Thermodynamic adsorption investigation plays a key role in estimating adsorptive mechanisms (i.e., physical or chemical). Accuracy estimation of the thermodynamic parameters is directly dependent on the equilibrium constant between two phases (KC; dimensionless). In this study, the thermodynamic parameters were calculated from the KC constants derived from the adsorption isotherm constants (i.e., Langmuir, Freundlich, and Henry) and partition coefficient, with and without dimensionality consideration. Results showed that the optimal selection of KC is strongly dependent on: the adsorption characteristics (i.e., Henry, Freundlich, and Langmuir) where equilibrium data are actually located; and the correlation coefficient of the van’t Hoff equation. Both the Langmuir and Freundlich constants (dimensionless) are appropriate to calculate the thermodynamic parameters. The Langmuir constants from its four linear forms can be applied to calculate the thermodynamic parameters without significant difference. The Cd(II) biosorption process onto the orange peel (OP) occurred spontaneously (−ΔG°), in an exothermic nature (−ΔH°), and with increased randomness (+ΔS°). The biosorption process involved physical adsorption with minimal activation energy (Ea) and adsorption energy (E). The biosorption phenomenon reached fast equilibrium and reversibility. The negatively charged carboxylic groups (–COO−) on the OP’s surface play an important role (approximately 90%) in Cd2+ biosorption through electrostatic attractions (out-sphere complexes).

Thermodynamic parameters of cadmium adsorption onto orange peel calculated from various methods: A comparison study

Biosorption of toxic metals from aqueous solutions by bacteria strains isolated from metal-polluted soils

Biosorption properties of extracellular polymeric substances (EPS) towards Cd, Cu and Pb for different pH values.

While diatoms are widely present in terms of diversity and abundance in nature, few species are currently used for biotechnologically applications. Most studies have focussed on intracellularly synthesised eicosapentaenoic acid (EPA), a polyunsaturated fatty acid (PUFA) used for pharmaceutical applications. Applications for other intracellular molecules, such as total lipids for biodiesel, amino acids for cosmetic, antibiotics and antiproliferative agents, are at the early stage of development. In addition, the active principle component must be identified amongst the many compounds of biotechnological interest. Biomass from diatom culture may be applied to: (1) aquaculture diets, due to the lipid- and amino-acid-rich cell contents of these microorganisms, and (2) the treatment of water contaminated by phosphorus and nitrogen in aquaculture effluent, or heavy metal (bioremediation). The most original application of microalgal biomass, and specifically diatoms, is the use of silicon derived from frustules in nanotechnology. The competitiveness of biotechnologically relevant products from diatoms will depend on their cost of production. Apart from EPA, which is less expensive when obtained from Phaeodactylum tricornutum than from cod liver, comparative economic studies of other diatom-derived products as well as optimisation of culture conditions are needed. Extraction of intracellular metabolites should be also optimised to reduce production costs, as has already been shown for EPA. Using cell immobilisation techniques, benthic diatoms can be cultivated more efficiently allowing new, biotechnologically relevant products to be investigated.

Diatom cultivation and biotechnologically relevant products. Part II: Current and putative products

The last quarter of the twentieth century had witnessed a global surge in awakening against the unabated menace of environmental pollution. Among the various types of environmental pollution, water pollution is an age-old problem but it has gained an alarming dimension lately because of the problems of population increase, sewage disposal, industrial waste, radioactive waste, etc. Present scenario of water pollution calls for immediate attention towards the remediation and detoxification of these hazardous agents in order to have a healthy living environment. The present communication will deal with the toxicological effects of major environmental pollutants, viz. heavy metals, pesticides, and phenols.

Toxicological effects of major environmental pollutants: an overview.

Cadmium biosorption by free and immobilised microorganisms cultivated in a liquid soil extract medium: effects of Cd, pH and techniques of culture.

Adsorption of cadmium on different granulometric soil fractions: Influence of organic matter and temperature

Modelling of stimulus response experiments in the feed channel of spiral-wound reverse osmosis membranes

We studied copper uptake by maize grown on soils that have been contaminated with CuSO4. In soil the total copper level ranged from 24 to 135 mg kg−1. The copper distribution in soil fractions was assessed by sequential extraction, showing that anthropogenic copper is mainly concentrated in oxides fractions. The copper concentration of maize at the maturity stage reached values from 36.3 to 65.9 mg kg−1 compared to copper levels usually found in non-contaminated crops (5–30 mg kg−1). Here we demonstrate that copper can be accumulated by maize and that copper concentration in maize can be predicted by equations including copper concentration of soil fractions.

Sequential extraction of copper from soils and relationships with copper in maize

Agricultural practices can lead to copper accumulation in soils and at high concentration it can become toxic for plants. One common toxic effect of copper on plants is a decrease of crop yield. Here, we studied 1) the crop yield of maize grown on plots of a soil intentionally enriched with copper sulphate and 2) the possible relationship between the copper concentration in chemical soil fractions and the maize crop yield. Anthropogenic copper is mainly bound to manganese oxides, to iron oxides and to the organic matter. Maize (Zea maize L.) was grown on outdoor experimental plots. The crop yield was evaluated for three development stages: the 6–10 leaf stage, the female flowering stage and the maturity stage, 2, 4 and 6 years after the soil copper enrichment. Strong crop yield reductions, proving a toxic effect of copper on maize growth were noted 2 years after the copper input at the maturity stage and 4 years after the copper input at the 6–10 leaf stage. Variations in maize crop yield are described with linear multiple regression equations including the variable copper content in soil, and other variables when needed such as soil pH, soil organic carbon level and the climatic variables, the precipitation rate and the ambient temperature. The crop yield study at the 6–10 leaf stage and at the female flowering stage does not provide significant regression equations, while the crop yield study at the maturity stage does. Request variables for the models are the total copper content or the copper bound to the organic matter and the meteorological data.

Bernard Fabre

Papers

Cadmium biosorption by free and immobilised microorganisms cultivated in a liquid soil extract medium: effects of Cd, pH and techniques of culture.

Adsorption of cadmium on different granulometric soil fractions: Influence of organic matter and temperature

Modelling of stimulus response experiments in the feed channel of spiral-wound reverse osmosis membranes

Sequential extraction of copper from soils and relationships with copper in maize

Copper distribution in chemical soil fractions and relationships with maize crop yield