Neutral or acidic pH for the removal of contaminants of emerging concern in wastewater by solar photo-Fenton? A techno-economic assessment of continuous raceway pond reactors.

As far as the authors know, no in-depth comparison has been made between the different performances of the solar photo-Fenton process for the removal of contaminants of emerging concern (CECs) as a function of pH. To this end, real WWTP secondary effluents were treated in continuous flow mode at pilot plant scale. The effect of hydraulic residence time (HRT), liquid depth and percentage of CEC removal on treatment capacity was studied. At acidic pH (2.8), the iron source was FeSO4 and at neutral pH (7.0), it was Fe(III)-EDDS. At both pH values, 2250 L m-2 d-1 can be treated in 15-cm deep raceway pond reactors at 30 min HRT with 0.1 mM iron and 0.88 mM H2O2 in order to achieve 80% CEC removal. Treatment costs were 0.25 € m-3 and 0.56 € m-3 at acidic and neutral pH, respectively. This study paves the way for the solar photo-Fenton process to be employed on a commercial scale.

Removal of contaminants of emerging concern by continuous flow solar photo-Fenton process at neutral pH in open reactors.

For the first time, the operational feasibility of the solar photo-Fenton process at neutral pH in continuous flow has been tested for three consecutive days. The aim of the treatment was to remove of contaminants of emerging concern (CECs) from wastewater treatment plant secondary effluents. To this end, a 5 cm-deep raceway pond reactor was run in continuous flow mode and the degradation of the CECs present in real secondary effluents was monitored at their natural concentrations. To keep dissolved iron at neutral pH, ethylenediamine-N,N'-disuccinic acid (EDDS) was used to form the complex Fe(III):EDDS as an iron source for the photo-Fenton reactions. At pilot scale the effects of the Fe(III):EDDS molar ratio (1:1 and 1:2) and hydraulic residence time (HRT) (20 and 40 min) on CEC removal were studied. The best operating condition was 20 min of HRT, giving rise to a treatment capacity of 900 L m-2 d-1 with CEC removal percentages of around 60%. The reactant concentrations were 0.1 mM Fe(III):EDDS at a 1:1 M ratio and 0.88 mM H2O2. Under these operating conditions, the short-term stability of the process was also demonstrated, thus pointing out the potential of this solar technology as a tertiary treatment.

Low cost UVA-LED as a radiation source for the photo-Fenton process: a new approach for micropollutant removal from urban wastewater.

Light Emitting Diode (LED) technology has matured sufficiently to be considered as an alternative UVA radiation source in photoreactors. Currently, low energy consuming LEDs with a wide range of wavelengths and radiant flux are readily available. In this study, UVA-LEDs were used as a radiation source for the photo-Fenton process as tertiary treatment. The water matrix used was a simulated secondary effluent doped with 200 µg L-1 of the pesticide acetamiprid (ACTM) due to its recalcitrant nature. All experiments were carried out in a LED-box reactor at pH 2.8. The main purpose of this research was to gain some insight into the relationships among energy supply, LED consumption, UVA irradiance and reaction rate. The effect of LED wavelength on energy efficiency for ACTM degradation was studied by varying the iron concentration and liquid depth. Three wavelengths (365, 385 and 400 nm) and two iron concentrations (5 and 11 mg L-1) for two different liquid depths (5 and 15 cm) were evaluated in order to obtain more energy efficient conditions. The results suggest that while the wavelength of 365 nm with 11 mg Fe2+ L-1 was the best condition for ACTM degradation, the wavelength of 385 nm had slower kinetics, but higher energy efficiency.

Effect of pesticide concentration on the degradation process by combined solar photo-Fenton and biological treatment.

