BITS Faculty Publications
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Item Adsorption of heavy metals by road deposited solids(IWA, 2013-06) Goonetilleke, AshanthaThe research study discussed in the paper investigated the adsorption/desorption behaviour of heavy metals commonly deposited on urban road surfaces, namely, Zn, Cu, Cr and Pb, for different particle size ranges of solids. The study outcomes, based on field studies and batch experiments, confirmed that road deposited solids particles contain a significantly high amount of vacant charge sites with the potential to adsorb additional heavy metals. Kinetic studies and adsorption experiments indicated that Cr is the most preferred metal element to associate with solids due to the relatively high electronegativity and high charge density of trivalent cation (Cr3+). However, the relatively low availability of Cr in the urban road environment could influence this behaviour. Comparing total adsorbed metals present in solids particles, it was found that Zn has the highest capacity for adsorption to solids. Desorption experiments confirmed that a low concentration of Cu, Cr and Pb in solids was present in water-soluble and exchangeable form, whilst a significant fraction of adsorbed Zn has a high likelihood of being released back into solution. Among heavy metals, Zn is considered to be the most commonly available metal among road surface pollutants.Item Adsorption and mobility of metals in build-up on road surfaces(Elsevier, 2015-01) Goonetilleke, AshanthaThe study investigated the adsorption and bioavailability characteristics of traffic generated metals common to urban land uses, in road deposited solids particles. To validate the outcomes derived from the analysis of field samples, adsorption and desorption experiments were undertaken. The analysis of field samples revealed that metals are selectively adsorbed to different charge sites on solids. Zinc, copper, lead and nickel are adsorbed preferentially to oxides of manganese, iron and aluminium. Lead is adsorbed to organic matter through chemisorption. Cadmium and chromium form weak bonding through cation exchange with most of the particle sizes. Adsorption and desorption experiments revealed that at high metal concentrations, chromium, copper and lead form relatively strong bonds with solids particles while zinc is adsorbed through cation exchange with high likelihood of being released back into solution. Outcomes from this study provide specific guidance for the removal of metals from stormwater based on solids removal.Item Quantifying the influence of surface physico-chemical properties of biosorbents on heavy metal adsorption(Elsevier, 2019-11) Goonetilleke, AshanthaHeavy metals present in industrial wastewater contribute to human and ecosystem health risk when discharged without proper treatment. Low-cost biosorbents with high metal-binding capacity are increasingly being utilized for the removal of heavy metals. Inherent physico-chemical properties of biosorbents significantly influence their adsorption capacity. Studies quantifying the influence exerted by these properties on adsorption capacity are scarce. This study quantifies the influence and relative importance of selected physico-chemical properties on the adsorption capacity of three divalent heavy metals; Cu2+, Cd2+ and Pb2+ using multivariate analysis. Twenty one biosorbent mixtures were created, systematically varying their physico-chemical properties using tea factory waste and coconut shell biochar. Their adsorption capacities were measured using batch sorption studies. The influence of physico-chemical properties on the adsorption capacity is comparable for all three metal cations. Regression models were developed to quantify the influence of physico-chemical parameters on the adsorption capacity based on regression coefficients. All models were found to have high reliability with R2 values above 0.98. Acidic surface functional groups were found to act as the key property that governs the adsorption capacity of Pb2+, Cu2+ and Cd2+. Carboxylic groups played a major role in the adsorption of Cu2+ and Pb2+, while lactonic groups were more important in providing binding sites to Cd2+. SSA failed to demonstrate a significant impact on the adsorption capacity of these three metals on its own when the biosorbent had a low surface functional group density.Item Application of Chlorella pyrenoidosa embedded biochar beads for water treatment(Elsevier, 2021-04) Goonetilleke, AshanthaThe ability of biochar beads embedded with freshwater algae ̶ Chlorella pyrenoidosa (Bc-Cp beads) were investigated for their efficiency in the removal of pollutants. Combining these is an innovative concept which can result in improvements in pollutant removal since both, biochar and algae have the ability for adsorbing/absorbing pollutants. Additionally, only limited work on embedding freshwater algae (common algae existing in surface water and having low ecological risks since they are native species) into biochar for the removal of water pollutants has been undertaken to-date. It was found that Bc-Cp beads prepared using 10 mL of algae (9 × 108 cell/mL), 0.3 g of biochar, 40 g/L of sodium alginate, and 20 g/L of CaCl2 displayed the optimum characteristics including mechanical strength (2.548 N), promotion of algae growth (191.70 % growth rate) and pollutant removal ability with the removal efficiency of ammonia nitrogen, total nitrogen and total phosphorus, total organic carbon, zinc and copper were up to 69.2 %, 43.0 %, 73.8 %, 81.0 %, 74.4 % and 81.0 %, respectively. The algae within the beads were primarily responsible for the removal of nutrients by assimilation, while biochar mainly exerted influence on the removal of organic matter and heavy metals by chemisorption. The study outcomes also confirmed that Bc-Cp beads possess high potential to be used in estuarine environments and saline groundwater.Item Removal of heavy metals from water using engineered hydrochar: kinetics and mechanistic approach(Elsevier, 2021-04) Goonetilleke, AshanthaThe isotherm, kinetics, and thermodynamics parameters, and mechanisms involved in the adsorption of Pb2+ and Cu2+ ions from an aqueous solution using engineered hydrochar were investigated. The hydrochar was produced through catalytic hydrothermal carbonization