Characterization of the Bacterial Population in RO Distribution Systems andtheir ability to form Biofilms on Pipe Surfaces

摘要

The Water Authority-Cayman (WAC) supplies drinking water to approximately 11,000rncustomers in Grand Cayman, Cayman Islands. The WAC water system in the capitalrnGeorge Town consists of two reverse osmosis (RO) plants and nearby pumpingrnfacilities capable of producing a total of 2.1 million US gallons/day. A third RO plant isrnlocated at Lower Valley, approximately 10 miles east of George Town. The twornGeorge Town plants are linked to three storage reservoirs with a combined storagerncapacity of 3.2 million US gallons. Water is produced from both plants via RO, byrnpumping saline groundwater from 100 – 200 ft deep wells through a series ofrnprefilters to remove silt before circulation through a series of RO membranes. Thernfeed water to both plants contains approximately 1-2 mg/L H2S. The product water isrnpassed through a counter flow degasifier, to oxygenate and, is treated with acid tornreduce the pH to 6.0 or less. Water is disinfected with Ca hypochlorite, Znrnorthophosphate is added to inhibit corrosion and NaOH is added to control the pH.rnA pilot study was conducted over a 14-month period comparing the type and quantityrnof bacteria present in the WAC distribution system using a combination of HPCrnculture methods and fatty ester methyl ester (FAME) analysis techniques. The studyrnwas divided into two distinct phases: in the first phase HPC bacteria in the bulkwaterrnwere isolated from inlet (feedwater) to outlet (treated distribution water) and furtherrncharacterized down to genus or species depending on an available database match,rna pipe-loop system was constructed for the second phase of the study to examinernthe rate of biofilm growth on different pipe surfaces (PVC, ductile iron, steel, PE,rnbrass, copper) and to compare the type of biofilm organisms to those in the bulk fluid.