The influence of pesticide concentration, expressed as dissolved organic carbon (DOC), on combined solar photo-Fenton and biological oxidation treatment was studied using wastewater containing a mixture of five commercial pesticides, Vydate, Metomur, Couraze, Ditumur and Scala. Two initial DOC concentrations, 200 mg L(-1) and 500 mg L(-1) were assayed. Variation in biodegradability with photocatalytic treatment intensity was tested using Pseudomonas putida. Thus the mineralisation required for combining with biodegradation of intermediates by activated sludge was 33% and 55% at 200 mg L(-1) and 500 mg L(-1), respectively. Biotreatment was carried out in a stirred tank in sequencing batch reactor (SBR) mode. As revealed by the biodegradation kinetics, intermediates generated at the higher pesticide concentration caused lower carbon removal rates in spite of the longer photo-Fenton treatment time applied. One strategy for treating water with high concentrations of pesticides and overcoming the low biodegradability of photo-Fenton intermediates is to mix it with a biodegradable carbon source before biological oxidation. This combination of photo-Fenton and acclimatized activated sludge in several SBR cycles led to complete biodegradation of a concentrated pesticide solution of 500 mg L(-1) DOC in approximately 5h with a carbon removal efficiency of 90%.

Degradation of alachlor and pyrimethanil by combined photo-Fenton and biological oxidation.

Biodegradability of aqueous solutions of the herbicide alachlor and the fungicide pyrimethanil, partly treated by photo-Fenton, and the effect of photoreaction intermediates on growth and DOC removal kinetics of the bacteria Pseudomonas putida CECT 324 are demonstrated. Toxicity of 30-120 mg L(-1) alachlor and pyrimethanil has been assayed in P. putida. The biodegradability of photocatalytic intermediates found at different photo-treatment times was evaluated for each pesticide. At a selected time during batch-mode phototreatment, larger-scale biodegradation kinetics were analysed in a 12 L bubble column bioreactor. Both alachlor and pyrimethanil are non-toxic for P. putida CECT 324 at the test concentrations, but they are not biodegradable. A approximately 100 min photo-Fenton pre-treatment was enough to enhance biodegradability, the biological oxidation response being dependent on the pesticide tested. The different alachlor and pyrimethanil respiration and carbon uptake rates in pre-treated solutions are related to change in the growth kinetics of P. putida. Reproducible results have shown that P. putida could be a suitable microorganism for determining photo-Fenton pre-treatment time.

Influence of power supply in the feasibility of Phaeodactylum tricornutum cultures.

The influence of fluid-dynamic conditions on the yield of Phaeodactylum tricornutum microalgal cultures was analyzed in two stages: first, the influence of air flow rate; second, the influence of using fluid-moving pumps for recirculating the culture. With respect to the air flow rate, the yield of the cultures increased with the aeration rate up to values of 2.0 v/v/min, then stress was observed and the yield of the cultures decreased. With respect to the influence of mechanical power supply for liquid impulsion, three different types of pumps--centrifugal, pulse, and peristaltic--were essayed at different power supplies. The cultures were stressed for the three types of pumps essayed. For each pump, the higher the power supply the lower was the Fv/Fm value and the higher was the stress at which cells were exposed. The highest measured stress was when the culture was moved with the centrifugal pump. Despite measured stress, for all the experiments stable steady states were reached, thus indicating that cells reduced their yield but did not die, as was verified by cell viability measurements. It was observed that the increase of the power supply improved the frequency of light exposition thus enhancing the yield of the cultures. However, the higher the power supply, the lower the microeddy length scale; therefore, stress could appear. Data demonstrated that the microeddy length scale was always much higher than cell size and therefore the turbulence was not responsible for stress. Also, the mass transfer was discarded as responsible for yield reduction. It was concluded that the shear rate was the factor determining the existence of stress phenomena. The evaluation of these shear rates demonstrated that values above 30-80 s(-1) damaged the cells strongly. These data were verified in an outdoor pilot-scale tubular photobioreactor that was implemented with the same type of pumps, thus demonstrating the necessity to take into account this factor in the design and scale-up of microalgal photobioreactors.

Minimization of carbon losses in pilot-scale outdoor photobioreactors by model-based predictive control.

