Ph reduction question

[malcnunn]

I want to reduce the Ph in a small lake of 10,000,000L from 8.9 to 8.1 . I have been reading that total alkalinity and hardness have a direct relationship in regards to where Ph would sit .

total alkalinity is 190ppm and hardness is 120ppm , my thinking is if I increase hardness by using gypsum I'll possibly increase overall Ph as it falls in level with alkalinity , so I should reduce Alkalinity by around 70ppm .

My thoughts were to use muriatic acid but unsure of a. the volume of acid required b. how much free chlorine would be released from the breakdown as there is aquatic life present.

I'm thankful in advance to any advice !

 

[chenbeier]

Because we do not know the matrix of your water, easier it would be to take 1 l in a beaker , put a pH probe in and add slowly the acid during stirring. The consumed amount times 10,000,000 l gives the amount you have to add. There will be no free chlorine.

[malcnunn]

Thankyou sir , much appreciated , I shall go and test

[exchemist]

3 hours ago, malcnunn said:

I want to reduce the Ph in a small lake of 10,000,000L from 8.9 to 8.1 . I have been reading that total alkalinity and hardness have a direct relationship in regards to where Ph would sit .

total alkalinity is 190ppm and hardness is 120ppm , my thinking is if I increase hardness by using gypsum I'll possibly increase overall Ph as it falls in level with alkalinity , so I should reduce Alkalinity by around 70ppm .

My thoughts were to use muriatic acid but unsure of a. the volume of acid required b. how much free chlorine would be released from the breakdown as there is aquatic life present.

I'm thankful in advance to any advice !

 

Just out of curiosity, do you know what makes the pH in this lake so high? I had no idea natural water could have such a high pH as this. 

[sethoflagos]

52 minutes ago, exchemist said:

Just out of curiosity, do you know what makes the pH in this lake so high? I had no idea natural water could have such a high pH as this. 

It's similar to the pH range of Malham Tarn, a Site of Special Scientific Interest and a national nature reserve in the UK.

The pH of lakes is determined not so much by what is in the water (an effect) but by the underlying sediments either of the catchment area or the lake itself. Does the OP proposal consider destruction of eg. a 100 foot thick bed of marl, along with potentially a productive and highly specialised ecosystem?  

[exchemist]

1 hour ago, sethoflagos said:

It's similar to the pH range of Malham Tarn, a Site of Special Scientific Interest and a national nature reserve in the UK.

The pH of lakes is determined not so much by what is in the water (an effect) but by the underlying sediments either of the catchment area or the lake itself. Does the OP proposal consider destruction of eg. a 100 foot thick bed of marl, along with potentially a productive and highly specialised ecosystem?  

Hmm interesting it can get as high as 8.6. It will be, I imagine, the combination of being fed by water trickling through limestone with a not specially high rate of turnover of the water in the tarn.

But indeed I was wondering the same thing: if the pH of the OP's lake is driven by the geology of the catchment area that feeds it, it may a Canutelike exercise trying to reduce it artificially.   

Edited July 29 by exchemist

[sethoflagos]

6 minutes ago, exchemist said:

if the pH of the OP's lake is driven by the geology of the catchment area that feeds it, it may a Canutelike exercise trying to reduce it artificially.   

Quite. And 'liberating' vast quantities of sequestered carbon dioxide in the attempt. 

[John Cuthber]

8 hours ago, malcnunn said:

I want to reduce the Ph in a small lake of 10,000,000L from 8.9 to 8.1

Why?

[malcnunn]

Our lake is situated in Thailand , close to the Cambodia border . It was man made about 4 years ago with the base sediment being clay .

We filled it from a 65m Bore hole pump that took around 1yr + the rainy season here (total is averaging 10M litres but full would be around 16mLitres.

The catchment water is actually the same as the lake (high in hardness and alkalinity) BUT the PH is actually lower at 7.8 or thereabouts . I don't have the answer to this difference other than to think the catchment water is sat there in the dark, anaerobic with little to no Dissolved 02 

We did build some huge concrete raceways which would have increased the Ph but these should have long cured by now (3yrs) .

I have also used quite alot of Aluminium sulphate to lose some of the clay turbidity, which has worked really well and lowered the Ph when adding it , but the Ph slowly creeps back up again .

The only other thing I can think of is we use air blowers to oxygenate the water to almost saturation levels and wondered maybe this has an effect on Ph ?

 

 

18 hours ago, John Cuthber said:

Why?

Livestock mainly . Out Ph seems to be on the very high end of keeping them happy . That and our suppliers grow out at around 7.4 so would also mean much less of a quarantine period . 

[StringJunky]

The air blowers will reduce the amount of natural carbonic acid, which is highly unstable in a turbulent environment. You might knock it down to the same pH as the catchment water if you turn off the blowers to find out. You only need to expose the lake surface to the atmosphere for it to oxygenate. The air blowers function is to temporarily disrupt the surface tension to allow gas exchange, it doesn't actually force air into the water directly. A bottom/up circulation should provide sufficient exchange without agitating the water too much, such that it liberates the carbonic acid as carbon dioxide.

