Francisco Jesus Fernandez-Morales

Modelling aerobic biodegradation of atrazine and 2,4-dichlorophenoxy acetic acid by mixed-cultures

The aim of this work was to study and to model the biodegradation of atrazine and 2,4-dichlorophenoxy acetic acid by aerobic mixed cultures. Slow removal rates were observed when biodegrading atrazine, in spite of the initial concentrations. However, high removal rates were obtained when biodegrading 2,4-D, removing up to 100mg/L in about 2months. Regarding the 2,4-D it must be highlighted that a lag phase appears, being its length proportional to the initial 2,4-D concentration. The biodegradation trends were fitted to a Monod based model and the value of the main parameters determined. In the case of atrazine they were µmax: 0.011 1/d and Y: 0.53g/g and in the case of 2,4-D µmax: 0.071 1/d and Y: 0.44g/g, indicating the higher persistence of atrazine. Once finished the experiments the microbial population was characterized being the major genus Pseudomonas when treating atrazine and Rhodococcus when treating 2,4-D.

Influence of the cathode platinum loading and of the implementation of membranes on the performance of air-breathing microbial fuel cells

AbstractThe use of catalysts and membranes in microbial fuel cells (MFCs) is rather controversial. Platinum is the best catalyst to improve the oxygen reduction reaction and the implementation of an ion exchange membrane may help to avoid the oxygen leakages from the cathode to the anode compartments and, therefore, the losses of efficiencies associated to the use of oxygen by microorganisms as the immediate electron acceptor. In this work, it is studied the influence of the platinum loading in the cathode and the implementation of membrane on the performance of an air-breathing MFC. To do this, four cells were operated for 50xa0days in order to clarify the effect of the platinum loading contained in the cathode (0.25, 0.50, 1.00, and 2.00xa0mgxa0Ptxa0cm−2) and two additional MFCs for more than 100xa0days in order to evaluate the effect of the membrane on the performance of the MFC. The results obtained point out that the performance of the MFC, in terms of maximum current density and power density from the polarization curves, dependsxa0strongly on the Pt content of the cathode. This indicates thatxa0under open-circuit conditions the cathode controls the performance. Nonetheless, during the closed-circuit operation (under 120xa0Ω resistance), the performance is not cathodically limited as there are no significant changes between the four cells. This suggests that the performance of the MFC is limited by the anodic process. Likewise, the separation of the anode and cathode by a membrane attains a faster stabilization of the MFC and a slight improvement in the production of electricity, although for air-breathing MFC, this element does not seem to be as crucial as for other types of MFCs.n Graphical AbstractAn illustration of the influence in air-breathing MFC performance and the influence of the Pt loading in air-breathing MFC performance

Improving biodegradability of soil washing effluents using anodic oxidation

In this work, a combination of electrochemical and biological technologies is proposed to remove clopyralid from Soil Washing Effluents (SWE). Firstly, soil washing was carried out to extract clopyralid from soil. After that, four different anodes-Ir-MMO, Ru-MMO, pSi-BDD and Carbon Felt (CF)-were evaluated in order to increase the biodegradability of the SWE. CF was selected because was the only one able to transform the pesticide to a more biodegradable compounds without completely mineralizing it. Finally, biological oxidation tests were performed to determine the aerobic biodegradability of the SWE generated. From the obtained results, it was observed that at the beginning of the electrolysis the toxicity slightly increased and the biodegradability decreases. However, for electric current charges over 2.5u202fA·hu202fdm-3 the toxicity drastically decreased, showing an EC50 of 143u202fmgu202fL-1, and the BOD5/COD ratio increased from 0.02 to 0.23.

Driving force behind electrochemical performance of microbial fuel cells fed with different substrates

The performance of miniaturized microbial fuel cells operating with five different substrates (acetate, lactate, glucose and octanoate) were studied with the aim to identify the reason for its different performance. In all cases, the COD removal rate was about 650u202fmg COD L-1 d-1. However, the bio-electrochemical performance of the MFC was very different, showing the MFC fed with acetate the best performance: 20 A m-2 as maximum current density, 2u202fWu202fm-2 of maximum power density, 0.376u202fV of OCV and 12.6% of CE. In addition, the acetate showed the best bio-electrochemical performance in the polarization curves and cyclic voltammetries. These polarization curves were modelled and the key to explain the better electrical performance of acetate was its lower ohmic losses. When working with acetate, its ohmic losses were one log-unit below those attained by the other substrates. These lower ohmic losses were not associated to the electrolyte conductivity of the fuel but to the lower ohmic loses of the biofilm generated.

Biological treatment of wastewater polluted with an oxyfluorfen-based commercial herbicide

Fluoxil-24 is a commercial herbicide based on oxyfluorfen (a hazardous non-soluble organochlorinated compound) and additional compounds used as solvents. The aim of this work is to study the biotreatability of this commercial herbicide in water through batch experiments performed at different temperatures (15, 20, 25 and 30u202f°C) and initial concentrations (85, 150, 300 and 500u202fmgu202fL-1 of oxyfluorfen). Activated sludge from an oil refinery wastewater treatment plant was acclimated and used for biodegradation experiments. Two main mechanisms, volatilization and biodegradation, were observed to be responsible of the herbicide removal. Fluoxil-24 removal efficiencies between approximately 40% and 80% were reached after 70u202fh, depending on the conditions used, and oxyfluorfen was not completely removed. Regarding the influence of the temperature, thermal inhibition problems appeared at 30u202f°C, and the volatilization rate of solvents increased, causing oxyfluorfen to become unavailable for microorganisms. An increase of herbicide initial concentration did not clearly affect the herbicide removal efficiency, whereas it negatively affected the biological mechanism. The experimental results were fitted to a mathematical model that included both simultaneous mechanisms of volatilization and Monod biodegradation kinetics. The model was able to predict the experimental results, and the calculated model parameters confirmed the effect of the variables under study.