Effect of conditions of air-lift type reactor work on cadmium adsorption

Abstract

We investigated cadmium sorption by activated sludge immobilized in 1.5% sodium alginate with 0.5% polyvinyl alcohol. Experiments were conducted in an air-lift type reactor at the constant concentration of biosorbent reaching 5 d.m./dm³, at three flow rates: 0.1, 0.25 and 0.5 V/h, and at three concentrations of the inflowing cadmium solution: 10, 25 and 50mg/dm³. Analyses determined adsorption capacity of activated sludge immobilized in alginate as well as reactor’s work time depending on flow rate and initial concentration of the solution. Results achieved were described with the use of Thomas model. The highest adsorption capacity of the sorbent (determined from the Thomas model), i.e., 200.2 mg/g d.m. was obtained at inflowing solution concentration of 50 mg/dm³ and flow rate of 0.1 V/h, whereas the lowest one reached 53.69 mg/g d.m. at the respective values of 10 mg/dm³ and 0.1 V/h. Analyses were also carried out to determine the degree of biosorbent adsorption capacity utilization at the assumed effectiveness of cadmium removal — at the breakthrough point (C=0.05*C₀) and at adsorption capacity depletion point (C-0.9*C₀). The study demonstrated that the effectiveness of adsorption capacity utilization was influenced by both the concentration and flow rate of the inflowing solution. The highest degree of sorbent capacity utilization was noted at inflowing solution concentration of 50 mg/dm³ and flow rate of 0.1 V/h, whereas the lowest one at the respective values of 10 mg/dm³ and 0.1 V/h. The course of the process under dynamic conditions was evaluated using coefficients of tangent inclination — a, at point C/C₀=½. A distinct tendency was demonstrated in changes of tangent slope a as affected by the initial concentration of cadmium and flow rate of the solution. The highest values of a coefficient were achieved at the flow rate of 0.1 V/h and initial cadmium concentration of 50 mg/dm³.