Environmental Sciences

The biosorption efficiency of Cd 2? using rice straw was investigated at room temperature (25 ± 4°C), contact time (2 h) and agitation rate (5 Hz). Experiments studied the effect of three factors, biosorbent dose BD (0.1 and 0.5 g/L), pH (2 and 7) and initial Cd 2? concentration X (10 and 100 mg/L) at two levels ''low'' and ''high''. Results showed that, a variation in X from high to low revealed 31 % increase in the Cd 2? biosorption. However, a discrepancy in pH and BD from low to high achieved 28.60 and 23.61 % increase in the removal of Cd 2? , respectively. From 2 3 factorial design, the effects of BD, pH and X achieved p value equals to 0.2248, 0.1881 and 0.1742, respectively, indicating that the influences are in the order X [ pH [ BD. Similarly, an adaptive neurofuzzy inference system indicated that X is the most influential with training and checking errors of 10.87 and 17.94, respectively. This trend was followed by ''pH'' with training error (15.80) and checking error (17.39), after that BD with training error (16.09) and checking error (16.29). A feed-forward back-propagation neural network with a configuration 3-6-1 achieved correlation (R) of 0.99 (training), 0.82 (validation) and 0.97 (testing). Thus, the proposed network is capable of predicting Cd 2? biosorption with high accuracy, while the most significant variable was X.

Phytoextraction or immobilization is more cost-effective in the field of removal of heavy metals from contaminated soils. These techniques have fewer side effects than physical and chemical techniques. It is the main and most promising technique, in situ or ex situ treatment/removal of contaminated soils, sediments and water. The use of plants as phytoremediators reduces the amount of inorganic components of soil impurities (heavy metals). The main aim of current study is focus on plants which could accumulate large amounts of these pollutants, but are also characterized by high growth rates, tolerate the toxic effects of heavy metals, and mostly adapted to the local environment and climate. Besides they must be resistant to pathogens and pests, easy to grow and exclude the possibility of contamination of animals and humans through the food chain. This study provides a systematic review of publications related to advances in the phytoremediation treatment of contaminated soils, and briefly explains the current limitations in the use of plants to removal heavy metals from the contaminated soil. The main limiting factor is the entry of heavy metals into animals and humans through the food chain. Another limiting factor is the possible negative impact on the genetics of plants used for soil treatment, because this may facilitate to the extinction of this species plants. The investigation showed that the questions of the influence of heavy metals on plant genes deserve serious attention. This is important to prevent reduce species diversity in nature. However, today these issues are very little studied.