How do organic septic tanks work

Small sewage treatment shop

Regardless of the system used, biological sewage treatment plants always work according to the same principle. Both in biofilm-based systems such as the method of the submerged and ventilated fixed bed, the Rotation submersible and the Trickling filter or also in sludge-based systems, such as SBR systems, the wastewater first goes through a mechanical one Primary clarification. There heavy solids sink to the bottom in the container, fats, oils and other light substances float up.
The cleanest water of the primary treatment is located between the layer on the bottom (Bottom sludge) and the layer that floats on the water (Floating mud) and is removed from there for the next stage or flows into the next chamber in a free fall. Incidentally, this process is also used by every separator and every traditional multi-chamber system, the so-called septic tank.

A biological sewage treatment plant also removes the dissolved pollutants from the wastewater. This biological cleaning is carried out by bacteria that are naturally already present in the wastewater. So that the biological wastewater treatment works in a relatively small space, the bacteria must be offered good conditions for metabolism and reproduction. This takes place in a biological sewage treatment plant after the primary treatment in a separate chamber, the biological reactor, in which different fixtures or fillings are available depending on the process. In Biofilm process the bacteria is offered the largest possible surface area through a wide variety of packing elements, which can both be firmly anchored in the reactor (= Fixed bed) or be able to move freely in the reactor (= Floating bed). By overgrowing the packing with bacteria (= Biofilm) a high density of bacteria can be kept in the reactor. in theActivated sludge process on the other hand, an attempt is made to keep the bacteria themselves in suspension and to prevent their discharge from the chamber or to lead them back into the reactor from a downstream settling chamber in order to obtain the highest possible density of bacteria in the reactor.
The bacteria need a lot of oxygen for their metabolism, one of the main reasons why wastewater treatment is necessary on a technical scale, as this oxygen would otherwise be withdrawn from natural waters. So that the bacteria can work, air has to be brought into the water. This is usually done using a compressor that sucks in air from the outside and distributes it in fine bubbles in the biological reactor through a tubular or plate-shaped membrane.
As the bacteria multiply, additional biomass is created, which in turn has to be removed from the wastewater. This is done in the After clarification, which in principle works in the same way as the primary clarification, namely by gravity.

Most types of sewage treatment plants have a continuous flow. Make an exception SBR Small sewage treatment plants. As the name suggests (SBR = Sequencing Batch Reactor), work SBR Systems sequentially. To do this, the water has to be pumped back and forth between two chambers. The treated wastewater can be discharged into a receiving river or infiltrated on the property.

There are offers for a wide variety of technologies on the market (including SBR, Trickling filter, Fixed bed, Floating bed and Compact filter), both as a complete system including container, as well as for retrofitting old 3-chamber pits with a kit. No matter if with SBR or Biofilm process, retrofitting has the advantage that the old container can still be used. This is of course reflected in the cost of the investment. However, this aspect can also be a considerable disadvantage at the same time, as the old concrete tank has been exposed to corrosion from aggressive sewage for several years and the building fabric is often inadequate and not suitable for retrofitting. In addition, it should be noted that in complete systems, of course, the container shape was designed from the outset for biological treatment and is therefore perfectly coordinated with one another. If in doubt, building a new system is the more durable and sustainable option.