Development of Functionalized Solvochar for Wastewater Treatment

Rice (Oryza sativa) husk (RH) is one of the major agricultural waste residues worldwide. In Australia alone, rice cultivation covers approximately 8000 km2 land by almost 2000 rice farms. Around 200,000 tons of RH is produced annually as agro-waste in Australia. The research on application of RH for adsorbent development has been well-documented in the literature due to its’ rich lignocellulosic components, intrinsic carbon-silica matrix, granular structure, physicochemical stability, renewable nature, low cost and abundance. In this thesis, an attempt is made to synthesize novel multi-functional RH-based adsorbent/s for wastewater treatment in particular, for heavy metal removal and antibacterial activity. Hydro/solvothermal carbonization techniques using different solvents such as water, ethanol, and isopropanol have been applied to convert RH into hydro/solvochar. Comprehensive experimental work has been carried out at different temperatures and reaction times to determine the optimized hydro/solvochar yield and physicochemical functionalities. Alkaline treatment of pristine RH and hydro/solvochar by activating agent, potassium hydroxide (KOH), and one-pot solvothermal carbonization with and without KOH have been performed for adsorbent production. These adsorbents were comprehensively characterized for enhancing the surface area, porosity, functional groups, crystallinity, surface morphology, surface charge, organic-inorganic compounds, and thermal stability to evaluate its ability for heavy metal removal from wastewater. Furthermore, the hydro/solvochar were treated with silver nanoparticles (AgNPs) to integrate the anti-microbial properties. The novelty of this doctoral dissertation lies in the introduction of a pioneering methodology for the synthesis of multifunctional AgNPs-modified RH-derived hydro/solvochar to enhance the overall physico-chemical properties, with the explicit aim of achieving improved efficacy in the treatment of wastewater. Fixed-bed continuous flow column adsorption experiments were performed for studying the removal of copper (Cu(II)), iron (Fe(III)), manganese (Mn(II)), lead (Pb(II)) and zinc (Zn(II)) ions from wastewater. Dynamic changes in surface area, porosity, and chemical functionalities were analyzed by passing set amount of wastewater in a single cycle and performing cyclic experiments upto three cycles (till adsorbents reaching saturation point). The adsorption experimental data were then fitted into the adsorption kinetic modeling, intra-particle diffusion (IPD) to derive kinetic parameters and derive mechanism. Among the studied hydro/solvochars, calcined-Ag-modified-RH hydro/solvochars presented a very high multi-heavy metal uptake till saturation point, comparable to commercial activated carbon. Followed by this, these adsorbents were experimented against Gram-positive bacteria, Staphylococcus aureus, and Gram-negative bacteria, Escherichia coli, with different concentrations of dosages. Very low concentration of Ag-loaded hydro-solvochar successfully inhibited the growth of all colonies of both bacteria. The adsorbents developed in this thesis can be deployed in wastewater treatment as part of their tertiary treatment unit, upon completion of long-term performance assessment and techno-commercial feasibility analysis.