Destratification of shallow ponds

[10Gallen]

Hi all,
Does anyone have any insights regarding the following:
A large sewerage treatment secondary pond 200x100x0.9m is stratifying to 0.3-0.6m resulting in blue-green algae bloom, pushing pH to 9-10 and knocking out the green algae. I'm looking at two options to mix the pond, one is a propellor type submersible (Brio), the other is an aerator submersible (Eolo-2). Both are low power, approx 0.5hp, single phase, 1400rpm units.
My feeling with the aerator is that it will stir up the anoxic zone at the bottom 0.3m of pond where sludge breakdown is occurring, increase turbidity and possibly short circuit the pond. The short circuiting is a concern I have with regard to the Brio also.
The ponds treat 3000EP @ 200 litres pp/day, no data available on peak flows.
The site is in the monsoonal region of the Northern Territory, Australia, so is only a 6-8month per year problem.
Any opinions or previous experience with this type of problem appreciated.
Cheers,
GAllen

 

[BobPE]

was the pond originally designed as an anoxic or anarobic digester? I would have to guess no, but I really don't know your situation. Give us a better description of your process, what is upstream? If it is acting as a settling basin then sludge handling or removal might be considered. How do you remove the sludge now? Give us more info, we love this stuff....

BobPE

 

[10Gallen]

Hi all, sorry for the delay, been bush.
There are 3 ponds, all anaerobic, gravity feed from one to the other. The ponds are designed on 19 day detention time for P removal, nludge removal on about a 10 year basis. No aeration provided due to cost.
Primary pond fed from rising main with macerator pump in wet well, settles all solids. Ideally aeration would be provided at third pond, but discharge requirements are low, 20/10 SS/BOD.
As the problem of stratification is with the larger 2nd & 3rd ponds, and that anaerobic sludge digestion is still occurring in the bottom 300mm, lifting the sludge up throws the results on final effluent.
To convert the ponds to aerobic ponds will use a lot more power than the mixing pumps I am considering.
Cheers,
GAllen