Decontamination kinetics of tannery waters using bioflocculants

Abstract

In this research, the kinetics of the reduction of the initial turbidity (1455 NTU) of wastewater from a tannery industry was evaluated by applying direct bioflocculants prepared from the algae Chondracanthus chamissoi (alginate) and the molts of the crustacean Emerita analoga (chitosan). The biological precursor material was collected on Lima, Peru's beaches; from this material, fibrous alginic acid was produced, and later sodium alginate. The processes of demineralization, deproteinization, and subsequent deacetylation were used to obtain chitosan from crustacean molts. The effect of pH, the doses of bioflocculants, and the equilibrium time of the process were evaluated. In addition, the kinetic order of the flocculation rate was determined using the jar test. The results indicated a turbidity removal of more than 99 % within the first 30 minutes for doses of 0.2 to 2 g/l of flocculants and acid pH (equal to 4); no significant differences were recorded at different pH values (4-12) and doses (0.2 to 2 g/l). The linear adjustment between flocculation time and turbidity generated significant first-order kinetic equations for both flocculants with rate constants k1 of the order of 10^-4 (1/NUT.min) and reduction times of half of particulate matter (average life: τ_1/2) less than 10 minutes. This can be considered as a criterion to measure the efficiency of the direct flocculation process in the treatment of tannery industrial waters.