River cleanup

[Illiad]

Our lecturer wants us to design a system to 'depollute' a river for a project. We are too choose a river, identify the source of pollution, and come up with a method to clean it up. It doesn't have to be new or anything, practicability is more important to engineers than groundbreaking discoveries =P. Now since the lab here is rather busy, she rather us come up with a way to remove turbidity than the toxins or unwanted dangerous bacteria in the river.

I thought all rivers are naturally turbid, at least in my country anyway and does it even matter? Through google, I found what i thought to be a simple and straightforward way to remove nasty lifeforms and toxins. An aerator ! aerators placed on the riverbed moves slower 'almost stagnant' water from below to the surface where oxygen 'neutralizes' toxins and sunlight kill harmful bacteria. But an increase in turbulence means a pressure drop right? Is it bad? how feasible are they? I found a website of a company that specialize in this

A Natural Method of River Improvement | CLEAN-FLO

Under articles, case studies.. interesting

[JMJones0424]

Perhaps I don't exactly understand the purpose, but generally speaking, if you are trying to reduce turbidity, turning over the water column would be counter-productive, wouldn't it? Of course, if the river has large anaerobic zones, eliminating them may be beneficial regardless of water clarity concerns. Ultimately, I think it would be important to determine what is causing the turbidity to begin with. If it is natural, then trying to clear up the water may be more harmful than just living with a "muddy" river. It is natural for some rivers to be quite cloudy from run-off waters carrying sediment into the water.

 

There are numerous chemical flocculants regularly used, I know a few people in my area that use iron sulfate to clean up their stock ponds. I have heard of (but have never tested the effectiveness of) a natural flocculant using seed cake remaining after removing oil from the seed of the Moringa tree. There is a lot of information available on the web about this tree, but I can't tell how much is legitimate and how much is just hype.

[Illiad]

thanks for the reply

No i didn't mean to suggest an aerator to remove turbidity, but to remove some toxins and unwanted bacterias. I wasn't that interested at first to remove turbidity at all since all of the river I known are naturally turbid anyway. A google later, I discovered that flocculation also removes harmful microorganisms too. About iron 2 sulfate, did your friends attempt to recover the iron sulfate after it was spent? And how was the aggregate collected? or did they just let it sink to the bottom?

Are the fishes in your friends' stock pond in any way, affected by the iron sulfate?

The tree was interesting. Unfortunately Wiki only has a mention of it's oil extract being used to treat turbid water.

But I found this

http://www.visbdev.net/visbdev/fe/Docs/water_seed.pdf

Looks credible to me. Best of all extracting the oil doesn't sound that hard and villagers near the river could be persuaded to do it if the river there is unnaturally turbid.

Great idea. At least my project has a general direction now =D

[Illiad]

Eh, a thought just occurred to me. For argument sake lets say half of the turbidity from a very turbid river comes from sewage runoff from a nasty place. 'Flocculants' are not specific aren't they? So only around 50% of stuff removed is sewage and the other 50% is from natural silt? The silt is important because over time they are deposited at the river mouth to form fertile deltas. Anyone got a comment or idea?

[maikeru]

Perhaps I don't exactly understand the purpose, but generally speaking, if you are trying to reduce turbidity, turning over the water column would be counter-productive, wouldn't it? Of course, if the river has large anaerobic zones, eliminating them may be beneficial regardless of water clarity concerns. Ultimately, I think it would be important to determine what is causing the turbidity to begin with. If it is natural, then trying to clear up the water may be more harmful than just living with a "muddy" river. It is natural for some rivers to be quite cloudy from run-off waters carrying sediment into the water.

 

There are numerous chemical flocculants regularly used, I know a few people in my area that use iron sulfate to clean up their stock ponds. I have heard of (but have never tested the effectiveness of) a natural flocculant using seed cake remaining after removing oil from the seed of the Moringa tree. There is a lot of information available on the web about this tree, but I can't tell how much is legitimate and how much is just hype.

 

Interesting, I just happened on the moringa tree tonight in my internet wanderings. Seems to have much potential.

 

Illiad, you may want to take a look at "artificial wetlands" and the types of plants that are used to purify and treat water.

 

Constructed wetland - Wikipedia, the free encyclopedia

 

In nature, anyway, trees such as willows and alders, rushes, grasses, ferns, etc. grow by the sides of rivers and waterways and aid in the purification and processing of the water. They soak up excess nutrients in the water and the microbes they house in and by their roots are powerful natural filters and often can process many toxic chemicals or suck up nasties like heavy metals.

[Illiad]

I like the idea of constructed wetlands. Rather ingenious :) Build it right and it will be a nice little patch for a homeless orge to call home too. A big project no doubt, also a long term solution and can I say self maintaining? or maybe every now and then someone should go and trim any unwanted overgrowth:shrug:

by the way JMJones0424, what about the iron sulfate?

About iron 2 sulfate, did your friends attempt to recover the iron sulfate after it was spent? And how was the aggregate collected? or did they just let it sink to the bottom?

Are the fishes in your friends' stock pond in any way, affected by the iron sulfate?

Edited August 17, 2010 by Illiad
added some words

[JMJones0424]

I'm sorry, I went on vacation shortly after my last post, and lost track of this thread between that and the forum switch.

 

I, and the people I have talked to, only have experience with using flocculants in ponds. I have not observed any ill effects on the fish from the use of iron sulfate. Evidently, aluminum sulfate is used more regularly, but soils in my area are usually low on iron. Generally speaking, algae is able to outcompete aquatic plants when iron is the limiting factor, and aquatic plants are able to outcompete algae when phosphorous is the limiting factor. Because most people in my neck of the woods with managed stock tanks either fertilize their pastures with synthetic fertilizers and/or have livestock on their property, the water in the ponds usually has a high enough level of phosphorous that algae is a concern. Using iron sulfate kills two birds with one stone. The iron sulfate is allowed to accumulate at the bottom of the pond and it provides a (very) slow release iron supplement for aquatic plants. I think there could be an issue with overdosing though, as flocculants work because of their charge, and they are attracted to fish gills as well as other particulates in the water. (Literature on this topic that I have found though is either over my head, anecdotal, or contradictory). Also, high concentrations of soluble iron and aluminum are both toxic to fish.

 

Typically, when a tank is first built, it is lined with clay. For the first few years the water is usually quite cloudy after every heavy rain, and unless something is done to reduce turbidity, aquatic plants never get a chance to become established and anchor the clay lining down. Afterwards, turbidity shouldn't be a problem as long as there is not a significant amount of silt in the runoff captured by the pond, as long as the nutrient input never far exceeds the aquatic plants' ability to remove it from the water, and as long as algae is not allowed to become a huge problem and shade out the aquatic plants.

 

In my limited experiences, flocculants are used sparingly, and only to treat symptoms of the underlying problem. Ultimately, the source of turbidity must be dealt with.