Middle-sized wastewater treatment plants - circular design

Montované čistiarne odpadových vôdAT 30 to AT 900 wastewater treatment plants were invented to purify sewage water for blocks of houses, small village, parts of a village, accommodation properties, restaurants, recreational properties, manufacturing factories, industrial parks, meat processing factories, dairy factories and slaughterhouse. Furthermore the purified water can either discharge into the surface or to be utilized for irrigation.

Basic description

AT30 - AT900 wastewater treatment plants are delivered as a complete technological line consisting of one or more plastic biological reactors with a circular ground plan, a pump station with a mechanical pretreatment and a sludge tank. The treatment technology ensures the high quality of purified water, low investment and operation costs. The technology also can be found under the international name of Vertical Flow Labyrinth - VFL.

Vertical Flow Labyrinth – VFL® - Treatment process

Montované čistiarne odpadových vôd

The technology uses a continuous-flow activated sludge process with biological nitrogen and phosphorus removal, which combines the following processes in a single tank:  mechanical pre-treatment, excess sludge collection, biological treatment using a low-loaded activated sludge process, separation of the treated water from activated sludge in the final clarification chamber, flow balancing of fluctuating inflow of wastewater in the retention chamber. The treatment process consists of several technological processes. Raw wastewater flows into the non-aerated activated sludge chamber with anaerobic and anoxic zones creating and admixture with the recirculated activated sludge, the mechanical pre-treatment of inflowing raw wastewater and the decomposition of coarse impurities, denitrification and accumulation of readily degradable organic contamination is taking place in the non-aerated activated sludge chamber, which is divided by inner partition walls to create a vertical flow labyrinth, where internal circulation is established. 

Furthermore, allowing the admixture flow gravitationally into the aerated activated sludge chamber with includes fine-bubble diffusors. In oxic conditions the biological degradation of organic contamination, nitrification and phosphorus uptake is taking place.  The activated sludge flows into the final clarification chamber, where the activated sludge is separated from the treated wastewater. The treated wastewater is discharged into a water flow, infiltrated or recycled and the separated activated sludge is recirculated by air-lifts.
A flow regulator is installed at the water level in the final clarification chamber which controls the outflow in order to maintain the water level between the normal and maximum level in the tank (integrated retention chamber).
The pressurized air is supplied by blowers for aeration of the activated sludge chamber and for recirculation via air-lift pumps. 

Vertical Flow Labyrinth – VFL®

The recirculation and aeration is controlled by a microprocessor control unit which also enables the wastewater treatment plant to work in various modes depending on the loading.
The technology Vertical Flow Labyrinth – VFL®, used in the biological reactor, is protected internationally by patent. The purification technology ensures the high quality of purified water, low investment and operation costs.

Technological parameters

The quality of purified water corresponds with the Directive No. 269/2010 requirements in the Collections of Laws for discharging the water into the ground or on the surface.

The guaranteed and commonly achieved parameters from the outpour of the wastewater treatment plant are shown in the table below:Montované čistiarne odpadových vôd


Commonly  achieved  values

Guaranteed values


35 mg/l

75 mg/l


10 mg/l

15 mg/l


10 mg/l

20 mg/l


2 mg/l

5 mg/l


15 mg/l

25 mg/l


3 mg/l

7 mg/l

Technical parametres:


design flow



[kg BOD5/d]







Nr. of

AT 30 3,75 1,5 2400 2700 2200/2000 1
AT 40 5,25 2,1 2850 2700 2200/2000 1
AT 50 7,5 3,0 2950 3000 2800/2600 1

AT 75



3250 3000 with pump station 1

AT 100

15,0 6,0 3500 3000 with pump station 1

AT 120

18,0 7,2 4000 3000 with pump station 1

AT 150

22,5 9,0 4500 3000 with pump station 1

AT 200

30,0 12,0 5000 3000 with pump station 1

AT 250



5300 3000 with pump station 1

AT 300

45,0 18,0 5500 3000 with pump station 1
AT 400 60,0 24,0 5000 3000 with pump station 2

AT 500

75,0 30,0 5300 3000 with pump station 2

AT 600

90,0 36,0 5500 3000 with pump station 2

AT 750

112,5 45,0 5300 3000 with pump station 3

AT 900

135,0 54,0 5500 3000 with pump station 3


Montované čistiarne odpadových vôd

The wastewater treatment plant installation

AT30 - 900 biological reactor and the sludge tank are installed as partly underground tanks on the concrete base slab (thickness 200-300 mm) allowing the top edge to protrude 1000 mm over the surface. The tanks max. depth without additional static support is 2000 mm. When deeper placing is needed or if the project documentation requires it, there is a necessity to make a concret.

The detailed instructions for wastewater treatment plant mounting are listed in the Operation Manual.