Recent advances in biosorption of heavy metals: support tools for biosorption equilibrium, kinetics and mechanism

Heavy metals are increasingly present in industrial wastes and effluents, which can generate serious concerns for environmental quality and human health. Consequently, there is a continuous expansion of researches for new approaches and developments to guarantee environmental cleaning-up. Although there are some physico-chemical established methods for the removal of heavy metals from various environmental compartments, biosorption gains further confidence as a reliable alternative compared to classical technologies, which are expensive and sometimes unreliable. This paper aims to analyze the biosorption as a biotechnological strategy for the decontamination of aqueous effluents containing heavy metal ions, in terms of its potential for metal immobilization and uptake. The paper also focuses on the most important parameters affecting the removal of heavy metals by various categories of biosorbents both living and non-living forms of biomass and provides new alternatives for modeling and optimization of process equilibrium and kinetics. A special attention was paid to biosorption mechanism, as a factual challenge for process optimization and scale-up. The potential benefits and problems associated to metal removal by biosorption are highlighted.Roumanian National Authority for Scientific Research, CNCS – UEFISCDI, project number PN-II-ID-PCE-2011-3-0559”, Contract 265/2011

Rhizobacteria and plant symbiosis in heavy metal uptake and its implications for soil bioremediation

Certain species of plants can benefit from synergistic effects with plant growth-promoting rhizobacteria (PGPR) that improve plant growth and metal accumulation, mitigating toxic effects on plants and increasing their tolerance to heavy metals. The application of PGPR as biofertilizers and atmospheric nitrogen fixators contributes considerably to the intensification of the phytoremediation process. In this paper, we have built a system consisting of rhizospheric . Azotobacter microbial populations and . Lepidium sativum plants, growing in solutions containing heavy metals in various concentrations. We examined the ability of the organisms to grow in symbiosis so as to stimulate the plant growth and enhance its tolerance to Cr(VI) and Cd(II), to ultimately provide a reliable phytoremediation system. The study was developed at the laboratory level and, at this stage, does not assess the inherent interactions under real conditions occurring in contaminated fields with autochthonous microflora and under different pedoclimatic conditions and environmental stresses. . Azotobacter sp. bacteria could indeed stimulate the average germination efficiency of . Lepidium sativum by almost 7%, average root length by 22%, average stem length by 34% and dry biomass by 53%. The growth of . L. sativum has been affected to a greater extent in Cd(II) solutions due its higher toxicity compared to that of Cr(VI). The reduced tolerance index (TI, %) indicated that plant growth in symbiosis with PGPR was however affected by heavy metal toxicity, while the tolerance of the plant to heavy metals was enhanced in the bacteria-plant system.A methodology based on artificial neural networks (ANNs) and differential evolution (DE), specifically a neuro-evolutionary approach, was applied to model germination rates, dry biomass and root/stem length and proving the robustness of the experimental data. The errors associated with all four variables are small and the correlation coefficients higher than 0.98, which indicate that the selected models can efficiently predict the experimental data.</p