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#124129 - 07/06/08 08:27 PM Water meal and duckweed skimming systems?
knapster Offline

Registered: 07/06/08
Posts: 1
Loc: Minnesota, USA
I'm looking for an effective device for skimming water meal and duckweed off the surface of a suburban neighborhood storm water containment pond -- one acre, average depth about 8 feet. Seems like a pump and filter system or mechanical skimmer should be out there on the market somewhere. You know of anything like that?

As further background...We're avoiding aquatic herbicide treatments as they've proven ineffective. Instead, we've added three pond-bottom aerators and have begun bacterial applications to try to improve the water quality, reduce nutrient levels and, in the end, make the water less conducive to water meal and duckweed propagation.

But because the pond is fed with neighborhood runoff rich in lawn fertilizer and soil nutrients, it's going to take a number of years to reduce the nutrient levels in the water sufficiently to reduce the amount of water meal that flourishes. So I'm hoping there's a good way to skim or suck or otherwise mechanically remove the water meal and duckweed that floats on, and on a windless day covers, the entire surface.

Open to any ecofriendly ideas!

#124133 - 07/06/08 08:59 PM Re: Water meal and duckweed skimming systems? [Re: knapster]
Theo Gallus Online   content

Registered: 05/14/04
Posts: 12358
Loc: Central Ohio
Howdy, Knapster, and welcome to the forum.

Here's one idea, the sticky (or prickly) rope.

Non carborundum illegitimatus!
(totus res in temperantia)

I subscribe, but won't pay Photobucket.

#124633 - 07/11/08 12:18 AM Re: Water meal and duckweed skimming systems? [Re: Theo Gallus]
DJT Offline

Registered: 02/25/07
Posts: 343
Loc: SW Illinois
I made something recently to help with removing duckweed. Went to Walmart and bought a large fishing dip net. Then went to the fabric department and bought 2 square yards of nylon mesh material($1.50). It is the stuff they use on wedding veils. The mesh holes are about the size of a BB. I laid this inside of the dip net's existing net and attached it to the hoop with zip ties. Now I have dip net with the strength of standard net but with a tiny hole size. In a couple minutes (with wind cooperation) I was able to fill a wheelbarrow with duckweed. Much more effective than a leaf rake.
Does the name Pavlov ring a bell?

#124689 - 07/11/08 02:16 PM Re: Water meal and duckweed skimming systems? [Re: DJT]
bobad Offline

Registered: 06/02/05
Posts: 2365
Loc: Eunice, Louisiana
Great idea. Should really help out for smaller ponds.

DW is really bad for lakes and larger ponds, as Sonar would be cost prohibitive.

Too bad there's not a solar or wind powered robotic DW collector that randomly floats around the pond.

#128307 - 08/07/08 06:30 AM Re: Water meal and duckweed skimming systems? [Re: bobad]
dr. dave Offline

Registered: 08/07/08
Posts: 5
Loc: wisconsin
I've been looking into mechanical removal of pondweed for some time now. I live in wisconsin on a 2 acre pond which is hypereutrophic. When I bought the place, I was told there were a ton of fish but it quickly became apparent to me that there had been a fish kill. Oxygen levels about 2ppm (5-7 ppm being necessary for game fish). By the end of the summer, it was apparent why. The pond looked like a golfing green. Aerators didn't touch it. Initially I was going to use Sonar, but a little research showed me that duckweed could actually clean out a lot of nutrients from the water if I could remove it instead of just killing it and adding more organic compost to the bottom of the pond. In fact, there are some wastewater treatment facilities that specifically use duckweed to remove phosphorous and nitrogen and then skim it off.
There's the problem. How to skim the duckweed. I tried a seine- both commercial and homemade. Ridiculously tedious. Here's how to make a homemade one: http://www.nativefish.org/articles/duckweed.php.
It works, but if your pond is more than one acre, plan a weekend. I was able to find a product called ProSkim which is built by a guy out of Connecticut which looks REALLY cool- basically an onshore pump with a floating intake hose which he says will clean up a pond within 48 hours. The before and after pictures look great. The downside is that he wants over $6500 a unit. Plus, I'm not sure he's even in business any more since he didn't return my phone calls after many attempts and his voicemail is full and won't accept messages.
So my brother and I decided to try to build our own pump device. Easier said than done. The main issue is finding an appropriate pump. You would need a "grinder pump" due to the weeds and debris, but every grinder pump we've been able to find is submersible only. What we need is a "self-priming grinder pump" which could be place on shore and suction from a floating intake hose. I've tried about 5 different pump dealers so far without success. We've messed around with some ideas using a submersible but it seems very impractical. There are also "trash pumps" which are much more powerful and self-priming, but only run on gasoline, not electric. So basically, we're still working on it.
Wow. That was long-winded. I'll post more if we come up with anything. If anyone gets any ideas or a line on a mechanical removal product, PLEASE, drop me a line.

