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

The 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): 241.66mA I250mA, [TC](0)=50mg L-1 and 120.0min t(elecrolysis) 132.9min for TC and 50mA I80mA, 10mg L-1 [Tylo](0)13mg L-1 and t(elecrolysis)=240min for Tylo. Under these conditions, the obtained yields of COD abatement were congruent to 80% and congruent to 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 250mA, 50mg L-1 initial TC or Tylo and during 240.0 and 180.35min 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.