RBC PROCESS DESCRIPTION
Pre-Treatment Step
In the mechanical pre-treatment step solids are separated. This includes both, sediment particles and
floating particles such as fats and grease. Different technologies are being used for this separation,
depending on the plant size and the particles in the waste water.
For smaller units, a multi-chamber pit is recommended. The first chamber represents the main part of
the total volume. In this chamber, the primary sludge is separated. Primary sludge consists mainly of
faeces, cellulose, food rests. In addition, secondary sludge that is already processed is stored as in
inoculum. By cultivating different bacteria conditions in the additional chambers a further increase in
efficiency can be achieved. The individual chambers are connected via diving walls so that floating
sludge cannot pass through. In 3-chamber pits, a reduction of the organic load of about one third can
be achieved.
For bigger plants more advanced pre-treatment steps are used, such as an emscher tank. Additional
reaction tanks in the pre-treatment area are required. If an up-flow denitrification (see also biological
step) is foreseen. With these tanks a further reduction of the organic load can be achieved.
The pre-treatment step can be extended on request by elements such as screening units, rotating drum
sieves, grit chambers and grease traps.
For dimensioning, the retention time of the raw wastewater in the pre-treatment step should be less
than 1.5 – 2 hours.
For small units, Alpha-Disc© relies on traditional and economical multi-chamber pits in prefab
construction. For bigger Alpha-Disc© wastewater treatment plants, additional rotating drum sieves are
used. If treatment plants are fed with mixed sewage, additional steps have to be taken into
consideration for the treatment of the rain and storm water parts of the inflow. Depending on the size
and the flow rate, mixed systems can be easily treated by simple adaptations of the Alpha-Disc©
treatment plant when ponds are available. Already existing non-aerated wastewater ponds can be
extended or easy-to-build tanks or ponds can be used. Separate channels for storm water and waste
water are recommended for bigger sized plants. In this way, storm water can be buffered and easily
released from floating particles, such as grease or oils from the roads. These can be separated for
example in a grit chamber.
Following the current state-of-the-art design of Alpha-Disc© waste water treatment plants in
combination with separate inflow channels, an economic solution can be realised for both kinds of
mixed sewage treatment systems.
The Biological Treatment Step
In the biological treatment step, the dissolved and fine dispersed organic loads are converted into clean
water and sediment solids through bacteria in an aerobe purification process. The sediment solid is
often referred to as excess sludge.
In the aerobe biological wastewater treatment there is a differentiation between the activated sludge
technology and the fixed film technology.
In the activated sludge systems the biomass is suspended in the wastewater and supplied with oxygen
by aerators. The wastewater can either pass continuously through the treatment tanks or can be treated
in a batch system (SBR-systems)
In fixed film systems, the biomass grows on supporting plates. The bacteria consume the required
oxygen from the surrounding atmosphere. In trickling filters, the growing surface consists of an open
grating structure, which allows the biofilm to be surrounded at the same time by wastewater and
atmosphere. In immersion disc plants, the biofilm situated on the growing surface is intermittently
exposed to the atmosphere and the wastewater to be treated. For special applications, combinations of
the above mentioned technologies are used.
The aerobe biological treatment process leads first of all to the reduction of organic carbon
compounds, described by the values of BOD5 and COD. Furthermore, the harmful and volatile
ammonia nitrogen is converted into immobile nitrate nitrogen. This process is called nitrification. For
both processes, treatment efficiencies of up to 99% can be reached. If the treated wastewater is recirculated into an upstream reaction tank, denitrification can also be achieved. In this process, the
carbon compounds of the reaction tanks detract the oxygen fixed in the nitrate so that the nitrogen can
escape in elemental form.
The advantage of the aerobe biological technologies is the almost odourless process of the wastewater
treatment.
For high loaded industrial wastewaters, it is best to then use biological anaerobe technologies using a
digestive processes.
Alpha-Disc© uses the rotating immersion disc technology for the biological wastewater treatment.
This technology represents a combination of trickling filter and biological contactors. The rotating
immersion discs provide the most energetically efficient technological process, as only the rotor with
the biomass turns so as to keep mechanical abrasion minimal. For the dimensioning of the biological
rotating immersion disc step, Alpha-Disc© follows the ATV-guideline A 281. For other climate
zones, this guideline is appropriately modified thanks to the Alpha-Disc© experience of more than 20
years. Plants in which the required oxygen is brought into the wastewater via compressed air or
surface aerators have an energy demand of 50% more that plants based on biodisc technology.
The high sludge age of the biomass achieved through the fixed film process used by Alpha-Disc©
proves that the excess sludge production is up to 50% less .
The Final Clarification Step
In the mechanical clarification step, the particulate matter caused by the biological process is
separated out as excess sludge via sedimentation.
For this process two technical conditions must be fulfilled: the sludge has to be heavier than the
surrounding water and second, turbulences in the clarifier tank must be avoided. The excess sludge
sinks to the tank bottom due to its higher density and is withdrawn from the tank bottom in certain
intervals for storage in the sludge tank. For this withdrawal it is important that the sludge remains not
too long in the clarifier tank, as otherwise it will float due to anaerobe digesting and gas formation.
This floating sludge can be removed under normal conditions, although rather difficultly. In the field
of final clarification, Alpha-Disc© has worked with the lamella separators for decades. These
separators are specially adapted to the technology of the rotating immersion discs. The higher density
and resulting higher sinking velocity of the fixed film excess sludge are helpful in this process. The
construction concept of very short settling distances leads to an extremely compact construction.
Alpha-Disc© lamella separators require only about 20% of the surface of conventional clarifiers. This
allows the settled sludge to be thickened up to 1,5%-vol of dry matter.
Alpha-Disc© lamella separators are also used as intermediate clarifiers and in a wide range of
technical sedimentation processes for industrial applications.