Evaluation of ultraviolet disinfection of microalgae by growth modeling: application to ballast water treatment

Abstract

Ultraviolet disinfection is a frequent option for eliminating viable organisms in ballast water to fulfill international and national regulations. The objective of this work is to evaluate the reduction of microalgae able to reproduce after UV irradiation, based on their growth features. A monoculture of microalgae Tisochrysis lutea was irradiated with different ultraviolet doses (UV-C 254 nm) by a flow-through reactor. A replicate of each treated sample was held in the dark for 5 days simulating a treatment during the ballasting; another replicate was incubated directly under the light, corresponding to the treatment application during de-ballasting. Periodic measurements of cell density were taken in order to obtain the corresponding growth curves. Irradiated samples depicted a regrowth following a logistic curve in concordance with the applied UV dose. By modeling these curves, it is possible to obtain the initial concentration of organisms able to reproduce for each applied UV dose, thus obtaining the dose-survival profiles, needed to determine the disinfection kinetics. These dose-survival profiles enable detection of a synergic effect between the ultraviolet irradiation and a subsequent dark period; in this sense, the UV dose applied during the ballasting operation and subsequent dark storage exerts a strong influence on microalgae survival. The proposed methodology, based on growth modeling, established a framework for comparing the UV disinfection by different devices and technologies on target organisms. This procedure may also assist the understanding of the evolution of treated organisms in more complex assemblages such as those that exist in natural ballast water.

Enumerating viable phytoplankton using a culture-based Most Probable Number assay following ultraviolet-C treatment

“…We developed an objective method to do so, based on linear regression of the growth curve to a day-0 value. Other researchers (Redford and Myers 1951 ; Romero-Martínez et al 2016 ) have used the intercept from the regression of a growth curve as a direct estimate of the number of viable cells—this treatment differs in using the regression as a quality-control criterion on the MPN estimate rather than as an estimate in its own right. An increase in fluorescence in the least-diluted samples can be fitted by linear regression of ln-transformed values greater than LLD F on time (Fig.…”

Comparing the inactivating efficacy of enteric bacteria in seawater treated with different configurations of continuous flow‐through ultraviolet devices: single‐pass and recirculation

“…The inactivation kinetics following a biphasic model has been commonly found in different studies on disinfection of bacteria, viruses, and other organisms subjected to UV and chemical disinfectants . In terms of practical application to water disinfection, the tailing implies the treatment becomes ineffective after a certain degree of inactivation.…”

“…The inactivation kinetics following a biphasic model has been commonly found in different studies on disinfection of bacteria, viruses, and other organisms subjected to UV and chemical disinfectants. 8,12,[35][36][37][38] In terms of practical application to water disinfection, the tailing implies the treatment becomes ineffective after a certain degree of inactivation. The origin of the tailing phenomenon is still unclear and is attributed to the particles aggregation, [39][40][41][42][43] shading due to the experimental design, 44 the screening effect of suspended solids, 45 and different resistance of the organisms.…”

“…Growth rate and modifications of the enzyme profile by osmotic stress are two factors affecting the specific resistance of the organisms to the UV treatment . However, the organisms have photoreactivation mechanisms that repair the DNA damage caused by the UV irradiation to a great extent if treated organisms are released into an illuminated environment . Other features are also involved in the UV treatment of seawater such as the mechanical stress caused by the pumping in dynamic UV devices …”

“…[9][10][11] However, the organisms have photoreactivation mechanisms that repair the DNA damage caused by the UV irradiation to a great extent if treated organisms are released into an illuminated environment. 12,13 Other features are also involved in the UV treatment of seawater such as the mechanical stress caused by the pumping in dynamic UV devices. [14][15][16] The efficacy of the UV treatment is commonly evaluated through the disinfection profiles expressed as dose-survival curves.…”