of rice straw at 200 °C with (engineered hydrochar) and without (hydrochar) FeCl3 (1.2 %) as iron catalyst which has been reported to have the ability to enhance surface properties. Batch experiments were conducted to examine the effect of sorbent dosage, pH, and initial metal ion concentration on the adsorptive performance. The results obtained revealed that the addition of iron catalyst increased the surface functional groups, and exhibit better adsorptive performance compared to non-treated hydrochar. The adsorptive performance of engineered hydrochar was higher for Pb2+ compared to Cu2+, which can be explained by surface complexation, cationic- π interaction, and mass diffusion process with the initial removal performance limited by mass transfer process. The Langmuir isotherm model gave the best fit for the adsorption of both metals compared to the other models tested. The adsorption kinetics followed the Lagergren’s pseudo-second order model. Thermodynamic parameters revealed that Pb2+ and Cu2+ adsorption by engineered hydrochar is a spontaneous and endothermic process. Moreover, this study created new knowledge by providing an in-depth understanding of the effect of iron catalyst on the functional properties of engineered hydrochar and its adsorption mechanisms. Research on the use of catalysts in engineered hydrochar for pollutant removal is very limited. In addition, the study outcomes would contribute to the production of highly efficient magnetic hydrochars.Item Lab-scale engineered hydrochar production and techno-economic scaling-up analysis(Elsevier, 2024-02) Goonetilleke, AshanthaDespite the extensive use of engineered hydrochar (EHC) for contaminants adsorption in water, little is known about the scaling-up of EHC production which has kept the technology at a low readiness level (TRL). Full-scale EHC production was simulated to help bridge this knowledge gap. A systematic analysis was performed where EHC was produced from rice straw using hydrothermal carbonization (HTC) at 200 °C with iron addition. A techno-economic evaluation model was employed to simulate the production process and to estimate energy requirements, configuration, and cost scenarios for the HTC process. The minimum selling price (MSP) analysis of the engineered hydrochar was found to be almost half compared to the market price for other similar sorbents ($ 76/t vs. $136/t) suggesting that EHC production is feasible for scaling up. Finally, as a trial, the resulting material was tested for its efficacy in the adsorption of an anionic organic contaminant (e.g., Congo Red, C32H22N6Na2O6S2) in water to identify its potential for water treatment. Experimental results showed that EHC adsorbed > 95% CR suggesting significant adsorption capability and feasibility for production scale-up.Item Optimizing the upcycling of microplastics to a carbon-based adsorbent for water treatment: An integrated experimental and computational approach(Elsevier, 2026-05) Goonetilleke, AshanthaMicroplastics (MPs) are an escalating environmental hazard because they persist in aquatic ecosystems and resist removal by conventional water treatment technologies. A novel data-driven strategy that upcycles MPs into engineered carbonaceous adsorbents via hydrothermal carbonization (HTC) is presented. By systematically varying three synthesis variables – feedstock loading, acid type and acid concentration – a range of carbonaceous materials (CMs) was produced and evaluated for their ability to adsorb Reactive Orange 84 dye. An integrated full factorial design of experiments encompassing both, material synthesis variables (acid type, acid concentration, and polyester (PES) material concentration) and the application variables (CM dose) was implemented. Subsequent statistical analysis and PCA identified acid type, acid concentration, CM dose, and PES concentration as dominant factors controlling adsorption capacity (q_e) and removal percentage. To refine the optimization, several machine learning (ML) models – linear regression, support vector machines, ensemble methods, and neural networks – were trained on the experimental dataset. Acid treated CMs consistently outperformed those synthesized under neutral conditions, with optimal performance observed at moderate acid concentrations. The key innovation in this study lies in the integrated experimental-computational framework that models the entire process (synthesis −> application), coupling rigorous statistical screening with advanced ML prediction. This delivers actionable guidance for the rational design of acid-modified carbonaceous adsorbents and advances the upcycling of MPs for water treatment applications.Item Biogenic carbon matrix with dual-mode adsorption capability: synthesis, characterization and mechanistic insights(Elsevier, 2026-04) Goonetilleke, AshanthaThe transformation of biowaste into high-performance functional materials presents a promising strategy for sustainable environmental technologies. In this study, a novel biogenic carbon-based catalytic matrix (CBCM) was synthesized from prawn shell waste, integrating chitin-derived carbon and in-situ formed calcite to yield a hybrid material with distinctive structural and surface characteristics. Comprehensive characterization using X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) revealed a composite architecture featuring both organic (Chitin) and inorganic (Calcite) crystalline domains, along with abundant surface oxygenated functional groups (Osingle bondH, Cdouble bondO, CO-NH, and Csingle bondO). These structural attributes underpin the CBCM's dual-mode adsorption capability, enabling simultaneous and efficient uptake of both cationic (Malachite green) and anionic (Congo red) dyes. Kinetic and isotherm analyses highlighted the dominant roles of hydrogen bonding and π-π interactions, directly linked to the material's functional groups and porous surface morphology. Response surface modeling confirmed strong agreement between predicted and experimental adsorption capacities (R2 = 0.978), underscoring the reliability of the structure-function correlation. This work demonstrates how rational design and valorization of marine biowaste can yield multifunctional materials, with the CBCM serving as a proof-of-concept platform for pollutant capture and broader environmental applications.