Pyrolysis is a promising thermochemical conversion process that transforms biomass into biochar, a carbon-rich solid material, in an oxygen-limited environment. This study focuses on the utilization of rice byproducts, namely rice straw and rice husk as feedstock for biochar production through low-temperature pyrolysis. The aim is to explore the potential of these biochars as cost-effective adsorbents for removing metal contaminants from aqueous solutions, with a particular emphasis on Pb(II) removal. Physicochemical properties of the biochars produced at a low temperature of 300 °C were thoroughly investigated, including surface morphology and their adsorption capacity for Pb(II). Remarkably, the rice straw biochar (RSB) produced at 300 °C exhibited exceptional Pb(II) adsorption capacity, with a value of 390.10±0.30 mg/g, and demonstrated a high Pb(II) removal efficiency of 96.10±0.30% when modified with 30% w/w H2O2. A crucial aspect of this study lies in the evaluation of the cost-effectiveness of the biochar production process, particularly when compared to commercially available adsorbents. By demonstrating the potential of rice byproduct-derived biochar as an efficient Pb(II) biosorbent in aqueous environments, this work not only provides new insights into the preparation of biochar using low-temperature pyrolysis but also offers a viable and economical solution for metal-contaminated water treatment. The findings of this research contribute to the field of sustainable waste utilization and highlight the significant potential of rice byproduct-based biochar as an environmentally friendly adsorbent for heavy metal removal.

In this study, a strain of lactic acid bacteria Streptococcus salivarius was studied for its capacity to remove hexavalent chromium (Cr (VI)) from a liquid medium and to form biofilm. Both properties are useful for using the strain in bioremediation of metal-contaminated effluents. For biofilm formation capacity, three methods were used: the tube method (TM), the Congo red agar method (CRA) and adherence to polystyrene tissue culture plate method (TCP). S. salivarius, showed a positive-biofilm and a correlation between the three methods was noted. The bacterial surface hydrophobicity was studied using the microbial adhesion to solvents method (MATS). On AISI-316 L stainless steel, the strain with a hydrophobic surface showed a good adhesion on this support after 18 h incubation. The colonization of the supports and the biofilms formation by the bacterial cell was observed using scanning electron microscopy (SEM). The minimum inhibitory concentration (MIC) of Cr(VI) on S. salivarius was determined on MRS broth, it was relatively high and equal to 400mg/l. In addition, it displayed a remarkable capacity to reduce Cr(VI) concentration on the liquid medium containing initially 50 mg/l of Cr(VI) ; the percent removal rate was equal to approximately 42% after 72 h of incubation at 37 °C. In addition to its GRAS status, the obtained results suggested that S. salivarius could be successfully used in Cr(VI) bioremediation.

Cong-red dye is a precursor of various products of cotton industry and its toxicity in the aquatic environment is a great concern. Present study was highlighted on the efficacy of the fish scale char (FSC) towards removal of congo red from aqueous solution. The prepared FSC was characterized by zero point charge (pHZPC), scanning electron micrograph with elemental analysis (SEM-EDX) and fourier transform infrared (FTIR). Based in the equilibrium and kinetic study, the Langmuir (R2 = 0.967) and Pseudo-second-order (R2 = 1.00) models are appropriate to describe the dye adsorption process. The randomness and exothermic nature of the system were confirmed by the negative values of both entropy and enthalpy, respectively. Finally, optimization by Response Surface Methodology (RSM) study revealed that the experimental data were nicely fitted with central composite design with very high F value (F = 1596.24, p < 0.0001). Perturbation plot suggested that congo-red dye removal is more sensitive with respect to biosorbent dose, pH and initial concentration. The exhausted adsorbent was regenerated with 0.5(M) NaOH solution. Therefore, it can be concluded that fish scale char could be a valuable materials towards purification of industrial effluent.

This study investigated the effects of adding biochar (BC) on the fate of ciprofloxacin (CIP) and its related antibiotic tolerance (AT) in activated sludge. Three activated sludge reactors were established with different types of BC, derived from apple, pear, and mulberry tree, respectively, and one reactor with no BC. All reactors were exposed to an environmentally relevant level of CIP that acted as a definitive selective pressure significantly promoting AT to four representative antibiotics (CIP, ampicillin, tetracycline, and polymyxin B) by up to two orders of magnitude. While CIP removal was negligible in the reactor without BC, the BC-dosed reactors effectively removed CIP (70–95% removals) through primarily adsorption by BC and biodegradation/biosorption by biomass. The AT in the BC-added reactors was suppressed by 10–99%, compared to that without BC. The BC addition played a key role in sequestering CIP, thereby decreasing the selective pressure that enabled the proactive prevention of AT increase. 16S rRNA gene sequencing analysis showed that the BC addition alleviated the CIP-mediated toxicity to community diversity and organisms related to phosphorous removal. Machine learning modeling with random forest and support vector models using AS microbiome data collectively pinpointed Achromobacter selected by CIP and strongly associated with the AT increase in activated sludge. The identification of Achromobacter as an important AT bacteria revealed by the machine learning modeling with multiple models was also validated with a linear Pearson's correlation analysis. Overall, our study highlighted Achromobacter as a potential useful sentinel for monitoring AT occurring in the environment and suggested BC as a promising additive in wastewater treatment to improve micropollutant removal, mitigate potential AT propagation, and maintain community diversity against toxic antibiotic loadings.

