Dear All,

Maybe my inputs provide some help to your endeavours.

Maybe see 19 min video presentation 2016 by Dr Ian Dodkins of Swansea University, UK about subject matters most:
Dr Ian Dodkins talks about the function and design of "Floating Treatment Wetlands". Looking at floating islands around the world Ian shows us how floating islands have been used to treat polluted water, protect coastal areas from erosion and used as a place to live.


Summary: clear statements regarding N&P !!! ~ 7% & ~ 6% "uptakes" (uptake by plants) compared to the ~ 62% N & ~ 75% P reduction effects by biofilm including sedimentation and periodic desludging of the sediments after a maximum of ~8 years.

Furthermore see PDF about Dr Ian Dodkins 2014 work: www.floatingislandinternational.com/wp-c...loads/2018/07/29.pdf
Kindly see page 33 for the picture of his theoretical model!

additional PDF by Headley & Prof. Tanner, NZ 2006: www.aucklandcity.govt.nz/council/documen...d%20Review-Final.pdf
picture source Headley & Tanner: www.aqua-verde.de/attachments/Image/Biof...jpg?template=generic

We use under our climatic conditions additional floating OLOIDs (see www.aqua-verde.de/attachments/Image/alle...jpg?template=generic) in pond-wwtp's and lakes to gently equalize water body and add O2. We call it an Open Source "Mangrove"-wwtp.

See picture of ~500 p.e. wwtp: www.aqua-verde.de/attachments/Image/2018...jpg?template=generic

Best Regards,

Detlef SCHWAGER

Dear all,

see attached a picture of a green fishpond in Zimbabwe. I was told there are hundreds of fish in this pond. Since there was no pump or any other equipment to add oxygen, I think it was a well balanced fishpond. No fish was at the surface, snaping for air.
The ec value was 450 micro-siemens (one crucial point?) and as far as I know, no human wastewater was poured in.
But I know from sweden the combination of fish production and wastewater treatment is possible in in well balanced system. It needs harvesting from time to time....

writes the farmer

Yes Water hyacinth grows profusely in the organic / chemical rich waters and they become a menace too. They putrefy waters and make them works for further use too. Though, they add good organic residue to the system. Collection and use of water hyacinth is another laborious one. Good to avoid them. There are kith and kin of this is tropics viz. Pistia, Hydrilla, Lemna, Salvinia and the major plans viz. Lilly, lotus are contribute to the chemical / organic rich waters. We need to create a constructed wetland to introduce them and remediate the waters. Reeds are the other ones that are studied widely for such purposes. Recent studies (20 years) show the use of Vettiver (Chrosopogon zizanoids) in remediating waste waters.

Mr. Viswanath
I am revisiting this page again after getting a reply from Elisabeth for my comment. I have few questions
1) how many ponds are seen with Blue Green Algal forms.
2) Do you have any data on the Blue green algal forms (names, quantity and problems?
3) How many months in a year you have notice BGA forms or other forms of algae?
4) What is the nitrate and phosphate levels in the pond waters over a period of months?
5) What is the depth of the pond water?
6) Can you associate with a few to conduct experiments / to initiate a remediation work in a small pond?

Dear Elisabeth,

There are ways to approach this subject. We are in tropics. The algal flora differs from place to place according to water quality and weather conditions. I had seen some ponds occupied by Chlamydomonas, Euglena, Scenedesmus, Melosira, Navicula, Nitzschia, Oscillatoria, Pediastrum, Chlorella, etc. In some areas, Euglena, a single species alone thriving when the water level goes down (organic and chemical enrichment happens). In other areas, Oscillatoria, is dominant and in some Scenedesmus is dominant. No harm in comparing temperate reports with tropical ones. Yes. algal blooms - microcystis producing toxins pose problems in few pockets. Literature survey will add more knowledge to this.
True there will be eutrophication, oxygen depletion and fish kill etc. associated to water ponds.

Ultimately our approach - what we are going to do and what technology we deploy to reduce the pollution, what will be the output - solid mass to liquid etc. matters for us to decide.
We worked on a technology to use only algae (select according to the substrate) to remediate waste waters.

Dear Sundaram,

You wrote: "I do not see any harm in algal blooms happening when the nutrient levels go up". I disagree with that. Algae blooms are indeed a problem, as was outlined in several posts in this thread before yours, e.g. by Dean and Ian. Ian wrote:

the main concern may be by-products of the algal blooms, namely toxic microcystins, which may enter the aquifers.

There is also the issue of oxygen depletion and fish kill which Dean already mentioned. See also the Wikipedia article on eutrophication:
en.wikipedia.org/wiki/Eutrophication

Eutrophication (from Greek eutrophos, "well-nourished"),[1] or hypertrophication, is when a body of water becomes overly enriched with minerals and nutrients which induce excessive growth of algae.[2] This process may result in oxygen depletion of the water body.[3] One example is an "algal bloom" or great increase of phytoplankton in a water body as a response to increased levels of nutrients. Eutrophication is often induced by the discharge of nitrate or phosphate-containing detergents, fertilizers, or sewage into an aquatic system.

Regards,
Elisabeth

Are these waters treated properly before letting into the lakes and streams. I am 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.

Thank you for that.

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

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

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

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