Removal of a mixture tetracycline-tylosin from water based on anodic oxidation on a glassy carbon electrode coupled to activated sludge

Synergistic low-temperature plasma degradation of tetracycline with ferrocene

Low-temperature plasma technology has been successfully applied to the treatment of persistent organic pollutants in water. By combining catalysts with low-temperature plasma, the degradation efficiency and energy utilization efficiency of pollutants can be effectively improved. In this study, ferrocene (Fc) was added as a new catalyst to the low-temperature plasma system to treat tetracycline (TC) found in wastewater. The degradation efficiency of TC after 60 min of plasma treatment, Fc adsorption, and Fc/plasma treatment was compared, indicating that Fc/plasma improved the removal compared with using plasma alone. The effects of primary parameters such as Fc dosage, initial pH, discharge voltage, and anions in wastewater on TC removal efficiency were investigated. Under the conditions of Fc dosage of 400 mg/L, pH of 9, and discharge voltage of 20 kV, the degradation efficiency of TC was 76.59%. Results of free quenching experiments indicated that hydroxyl radicals played an important role in the treatment of TC. The characterizations of Fc showed that the structure of Fc before and after use in the plasma system changed little. In addition, toxicity testing using toxicity assessment software showed that only two to three degradation intermediate products had slightly higher toxicity than TC. The iron leaching concentration was 2.5 mg/L, and the Fc dissolution concentration was 1.72 mg/L after the reaction.

Removal of chemical oxygen demand and ammonia nitrogen from high salinity tungsten smelting wastewater by one-step electrochemical oxidation: From bench-scale test, pilot-scale test, to industrial test

In recent years, electrochemical oxidation (EO) shows the characteristics of green and high efficiency in removing chemical oxygen demand (COD) and ammonia nitrogen (NH₃-N) from wastewater, which has been favored by researchers. However, at present, most of current studies on EO remain in laboratory stage, reports about pilot-scale or even industrial tests with large treatment capacity are few, which slowing down the use of the advanced technology to practical application. In this study, bench-scale tests, pilot-scale tests (treatment capacity 200-500 L/h), and industrial tests (treatment capacity 100 m³/h) were carried out by EO technology in view of the characteristics of tungsten smelting wastewater (TSW) with high salinity (NaCl), COD, and NH₃-N. Results showed that the removal of COD and NH₃-N was a competitive reaction in the EO process, and COD could be removed more preferentially than NH₃-N. When NH₃-N content was low, the influent pH had a minimal effect on its removal, and when NH₃-N content was high, increasing the influent pH was beneficial to its removal. Industrial tests showed that the one-step removal of COD and NH₃-N in TSW met the standard, and the power consumption per cubic meter of wastewater was only 4.2 kW h, and the treatment cost was much lower than the two-step process of "breaking point chlorination to remove NH₃-N and adding oxidant to remove COD". This study has successfully realized industrial application of EO technology in TSW treatment for the first time and provided a successful case, which is helpful to accelerate the popularization and application of this technology in the field of high salinity organic ammonia nitrogen wastewater treatment.

Activated persulfate by iron-carbon micro electrolysis used for refractory organics degradation in wastewater: a review

With the rapid economic development, the discharge of industrial wastewater and municipal wastewater containing many refractory organic pollutants is increasing, so there is an urgent need for processes that can treat refractory organics in wastewater. Iron-carbon micro electrolysis and advanced oxidation based on persulfate radicals (SO₄^-·) have received much attention in the field of organic wastewater treatment. Iron-carbon micro electrolysis activated persulfate (Fe-C/PS) treatment of wastewater is characterized by high oxidation efficiency and no secondary pollution. This paper reviews the mechanism and process of Fe-C/PS, degradation of organics in different wastewater, and the influencing factors. In addition, the degradation efficiency and optimal reaction conditions (oxidant concentration, catalyst concentration, iron-carbon material, and pH) of Fe-C/PS in the treatment of refractory organics in wastewater are summarized. Moreover, the important factors affecting the degradation of organics by Fe-C/PS are presented. Finally, we analyzed the challenges and the prospects for the future of Fe-C/PS in application, and concluded that the main future directions are to improve the degradation efficiency and cost by synthesizing stable and efficient catalysts, optimizing process parameters, and expanding the application scope.

Assessment of electrooxidation as pre- and post-treatments for improving anaerobic digestion and stabilisation of waste activated sludge

This study evaluates the effects of electro-oxidation as a means for enhancing sludge stabilisation. Boron-doped diamond electrodes were used to treat waste activated sludge and digestate under different operating parameters (current density, conductivity, pH, and time). Electro-oxidation runs affected the solubilisation of organic matter, which seemed to improve anaerobic digestion and dewaterability characteristics. Among the tested parameters, pre-treating sludge via electro-oxidation under alkaline conditions (Treatment T5) resulted in the highest increase in soluble organic material compared to that in the control, with total organic carbon (TOC) and soluble chemical oxygen demand (COD) values of 2753 and 7819 mg L^-1, respectively (control TOC and COD values were 385 and 1073 mg L^-1). This pretreatment also achieved a high hydrolysis rate (higher concentration in volatile fatty acids) with a concomitant increase in methane yield (approximately 18%). On the other hand, the application of electro-oxidation as a post-treatment for improving digestate dewaterability resulted in noticeable changes in the release of water during drying due to protein and aliphatic matrix modification of the sample.