Uranium, a radionuclide, is a predominant element utilized for speciality requirements in industrial applications, as fuels and catalyst. The radioactive properties and chemical toxicity of uranium causes a major threat to the ecosystem. The hazards associated with Uranium pollution includes the cancer in bones, liver, and lungs. The toxicological properties of Uranium are discussed in detail. Although there are many methods to eliminate those hazards, this research work is aimed to describe the application of bioremediation methods. Bioremediation methods involve elimination of the hazards of uranium, by transforming into low oxidation form using natural microbes and plants. This study deeply elucidates the methods as bioleaching, biosorption, bioreduction and phytoremediation. Bioleaching process involves bio-oxidation of tetravalent uranium when it gets in contact with acidophilic metal bacterial complex to obtain leach liquor. In biosorption, chitin/chitosan derived sorbents act as chelators and binds with uranium by electrostatic attraction. Bio reduction employs a bacterial transformation into enzymes which immobilize and reduce uranium. Phytoremediation includes phytoextraction and phytotranslocation of uranium through xylems from soil to roots and shoots of plants. The highest uranium removal and uptake reported using the different methods are listed as follows: bioleaching (100% uranium recovery), biosorption (167 g kg⁻¹ uranium uptake), bioreduction (98.9% uranium recovery), and phytoremediation (49,639 mg kg⁻¹ uranium uptake). Among all the techniques mentioned above, bioleaching has been proved to be the most efficient for uranium remediation.

The pollutants can enter water bodies at various point and non-point sources, and wastewater discharge remains a major pathway. Wastewater treatment effectively reduces contaminants, it is expensive and requires an eco-friendly and sustainable alternative approach to reduce treatment costs. Algae have recently emerged as a potentially cost-effective method to remediate toxic pollutants through the mechanism of biosorption, bioaccumulation, and intracellular degradation. Hence, before discharging the wastewater into the natural environment better solutions for environmental resource recovery and sustainable developments can be applied. More importantly, algae are a potential feedstock material for various industrial applications such as biofuel production. Currently, researchers are developing algae as a source for pharmaceuticals, biofuels, food additives, and bio-fertilizers. This review mainly focused on the potential of algae and their specific mechanisms involved in wastewater treatment and energy recovery systems leading to important industrial precursors. The review is highly beneficial for scientists, wastewater treatment plant operators, freshwater managers, and industrial communities to support the sustainable development of natural resources.

Bacteria and their secreted extracellular polymeric substances (EPS) are widely distributed in ecosystems and have high capacity for heavy metal immobilization. The knowledge about the molecular-level interactions with heavy metal ions is essential for predicting the behavior of heavy metals in natural and engineering systems. This comprehensive study using potentiometric titration, Fourier-transform infrared (FTIR) spectroscopy, isothermal titration calorimetry (ITC) and X-ray absorption fine structure (XAFS) was able to reveal the functional diversity and adsorption mechanisms for Pb onto bacteira and the EPS in greater detail than ever before. We identified mono-carboxylic, multi-carboxylic, phosphodiester, phosphonic and sulfhydryl sites and found the partitioning of Pb to these functional groups varied between gram-negative and gram-positive bacterial strains, the soluble and cell-bound EPS and Pb concentrations. The sulfhydryl and phosphodiester groups preferentially complexed with Pb in P. putida cells, while multifunctional carboxylic groups promoted Pb adsorption in B. subtilis cells and the protein fractions in EPS. Though the functional site diversity, the adsorption of Pb to organic ligands occurred spontaneously through a universal entropy increase and inner-sphere complexation mechanism. The functional group scale knowledge have implications for the modeling of heavy metal behavior in the environment and application of these biological resources.

