Why use sludge tanks when treating wastewater with Reverse Osmosis and Ultrafiltration membranes?

scanning: author: from: time:2021-03-24 classify:Industry Trends

Sludge tanks (and ponds) are key part of operations in a wastewater treatment plant (WWTP). They come in many shapes and sizes. They can be as simple as an upright tank with an open end, to a system of multiple lagoons.

The aims of operating a sludge tank is to:

hold sludge after it has been removed from the wastewater treatment system;

settle out sludge further so more  RO membrane  producing water  can be recovered; and

further digest the sludge before hauling away.

The tanks (or ponds) come in various shapes and sizes and are configured differently dependent on the site and requirements. Some have aeration and mixing that is delivered by mechanical and electrical means. This aids digestion of the sludge that has accumulated.

They can also be operated differently. Some tanks will only hold the sludge until it’s taken away. An alternative to this methodology is to use the tanks to concentrate the sludge. These tanks (and ponds) periodically allow the sludge to settle, at which point the clearer water is removed from the top where there is no longer sludge. (A process called decanting).

In most plants, after the sludge tank, the sludge is then drawn from the tank/pond and dewatered through a sludge press. After which, the drier product is hauled off as liquid for disposal off site.

Despite the differences, there are a lot of common problems that operators of Waste Water Treatment Plants need to overcome when operating sludge tanks/ponds. They are:

Sludge Disposal

  • Sludge hauling generally makes up 40-60% of the WWTP Budget

  • Is constantly created and needs to be removed


  • Require polymer to flocculate solids and expel  RO and  UF system wastewater;

  • Poor decanting (Removal of water from settled sludge)

  • Poor quality (turbid) water decanted from the settled sludge.

Odours and Fines 

  • Odour Control chemicals

  • Fines when limits are exceeded

Capital Expansion 

  • If throughput is too high, you may need to expand your storage capacity, which can cost money

So now you know a little about sludge tanks (and ponds). If you’d like to know more about sludge tanks or find out how you can ovecome the problems mentioned in this article, please contact us via this website.