The optimization of carbon use in pilot-scale outdoor tubular photobioreactors is investigated in this study. The behavior of a 0.20-m(3) tubular photobioreactor was studied, with and without algae, by steady-state and pulse dynamic-response analysis experiments. A model of the system was obtained and implemented in a programmable control unit and was used to control the reactor under normal production conditions. Results showed that, using and on-off control, the mean daily CO(2) flow in the reactor was 0.86 g min(-1), 19.7% of this being lost. By using a predictive control algorithm the mean daily CO(2) flow was reduced to 0.74 g min(-1), with losses being reduced to 15.6%. In this case, pH tracking was not adequate, especially at the beginning and end of the daylight period, because the variation in solar irradiance was not considered. Taking solar irradiance into account resulted in better performance, with mean daily CO(2) flow reduced to 0.70 g min(-1), and carbon losses reduced to 5.5%. pH tracking was improved and valve actuation was reduced. Improvement of pH control reduced pH gradients in the culture, which increased the photosynthesis rate and biomass productivity of the system. Biomass productivity increased from 1.28 to 1.48 g L(-1) day-(1) when on-off control was replaced by model-based predictive control plus solar irradiance effect mode. Implementation of this methodology in outdoor photobioreactors can increase productivity by 15% and reduce the cost of producing biomass by >6%. Clearly, application of effective control techniques, such as model-based predictive control (MPC), must be considered when developing these processes.

[Prune bell syndrome]. / Síndrome de abdomen en ciruela pasa.

The prune belly syndrome is a very rare entity, characterized by a marked deficiency of the abdominal muscles, bilateral cryptorchidism and urinary tract abnormalities. The etiology is still unknown; the best accepted theory is the embryologic, due to disturbance in development between the sixth to tenth week. Histologically renal dysplasia is found together with partial or total absence of muscle fibers in the ureter, instead of which there is connective tissue, hypertrophy of the bladder with normal ganglionar cells; the prostatic urethra is dilated. There are three clinical types: neonatal, neonatal urgency and late development. There is not as yet a good management program set out for these children in whom the damage is varied. The best treatment is prophylaxis, control of infection avoiding instrumentation and repeated urological examinations. The prognosis depends on the volumen of functional parenchima and its preservation. Depends also on the degree of dysplasia and of insufficiency and secondary damage due to infection. We are reporting three differents cases and their management; we have obtained good results and we expect a good prognosis according to the special characteristics of their evolution.

Reset of hippocampal rhythmical activities by afferent stimulation.

Physostigmine induced theta rhythm and unit activity were recorded from the dorsal hippocampus in immobilized locally anesthetized rats. Correlations between theta and rhythmical unit activity and their modifications by hippocampal afferent stimulation were studied. The principal finding was that electrical stimulation of afferents reset theta and rhythmical unit activity in phase. Poststimulus theta displayed a variable frequency which depended upon the structure stimulated. Lower frequencies were evoked by septal, higher frequencies by entorhinal and reticular formation stimulations. When theta rhythms were absent either by spontaneous disappearance or as a consequence of lesions in the fornix superior of septum, the reset was not observed. The reset of the theta rhythms and unit activity by afferent stimulation, suggests that the hippocampus may participate in timing mechanisms.

Analysis of unit pairs in the hippocampus.

Unit pairs were recorded from dorsal hippocampus in curarized rats injected with physostigmine, during spontaneous activity and stimulation of hippocampal afferents. Interactions between neurons and with the theta (theta) rhythm were investigated with statistical procedures which included: autocorrelations, crossocorrelations, peristimulus-time-histograms (PSTHs) and joint-peristimulus-scatter-diagrams (JPSs). Three types of pairs were found: (1) theta pairs, with rhythmical bursting units phaselocked with theta; (2) non-theta pairs, having non-rhythmical cells; and (3) mixed pairs. Theta pairs showed periodical crossrelation between units which fired in phase or out of phase. Non-theta pairs could interact or not. Many interacting non-theta pairs showed a degree of phaselocking with theta. Mixed pairs were rare, but when interacting they always revealed positive periodical crosscorrelations. Stimulus-elicited phase relationships (reset) and rhythmical interactions within the theta pairs suggest a common source for their rhythmicity and reset. In related non-theta pairs the stimulus usually modified their interactions suggesting loose functional connections.