Luffa Cylindrica -Alum Induced Coagulation And Flocculation Of Simulated Dye Wastewater: Kinetic And Optimization Studies

ABSTRACT

This study examined the treatment of simulated Cibacron green dye-based polluted wastewater. The simulated wastewater characterization revealed presence of high COD, colour, chromium, Lead and other pollutants through proximate analysis. Jar test procedure was applied using Luffa cylindrica seed extract (LCSE) as bio-coagulant, aluminum sulphate (alum) and the combination of both. The effects of coagulant dosage, pH, stirring time and temperature on the reduction of colour, COD, chromium and Lead ions were examined using the coagulants. The Luffa cylindrica seed (LCS) was also characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction analysis technique (XRD), X-ray fluorescence (XRF) and thermo gravimetric analysis (TGA). The process was optimized through response surface methodology (RSM) using a three-level Box-Behnken design (BBD). LCS was found to be a cationic polypeptide (polymer) with carboxylic and hydroxylic functional groups. Despite the good performance of alum and LCSE individually, the combination of LCSE and alum performed better with reduced alum dose and at better operating conditions. Comparative performance also indicated that LCSE performed better than alum with respect to the process conditions such as dosage and pH. It was observed that bio-coagulant used in combination with lower concentration of alum (LCSE+0.25g/L alum) was more effective in reducing colour, Chromium and Lead ion from the dye-based wastewater. This combination does not only achieve the highest reduction efficiencies but the process is also eco-friendly. The colour removal efficiency (97.294%), COD removal (55.3673%) and Chromium removal (87.3245%) were achieved at optimum dosage (5.14g/l), pH (7.68), stirring time (29.02mins) and temperature (31.12^oC), respectively. The statistical analysis showed that the model is adequate for the experimental data. The maximum kinetic rate constant, K_m, of 0.012 L/g/L, was obtained with coagulant dosage (6g/L), at pH (4), temperature (25^oC), stirring time (30mins) and coagulation period, t_1/2 of 183.6s while the minimum rate, K_m, of 0.0007 L/g/L, was observed with coagulant dosage (6g/L), pH (10), temperature of 25^oC, stirring time (30mins) and coagulation period, t_1/2 of 135.0s. From the foregoing, it is evident that the use of LCSE or in combination with alum, will not only treat dye-based wastewater effectively, but will contribute to greener environment.