A Complex Network Methodology for Travel Demand Model Evaluation and Validation

Networks and Spatial Economics - Travel demand can be viewed as a weighted and directed graph where nodes are the origins and destinations and links represent the trips between nodes. This paper...     

Photo-oxidation of phenol in aqueous solution: Toxicity of intermediates

The photodegradation of phenol was studied in a batch reactor system illuminated with a 400 W medium pressure mercury lamp. The effects of parameters such as pH, reaction time and initial phenol concentration on the photolytic degradation and toxicity assay have been studied. The experimental results have shown that lower pH and lower concentration of phenol favor the phenol degradation. The disappearance of phenol in each case approximately obeyed first-order kinetics with the apparent rate constants increasing with decreasing solute concentration. Bioassay tests showed that phenol was toxic to Daphnia magna and so resulted in quite low LC₅₀ values. Comparison of toxicity units (TU) between phenol and effluent toxicity has shown that TU value for effluent was 2.18 times lower than that obtained for phenol. Thus, photolysis is able to decrease the toxicity of by-products formed during the degradation of phenol.     

Biosorption of lead(II) and cadmium(II) by protonated Sargassum glaucescens biomass in a continuous packed bed column

Biosorption of lead(II) and cadmium(II) from aqueous solutions by protonated Sargassum glaucescens biomass was studied in a continuous packed bed column. The selective uptake of Pb2+ and Cd2+ was investigated in a binary system with initial concentration of 1 mM for each metal ion. The selective uptake capacities of Pb2+ and Cd2+ at complete exhaustion point were obtained 1.18 and 0.22 mmol/g, respectively; therefore, the biosorbent showed much higher relative affinity for Pb2+ than for Cd2+. The optimum range of empty bed contact time (EBCT) was identified as 5-10 min in the packed bed column. The efficiency of biosorbent regeneration by 0.1 M HCl was achieved about 60%, so that the maximum uptake capacity of Pb2+ by the regenerated biomass was determined to be 0.75 mmol/g while the same value for the original biomass was 1.24 mmol/g. The Thomas model was found in a suitable fitness with the experimental data (R2 > 0.90 and % < 50%) at all different operation stages. Monitoring of pH in the effluent of the column presented the simultaneous release of H+ with the uptake of heavy metals; hence, ion exchange was confirmed to be one of the main biosorption mechanisms.     

Superabsorbent polymers achieved by surface cross linking of poly(sodium acrylate) using microwave method

Surface cross linking is a post-treatment process for superabsorbent polymers (SAPs) leading to an increase in the absorbency under load (AUL). This process is typically carried out through conventional heating method. In the current study, for the first time, microwave method was used for surface treatment process of SAPs based on poly(sodium acrylate). Diglycidyl materials such as 1,4-butanediol diglycidyl ether (BDDGE), polyethylene diglycidyl ether (PEGDGE), and ethylene glycol diglycidyl ether (EGDGE) were utilized as surface cross-linking agents. Also, N,N-Dimethylaniline was used as a catalyst for surface treatment of poly(sodium acrylate) SAP with diglycidyl materials as the external cross linkers. The results showed that surface treatment time can be reduced from 1 to 3 h in the conventional heating to a few minutes by microwave method. The use of catalyst in surface treatment solution resulted in higher AULs. The AULs of SAPs were increased from 14 g/g for unmodified SAP to 17.5, 19 and 20.7 g/g after surface treatment for surface-treated SAPs with BDDGE, PEGDGE and EGDGE, respectively. These results present the microwave method as an effective alternative candidate for thermal surface treatment of SAP which can have economic benefits from the viewpoint of time and energy consumption industrially.