Water Journal : Water Journal April 2011
refereed paper water APRIL 2011 93 membranes & desalination periodic UF membrane cleaning as well as to protect the RO membranes from intermittent shock disinfection of the plant. All process streams were blended and returned to the ocean through a 600m-long outfall pipe. Water quality parameters were measured on-line and via manual sampling to ensure compliance with environmental discharge permit requirements. Analyses Flow Cytometry All experiments were performed using a FACSCalibur flow cytometer (Becton Dickinson, San Jose, CA, USA) equipped with an air-cooled 15mW argon ion laser, emitting at a fixed wavelength of 488nm. Fluorescent filters and detectors were all standard, with green fluorescence collected in the FL1 channel (530±30nm), orange fluorescence collected in the FL2 channel (585±42nm) and red fluorescence collected in the FL3 channel (>670nm). All parameters were collected as logarithmic signals. Data were analysed using CellQuestTM software (Becton Dickinson, USA). For bacterial enumeration, where quantification of sample volume analysed was required, the outer sample injection port envelope was removed and samples were placed in 12 x 75mm plastic tubes and weighed before and after analysis. Staining was performed by combining equal volumes of LIVE/DEAD® BacLightTM stains (SYTO-9 (3.34mM) and PI (20mM), dissolved in dimethyl sulfoxide (DMSO), prior to use and adding 1.0 μl of this mixture directly to 1.0ml of sample. Incubation was performed for the predetermined optimal staining time of 15 minutes (data not shown) in the dark at room temperature. 16S RNA Bacteria contained on the RO membrane surface, on the exterior case of the element and permeate tube, as well as on the cartridge filters, were cultivated using blood agar plates and the DNA was isolated using polymerase chain reaction as described in Gurtler and Stanisich (1996). This method isolates the 16S RNA component using specific DNA primers to amplify this region. The product DNA template was submitted to the Australian Genome Research Facility to sequence and identify the bacterial species. Results and Discussion Samples were taken of the raw sea water and through the plant after each treatment process to assess each component's ability to remove bacteria. Figures 3 and 4 show log removals for each process stream of live and dead bacteria, respectively. Differences in removal of live and dead bacteria were minimal, with neither live nor dead bacteria preferentially removed by any unit process. Results showed large variation and may be related to several operational factors such as the raw sea water bacteria concentration (Figure 5) for which large variations were observed. The FCM results may also depend on the operating conditions of the Memcor UF system and RO system, which were varied for investigations on a fortnightly basis. Variables included: shock chlorination concentration and frequency, shock acidification concentration and frequency, coagulant concentration, antiscalant concentration and RO flux. Each different treatment process varied in removal efficiency, as expected. Owing to the large pore size of the disc filtration unit, minimal bacteria were removed. The majority of bacteria were removed by the UF systems, which yielded maximum removals of 2.8 and 3.0 log removal values (LRV) for the Norit and Memcor systems, respectively. The cartridge filters showed an increase in bacteria at times (negative log removals). Initially, the cartridge filters were not included in the chlorination loop. As the pilot plant employed shock chlorination for biofouling control of the Memcor UF system, dechlorination with SMBS prior to the RO elements must be undertaken to avoid deterioration of the polyamide surface. Initially, dechlorination with SMBS was undertaken before the cartridge filters. Increases in differential pressure in the cartridge filters were experienced until they were included in the chlorination loop (ie, SMBS dosing was shifted downstream of the cartridge filters). Figure 6 shows the effects of this change and the restoration of feasible working differential pressure for the cartridge filters. Prior to the relocation of SMBS dosing the differential pressure 0.0 1.8 1.6 0.1 -0.2 -0.2 0.3 0.3 0.2 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Log Removal Values (LRV) Figure 3: Removal of live bacteria by each process stream. Mean log removal values are reported and error bars represent the variability of 21 sampling events. 0.1 1.3 1.3 0.0 -0.1 0.0 0.0 -0.1 0.1 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Log Removal Values (LRV) Mean Upper Lower Figure 4: Removal of dead bacteria by each process stream. Mean log removal values are reported and error bars represent the variability of 21 sampling events.
Water Journal March 2011
Water Journal May 2011