Water. Desalination + reuse
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TECHNOLOGY February-March 2015 | Desalination & Water Reuse | 29 | TECHNOLOGY three banks of ultra-filtration modules are used, fed by a recirculation system from a single bioreactor tank. An intensive aerobic environment is created in the AMBR using a Jetox aeration system. The plant produces a high-quality final effluent in a small footprint. However, the RO plant – commissioned in 2004 – had a history of fouling during periods of peak production. Autopsies on membrane elements and cartridge filters indicated that the foulant was mainly organic and microbiological in origin. Aluminium silicate was also present – originating from clay and soil removed in the salad washing process – and there were calcium phosphate deposits. Calcium phosphate scale formation caused the plant to trip out at high pressure on three occasions in 2006. These events were due to increased use by the factory's Pressure peaks The reason for the sudden increases in ndP is thought to be due to the presence of biofilm and clay that was only partially removed using conventional cleaning. The significantly more resilient reduction in ndP provides evidence that Genesol 704 worked more effectively in cleaning the membrane surface than its conventional counterpart. When inducted air and Genesol 704 were combined to create microbubbles and applied to RO pressure vessels the membranes were significantly cleaner still as indicated from a much slower fouling rate. The cleaning process reduces surface roughness in the membrane to slow down re-fouling. Furthermore it is thought that biofilm removal and disruption will significantly reduce the surviving microbial population. This can be expected to prevent microorganisms from replicating at the same rate despite the on-going nutrient source in the feed water. hygiene department of a phosphoric acid- based cleaning formulation that affected the phosphate balance in the RO plant feedwater. The plant operators subsequently gained better control over such incidents using a basic programme of cleaning with liquid alkaline agents which remained in place for seven years. But there remained an underlying high fouling rate and a need to clean every 7 – 14 days as the pressure required to maintain water production continually increased. The high frequency of cleaning resulted in membrane elements having to be changed every 18 months. In May 2013 a case study commenced using Genesys' powder-based, effervescing alkaline cleaner (Genesol 704) initially alone and then in conjunction with air microbubbles from October 2013. STudY TimELiNE After using conventional cleaning for six months, this was replaced by cleaning with Genesol 704 and the performances compared (see box Three cleaning regimes). Finally, microbubble cleaning was added to the set up and again the results were compared. Each cleaning regime reduced the normalised differential pressure (ndP) at stage one of the RO plant to differing degrees and with varied duration (figure 2). Conventional cleans using acid and alkaline liquid formulations, carried out every 10.5 days on average from January 2013 to 1 June 2013, restored permeate production and ndP. But re-fouling was rapid. On the 2 March all 30 of the membrane elements in five pressure vessels were Figure 1. Process flow diagram. Figure 2. Normalized differential pressure over time using different cleaning methods. Normalized Differential Pressure Bar 01-Jan-2013 01-Feb-2013 01-Mar-2013 01-Apr-2013 01-May-2013 01-Jun-2013 01-Jul-2013 01-Aug-2013 01-Sep-2013 01-Oct-2013 01-Nov-2013 01-Dec-2013 01-Jan-2014 01-Feb-2014 01-Mar-2014 01-Apr-2014 Normalized 1st Stage Differential Pressure