mgP/L solution, with initial concentrations <1.21 mgP/L preventing precipitation and reducing adsorption. Biochar produced would be suitable for the remediation of eutrophic waters via waterbed sediment inactivation and the prevention of eutrophication via the treatment of municipal wastewaters and trade effluents. Pot trials demonstrate the use of P-charged Ca-biochars to be suitable as a soil amendment capable of increasing germination and growth rate compared to control samples. The work presented in this thesis helps establish a best practice for the production of Ca-biochar for aqueous P recovery, providing key insights into the effects of the functionalisation process on the physicochemical properties and aqueous P-removal of biochars. A dual P-removal mechanism considering the effects of bulk precipitation is presented for the first time in the literature, providing essential insight into the P-cycling potential of biochar. The suitability of Ca-biochar for use in real water systems and supporting plant growth is demonstrated. These results provide proof of concept for a biochar circular process capable of recovering and recycling P within the environment.
- Advisor / supervisor
- Zhang, Xiaolei
- Fletcher, Ashleigh
- Resource Type
- DOI
- Date Created
- 2025
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