Use of alum does not solve all the problems but you can measure the parameters and take the remedial actions.

here i am attaching a file which may help u.

Alum is a well known coagulant that can only reduce lake turbidity improoving photosyntesis process and the corresponding oxygen level. However, after the coagulation/floculation process, coloidal NOM can be conduced to the bottom increasing anaerobic processes that can induce very negative impacts in the aquatic ecosystem, namely in it trophic conditions and odours production.

Alum will deal with the symptoms and create more problems. The flocculated matter will sink to the bottom and cause a demand for oxygen leading to hypoxia at night . While the clarified water will create more room for algal growth. Elevated Dissolved  Inorganic Al  can cause retarded  fish growth and at higher concentration cause deaths due to clogging of the gills

Some info are available in the following papers

http://www.sciencedirect.com/science/article/pii/S0269749102001926

http://link.springer.com/article/10.1023%2FA%3A1023914805034

pH of lake water is the most important parameter when u try to use alum compounds for control eutrophication. Lake water should have enough buffering capacity for pH remaining at safe range - between ca 6.5 - 8.

Regards :)

Adding Alum is no solution to the lake eutrofication.It is a very novice and half baked solution  and appears to be based on traditional processof municipal water treatment. Here it will aggravate and worsen  the problem.

The alum will  (if well mixed ) coagulate and fluculate the suspended solids whenever applied and the lake will appear clean.But what hapens to the settled material.It will have flocks of aluminium hydroxide with organic material,further cmplicating the situation.The Alum will pollute the lake with heavy metal (Al),change the lake pH and destroy the Benthic ( bottom of lake) ecosystem.

This will inturn destroy the whole lake ecosystem including fish which will be loaded with heavy metal Aluminium.

The scientific solution will be

A) to asses what is causing the eutrification is it excess of Phosphorus,Nitrogen or both.

B) Reduce the input of these nutrients by treating or isolation the majour sources

C) Remove the weeds/algae  by cleaning the lake

D) Areate the lake

E) Introduce Fish if dead

Beggining can be made by stopping polluted water inflow to the lake.

If practiced for 3 to 4 years the lake will be in prestin condition forever.

There is no shortcut, if any body is proposing a quick fix you are being taken for a ride. Stop the damage  any further.

i think for controling af algea in a larg lake we need high amount of alum and mixing alum is a problem.increase it alum is harmful for health

As already mentioned the first step must be controlling the sewage flow into the lake. Alum will be useful only if accompanied by removal of coagulants, either by filtration or sedimentation - out of the lake. This might be none trivial.

You will need much more data - where is the sewage coming from (domestic, industrial, agricultural?), how much and what is it rich in? Etc. etc.

This seem like a large project...

Good luck!

Yoram

Alum is a known flocculating agent. Use of it will not solve the problem of Eutrophication. Rather will form collloidal scum on the top layer and would enhance algal formation

In my opinion you should provide more information on the lake itself, at least size, inflow/outflow? The same for the "uncontrolled release of domestic sewage". But it is clear that these discharges have to be stopped or well treated first. What next depends on the details. Many measures can be recommended to fight eutrophication in a less harmful and more sustainable way.