Legionella pneumophila is known as the causative agent of Legionnaires’ disease and free-living amoebae (FLA) can serve as vehicles for legionellae. The aim of this study was to screen industrial waters for the occurrence of FLA and their co-occurrence with legionellae. A total of 201 water samples, including 129 cooling waters and 72 process waters, and 30 cooling lubricants were included in the study. Treated waters were screened periodically, pre and post treatment. Altogether, 72.6% of the water samples were positive for FLA, acanthamoebae being most prevalent (in 23.9% of the samples) followed by Vermamoeba vermiformis (19.4%). Only one cooling lubricant was positive (Acanthamoeba genotype T4). Legionella spp. were detected in 34.8% of the water samples and in 15% in high concentrations (>1000 CFU/100 ml). Altogether, 81.4% of the Legionella-positive samples were positive for FLA by standard methods. By applying a highly sensitive nested PCR to a representative set of random samples it was revealed that Legionella spp. always co-occurred with Acanthamoeba spp. Although the addition of disinfectants did influence amoebal density and diversity, treated waters showed no difference concerning FLA in the interphases of disinfection. It appears that FLA can re-colonize treated waters within a short period of time.
The electrochemical advanced oxidation process (EAOP) with diamond electrodes may serve as an additional technology to the currently approved methods for water disinfection. Only few data exist on the microbicidal effect of the EAOP. The aim of our study was to investigate the microbicidal effect of a flow-through oxidation cell with diamond electrodes, using Pseudomonas aeruginosa as the test organism. Without electrical current the EAOP had no measurable effect on investigated microbiological and chemical parameters. For direct electrical current a stronger impact was observed at low flow rate than at higher flow rate. Depending on the contact time of the oxidants and the type of quenching reagent added, inactivation of P. aeruginosa was in the range log 1.6-3.6 at the higher flow rate and log 2.4-4.4 at the lower rate. Direct electrical current showed a stronger microbicidal effect than alternating current (maximum reduction log 4.0 and log 2.9, respectively). The microbiological results of experiments with this EAOP prototype revealed higher standard deviations than expected, based on our experience with standard water disinfection methods. Safe use of an EAOP system requires operating parameters to be defined and used accurately, and thus specific monitoring tests must be developed.
The feasibility of an innovative electrokinetic soil remediation technique for an in situ application against fuel-contaminated soil has been studied in this work. This technique combines the anodic production of oxidizing agents on boron-doped diamond (BDD) electrode surfaces with their electrokinetic distribution in soil. In this study, the production of oxidizing agents, i.e., hydroxyl radicals (OH degrees ) and peroxodisulfate (S(2)O(8)(2 -)), from a 0.85 M sodium sulfate electrolyte with mechanically implanted BDD anodes at room temperature has been investigated. It was found that about 12 mmol/L of oxidants could be produced after 10 Ah/L with a current density of 200 mA/cm(2). For investigating the transport velocity of peroxodisulfate in soil a vertical column system has been created. Experimental results show linear velocity behaviour for the oxidants' migration in 100% sand soil reaching up to 2 cm/h at an electrical gradient of 4 V/cm. As for different soil textures which have been tested, the assays stated that the highest velocity can be achieved in a 100% silt soil with 3.3 cm/h.
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