Tetracycline antibiotics in the environment: a review

Tetracycline antibiotics are one of the primarily antibiotics groups used for veterinary purposes, for human therapy and for agricultural purposes. Amongst the different antibiotics used, more attention is paid to tetracycline’s as it exhibits serious environmental problems including ecological risks and human health damages. Due to their extensive usage, most of the actual evidence suggests that tetracycline antibiotics are omnipresent compounds found in different ecological compartments. After medication, more than 70 % of tetracycline antibiotics are excreted and released in active form into the environment via urine and feces from humans and animals. Their highly hydrophilic character and low volatility have resulted in significant persistence in the aquatic environment. Very few studies describe the fate and toxicity of tetracycline antibiotics in the environment. Here, we review several important issues with regard to: (1) the toxicity of these compounds on aquatic and terrestrial organisms; (2) their estrogenic effects; (3) their behavior in different ecological systems and; (4) the by-products generated during water treatment. These antibiotics residues promote the development of antibiotic resistant microorganisms, which can induce adverse effect to human health by increasing the risk of certain infections. Based on recent research results, the occurrence of tetracycline antibiotics in the environment inhibits the growth of some terrestrial and aquatic species. Besides, the residual concentrations of such drugs could affect steroidogenic pathway and consequently may cause endocrine disruption of aquatic species. Most of the wastewater treatment plants are not capable of removing effectively the tetracycline antibiotics. Therefore, there is a need to develop alternative processes to remove them from waters. Advanced oxidation processes have been proposed as alternative methods to ensure higher degradation and mineralization of tetracycline antibiotics are present in waters.     

Electrochemical treatment of domestic wastewater using boron-doped diamond and nanostructured amorphous carbon electrodes

The performance of the electrochemical oxidation process for efficient treatment of domestic wastewater loaded with organic matter was studied. The process was firstly evaluated in terms of its capability of producing an oxidant agent (H₂O₂) using amorphous carbon (or carbon felt) as cathode, whereas Ti/BDD electrode was used as anode. Relatively high concentrations of H₂O₂ (0.064 mM) was produced after 90 min of electrolysis time, at 4.0 A of current intensity and using amorphous carbon at the cathode. Factorial design and central composite design methodologies were successively used to define the optimal operating conditions to reach maximum removal of chemical oxygen demand (COD) and color. Current intensity and electrolysis time were found to influence the removal of COD and color. The contribution of current intensity on the removal of COD and color was around 59.1 and 58.8 %, respectively, whereas the contribution of treatment time on the removal of COD and color was around 23.2 and 22.9 %, respectively. The electrochemical treatment applied under 3.0 A of current intensity, during 120 min of electrolysis time and using Ti/BDD as anode, was found to be the optimal operating condition in terms of cost/effectiveness. Under these optimal conditions, the average removal rates of COD and color were 78.9?±?2 and 85.5?±?2 %, whereas 70 % of total organic carbon removal was achieved.     

Coupled electrocoagulation–electro-Fenton for efficient domestic wastewater treatment

This article reports the first use of coupled electrocoagulation and electro-Fenton (EF-EC) to clean domestic wastewater. Domestic wastewater contains high amounts of organic, inorganic and microbial pollutants that cannot be usually treated in a single step. Here, to produce an effluent suitable for discharge in a single process step, a hybrid process combining electrocoagulation and electro-Fenton was simultaneously used to decrease chemical oxygen demand (COD), turbidity and total suspended solids (TSS) from domestic wastewater. The electrocoagulation–electro-Fenton process was firstly tested for the production of H₂O₂ using Ti–IrO₂ and vitreous carbon- or graphite electrodes arranged at the anode and the cathode, respectively. The concentration of H₂O₂ recorded at 1.5 A of current intensity during 60 min of electrolysis using vitreous carbon- and graphite electrodes at the cathode was 4.18 and 1.62 mg L^?1, respectively. By comparison, when the iron electrode was used at the anode, 2.05 and 1.06 mg L^?1 of H₂O₂ were recorded using vitreous carbon and graphite, respectively. The H₂O₂ concentration decrease was attributed to hydroxyl radical formation generated by the Fenton reaction. Electro-Fenton using iron electrode at the anode and vitreous carbon at the cathode with a current density imposed of 0.34 A dm^?2 ensures the removal efficiency of 50.1 % COD_T, 70.8 % TSS and 90.4 % turbidity. The electrocoagulation–electro-Fenton technique is therefore a promising secondary treatment to simultaneously remove organic, inorganic and microbial pollutants from domestic, municipal and industrial wastewaters.