Photocatalytic degradation of malachite green using TiO2 and ZnO impregnated on fecal sludge derived biochar

The present study focused on the degradation of malachite green (MG) dye which is extensively used in the aquaculture and later disposed in water bodies. In order to treat the wastewater streams a sustainable and novel low cost material was synthesized using a waste i.e. fecal sludge. Later, the biochar obtained from the fecal sludge were impregnated with TiO2 and ZnOnano-particles to enhance its functional properties. The study reports the degradation of malachite green (MG) dye from aqueous solution under a parametric optimized condition by combined effect of adsorption and photocatalysis using TiO2 and ZnO impregnated on biochar (BC-TiO2-ZnO) synthesized from fecal sludge. The main contributing factors towards the dye degradation, namely catalyst dose (25-75 mg), dye concentration (50-150 mg/L), temperature (25-55 degrees C), pH (4-12) and stirring speed (50-250 rpm) were used as operation parameters for the experiments. The conditions thus obtained (catalyst dose of 50 mg, dye concentration of 100 mg/L, stirring speed of 150 rpm, temperature of 35 degrees C and at pH 8 for 30 min) were the optimal conditions for MG dye degradation (nearly 98% removal) using BC-TiO2-ZnO photocatalyst. Investigation revealed that adsorption-photocatalysis process is in good agreement with Langmuir-Hinshelwood kinetics. The kinetic data plots revealed the rate constant to be (k) = 0.087 min-1 having a 3% deviation from the experimental results (=0.09 min-1). Furthermore, the half-life of the reaction was calculated to be t1/2= 7.7 min while the value of R2 was 0.98. The photocatalyst showed no significant changes in its degradation efficiency even after 6th cycle indicating the appreciable reusability. MG has been used extensively in aquaculture as antimicrobial agent which leads to release of the residual molecules to the aquatic environment leading to multiplication of antibiotic resistant microbes. Therefore, the treated water obtained from the present process was investigated for its possible activity against E. coli and no remarkable antibacterial activity was noticed.

Automated summary

The present study focused on the degradation of malachite green (MG) dye using a sustainable and novel low-cost material synthesized from waste fecal sludge. The material, biochar obtained from the fecal sludge, was impregnated with TiO2 and ZnO nanoparticles to enhance its functional properties. Under optimized conditions, the BC-TiO2-ZnO photocatalyst showed a removal efficiency of nearly 98% for MG dye in aqueous solution through a combined effect of adsorption and photocatalysis. The photocatalyst demonstrated good reusability and its degradation efficiency remained stable even after six cycles. The treated water obtained from the process showed no remarkable antibacterial activity against E. coli.