Issue 2

Polycyclic aromatic hydrocarbons (PAHs) are a group of quotidian organic compounds having between two and six condensed aromatic rings braced in angular, cluster or linear forms possessing hydrogen and carbon atoms only. This work aims to evaluate the physicochemical characteristics of soil as determinants of PAHs distribution and fate. The study area is situated on the Benin River beneath the convergence of Jamieson River and River Ethiope. The weather and climatic conditions of the area are of the Niger Delta region. Sixteen priority PAHs were determined in ten sample stations. Upon extraction, purification and quantification of PAHs was done using GC-FID. According to the methods of Walkey-Blacks, Black and Bouyoucus, soil total organic carbon, pH and texture were analyzed respectively. Four replicate samples were chosen to create a composite and used as quality control. Kruskal-Wallis test with tied rank was used to determine a causative correlation between soil physicochemical parameters and ∑PAHs. Results showed that the study area is contaminated with high concentration of PAHs ranging from 60.76 – 271.11 239 µg.g-1 with higher percentages of HPAHs i.e. PAHs with LogKow > 4.0. It is observed that observed alkaline pH favour significant fungal, asperigellus and microbial degradation of PAHs, and hinder photo-catalytic degradation. However, acidification with elemental sulfur, ferrous sulfate and aluminum sulfate could enhance photo-catalytic degradation. Results of TOC and soil structure do not favour significant degradation of HPAHs. Kruskal-Wallis tied rank test revealed that there was a positive significant difference between pH, TOC, percentage clay, and silt fractions with ∑PAHs concentrations since calculated K is greater than critical K0.05, P<0.05 except percentage of sand fractions and ∑PAHs with P>0.05. A substantial percentage of these PAHs have no anthropic origin and are characterized as having high lipo-affinity, semi-volatility and resistance to biotic and/or abiotic transformations. Due to edaphic factors the observed HPAHs may partially degrade with the consequent formation of highly toxic by-products. Therefore, oral or dermal ingestion of soil in the study area may cause significant exposure of the human population to these PAHs. Risk assessment and probable toxicity effects on animal diversity should be carried out in soil samples of the study area.

Clay of the Middle Atlas Mountains region, Morocco, was used to investigate the removal of heavy metals ions (Cadmium and Copper) from aqueous solutions with respect to several experimental conditions including pH, contact time, initial solute concentrations, temperature and ionic strength. Kinetic study revealed that metal ions uptake was fast with 90% or more of the adsorption occurring within first 30 min of contact time. Adsorption rate increased with the increasing initial metal ions concentrations and the sorption rate was well fitted by the pseudo-second-order rate model. The data according to mass transfer and intraparticle diffusion models confirmed diffusion of solutes inside the clay particles as the rate-controlling step and more important for the adsorption rate than the external mass transfer.
The suitability of the adsorbent was tested by fitting the adsorption data with Langmuir and Freundlich isotherm models. Equilibrium and kinetic adsorption data showed that clay displays a high selectivity with an affinity order of Cd > Cu. Thermodynamic parameters including the Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) changes indicated that the present adsorption process was feasible and endothermic in the temperature range of 25–45 °C.

The aim of this study is to investigate the performance of the solar photocatalyst of TiO2/ZnO/Fenton process to treat the refinery wastewater and remove inorganic carbon (IC) which potentially toxic to human, aquatic and microorganism life. Central composite design with response surface methodology was used to evaluate the relationships between operating variables for TiO2 dosage, ZnO dosage, Fe2+ dosage, H2O2 dosage, and pH to identify the optimum operating conditions. Quadratic models for inorganic carbon (IC) removal and residual iron prove to be significant with low probabilities (<0.0001). The (IC) removal rates and residual iron correspond well with the predicted models. The maximum removal rate for IC and residual iron was 92.3% and 0.013, respectively at optimum operational conditions of a TiO2 dosage (0.3 g/l), ZnO dosage (0.58 g/l), Fe2+ dosage (0.02 g/l), H2O2 dosage (2.7 g/l), and pH (7). The treatment process achieved higher degradation efficiencies for IC and reduced the treatment time comparing with other related processes.

In this study, raw boron enrichment waste was treated with hydrochloric acid and ultrasound at 35-kHz frequency for 60 minutes. To optimize the adsorption conditions for removal of methylene blue (MB) from synthetic wastewaters using raw boron enrichment waste (BEW), acid modified boron enrichment waste (HBEW) and ultrasound modified BEW (UBEW) by adsorption process and to compare the adsorption efficiency of chemical and ultrasonic modifications of BEW were aimed. The optimum adsorption conditions were determined economically and eco-friendly aspect and MB removal percents were found as 80%, 80% and 92% at optimum conditions for BEW, HBEW and UBEW, respectively. The maximum regression coefficient values were obtained as 0.911, 0.998 and 0.984 for BEW, HBEW and UBEW, respectively at Langmuir isotherm model. The adsorption rate was fitted well to pseudo-second order kinetics according to a good correlation coefficient. The adsorption of MB onto adsorbents studied is spontaneous in nature and feasible because of negative ∆G values. The results indicated that the boron enrichment process waste could be a suitable adsorbent for removal of MB from aqueous solution. The maximum adsorption capacities were equal to about 107,0 mg/g, 160,7 mg/g and 145,3 mg/g for BEW, HBEW and UBEW adsorbents at 298 K, respectively. The maximum dye removal percent was achieved for UBEW as 92% and ultrasound assisted modification was found more efficient method compared with acidic modification for MB removal.