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Wastewater treatment issue: Turbidity problems


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January 19, 2021

Q. In pharma API (Active Pharmaceutical Ingredient) plant when effluent after primary treatment effluent passes through aeration tank-1 and aeration tank-2 effluent gets very turbid. So how to reduce this heavy turbidity? Where doI need to pass this effluent in PT RO (Plate & Tube Reverse Osmosis) plant?

Upendra sathe
- Mumbai India

Previous closely related Q&A's, oldest first:


Q. My project is to treat wastewater from photovoltaic wafers production industry. Wastewater contains HF, mixed acid etchant, SS, turbidity, SiO2, high oxide particle content. (pH of wastewater is between 2 and 4)
This wastewater is to be treated with Lime ( Ca(OH)2 ), PAC (polyaluminum chloride) coagulant plus polymer flocculant PAA (cationic polyacrylamide).

I intend to mix wastewater, lime milk and PAC in one-single rapidly stirred tank, then add PAA in a second slowly-stirred tank, following by lamella sedimentation.

I'd like to ask:
1) what is the optimum pH or pH range in the first mixing tank?
2) is addition of H2SO4 necessary in the beginning (before mixing e.g., in the equalization tank)?
3) does anyone knows the efficiency of this method in removing fluoride, silica?
4) if metals and P (PO4) are present in wastewater, would these be removed during the sedimentation process?

Thank you in advance..!

Stavros Lefkopoulos
- Thessaloniki, Greece


A. Don't add any more acid, it's quite unnecessary.

I'd suggest adding a combination of Calcium Chloride and lime such that the final pH is about 9, and there's an excess orf dissolved Ca in the liquid of about 500 mg/l. That ought to take the fluoride to less than 10 mg/l.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

Student project on Sand Filtration , SDI , Turbidity , Colloidal Silica


Q. I am Engineering Student working on Industrial Project dealing with water filtration .

This Project is to identify whether water of 20 NTU turbidity can be reduced to 0.2 NTU or SDI less than 3 in Pressure Sand Filter.

The media has selected is 700 mm depth of quartz sand with effective size - 0.5 mm &
300 mm depth of Anthracite with effective size - 0.8 mm

I am not getting the quality for a water sample from a river having 30 NTU & brought down to 5 NTU with pretreatment with ferric chloride. I am getting more than 1 NTU at the out let with 5 NTU inlet.

I have tried with other stored water of 20 NTU and I am getting 0.2 NTU at the outlet with the same media.

What could be the reason? Does presence of Colloidal Silica if any in the river water give higher turbidity values?

Does Colloidal Silica interfere with the turbidity readings in NTU?

If YES, How I can remove the Colloidal Silica If NO, What could be the reason for not getting the desired values at site?

What is the solution for the problem?

Please advise me.

Spandan Solanki
Student - Mumbai, India

June 30, 2008

A. 1. Sand filter best quality is about 2 NTU
2. If you are looking for < 0.2 , you need a secondary polishing filter which uses a cartridge or a precoat

Mazher, F
- Aurangabad, India

How to reduce COD from cardboard plant using starch

April 23, 2009

I need a help to know how to reduce the COD content from the effluent treated water.

recently I did a treatment to waste water and the got a reduction in turbidity to less than 5 NTU, means I have clear water but the problem still in high COD concentration around 3000 ppm.
other water parameters are : pH 12
chloride 1000 ppm; total hardness 550 ppm, Ca hardness: 320

Mohammed Younes
student - Amman, Jordan

simultaneous April 24, 2009

Add some hydrogen peroxide at the last step, just before the sampling point. Start with a few hundred ppm and increase from there if necessary. Cheap and effective.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina

April 27, 2009

This type of wastewater is best handled using a biological process.

An activated sludge reactor, with plenty of aeration would work. Such is likely to be very space intensive.

An anaerobic process is more often used in an industrial context.

I must admit I am very far from being an expert on this type of wastewater treatment. I'd suggest you look into municipal wastewater treatment, such as is used in handling domestic sewage.

dave wichern
Dave Wichern
Consultant - The Bronx, New York


November 2, 2017

Q. I have a water which has high turbidity and fluoride. What can we use to remove it?

Elijah Mwangi
- kenya

November 2017

A. Hi Elijah. We appended your question to a thread which may be helpful, but you probably need to provide good details of your situation to get proper responses.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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