Blue green algae in treated wastewater

  • Vishwanath
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Blue green algae in treated wastewater

In the state of Karnataka, India , specifically in the city of Bengaluru one of the worlds largest treated wastewater project for irrigation use is being run. 770 million litres per day of treated wastewater is being pumped to fill around 300 lakes in the surrounding districts which are drought prone. The waters will fill lakes upto a 120 km away.
The project is already under way and the water has started reaching the lakes. These waters are then allowed to recharge into the aquifers and then will be used by farmers for irrigation purpose.
There is a problem however with blue green algae blooms in some of these lakes , thanks to the Nitrates and Phosphates present in the waters.
How can the blue green algae blooms be reduced or eliminated ?
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  • muench
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Re: Blue green algae in treated wastewater

Dear Vishwanath,

This is "easy" to solve if the money is available: You need to add another stage to your wastewater treatment plants called Biological Nutrient Removal (BNR, see here for an intro: en.wikipedia.org/wiki/Sewage_treatment#B...cal_nutrient_removal ).

Many other cities have had to do that, too, e.g. here in Brisbane, Australia, where there was problems with water quality in Moreton Bay.

It is a proven process but it does add costs to your capital and O&M expenses.

Another thing do look out for is nutrient run off from agricultural practices (excessive fertiliser use). Also stormwater overflows could be an issue.

Oh, if farmers want to use the water for irrigation then they might be disappointed if you lower the nitrogen and phosphorus levels as it's a fertiliser to them. So you need to carefully assess the situation... Maybe the farmers could draw directly from the effluent channel of the wastewater treatment plant, rather than from the lakes? I guess that it tricky because of the distances involved. Hmmmm.....

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  • Heiner
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Re: Blue green algae in treated wastewater

Dear all,

"Oh, if farmers want to use the water for irrigation then they might be disappointed if you lower the nitrogen and phosphorus levels as it's a fertiliser to them"

As a farmer I agree 100%, Elisabeth. And this would counteract our efforts to close the loop all over the world.

But the engineers over there must have had any ideas when they created the lakes. Upcoming algae do not really surprise, I guess??

As an ordinary farmer (no scientist) I would throw some water hyacinth into the water of one lake and see what happens. If you are lucky they clean the water, suppress the algae and you can harvest them as green manure (dried or composting after semi dry).

Hope someone tells me why this wouldn't work, just to increase my knowledge....

Have a nice day,

Heiner

Heiner, the old farmer.....
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  • goeco
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Re: Blue green algae in treated wastewater

To reduce the algae the wastewater needs to be directly discharged to land as it is generated. I assume the problem is that there is a wet and dry season thus the requirement for storage. It was inevitable that using "lakes" as fertigation reservoirs would cause this problem. Algae aren't a problem for irrigation, so is there a problem in terms of the objective? Of course eutrophication of the lake would cause other problems such as death of fish resulting from oxygen depletion. The problem with macrophyte plants (e.g. water hyacinth) is that once decay rate reaches an equilibrium with biomass production the whole system can collapse because more oxygen is being used in decomposition than is being generated.

The solution is to harvest the water hyacinth, which removes nutrients from the lake. The plant matter can be composted or digested and the nutrients and carbon can be used for agriculture. But how expensive is that?

Fish can also be used to "digest" macrophyte plants in the lake but the high nutrient status will always be problematic, the balance is going to be precarious. Remove macrophytes and algae move in.... and too much photosynthetic biomass and oxygen depletion occurs.

cheers
Dean

Dean Satchell, M For. Sc.
Vermifilter.com
www.vermifilter.com
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  • Ian
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Re: Blue green algae in treated wastewater

Hi Vishwanath,
looking at Bengaluru on Google Earth, it seems that almost all the lakes in and around the city are heavily enriched with algae and/or hyacinth. This indicates that not only is the treated wastewater having an impact on the surface waters, but also the general runoff from the storm-water systems and other drainage which does not go to the treatment works. So there is no short term easy solution to the challenges you face.
However if your aim is to recharge the aquifers and not to use the water directly from the lakes for irrigation, the main concern may be by-products of the algal blooms, namely toxic microcystins, which may enter the aquifers. the algae themselves will not infiltrate into the aquifers. As mentioned by others, the health of the surface water resource is another matter. We normally avoid the use of hyacinth if possible as it can very quickly get out of hand chocking the water body, increasing evapo-transpiration, and rendering the water body un-usable for most recreation activities.
So finally assess the other runoff that may be entering each of the lakes to see if the improvement of the treated sewage through BNR will have a real impact before embarking on this costly upgrade, while also considering the multi-purpose use of each of the lakes. Good wishes, Ian
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  • Heiner
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Re: Blue green algae in treated wastewater

Dear all of you,
I understand very well your sceptical approach towards water hyacinth. And if there are other payable solutions with less danger to the whole environment....would be great.
Just to prevent misunderstandings: I am not talking about a self regulating biological system. More like this as one example:


In my mind I compare it with a agroforestry system. You have to cut (and use) the outgrowing leaves at the right time, you need a good management to get the benefits. If you don't you might end up with a forest and no food. But to increase the fertility and the humus content of the arable land (fixing Carbon), we need all sorts of organic including the minerals in them.

Cheers

Heiner, the old farmer.....
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  • Heiner
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  • I am a retired organic farmer and interested in nutrient cycles. As an volunteer I now travel mainly to poor countries and together with locals I would like to find new ways of sustainable agriculture. This is beyond the regulations of IFOAM.
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Re: Blue green algae in treated wastewater

Hi Dean,
just read an article (GEO, 2011) about algae...
Do you know the company "Aquaflow" in Blenheim? In this article was written they use successful varieties for wastewater treatment. Perhaps they can suppress the blue green algae?

Cheers,
Heiner

Heiner, the old farmer.....
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  • Vishwanath
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Re: Blue green algae in treated wastewater

Thank you for that.
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  • seshadri
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Re: Blue green algae in treated wastewater

Are these waters treated properly before letting into the lakes and streams. I SM skeptical. Presence of algae in lakes is always a healthy sign of nutrient conversion through biological system. I do not see any harm in algal blooms happening when the nutrient levels go up and if you see the algal composition also varies according to time. continuous replenishment of the waters through flow (than stagnation) to other downstream areas will reduce the impact.
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