RESUMO
This work examined the adsorption capacity of sugarcane bagasse (SB) for the removal of ciprofloxacin (CPX) from water using batch experiments and a fixed bed column and compared its adsorption performance with a powdered activated commercial carbon (PAC). Both adsorbents achieved a similar percentage removal of about 78% with doses of 3â¯gâ¯L-1 of SB and 0.3â¯gâ¯L-1 of PAC (20â¯mgâ¯L-1 initial CPX concentration at 30⯰C). The maximum removal was obtained at a pH between 6 and 8. SB adsorption isotherms were fitted to the Langmuir, BET and Freundlich models showing a maximum adsorption capacity of 13.6â¯mgâ¯g-1. The kinetic data for both SB and PAC fitted the pseudo second-order model (R2â¯=â¯0.99). The adsorption process was faster on the SB (65% of elimination in the first 5â¯min) than on the PAC. The study of the adsorbent properties shows that SB is a macroporous solid with a specific surface area 250 times smaller than PAC. The thermodynamic results show that SB adsorption was physical and exothermic. The main suggested interactions between CPX and SB are electrostatic attraction, hydrogen bonding and dipole-dipole interactions. The experiments carried out in a fixed bed show that the adsorption capacity at breakthrough increases with the bed height. The adsorption capacity at saturation time was 9.47â¯mgâ¯g-1 at a flow rate of 3â¯mLâ¯min-1, a bed height of 14â¯cm, and a diameter of 1.5â¯cm. The experimental data were fitted to the Bohart-Adams model (R2â¯=â¯0.98). These results highlight the capacity of sugarcane bagasse to adsorb ciprofloxacin from water, illustrating its potential as a low-cost adsorbent.
Assuntos
Saccharum , Poluentes Químicos da Água , Purificação da Água , Adsorção , Celulose , Carvão Vegetal , Ciprofloxacina , Equador , Concentração de Íons de Hidrogênio , Cinética , PósRESUMO
An experimental design methodology was applied to evaluate the decolourization of crystal violet (CV) dye by electrocoagulation using iron or aluminium electrodes. The effects and interactions of four parameters, initial pH (3-9), current density (6-28 A m(-2)), substrate concentration (50-200 mg L(-1)) and supporting electrolyte concentration (284-1420 mg L(-1) of Na(2)SO(4)), were optimized and evaluated. Although the results using iron anodes were better than for aluminium, the effects and interactions of the studied parameters were quite similar. With a confidence level of 95%, initial pH and supporting electrolyte concentration showed limited effects on the removal rate of CV, whereas current density, pollutant concentration and the interaction of both were significant. Reduced models taking into account significant variables and interactions between variables have shown good correlations with the experimental results. Under optimal conditions, almost complete removal of CV and chemical oxygen demand were obtained after electrocoagulation for 5 and 30 min, using iron and aluminium electrodes, respectively. These results indicate that electrocoagulation with iron anodes is a rapid, economical and effective alternative to the complete removal of CV in waters. Evolutions of pH and residual iron or aluminium concentrations in solution are also discussed.
Assuntos
Alumínio/química , Corantes/química , Violeta Genciana/química , Ferro/química , Eletroquímica , Eletrodos , Concentração de Íons de Hidrogênio , Indicadores e Reagentes , Cloreto de Sódio , Hidróxido de Sódio , Soluções , Espectrofotometria Ultravioleta , Ácidos Sulfúricos/química , ÁguaRESUMO
This work presents the application of experimental design for the ultrasonic degradation of alachlor which is pesticide classified as priority substance by the European Commission within the scope of the Water Framework Directive. The effect of electrical power (20-80W), pH (3-10) and substrate concentration (10-50mgL(-1)) was evaluated. For a confidential level of 90%, pH showed a low effect on the initial degradation rate of alachlor; whereas electrical power, pollutant concentration and the interaction of these two parameters were significant. A reduced model taking into account the significant variables and interactions between variables has shown a good correlation with the experimental results. Additional experiments conducted in natural and deionised water indicated that the alachlor degradation by ultrasound is practically unaffected by the presence of potential *OH radical scavengers: bicarbonate, sulphate, chloride and oxalic acid. In both cases, alachlor was readily eliminated ( approximately 75min). However, after 4h of treatment only 20% of the initial TOC was removed, showing that alachlor by-products are recalcitrant to the ultrasonic action. Biodegradability test (BOD5/COD) carried out during the course of the treatment indicated that the ultrasonic system noticeably increases the biodegradability of the initial solution.