The carbonic acid is an integral part of the lake's natural pH management system. My reference is experience in dealing with persistently rising pH in hydroponic systems. Took me a long time to figure it out. Look into the carbonic acid cycle if you want to understand it more deeply.

TLDR. Aim for water circulation from lower down to rise  to the water's surface for gaseous exchange without agitation. I think the pump can be lifted some way off the lake bed, say mid-water, to avoid making the water cloudy and turbid from sediments. Plan your pump arrangement so that the water body moves around in a manner that covers the majority of the lake. The rain and wind will also contribute to breaking up the surface tension for gas exchange, so it doesn't have to be all artificially generated.

You could try this as an experiment in a bath of the lake water and monitor the pH as you play around with it. To start, put some lake water in a mini-lake arrangement and leave it undisturbed, whilst monitoring the pH over time. It might take a few days. Then play around with your circulation pumps to find the best circulation pattern.

Edited July 30 by StringJunky
Added some more

[Sensei]

On 7/29/2024 at 6:06 AM, malcnunn said:

I want to reduce the Ph in a small lake of 10,000,000L from 8.9 to 8.1

Sounds like Sisyphean work, i.e. endless job. The lake gets ions from higher elevations and from the soil, over which you have no control.

Try different water filters and check the results before filtering and after filtering.

https://www.google.com/search?q=drinking+water+filter+for+hard+water

Instead of modifying all the water in the lake, try modifying only what the animals drink. It will be more economical.

Edited July 30 by Sensei

[sethoflagos]

55 minutes ago, malcnunn said:

Our lake is situated in Thailand , close to the Cambodia border . It was man made about 4 years ago with the base sediment being clay .

 

55 minutes ago, malcnunn said:

I have also used quite alot of Aluminium sulphate to lose some of the clay turbidity, which has worked really well and lowered the Ph when adding it , but the Ph slowly creeps back up again .

This is consistent with your base sediment clay being carbonate rich - ie a marl, as mentioned above. 

1 hour ago, malcnunn said:

Livestock mainly. Our Ph seems to be on the very high end of keeping them happy.

And your solution is to... change the environment? No qualms about social responsibility when it conflicts with short-term commercial interest?

 

[exchemist]

1 hour ago, sethoflagos said:

 

This is consistent with your base sediment clay being carbonate rich - ie a marl, as mentioned above. 

And your solution is to... change the environment? No qualms about social responsibility when it conflicts with short-term commercial interest?

 

Is altering the pH of a new, artificially created lake changing the environment, though? Or do you mean digging the lake? People have always built reservoirs.

Edited July 30 by exchemist

[sethoflagos]

30 minutes ago, exchemist said:

Is altering the pH of a new, artificially created lake changing the environment, though? Or do you mean digging the lake? People have always built reservoirs.

We are in the 21st century. Was no soil analysis performed prior to excavation? Never mind an EIA. Even now when the project seems to have gone tips up, the OP is trying to get free advice off the internet rather than employ the professional services that should have been on board before shovel touched dirt. The pH problem was foreseeable.

It doesn't surprise me that this project is based in Thailand. It has a very familiar ring to it. I've seen many similar scenarios over the years here in Nigeria. 

[malcnunn]

3 hours ago, sethoflagos said:

soil analysis was done but an environmental assessment was not . We did consult the locals including the government but that isn't what you would call an EIA .

As for the remark about short term commercial interest taking precedence over social responsibility you are so wrong it makes me laugh . I'll just say it has been a no profit venture (i retired early and used all my personal; pensions)that has produced numerous full time jobs for unemployed in the area . You are quite right about asking for free help here , I thought this would be a places to ask chemistry questions I am not 100% knowing myself . I 'm so sorry I wasn't aware and must have passed the pay button post asking . There's always someone like you lurking to have a dig at the expense of others , well sorry matey not gunna happen here . I will take my questions elsewhere , Thankyou very much to the other people here who kindly helped with the queries . 

 

 

[sethoflagos]

1 hour ago, malcnunn said:

There's always someone like you lurking to have a dig at the expense of others

And there's no possible justification for that?

Retired IT manager has a bash at terraforming tropical paradise. What could possibly go wrong?

 

[John Cuthber]

Dig a little (a few grams)  of the clay from the lake and weigh it.
Shake it with distilled water + let it settle.
Pour off that water and add some more distilled water and shake it up again and let it settle.

Add a pH indicator and see what the pH is.
Add acid until the pH indicator just changes, making a note of how much acid you add.

Shake it again and let it settle.
See if the pH has returned to the alkaline value.
If it has then repeat this until you find out how much acid you need to add in order to neutralise the available alkalinity in the clay.

From that you will be able to work out how much acid you will need to add to the lake.

An alternative would be to do a "back titration".
Take a known mass of clay and add a known  excess of acid, then measure (by titration) how much acid is left.
The difference is how much gets used up by the clay.

It's worth remembering that rocks are not very soluble.
Neutralising the alkalinity in the water will require neutralising the tiny fraction of the rock which is in solution but keeping the water neutral will require adding enough acid to react with all the alkali that is available from the sediments .
That might be a lot.