#169579 - 06/22/09 03:07 PM Re: Water meal and duckweed skimming systems? [Re: dr. dave]
Bennie Offline

Registered: 06/09/08
Posts: 55
Loc: SE Michigan
Dr. Dave, the link above doesn't work anymore. Could you resend? Proskim is expensive and built for commercial use, it seems.

Correction, the pump is in the floating unit and is submerged. Do a google search on Patent # 7,314,571--should be visable for free under Google.

What we need to find to make a similar product (although less elaborate) is a stainless steel ejector pump with a 2-3" inlet and a 2" outlet. the rest should be fun to replicate. He mentions in the patent a Stancor SC-50. I'm calling them next to see what they suggest.

send me an e-mail and let's bounce some ideas off each other.
LMB, HBG, YP, CC, FHM, located SE Michigan
1/3 acre 8-9' deep, aerated 24/7 1/4 hp rocking piston

#169592 - 06/22/09 03:50 PM Re: Water meal and duckweed skimming systems? [Re: Bennie]
Bennie Offline

Registered: 06/09/08
Posts: 55
Loc: SE Michigan

all sewage/ejector pump manufacturers. One of them has to make an affordable pump for our proof-of-concept.

Edited by Bennie (06/22/09 03:52 PM)
LMB, HBG, YP, CC, FHM, located SE Michigan
1/3 acre 8-9' deep, aerated 24/7 1/4 hp rocking piston

#169675 - 06/23/09 09:53 AM Re: Water meal and duckweed skimming systems? [Re: Bennie]
Bennie Offline

Registered: 06/09/08
Posts: 55
Loc: SE Michigan
stancor sc-50 is about $450. Not sure if the inlet is circular (to attach fittings) or if we would need to modify--need to create vortext to pull the debris into the mouth of the pump. Any suggestions?
LMB, HBG, YP, CC, FHM, located SE Michigan
1/3 acre 8-9' deep, aerated 24/7 1/4 hp rocking piston

#169678 - 06/23/09 10:08 AM Re: Water meal and duckweed skimming systems? [Re: knapster]
Bennie Offline

Registered: 06/09/08
Posts: 55
Loc: SE Michigan
i'm doing the same thing.

1) reduce the source of run-off if possible or plant a lot of nutrient loving plants at the source of the run-off. This will make your shoreline grow wonderful habitat and filter the amount going into the pond

2) make sure you're not mowing within 10-20 feet of the pond to increase the filtering effect.

3) remove branches that might catch the duckweed at the surface--want to ensure water can move at the surface. don't worry about taking out "fish habitat" you can always add a synthetic habitat back later which won't contribute nutrients

4) where possible, thin the trees/shrubs around the pond to allow airflow from the wind. Duckweed doesn't like wind.

5) aerate from the bottom for nutrient removal, but aerate with a pond fountain to move the water at the surface to move the duckweed further away. Bubbler aerators to the same thing but work in a smaller radius.

6) enzymes/bacteria will speed up nutrient reduction.

7) if you have the time and energy, skim the duckweed off periodically. It will grow back. (proskim-like machine or nets)

8) Grass carp and fish that eat the stuff. Helps but not completely. Check DNR regulations--not appropriate in all states.

9) Raking. Rake the muck out. Makes great compost when mixed with the duckweed. Dry out the muck and shoot it through a chipper shreddeder, then add it to fresh duckweed and come grass clippings in a compost tumbler and you'll make soil for all the plants/flowers in the neighborhood.

10) Pond dye. This is really a step after you've removed the duckweed, but it will keep any algae down that might be growing as well.

11) Inevitably, Whitecap or Sonar. One or two treatments go a long way and costs quite a bit less than all these other means. Must be a contained pond. Might need DEQ permit. You still might have duckweed after treatment, but a much more manageable amount.

Let's build a skimmer!
LMB, HBG, YP, CC, FHM, located SE Michigan
1/3 acre 8-9' deep, aerated 24/7 1/4 hp rocking piston

#191243 - 11/08/09 02:20 PM Re: Water meal and duckweed skimming systems? [Re: Bennie]
FarmerCharlie Offline

Registered: 09/04/09
Posts: 132
Loc: Auburn, AL
Has anyone done anything more on building a skimmer? My new pond is developing what appears to be a floating algae--probably related to the fertilizing I did for the rye grass I planted around the pond. I have seen several skimmers that appear to be mainly for small backyard ponds, such as the one here: http://www.youtube.com/watch?v=0cCmMe3MgDw.
I was thinking about building something similar, except using some sort of grinder pump and pumping the surface water out of the pond into a compost bin.


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