Biofilm and Siderophore Effects on Secondary Waste Water Disinfection N. Saidi • S. Kouki • I. Mehri • A. Ben Rejeb • A. Belila • A. Hassen • H. Ouzari Received: 18 February 2011 / Accepted: 4 July 2011 / Published online: 21 July 2011 Ó Springer Science+Business Media, LLC 2011 Abstract The efficiency of ultraviolet (UV) light disin- fection of wastewater effluent using a large-scale pilot system was studied. The relationship between biofilm and siderophore production and UV doses received by Pseu- domonas aeruginosa strain ATCC 15442 was determined. UV decreased pyoverdine production and enhanced biofilm production. Consequently external factors conditioned by both pyoverdine and biofilm may affect the UV effect on bacterial disinfection. Introduction Pseudomonas aeruginosa, a Gram-negative bacterium, commonly isolated from soil and water, is known for its nutritional and ecological variety. P. aeruginosa is also able to escape many stress factors, such as, heavy metals [13] antibiotics [5, 6] and ultraviolet (UV) light [24]. Ultraviolet light disinfection is commonly used in the treatment of both waste-water and potable drinking water since such treatment does not produce disinfectant by-products [24]. Bacteria exposed to UV light are often under extreme conditions, with survival and proliferation depending on the ability to produce biologically active compounds. Under extreme conditions, P. aeruginosa and other bacte- ria form biofilms [11] or produce siderophores [10]. Recently, attention was been drawn to various aspects of biofilm formation in disinfected water. Primarily, biofilm formation has been associated with technical and economic problems for water companies. Biofilms are complex, organized communities of bacteria that grow in association with wide biotic and abiotic surfaces [25]. Bacterial strains react differently in their resistance to UV light irradiation. These variations in resistance may be due to environmental conditions [22]. The physical and biochemical quality of the water may also affect the efficiency of UV transmis- sion. Pigments may provide protection against the dam- aging effects of visible light and light in the far-UV region, and indeed pigmentation was been considered as a possible mechanism for irradiated bacteria resistance [9]. Also, biofilms could form a layer able to reduce the UV-light disinfection. The aims of this study were: (1) to study the disinfection of waste water by UV irradiation in a semi-industrial pilot plant; and (2) to establish relationships among biofilms, pyoverdine production and amount of disinfection. Materials and Methods Pilot Plant Study The batch laboratory UV-device was built in cooperation with Guy Daric S. A. (Aubervilliers, France). This proto- type contained a sliding rack, with an irradiation board that held six Petri dishes (90 mm diameter). A germicidal low- N. Saidi (&) Á S. Kouki Á I. Mehri Á A. Ben Rejeb Á A. Belila Á A. Hassen University of Carthage, Tunis, Tunisia e-mail: neila_saidi@yahoo.fr N. Saidi Á S. Kouki Á I. Mehri Á A. Ben Rejeb Á A. Belila Á A. Hassen Centre de Recherche et de Technologie des Eaux, Laboratoire de Traitement des Eaux Use ´es, Technopark of Borj-Cedria, BP 273, 8020 Soliman, Tunisia H. Ouzari Faculte ´ Des Sciences de Tunis, Campus, Laboratoire de Biomole ´cules Actives, University of El Manar, Tunis, Tunisia 123 Curr Microbiol (2011) 63:337–340 DOI 10.1007/s00284-011-9983-4