Veolia Aqua UV System Options, Concept Design and Technical Specification for 3 Sites
Anticipated increases in recreational activities near Coliban’s waterways will have implications on meeting microbial log reduction targets for potable supplies drawing from these sources. The installation of UV disinfection technology at Bendigo (Sandhurst), Castlemaine (McCay) and Kyneton WTPs have been proposed as a solution to meeting the current log reduction deficit of protozoa at each treatment plant. CWT was engaged by Veolia to investigate UV system options, develop a concept design and technical specification for the three sites.
In more detail, the project scope of works included:
- An options and issues assessment, considering challenges with available footprint and hydraulics. The options assessment considered different types of UV systems (LPHO vs. MP), as well as several process locations.
- Reviewing water quality data, particularly UVT data.
- Reviewing and updating the log reduction value (LRV) basis of the existing processes.
- Discussing UV system technologies with UV suppliers.
- Developing separate concept designs for Bendigo, Castlemaine and Kyneton WTPs.
- Performing a risk assessment to highlight any issues identified at each of the three sites.
- Performing a hydraulic assessment to verify the hydraulic limitations at the proposed UV system locations.
- Developing a technical specification for the UV system scope of works.
- Preparing technical schedules in preparation for the tender submission phase.
The Health Based Targets Manual (2015) sets out health-based targets to be achieved by WTPs with respect to the source water risk category. The health-based targets are expressed as log reduction of pathogens: bacteria, viruses and protozoa. Public access and recreational activities within a catchment area have the potential to degrade source water quality and therefore require more stringent health-based targets. Category 4 sources are characterised as those which are typically unprotected with high contamination risk from humans, stock and/or industry. The increased recreational activities near Coliban’s waterways may elevate their source water to that of a Category 4 which attract higher health-based treatment target requirements. Category 4 health-based treated targets are 6.0-, 6.0- and 5.5-log reduction of bacteria, viruses and protozoa, respectively. This necessitates the implementation of additional treatment barriers.
A UV disinfection stage is to be installed as the primary disinfection step for the inactivation of pathogens; particularly protozoa such as Cryptosporidium and Giardia. UV light inactivates susceptible pathogens by disrupting the DNA sequence so that the pathogen cannot reproduce. UV disinfection is often used for the following reasons:
- It provides an additional treatment barrier against pathogens; mainly bacteria and protozoa, and supports the Australian Drinking Water Guidelines (NHMRC, NRMMC, 2011) guiding principle: implementation of a multi-barrier treatment approach;
- There is minimal water quality, environmental, operational and/or occupational, health and safety concern associated with the implementation and operation of a UV system;
- Compared to the operating costs associated with typical doses of ozone or chlorine as a primary disinfectant, UV disinfection is cost effective (Bukhari et. al., 1999);
- Dosing UV upstream of chlorine reduces the risk that UV radiation would deactivate chlorine residuals through photolysis, possibly reducing its effectiveness and potentially increasing required doses to maintain a residual in the network;
- Unlike chlorine and ozone for disinfection, UV disinfection does not contribute to the formation of disinfection by-products.
- Unlike chlorine and chloramination disinfection, UV disinfection is particularly effective against protozoa.
Implementation of a UV system will enhance disinfection capability at each of the WTPs, to ensure continued safe supply of drinking water to customers.