Kinetic assessment of antibiotic resistant bacteria inactivation by solar photo-Fenton in batch and continuous flow mode for wastewater reuse.

The presence of antibiotic resistant bacteria in municipal wastewater treatment plants represents a real risk to human health. For the first time, this paper shows that the inactivation rate of cefotaxime resistant bacteria is the same as total bacteria when secondary effluents are treated by the solar photo-Fenton process. To obtain this result, an exhaustive and comparative kinetic study on the inactivation of both total and cefotaxime resistant bacteria (Total coliform, Escherichia coli and Enterococcus sp) was carried out, taking into account the effects of the main operation conditions, such as solar irradiance and iron concentration, and operation mode (batch and continuous). In all the operation conditions studied, no significant differences were found between the first order inactivation rate constants, ki, of total and cefotaxime resistant bacteria. Additionally, ki increased with solar irradiance and iron concentration. As for the effect of the operation mode, the main finding of this work is much quicker inactivation in continuous flow mode than in batch mode, pointing out its potential application at large scale. The best continuous operation condition to inactivate the bacteria to the detection limit (1 CFU mL-1), was at 22.4 min of hydraulic residence time with 5 mg Fe2+ L-1 and 30 mg H2O2·L-1. This treatment time is approximately a third of that reported in batch mode. The efficiency, in terms of figure of merits, of the continuous flow operation was 2.7 m2 of solar collector area to reduce one log of E. coli concentration per m3 of treated water and per hour, in comparison with 2137 m2 calculated for batch operation under the same solar UVA irradiance, 30 W m-2. This paper encourages research into continuous solar disinfection processes due to its enhanced efficiency with regard to the commonly used batch wise operation and shows that efficient removal of total bacteria ensures the removal of antibiotic resistant bacteria.

A kinetics study on the biodegradation of synthetic wastewater simulating effluent from an advanced oxidation process using Pseudomonas putida CECT 324.

Bacterial growth on mixed substrates is employed for wastewater treatment. Biodegradation kinetics of Pseudomonas putida CECT 324 growth on formic acid, vanillin, phenol and oxalic acid mixtures is described. The experiments were carried out in a stirred-tank fermentor in batch mode at different temperatures (25, 30 and 35 degrees C) and pH (5, 6 and 7). The four compounds selected are typical intermediates in pesticide-contaminated water treated by advanced oxidation processes (AOPs). The toxicity of intermediates was investigated for a combined AOP-biological treatment, and the minimum DOC inhibitory concentration of the intermediate mixture was 175 ppm. The resulting biodegradation and growth kinetics were best described by the sum kinetics with interaction parameters (SKIP) model. Phenol and oxalic acid inhibit P. putida growth, and formic acid consumption strongly affects the biodegradation of oxalic acid. At all the temperatures tested and at pH between 5 and 7, P. putida CECT 324 was able to degrade the four substrates after culture times of 30 h at 30 degrees C and pH 7, which were the best conditions, and after 70 h, under the worst, at 35 degrees C.

Effects of the sporulation conditions on the lovastatin production by Aspergillus terreus.

The production of biomass and lovastatin by spore-initiated submerged fermentations of Aspergillus terreus ATCC 20542 was shown to depend on the age of the spores used for inoculation. Cultures started from older spores produced significantly higher titers of lovastatin. For example, the lovastatin titer increased by 52% when the spore age at inoculation rose from 9 to 16 days. The lovastatin titer for a spore age of 16 days was 186.5+/-20.1 mg L(-1). The time to sporulation on surface cultures was sensitive to the light exposure history of the fungus and the spore inoculation concentration levels. A light exposure level of 140 muE m(-2 )s(-1) and a spore concentration of 1,320 spore cm(-2) produced the greatest extent of sporulation within about 50 h of inoculation. Sporulation was slowed in the dark and with diluted inoculants. A rigorous analysis of the data of statistically designed experiments showed the above observations to be highly reproducible.

Comparative analysis of the outdoor culture of Haematococcus pluvialis in tubular and bubble column photobioreactors.

The present paper makes a comparative analysis of the outdoor culture of H. pluvialis in a tubular photobioreactor and a bubble column. Both reactors had the same volume and were operated in the same way, thus allowing the influence of the reactor design to be analyzed. Due to the large changes in cell morphology and biochemical composition of H. pluvialis during outdoor culture, a new, faster methodology has been developed for their evaluation. Characterisation of the cultures is carried out on a macroscopic scale using a colorimetric method that allows the simultaneous determination of biomass concentration, and the chlorophyll, carotenoid and astaxanthin content of the biomass. On the microscopic scale, a method was developed based on the computer analysis of digital microscopic images. This method allows the quantification of cell population, average cell size and population homogeneity. The accuracy of the methods was verified during the operation of outdoor photobioreactors on a pilot plant scale. Data from the reactors showed tubular reactors to be more suitable for the production of H. pluvialis biomass and/or astaxanthin, due to their higher light availability. In the tubular photobioreactor biomass concentrations of 7.0 g/L (d.wt.) were reached after 16 days, with an overall biomass productivity of 0.41 g/L day. In the bubble column photobioreactor, on the other hand, the maximum biomass concentration reached was 1.4 g/L, with an overall biomass productivity of 0.06 g/L day. The maximum daily biomass productivity, 0.55 g/L day, was reached in the tubular photobioreactor for an average irradiance inside the culture of 130 microE/m2s. In addition, the carotenoid content of biomass from tubular photobioreactor increased up to 2.0%d.wt., whereas that of the biomass from the bubble column remained roughly constant at values of 0.5%d.wt. It should be noted that in the tubular photobioreactor under conditions of nitrate saturation, there was an accumulation of carotenoids due to the high irradiance in this reactor, their content in the biomass increasing from 0.5 to 1.0%d.wt. However, carotenoid accumulation mainly took place when nitrate concentration in the medium was below 5.0mM, conditions which were only observed in the tubular photobioreactor. A similar behaviour was observed for astaxanthin, with maximum values of 1.1 and 0.2%d.wt. measured in the tubular and bubble column photobioreactors, respectively. From these data astaxanthin productivities of 4.4 and 0.12 mg/L day were calculated for the tubular and the bubble column photobioreactors. Accumulation of carotenoids was also accompanied by an increase in cell size from 20 to 35 microm, which was only observed in the tubular photobioreactors. Thus it may be concluded that the methodology developed in the present study allows the monitoring of H. pluvialis cultures characterized by fast variations of cell morphology and biochemical composition, especially in outdoor conditions, and that tubular photobioreactors are preferable to bubble columns for the production of biomass and/or astaxanthin.