Mechanism of Adsorptive Removal of Methylene Blue Using Dried Biomass of Rhizopus oryzae

Preparation of high surface area sludge-based activated hydrochar via hydrothermal carbonization and application in the removal of basic dye

Conventional methods to produce sludge activated carbon require high-energy due to high moisture content and poor dewaterability of the wet sludge. Recently hydrothermal carbonization (HTC) has been emerged as a promising thermo-chemical wet biowaste conversion technology for the valorization by converting these precursors into high value-added products such as a nanostructured carbon. In this study, sludge-based activated hydrochars (SAC) were prepared from high moisture content (88.9%) wastewater sludge (without pre drying) via HTC followed by physical (P-SAC) and chemical (C-SAC) activation with CO₂ and KOH, respectively. Further, the effects of HTC temperatures (170, 200, 230 and 260 °C) and the activation methods on the physicochemical characteristics of hydrochar and SACs were investigated through ultimate analysis (CHNO), SEM, BET, BJH, FT-IR, Boehm back titration and zeta potential. The result showed that KOH-activation at 700 °C could significantly enhance the surface area of hydrochars (from 6.3 to 1613.9 m²/g) compared with CO₂-activation even at 900 °C (261.6 m²/g). The mesopore P-SAC prepared from hydrochar at lower HTC temperature due to the presence of ash content. While, the negatively charged microspores C-SAC (V_Total: 0.88 cm³/g and V_micro/V_Total: 73.3%) with high S_BET was synthesized at higher HTC temperature. Prepared hydrochars were applied for the removal of a basic dye (such as methylene blue, MB) from aqueous solution. Based on Langmuir isotherm model (R²>99.4%), the maximum monolayer MB adsorption capacity of hydrochar, P-SAC and C-SAC were 63.3, 122.4, and 588.2 mg/g, respectively at pH > 8.0. The MB adsorption on C-SACs followed the pseudo-second-order kinetic model and a spontaneous endothermic reaction from 298 to 328 K. The commercial ACs also was compared with our materials and found that produced activated hydrochars showed superior results for MB removal. Therefore, HTC can be the potential carbonization method for wet biomass conversion to valuable carbonaceous material in a cost-effective way.

Utilization of two agrowastes for adsorption and removal of methylene blue: kinetics and isotherm studies

Fresh water streams contaminated with synthetic dye-containing effluents pose a threat to aquatic and human life either by preventing aquatic photosynthesis or by entering into the food chain. Adsorptive removal of such dyes with potent biosorbents is an important technique to reduce bioaccumulation and biomagnifications of the dyes in human life. We report use of betel nut (BN) husk and banana peel (BP), two most abundant ligno-cellulosic wastes, as efficient adsorbents for the removal of the basic dye methylene blue (MB). The adsorption by BN and BP was consistently high over wide ranges of pH and temperature, suggesting their dye removal potential in diverse conditions. Physico-chemical studies, e.g. scanning electron microscopy and Fourier transform-infrared spectroscopy studies, revealed changes in surface topology and functional moieties of BN and BP post adsorption, implying dye interaction with the biomass surface. The dye adsorption in both cases followed pseudo-second-order kinetics. While adsorption of MB by BN was better fitted with the Temkin isotherm model, adsorption with BP followed both Langmuir and Freundlich isotherm models. Our studies concluded that both adsorbents efficiently remove MB from its aqueous solution with BP proved to be marginally superior to BN.

Surface Modification of Naturally Available Biomass for Enhancement of Heavy Metal Removal Efficiency, Upscaling Prospects, and Management Aspects of Spent Biosorbents: A Review

Heavy metal pollution in water emerges as a severe socio-environmental problem originating primarily from the discharge of industrial wastewater. In view of the toxic, non-biodegradable, and persistent nature of most of the heavy metal ions, remediation of such components becomes an absolute necessity. Biosorption is an emerging tool for bioremediation that has gained momentum for employing low-cost biological materials with effective metal binding capacities. Even though biological materials possess excellent metal adsorption abilities, they show poor mechanical strength and low rigidity. Other disadvantages include solid-liquid separation problems, possible biomass swelling, lower efficiency for regeneration or reuse, and frequent development of high pressure drop in the column mode that limits its applications under real conditions. To improve the biosorption efficiency, biomasses need to be modified with a simple technique for selective/multi-metal adsorption. This review is intended to cover discussion on biomass modification for enhanced biosorption efficiency, mechanism studies using various instrumental/analytical techniques, and future direction for research and development including the fate of spent biosorbent. In most of the previously published researches, difficulty of the process in scaling up has not been addressed. The current article outlines the application potential of biosorbents in the development of hybrid technology integrated with membrane processes for water and wastewater treatment in industrial scale.