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A further issue is associated with the pressure decay rate (PDR). The Victorian water quality regulator required that the GWF demonstrate a log removal value for virus (LRV) of six when operating in the reclamation mode. This was partially accomplished in the initial design of the GWF by including a requirement to maintain the domestic MBR membrane PDR less than 7 kPa/min (GWF 2010). Experience demonstrated, however, that the frequency of membrane repair (pinning) required to maintain this level of integrity was neither practical nor necessary. With the full-scale plant in operation, it was demonstrated that the required level of overall reclamation treatment train LRV could be demonstrated by monitoring total organic carbon (TOC) removal across the downstream RO system, thereby gaining two logs of virus removal by the overall treatment system. This relieved some of the treatment performance validation requirement from the ultrafiltration system and the PDR requirement was relaxed to 70 kPa/min, which, although still an onerous performance requirement, permits a practicable level of membrane maintenance activity. Table 5 summarizes LRV values provided by the facility with this change.

Table 5

LRV values provided by the GWF with revised monitoring of RO system

Process stepVirusBacteriaProtozoa
MBR (UF) 
Chloramination 
RO 
Final chlorination 
Total 
Process stepVirusBacteriaProtozoa
MBR (UF) 
Chloramination 
RO 
Final chlorination 
Total 

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