Modelling of reactivation after UV disinfection: Effect of UV-C dose on subsequent photoreactivation and dark repair

• Published in: Water research (Oxford) Vol. 41; no. 14; pp. 3141 - 3151
• Main Authors: Nebot Sanz, E., Salcedo Dávila, I., Andrade Balao, J.A., Quiroga Alonso, J.M.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-07-2007; Elsevier Science
• Subjects: Applied sciences; bacteria; biological resistance; Dark repair; decontamination; Disinfection; DNA damage; DNA repair; dosage; Exact sciences and technology; Faecal microorganisms; feces; irradiation; Kinetics; light intensity; mathematical models; microbial resuscitation; Microbial Viability - radiation effects; Models, Biological; Other industrial wastes. Sewage sludge; pathogen survival; Photochemistry; Photoreactivation; Pollution; radiation injury; radiation resistance; reaction kinetics; sewage effluent; Ultraviolet irradiation; ultraviolet radiation; Ultraviolet Rays; Wastes; Wastewater; wastewater treatment; water pollution; Water treatment and pollution; Model; Photoreactivation; Dark repair; Ultraviolet irradiation; Wastewater; Faecal microorganisms; Drinking water treatment; Ultraviolet radiation; Ultraviolet irradiation Photoreactivation Dark repair Wastewater Faecal microorganisms Model; Disinfection; Kinetics; Feces; Waste water purification; Repair; Modeling; Waste water
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2007.04.008

The increased use of UV radiation as a wastewater treatment technology has stimulated studies of the repair potential of microorganisms following treatment. In this study, samples of unfiltered secondary effluent were irradiated with seven levels of UV-C doses (50–200
mW
s/cm
2) from six low-pressure lamps in an open-channel UV disinfection system. Following irradiation, samples were incubated at 20
°C under photoreactivating light or in darkness. Samples were analysed for 240
min following incubation.
The logistic model is proposed to explain the relation between photoreactivation and the UV-C dose received by the microorganisms. That model accurately fitted the data obtained in photoreactivation experiments, permitting interpretation of the estimated kinetic parameters:
S
m and
k
2. In the experiments carried out in darkness, a slight reactivation is observed (<0.1%), followed by a decay period in which survival decreases. In order to model this last period, a modification was made to the logistic model by including a term of mortality that assumes a zero-order kinetic. The parameters
S
m and
k
2, in both photoreactivation and darkness, show an exponential dependence on the UV-C inactivating dose. It is possible to predict their values, and hence the reactivation curve, from the equations proposed in this work.