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RE: Disinfection

J.W.Koch — Wed, 22 Aug 2007 08:05:07 GMT

Have you checked your effluent for nitrite ? Is your plant achieving any degree of nitrification ? Ammonia compounds will increase chlorine demand.

RE: Disinfection

Dookie — Mon, 20 Aug 2007 16:48:54 GMT

We typically need to run at least 1.5 at a minimum to 5mgl at the end of our CCT to give up fecals in the less than 20 range. This is with approximatly 2 to 3 hrs contact time. In the 2 facilities I have worked at withe CCTs we have setup scouer systems at the bottoms of each pass and corners made of 2" sch 80 with perforations every 12" or so to keep the tank mixed better and prevent settling solids from accumulating on the bottom. The few incidents where the scouer system was off we ran into coliform test issues within a couple weeks following its shutdown. I couldent even imagine having to drain a CCT every week to clean the floor of solids.

RE: Disinfection

Victor — Thu, 02 Aug 2007 19:21:09 GMT

Joe:

Daphnia, Bosmina, Leptodora, and Diaphanosoma are all Cladocerans or in layman's terms "water fleas". Similar to "water monkeys" except that these are freshwater whereas the sea monkeys are brine "shrimp". They are seasonal organisms in the sense that they usually "bloom" right after the first algal blooms right around this time of year. In a way, you should be patting yourself on the back for the simple reason that these organisms are utilized as test organisms in bioassays and in order for your clarifiers to support such as wide and diverse number of Cladocerans you must be putting out some excellent quality water in terms of not having toxicants present. That said, you may be having some of these cladocerans going over the clarifier weirs and into your T plant. Check your tertiary effluent, centrifuge, and try to see if you can microscopically ID any antennules or parts of the water fleas. They may be exerting a chlorine demand.

RE: Disinfection

John Sansalone — Thu, 02 Aug 2007 18:42:37 GMT

A few thoughts:

1. Although 0.40 is not bad, it might need to be tweaked a bit. The old standard around here used to be that you needed 0.5 - 20. mg/l (total residual) for effective disinfection. With clearer effluent now common, lower residuals generally work, but not always.

2. Which type of test are you using for residual ? Some of them can have interferences that you may need to look for.

3. Is there some algae on the walls that the crustaceans are eating, despite the tank cleaning ? Could that be interferring ?

4. How soon after the cleaning were the samples ? If too soon, possible that picked up a few solids still floating around.

Just some ideas to kick around.

RE: Disinfection

TerryF — Thu, 02 Aug 2007 17:03:46 GMT

Joe,

Even though you have a reasonable chlorine residual perhaps you have substantial amounts of suspended solids in sizable floc which shields some of the fecal matter from the chlorine. As for the crustaceans well may be they are the source of the fecal matter in the first place.

Regards

TerryF

Disinfection

Joe Amabeli — Thu, 02 Aug 2007 13:35:21 GMT

We cleaned our chlorine contact tank one week and started to have problems with high fecal counts the following week (not sure they are related). We have over two hours detention time and our residual is 0.40 mg/l before dechlorination.

Checked out everything in the lab, all okay.

We also noticed a lot of Crustaceans on our secondary clarifiers. We identified them as Leptodora, Daphnia, Bosmina & Diaphanosoma. Can these have any effect on our problem?