UV reinfection in transfer main

[Rich240674]

I am currently looking at the potential for siting a wastewater treatment works, containing secondary treatment and UV disinfection, inland and discharging the final effluent through a long sea outfall about 5km away. The disinfected final effluent will be transferred along a transfer main.

Does anybody have information on the potential for microorganism regrowth or reactivation in the transfer main? Could this potentially be an issue which could mean we would have to relocate the UV treatment and has anybody had previous experience with this issue?

Thanks in advance!

 

[bimr]

I assume that you will be using a force main. Force mains are regularly used to pump raw sewage with minimal problems. You should have minimal problems pumping only secondary effluent.

Since you are pumping treated effluent there are minimal solids to settle out. Since you are using a force main, you will be pumping at a rate that will keep the solids suspended.

 

[stanier]

The Cronulla STP in NSW Australia has tertiary tyreatment and UV disinfection by a Wedeco system. The plant handles up to 5000 L/s.

Treated effluent then flows by gravity to a cliff face outfall. No regrowth has been experienced thus far.

During the design phase of the project I managed to get information from studies of regrowth from Wedeco, Trojan and Lyonnais Des Eaux. Some of this was confidential. The best source of data would be from a large UV manufacturer.

The potential for regrowth is going to be higfher with a secondary treatment plant as there is more potential for shielding of organisms in the effluent.

What performance level is the STP designed for. What level of turbidity to you aim to get? Are you using ferric chloride in your secondary clarifiers? Sharing knowledge is a way to immortality

 

[Rich240674]

The plant will be treating about 1000 l/s up to a SS of 30 mg/l.

The transfer line is going to be about 8km - including outfall.

We are using CAPS in our Primarys.

Have talked to WEDECO - who are being helpful but are away looking at info.

 

[stanier]

The SS between 20 and 50 mg/L is reported as the worst for obscuring particles that may contain organisms. If an organism is embedded in a particle and shielded from the UV then reactivation is more likely.

Sorry but I am unfamiliar with the term CAPS. Are you using ferric or alum in your secondaries?

There is a book that compares the efficiency of UV versus chlorination for disinfection of wastewater. I am unsure of the name but it is certainly worth a read. Sharing knowledge is a way to immortality

 

[Rich240674]

Sorry, everybody speaks in acronyms around here!

CAPS is chemically aided primary settlement and we tend to use Ferric. The 30 mg/l SS limit was chosen to comply with a governmental guidance note for UV disinfection.

I'd be interested in the name of that book.