Sedimentation Processes in Waste-water Treatment

As stated earlier in one of our previous articles, we have primary and secondary sedimentation in waste-water treatment. In the primary sedimentation stage, sewage flows through large tanks, commonly called “pre-settling basins”, “primary sedimentation tanks” or “primary clarifiers” (Huber Company, Berching, Germany, 2012).

The tanks are used to settle sludge while grease and oils rise to the surface and are skimmed off. Primary settling tanks are usually equipped with mechanically driven scrapers that continually drive the collected sludge towards a hopper in the base of the tank where it is pumped to sludge treatment facilities. Grease and oil from the floating material can sometimes be recovered for saponification.

This removes as much as possible the organic matter of sewage. The sewage is allowed to flow in a rectangular tank. Some of them have paddles which help to rotate the sewage and collect the heavy particles (solid organic matter, inorganic matters) together and make them to sink as sediment.

Read Also: Types and Sources of Waste-Water

Within the tank, it stays 2-8 hours. At the end of 2-8 hrs, this process removes about 60% of suspended solids and about 40% of Bio-chemical Oxygen Demand (BOD). According to Sridhar (2007), the rate of sedimentation is increased in some industrial waste treatment stations by incorporating processes called chemical coagulation and flocculation in the sedimentation tank.

Coagulation is the process of adding chemical such as aluminum sulfate, ferric chloride or polyelectrolyte to the waste-water; this causes the surface characteristics of the suspended solids to be altered so that they attach to one another and precipitate. Flocculation causes the suspended solids to coalesce.

Sedimentation Processes in Waste-water Treatment

These two processes can remove more than 80 percent suspended solids. The solid particles are directed to the sludge digester for treatment and the effluent to the next apartment called the activated sludge (surplus) or filtration/Aeration chamber

Final Sedimentation

This occurs during the secondary treatment of the waste-water. Here the still remaining solids settle on top while the effluent goes into a lake or river, sea or any other place while the surplus activated sludge should be collected and re-cycled starting from the primary sedimentation (rear side of it).

Read Also: Impacts of Waste-water on the Environment, Treatment objectives and Disposal Regulations

It should be directed to the sludge digester and have the action is anaerobic (no more aerobic). The sludge is pumped into digested anaerobic sludge, dewatered and tarry odour (innocuous). Gas could be produced (as fuels etc) while the effluent is discharged into the river. Dewatering means ―air drying.

Do you have any questions, suggestions, or other contributions? Kindly use the comment box provided below for all your contributions. You are also encouraged to please kindly share this article with others you feel can benefit from this information if found useful enough as we may not be able to reach everyone at the same time. Thank you so much for sharing!

Benadine Nonye

An Agric. Consultant & a Writer (With over 12 years of professional experience in the agricultural industry) - National Diploma in Agricultural Technology - Bachelor's Degree in Agricultural Science - Master's Degree in Science Education... Visit My Websites On: - It's All About Agriculture, The Way Forward! - The Most Reliable Global Agricultural Forum! - The Most Reliable Agricultural Job Board! - For Everything Premium Agriculture! - For Proper Waste Management and Recycling Practices. Join Me On: Twitter: @benadinenonye - Instagram: benadinenonye - LinkedIn: benadinenonye - YouTube: Agric4ProfitsTV - Pinterest: BenadineNonye4u - Facebook: BenadineNonye

Leave a Reply

Your email address will not be published. Required fields are marked *