The degradation, biodegradability and toxicity evaluation of sulfamethazine antibiotics by gamma radiation

This study evaluated gamma radiation-enhanced sulfamethazine (SMT) degradation, which belongs to the heterocyclic sulfonamides, in different conditions in aqueous solution. The results showed that gamma irradiation could increase the SMT removal in aqueous solution, and the SMT degradation kinetic follow the modified pseudo-first-order kinetic. The degradation rate was nearly 95% at the absorbed dose of 4 kGy. The removal of total organic carbon (TOC) and total nitrogen (TN) could be also induced. When the radiation dose was 5 kGy, the removal rates were only about 6.8% and 10.5% for TOC and TN, respectively. Some ions including HCOO−, CH3COO− and SO42− released during SMT degradation were studied. The biodegradability and toxicity of intermediate products of the SMT degradation were also proposed in this experiment. The biodegradability of the SMT can be improved by the intermediate products of SMT degradation at the radiation dose of 1, 2 and 5 kGy. Gamma radiation could be used as a pretreatment technology before the biodegradation process of pharmaceutical waste water.

Adsorption of pharmaceutical residues on adsorbents prepared from olive stones using mixture design of experiments model

In this work, inexpensive and easily available olive stone (OS) waste was used as the source material to prepare activated carbons (ACs) by chemical activation with phosphoric acid and zinc chloride. The mixture design of experiments (MDOE) method was applied to study the effect of the composition of the mixture of unmodified olive stones (UOS) and ACs prepared from olive stones activated with ZnCl₂ (ACOS ZnCl₂) and H₃PO₄ (ACOS H₃PO₄) on the absorption of pharmaceutical residues. The adsorbed tetracycline (TC) amounts at equilibrium predicted from the model equation developed using Microsoft Excel were found to be in good agreement with the experimental values (R² = 0.999). Based on the results of the model, the amount of TC removed increased as the proportion of ACOS H₃PO₄ in the adsorbent mixture increased and the highest amount of TC adsorbed was obtained with an adsorbent made up entirely of ACOS H₃PO₄. Separate adsorption tests for sulfamethazine (SMT) and amoxicillin (AMX) on ACOS H₃PO₄ showed that SMT was adsorbed best (189.81 mg/g), followed by TC (183.11 mg/g) then AMX (155.69 mg/g). However, when these molecules were present together in the same solution, it was TC that adsorbed best, followed by SMT then AMX. In addition to this, the sorption process studied was best described by a pseudo-first-order model and it was the Langmuir model that satisfactorily described the equilibrium data.

Sulfamethazine removal by means of a combined process coupling an oxidation pretreatment and activated sludge culture - preliminary results

A coupled electrochemical process and biological treatment was used to remove a biorecalcitrant antibiotic: sulfamethazine (SMT). The pretreatment was performed in a home-made flow cell involving graphite felt as a working electrode at potentials of 1 and 1.6 V/saturated calomel electrode (SCE); it was followed by a biological process involving activated sludge purchased from a local wastewater treatment plant. Activated sludge cultures of pretreated and non-pretreated SMT solution were carried out for 3 weeks, and different parameters were monitored, especially total organic carbon (TOC) and SMT concentrations. high-performance liquid chromatography results revealed that the target molecule was not assimilated by activated sludge. However, and confirming the improvement previously observed for the biological oxygen demand/chemical oxygen demand (BOD₅/COD) ratio, from 0.08 before electrolysis to 0.58 after electrolysis, a pretreatment step in oxidation at 1.6 V/SCE led to a fast decrease of TOC during the subsequent biological treatment, since the mineralization yields increased from 10% for a non-pretreated SMT solution to 76.6% after electrolysis in oxidation (1.6 V/SCE), confirming the efficiency of coupling the electro-oxidation process with a biological treatment for the mineralization of SMT. Moreover, when the electrolysis was performed at 1 V/SCE, no biodegradation was observed, underlining the importance of the electrochemical pretreatment.

Direct and indirect electrochemical reduction prior to a biological treatment for dimetridazole removal

Two different electrochemical reduction processes for the removal of dimetridazole, a nitroimidazole-based antibiotic, were examined in this work. A direct electrochemical reduction was first carried out in a home-made flow cell in acidic medium at potentials chosen to minimize the formation of amino derivatives and then the formation of azo dimer. Analysis of the electrolyzed solution showed a total degradation of dimetridazole and the BOD₅/COD ratio increased from 0.13 to 0.24. An indirect electrochemical reduction in the presence of titanocene dichloride ((C₅H₅)₂TiCl₂), which is used to reduce selectively nitro compounds, was then investigated to favour the formation of amino compounds over hydroxylamines and then to prevent the formation of azo and azoxy dimers. UPLC-MS/MS analyses showed a higher selectivity towards the formation of the amino compound for indirect electrolyses performed at pH 2. To confirm the effectiveness of the electrochemical reduction, a biological treatment involving activated sludge was then carried out after direct and indirect electrolyses at different pH. The enhancement of the biodegradability was clearly shown since mineralization yields of all electrolyzed solutions increased significantly.

