Inactivation of cryptosporidium parvum oocysts using medium- and low-pressure ultraviolet radiation

Journal of Photochemistry and Photobiology A: Chemistry

et al. 2014

a b s t r a c tA 4-factor, multilevel, full factorial design of 240 experiments was performed in order to investigate the effect of temperature on the inactivation efficiency of spiked Escherichia coli in simulated solar disinfection of a synthetic secondary effluent. The initial population of the microorganisms was 10 3 , 10 4 , 10 5 and 10 6 CFU/mL, the exposure time 1, 2, 3 and 4 h, the treatment temperature 20, 30, 40, 50 and 60• C and the sunlight intensity 0, 800 and 1200 W/m 2 . Radical changes in bacterial behavior, process efficiency and remaining populations were observed, while treating effluents in discreet temperatures. Elevating treatment temperature from 20 to 40• C drastically impaired disinfection. Thermal inactivation with no regrowth predominated at 50• C and total inactivation of microorganisms was observed at 60• C in nonirradiated samples. Irradiation at 800 and 1200 W/m 2 much increased inactivation efficiency, especially at 50 and 60• C, proving sensitive light-temperature synergy at those temperatures. Total inactivation was achieved within 4 h under a range of treatment conditions, including all samples at 1200 W/m 2 , or 60• C samples at 800 W/m 2 . Also, 99.9-100% efficiencies and final population below 1000 CFU/100 mL were obtained at 800 W/m 2 and temperatures of 50 • C and above. Treatment time, temperature and intensity are the critical parameters for the disinfection process, while initial population is insignificant for removal efficiency. An explanation of the mechanism of the process as well as a general linear model predicting the outcome of the experiments is also suggested.

Section: High Irradiance Experiments (1200 W/m 2 ) -Effects Of Reactimentioning

confidence: 89%

Section: Temperature Influence and Evolution Of Experimentsmentioning

confidence: 99%

The antagonistic and synergistic effects of temperature during solar disinfection of synthetic secondary effluent

Journal of Photochemistry and Photobiology A: Chemistry

et al. 2014

“…However, the tailing effect is attributed to i) the new generations of the cells which have developed photo-resistance (Quek and Hu, 2008) and the ones that have escaped illumination due to shielding, aggregation etc. (Craik et al, 2001). The latter ones maintain their cultivability, thus continue to replicate and delay total inactivation for 120 and 90 min, for 500 and 600 W/m 2 , respectively.…”

Section: Irradiance Effects On Solar Wastewater Disinfectionmentioning

confidence: 99%

Environmental considerations on solar disinfection of wastewater and the subsequent bacterial (re)growth

Photochem Photobiol Sci

et al. 2015

In this work, solar disinfection of wastewater was studied, focused on the effect of selected environmental variables, namely, light intensity, continuous/intermittent light delivery, and post-irradiation storage as well as dilution in lake water. These variables were studied for their effect on disinfection efficiency and on post-irradiation survival/regrowth in undiluted wastewater and in wastewater diluted in lake water at different dilution rates. The bacterial inactivation curves were studied, and distinct kinetic phases were identified and interpreted. Dose primarily influenced the phases' demonstration and total inactivation times, independently from the irradiance. Intermittent illumination un-evenly prolonged the required exposure time and pointed to extended longer required illumination times when unstable weather conditions are to be expected. Post-irradiation survival/regrowth in undiluted wastewater showed three distinct kinetic profiles, with the transitions among them largely determined by the inflicted light dose.Lower doses resulted in similar inactivation profiles as high ones, when irradiation was followed by prolonged storage at high dilution rates in lake water. The studied factors show significant design and operation implications for solar wastewater applications, based on local environmental conditions and water receptor restrictions.

“…Although [16] supported that no significant correlation exists between regrowth and the initial number of coliforms in wastewater, at any dose, they found out that in low doses, the surviving coliforms affected the reactivation rates. Craik et al [6] explained this noting that if the initial population is high, there is a big chance that there will be a part of it going through unharmed due to shielding (by each other) and bad mixing.…”

Section: Parameters Affecting Survival and Regrowth After 0 W/m 2 Irrmentioning

confidence: 99%

“…There is extensive literature on the genetic interpretation of regrowth, as well as experimental findings on the factors that affect this process; among the most common factors affecting regrowth are the effects of temperature [5,37], the salt and nutrient contents of the treated water [22,30], the effect of UV dosage and light intensities [16,23], the pre-illumination with non-coherent visible and infrared wavelengths [15], the initial bacterial population [6,10] and the type of bacterial strain [31]. However, most of the works either focus on photoreactivation, employ artificial UVC irradiation, focus on drinking water or treat regrowth exclusively as added value on the evaluation of a treatment method.…”

Section: Introductionmentioning

confidence: 99%

Elucidating bacterial regrowth: Effect of disinfection conditions in dark storage of solar treated secondary effluent

Journal of Photochemistry and Photobiology A: Chemistry

et al. 2014

a b s t r a c tIn this study, we systematically investigate solar disinfection of synthetic secondary wastewater, with the effort to decrypt the effects disinfection conditions have on post-irradiation bacterial regrowth in the dark. A full factorial design of 240 experiments was employed to investigate the effects of (i) exposure time (1, 2, 3 and 4 h), (ii) treatment temperature (20, 30, 40, 50 and 60 • C), (iii) initial bacterial concentration (10 3 , 10 4 , 10 5 and 10 6 CFU/mL) and (iv) sunlight intensity (0, 800 and 1200 W/m 2 ) on Escherichia coli survival for a subsequent 48-h dark control period. The decisive implications treatment temperature inflicted in regrowth were monitored and interpreted within two temperature ranges, from 20 to 40• C and 40 to 60• C. In dark tests, bacterial populations presented initial moderate growths at 20-40 • C range, followed by intense regrowth. At 40-60• C range, acute thermal inactivation without long-term regrowth predominated at 50• C and was total at 60 • C, within the 4-h treatment period. Introduction of light resulted in higher removal rates or permanent inactivation for 800 and/or 1200 W/m 2 , respectively. No post-treatment regrowth in the dark was observed after 24 and 48 h, in completely inactivated samples, and its demonstration, when observed, was well correlated to the bacterial numbers at the end of the disinfection period. Statistical observations on the transferred bacterial populations from day to day are also discussed in this paper.