Middle-sized wastewater treatment plants - oval design

wastewater treatment plant Aquatec VFLAT 30 to AT 300 oval 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. After preliminary purification of industrial wastewater with organic pollution the plants serve as biological treatment for meat processing factories, dairy factories and slaughterhouse, wineries, etc. Furthermore the purified water can either discharge into the surface or to be utilized for irrigation.

Basic description

AT 30 - AT 300 oval wastewater treatment plants are delivered as a complete technological line consisting of one or more plastic biological reactors with a oval ground plan, a pump station with a mechanical pretreatment and a sludge tank. The oval ground plan and dimensions of the plants are mainly intended for implementation in widely distant locations, they are ideally suited for transporting by a regular truck.

Vertical Flow Labyrinth – VFL® - Treatment process

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. 

wastewater treatment plant AT100 insallation wastewater treatment plant Aquatec VFL

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. 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 plants are shown in the table below:


Commonly  achieved  values

Guaranteed values

wastewater treatment plant Aquatec VFL  


35 mg/l

70 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 parameters:


design flow



[kg BSK5/d]

Length x width
of reactor

of reactor

Nr. of




Bottom height


AT 30oval



3350x2150 2250 1 150/150 1700 / 1500

AT 40oval

6,0 2,4 4222x2150 2250 1 150/150 1700 / 1500

AT 50oval

7,5 3,0 4222x2150 2440 1 150/150 2100 / 1900

AT 60oval

9,0 3,6 4342x2150 2440 1 150/150 2100 / 1900

AT 75oval

11,3 4,5 4466x2150 2440 1 150/150 2100 / 1900

AT 100oval



6300x2200 2500 1 150/150 2100 / 1900

AT 120oval

18,0 7,2 7000x2200 2500 1 150/150 2100 / 1900

AT 150oval

22,5 9,0 7900x2200 2500 1 150/150 2100 / 1900
AT 200oval 30,0 12,0 6300x2200 2500 2 150/150 2100 / 1900
AT 250oval 37,5 15,0 7000x2200 2500 2 150/150 2100 / 1900
AT 300oval 45,0 18,0 7900x2200 2500 2 150/150 2100 / 1900

The wastewater treatment plants installation

Biological reactors and sludge tank for wastewater treatment plant AT30-300 oval are installed as partly underground tanks on the concrete base slab (thickness 200-300 mm) so that the upper edge of the tank protrude approx. 100 mm above the ground.
Tanks need concrete encasement from dry concrete, or are placed into prepared holes made from concrete blocks and backfilled with sorted material, up to the top.
Concrete encasement or backfill needs to be done in layers according to the back pressure of water in the tank.

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