Combination of the Electro/Fe3+/peroxydisulfate (PDS) process with activated sludge culture for the degradation of sulfamethazine

In this paper, the major factors affecting the degradation and the mineralization of sulfamethazine by Electro/Fe³⁺/peroxydisulfate (PDS) process (e.g. current density, PDS concentration, Fe³⁺ ions concentration and initial sulfamethazine (SMT) concentration) were evaluated. The relevance of this process as a pretreatment prior to activated sludge culture was also examined. Regarding the impact on SMT degradation and mineralization, the obtained results showed that they were significantly enhanced by increasing the current density and the PDS concentrations in the ranges 1-40mAcm^-2 and from 1 to 10mM respectively; while they were negatively impacted by an increase of the initial SMT concentration and the Fe³⁺ concentration, from 0.18 to 0.36mM and from 1 to 4mM respectively. The optimal operating conditions were therefore 40mAcm^-2 current density, 10mM PDS concentrations, 1mM Fe³⁺, and 0.18mM SMT. Indeed, under these conditions the degradation of SMT and its mineralization yield were 100% and 83% within 20min and 180min respectively. To ensure a significant residual organic content for activated sludge culture after Electro/Fe³⁺/PDS pre-treatment, the biodegradability test and the biological treatment were performed on a solution electrolyzed at 40mAcm^-2, 10mM PDS concentrations, 1mM Fe³⁺, and 0.36mM SMT. Under these conditions the BOD₅/COD ratio increased from 0.07 to 0.41 within 6h of electrolysis time. The subsequent biological treatment increased the mineralization yield to 86% after 30days, confirming the relevance of the proposed combined process.

Removal of herbicidal ionic liquids by electrochemical advanced oxidation processes combined with biological treatment

Recently a new group of ionic liquids (ILs) with herbicidal properties has been proposed for use in agriculture. Owing to the design of specific physicochemical properties, this group, referred to as herbicidal ionic liquids (HILs), allows for reducing herbicide field doses. Several ILs comprising phenoxy herbicides as anions and quaternary ammonium cations have been synthesized and tested under greenhouse and field conditions. However, since they are to be introduced into the environment, appropriate treatment technologies should be developed in order to ensure their proper removal and avoid possible contamination. In this study, didecyldimethylammonium (4-chloro-2-methylphenoxy) acetate was selected as a model HIL to evaluate the efficiency of a hybrid treatment method. Electrochemical oxidation or electro-Fenton was considered as a pretreatment step, whereas biodegradation was selected as the secondary treatment method. Both processes were carried out in current mode, at 10 mA with carbon felt as working electrode. The efficiency of degradation, oxidation and mineralization was evaluated after 6 h. Both processes decreased the total organic carbon and chemical oxygen demand (COD) values and increased the biochemical oxygen demand (BOD₅) on the COD ratio to a value close to 0.4, showing that the electrolyzed solutions can be considered as 'readily biodegradable.'

Variation in properties of the sediment following electrokinetic treatments

Many studies have reported variation in properties of the sediment within electrokinetic treatments (EKTs). However, we aim to reveal the variation in properties of the sediment following EKTs through laboratory experiments. We collected sewage-derived sediment from a littoral region, and passed it through a 2-mm sieve. We used a potentiostat to cause electrical current in EKT. We measured the sediment properties such as pH, redox potential (ORP), and hydrogen sulphide (H₂S) concentration at the end of EKT and at 30 days following EKT. Results showed decreases in pH, increases in ORP, and decreases in H₂S concentration at the end of EKT. Compared with the sediment without EKT, the decrease in ORP for the sediment within EKT was higher at 30 days following EKT. These suggest that anaerobic digestion of organic compounds occurs in the sediment following EKT, of which the oxidants produced by EKT serve as electron acceptors and organic compounds serve as electron donors. Furthermore, we found that EKT can remove H₂S from the sediment and reduce H₂S production in the sediment within EKT when compared to the case without EKT. These ensure that EKT can be used to remove H₂S and control H₂S production in the sediment.

Heterogeneous Fenton oxidation of ofloxacin drug by iron alginate support

A new catalytic wet peroxide oxidation of ofloxacin antibiotic is presented in this work. The removal was achieved using a biodegradable sodium alginate-iron material. Several parameters were studied such as iron content, drying duration of the catalytic support, temperature, solid amount and initial drug concentration. The process showed a strong oxidative ability; at optimum conditions, a nearly complete removal of the drug (around 98%) has been reached after three h of treatment. A relatively low decrease of support activity (around 10%) has been observed after three successive oxidation runs and a low iron leaching has been detected (1.2% of the incorporated quantity). The removal of the substrate has been also examined in the absence of hydrogen peroxide in order to discriminate between the contributions of simple adsorption and oxidation processes in the drug disappearance. We also discussed the influence of the studied experimental parameters on the removal kinetic.