The feasibility of combining an electrochemical treatment on a carbon felt electrode and a biological treatment for the degradation of tetracycline and tylosin – application of the experimental design methodology

Abstract

ABSTRACTThe feasibility of combining an electrochemical treatment on a carbon felt electrode and a biological treatment for the degradation of tetracycline (TC) and tylosin (Tylo) is presented. Central composite design (CCD) was employed to optimize the effects of the operating parameters on the electrochemical treatment efficiency. The variables investigated were the electrolysis time, the applied current intensity and the initial TC and Tylo concentrations. The second-order model obtained by CCD led to the following optimal conditions for the abatement of the chemical oxygen demand (COD): 241.66 mA ≤ I ≤ 250 mA, [TC]0 = 50 mg L−1 and 120.0 min ≤ telecrolysis ≤ 132.9 min for TC and 50 mA ≤ I ≤ 80 mA, 10 mg L−1≤ [Tylo]0 ≤ 13 mg L−1 and telecrolysis = 240 min for Tylo. Under these conditions, the obtained yields of COD abatement were 80% and 69% for TC and Tylo, respectively. To assess the effectiveness of electrolysis as a pretreatment before a biological process, biodegradability tests were conducted on a solution electrolyzed at 250 mA, 50 mg L−1 initial TC or Tylo and during 240.0 and 180.35 min for TC and Tylo, and showed an improvement of the BOD5/COD ratio, from 0.033 to 0.46 and from 0.04 to 0.33 for TC and Tylo, respectively. From this, the electrochemical pretreatment of TC and Tylo generated intermediate products, which are at least partially biodegradable. The combination of an electrochemical pretreatment in the same conditions with a biological treatment involving activated sludge confirmed these positive results, since it showed an overall dissolved organic carbon (DOC) removal close to 92% and 89% for TC and Tylo, respectively.