Sorption filters

Sorption post-treatment explained

Sorption post-treatment means passing water that has already been through the main treatment stage through a filter medium that holds back some of the remaining pollutants. Such a unit does not work on its own and does not replace a septic tank or treatment plant; it supplements them where the design provides for it.

The word "filter" suggests that the water coming out is as clean as tap water. In reality post-treatment is just one link in the chain, and its benefit depends entirely on how well everything before it is working.

— Editor's note

History of this address

Archived address · now a reference page

This address used to hold a seller's page describing a sorption unit. The former site no longer works, and our guide has no connection with it.

Now it explains how sorption post-treatment works in general. We do not recommend specific products and we take no orders.

How it works

Water from a septic tank or biological treatment plant passes through a layer of filter material. Its particles hold on to some of the pollutants that the earlier stages did not remove, and the water leaves the unit noticeably cleaner than it entered.

Over time the medium becomes saturated with what it has captured and works less and less well. That is why it is replaced from time to time; how and when is stated in the manual for the specific equipment.

Where post-treatment is used

After a septic tank, when treatment in the ground is difficult because of the soil or groundwater.
After a biological treatment plant, if the design calls for an additional stage.
Where the treated water is to be discharged into a ditch or onto the ground surface, if the regulations and the design allow it.
In every case the decision on post-treatment and its type is made by the designer.

Servicing and replacing the medium

How often to replace it and which material is suitable are stated in the unit's manual.
A sign that the medium is spent can be poorer water quality at the outlet; this is assessed by the service company.
Replacement is carried out by a service company: the work involves an installation where dangerous gases may be present.
The used medium is disposed of according to the rules your service company will explain.

What this text is based on

SP 32.13330 "Sewerage. External networks and facilities" (Russian code of practice)
Russian sanitary rules and standards (general provisions)
Equipment manufacturers' instructions (general provisions)

Rules, requirements for treatment facilities and equipment manuals are updated from time to time, so the final word belongs to the design, the regulations in force and the documentation of your particular system. The texts here cite Russian standards; other countries have their own building and sanitary rules, so check local regulations and permits. This guide explains how systems work and why decisions are made, but it does not replace a designer, an installer or a service company.