Pump Fault Causes Chemical Over Feed at Local WTP

Very interesting read and every WTP staffs nightmare. No one ever wants to end up on national news. Instrumentation work distracts staff and causes chemical overfeed.

Plant was shut down for a couple days while they were cleaning out the clear wells. They were able to get water from an interconnection with another municipality. Then a water main broke and interconnection was shut down. It got ugly.


https://www.owasa.org/Data/Sites/1/...f-function-of-the-jones-ferry-wtp_10feb17.pdf

https://www.owasa.org/

Why would they put in a pump large enough to overfeed such a high amount? I don't know water treatment. Does flouride come in different concentrations which would necessitate a pump this large to normally run around 10% design flowrate?

Most plants I have worked in mix a lot their own chemicals to the concentrations they need, haven't worked around hydrofluorosilicic acid though so not sure.

Saturn_Europa said:

No one ever wants to end up on national news.

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Been there...

rootboy said:

Been there...

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For something good I hope!!

shawn_75 said:

Why would they put in a pump large enough to overfeed such a high amount? I don't know water treatment. Does flouride come in different concentrations which would necessitate a pump this large to normally run around 10% design flowrate?

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Almost all municipal water and wastewater treatment process equipment is grossly over-sized. This is due to several factors:

- Plants are designed for 20+ year lives and include generous allowances for population growth. Most facilities operate around 1/3 of their design flow.

- Plants are designed to accommodate peak loads. Most plants experience at least a 2:1 ratio between night time low and day time high flow demands. That means that they often run at 1/6 or less of rated capacity.

- Equipment is designed to meet worst case process conditions. The highest demand at the highest flow rate is used. A safety factor is applied, which is normal engineering practice. Then the next larger size equipment is selected.

- by EPA regulations standby equipment must be installed so that with the largest unit out of service the system can provide worst case design loads.

- To minimize equipment cost engineers often specify one unit meeting full design load, plus a standby instead of multiple smaller units.

It is a fact of life for municipal operators that they have to operate a plant that is over-sized for current needs.

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This is what happens when a dual redundant CLX major faults on christmas!!!

Oceansoul said:

Google Link
This is what happens when a dual redundant CLX major faults on christmas!!!

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I love the comments on that story ." Good excuse to start drinking early!! "

labeledas said:

Most plants I have worked in mix a lot their own chemicals to the concentrations they need, haven't worked around hydrofluorosilicic acid though so not sure.

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Each shift usually fills a day tank. But even then you can still get yourself in trouble. Fluoride is pretty serious

Tom Jenkins said:

Almost all municipal water and wastewater treatment process equipment is grossly over-sized. This is due to several factors:

- Plants are designed for 20+ year lives and include generous allowances for population growth. Most facilities operate around 1/3 of their design flow.

- Plants are designed to accommodate peak loads. Most plants experience at least a 2:1 ratio between night time low and day time high flow demands. That means that they often run at 1/6 or less of rated capacity.

- Equipment is designed to meet worst case process conditions. The highest demand at the highest flow rate is used. A safety factor is applied, which is normal engineering practice. Then the next larger size equipment is selected.

- by EPA regulations standby equipment must be installed so that with the largest unit out of service the system can provide worst case design loads.

- To minimize equipment cost engineers often specify one unit meeting full design load, plus a standby instead of multiple smaller units.

It is a fact of life for municipal operators that they have to operate a plant that is over-sized for current needs.

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Thank you for that explanation.

It seems to me that there'd be more safeguards built in to prevent such problems. Perhaps the system would allow only a certain range of pump speed based on plant output. I know that any chemicals used in drinking water treatment can be a problem at too high or too low concentration, but flouride, it seems, can never be too low.

Saturn_Europa1 said:

For something good I hope!!

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Well, yes. One of my machines made it to the cover of a construction magazine, and I had an article on tracking ghost-written for me for another magazine.

But I was actually thinking of the time that the Associated Press called up the plant and asked if there had been a fire there.

The reason for their interest was that my knuckleheaded boss decided to add a bunch of material to a retort process without my knowing about it, and then instructed me to raise the temperature of the retort from 1200 degrees (its safe maximum) to 1600.

I pointed out that they had already replaced one retort vessel because of running it over-temperature, and I couldn't imagine why they wanted to do it again.

Meanwhile, the slug of extra material made its way to the retort, and the higher temperature liquefied the tar that had been sitting dormant in the crossover pipe and it ran back into the stack.

About that time all heck broke loose. My stack was on fire, the vessel was way over-pressured, I had waste gas that I would normally burn getting vented (which made a 50 foot rooster tail over the machine but didn't catch on fire - thankfully). I'm pretty sure you could see it from Arizona, and for darn sure from Palm Springs.

That's when he and the plant manager wanted to know what I thought I was doing. I summarily threw them out of the control shack and started getting things under control.

Oh, and six months later (I had left and gone to work for Schneider), my old partner sent me a picture of the retort screw. They had continued running the retort at the higher temperature, and had melted it in two.

shawn_75 said:

Thank you for that explanation.

It seems to me that there'd be more safeguards built in to prevent such problems. Perhaps the system would allow only a certain range of pump speed based on plant output. I know that any chemicals used in drinking water treatment can be a problem at too high or too low concentration, but flouride, it seems, can never be too low.

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There was a rapid drop tank alarm that was never configured.

I've been in maintenance and Operations for 10 years and rapid drop alarms are high up on the list for chronic nuesance alarms. Very few are configured correctly and alarm anytime a re circulation pump comes on, ect

It could have saved a lot of grief on this one though.

I'm not sure how fluoride can be good for your teeth.

I have seen the chemical rooms in two plants that had used it...neither of them still do. The concrete floor, the brick walls and all the equipment was heavily corroded.

One thing I have learned all too well after working in this industry for a little over two years: DON'T DRINK THE WATER... unless it comes from your own well and you filter and test it yourself.