To explore a novel strategy for the remediation of soils polluted with Cu and Cd, three strains of plant-growth-promoting rhizobacteria (PGPRs) isolated from contaminated mines and two grass species (perennial ryegrass and tall fescue) were selected in this study. The performance of PGPR strains in metal adsorption, maintaining promotion traits under stress, and ameliorating phytostabilization potential was evaluated. Cd²⁺ exerted a stronger deleterious effect on microbial growth than Cu²⁺, but the opposite occurred for grass seedlings. Adsorption experiment showed that the growing PGPR strains were able to immobilize maximum 79.49% Cu and 81.35% Cd owing to biosorption or bioaccumulation. The strains exhibited the ability to secrete indole-3-acetic acid (IAA) and dissolve phosphorus in the absence and presence of metals, and IAA production was even enhanced in the presence of low Cu²⁺ (5 mg L⁻¹). However, the siderophore-producing ability of the isolates was strongly suppressed under Cu and Cd exposure. Ryegrass was further selected for pot experiments owing to its higher germination rate and tolerance under Cu and Cd stress than fescue. Pot-experiment results revealed that PGPR addition significantly increased the shoot and root biomasses of ryegrass by 11.49%–44.50% and 43.53%–90.29% in soil co-contaminated with 800 mg Cu kg⁻¹ and 30 mg Cd kg⁻¹, respectively. Metal uptake and translocation in inoculated ryegrass significantly decreased owing to the reduced diethylenetriamine pentaacetic acid-extractable metal content and increased residual metal-fraction percentage mediated by PGPR. Interestingly, stress mitigation was observed in these inoculated plants; in particular, their malondialdehyde content and superoxide dismutase activity were even significantly lower than those of ryegrass under normal conditions. Therefore, PGPR could be a promising option to enhance the phytostabilization efficiency of Cu and Cd in heavily polluted soils.

Fungi have an exceptional capability to flourish in presence of heavy metals and pesticide. However, the mechanism of bioremediation of pesticide (lindane) and multimetal [mixture of cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), zinc (Zn)] by a fungus is little understood. In the present study, Aspergillus fumigatus, a filamentous fungus was found to accumulate heavy metals in the order [Zn(98%)>Pb(95%)>Cd(63%)>Cr(62%)>Ni(46%)>Cu(37%)] from a cocktail of 30 mg L⁻¹ multimetal and lindane (30 mg L⁻¹) in a composite media amended with 1% glucose. Particularly, Pb and Zn uptake was enhanced in presence of lindane. Remarkably, lindane was degraded to 1.92 ± 0.01 mg L⁻¹ in 72 h which is below the permissible limit value (2.0 mg L⁻¹) for the discharge of lindane into the aquatic bodies as prescribed by European Community legislation. The utilization of lindane as a cometabolite from the complex environment was evident by the phenomenal growth of the fungal pellet biomass (5.89 ± 0.03 g L⁻¹) at 72 h with cube root growth constant of fungus (0.0211 g¹/³ L⁻¹/³ h⁻¹) compared to the biomasses obtained in case of the biotic control as well as in presence of multimetal complex without lindane. The different analytical techniques revealed the various stress coping strategies adopted by A. fumigatus for multimetal uptake in the simultaneous presence of multimetal and pesticide. From the Transmission electron microscope coupled energy dispersive X-ray analysis (TEM-EDAX) results, uptake of the metals Cd, Cu and Pb in the cytoplasmic membrane and the accumulation of the metals Cr, Ni and Zn in the cytoplasm of the fungus were deduced. Fourier-transform infrared spectroscopy (FTIR) revealed involvement of carboxyl/amide group of fungal cell wall in metal chelation. Thus A. fumigatus exhibited biosorption and bioaccumulation as the mechanisms involved in detoxification of multimetals.

Rare earth elements (REE) present multiple applications in technological devices but also drawbacks (scarcity and water contaminant). The current study aims to valorise the banana wastes - banana rachis (BR), banana pseudo-stem (BPS) and banana peel (BP) as sustainable adsorbent materials for the recovery of REE (Nd³⁺, Eu³⁺, Y³⁺, Dy³⁺ and Tb³⁺). The adsorbent materials were characterized using analytical techniques such as: Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, zeta potential and scanning electron microscopy with energy dispersive X-ray probe. The adsorption performance and mechanisms were studied by pH dependence, equilibrium isotherms, kinetics, thermodynamics, ion-exchange and desorption evaluation. The results show good adsorption capacities for the three materials, highlighting BR that presents ∼100 mg/g for most of the REE. The adsorption process (100 mg REE/L) reaches the 60% uptake in 8 min and the equilibrium within 50 min. On the other hand, the thermodynamic study indicates that the adsorption is spontaneous and exothermic (ΔH° < 40 kJ/mol). The adsorption mechanism is based on the presence of carboxylic groups that induce electrostatic interactions and facilitate the surface nucleation of REE microcrystals coupled to an ion exchange process as well as the presence of other oxygen containing groups that establish weak intermolecular forces. The recovery of REE from the adsorbent (∼97%) is achieved using EDTA as desorbing solution. This research indicates that banana waste and particularly BR is a new and promising renewable bioresource to recover REE with high adsorption capacity and moderated processing cost.