The contract "GL-CL-03 - New Wastewater Treatment Plant in Lieşti. New Wastewater Treatment Plant in Pechea” was signed on April 22, 2013. The contract started on May 9, 2013.
Under this contract, a Wastewater Treatment Plant was constructed in Lieşti, including, as technical components, a receiving station and a tank for sludge from septic tanks, extended aeration tanks for removal of nutrients (nitrogen and phosphorus) and simultaneous stabilization of sludge, settling tanks, installations for sludge thickening and sludge dewatering, intermediate storage area for the dewatered sludge, a discharge pipe into the emissary and a quality monitoring system.
Technical components of the new Wastewater Treatment Plant Pechea include a receiving station and a tank for sludge from septic tanks, extended aeration tanks for removal of nutrients (nitrogen and phosphorus) and simultaneous stabilization of sludge, settling tanks, installations for sludge thickening and sludge dewatering, intermediate storage area for the dewatered sludge, an effluent pumping station and a quality monitoring system.
The reception at work completion was finalized on January 14, 2016.

GL-CL-03 – New Wastewater Treatment Plant in Lieşti. New Wastewater Treatment Plant in Pechea

Reliable design. Lifetime: >50 years
Guaranteed maximum annual operating costs
Reliable operation, without faults.
Guarantee: up to 25 years

The technological objects of the two plants are similar (but different sized, depending on influent flow rates), the difference being the necessity to build an effluent pumping station in Lieşti, because of the long distance (1.8 km) to emissary - Siret River.

Lieşti

Connection value: 27,005 p.e.
Type of the sewage system: mixed
Type of admission: Pressure pipe
Average daily flow: 5,025 m³/day
Maximum daily flow: 6,722 m³/day
Max. flow dry weather: 375 m³/h
Max. flow rainy weather: 502 m³/h

Pechea

Connection value: 15,615 p.e.
Type of the sewage system: mixed
Type of admission: Pressure pipe
Average daily flow: 2,759 m³/day
Maximum daily flow: 3,518 m³/day
Max. flow dry weather: 191 m³/h
Max. flow rainy weather: 248 m³/h

Effluent parameters

Maximum values for effluent:

BOD₅ Concentration: 20.0 mg/l
COD Concentration: 100.0 mg/l
Nitrogen (N) Concentration: 10.0 mg/l
Phosphorus (P) Concentration: 1.0 mg/l
Suspended solids: 35.0 mg/l

Aerial view of WWTP Pechea, Romania (15,615 p.e.)

Inlet

Wastewater is transported through the inlet pipeline of the sewer system or, if using cesspool emptiers, through a septic sludge receiving station to the inlet pipe fitted with a flow meter. Thanks to the advanced technological design, the treatment plant can work effectively even in case of large variations of the influent flow.

Pre-treatment

Retention of solids from the wastewater is done using a compact system consisting of two technological lines, each containing 1 coarse screen and 1 fine screen. Particles less than 2 mm and floating matters are separated and removed by grit and grease separator. A sand classifier takes the retained particles which are then washed, compacted and stored in a container.

Phosphorus removal

For phosphorus removal and industrial water coagulation (reduction of organic substances - COD, suspended solids - SS, ammonium - NH₄₊, etc.) a solution of ferric chloride - FeCl₃ is used. For this purpose, a FeCl₃ dosing station is provided. The solution is introduced through a pipe system into the distribution chamber to the anaerobic tanks, being mixed with the wastewater.

Anaerobic treatment

The biological treatment starts after introducing the wastewater into the distribution chamber to the anaerobic tanks and mixing it with the recycled activated sludge, then the mixture of wastewater and activated sludge is passed to one of the two adjacent tanks, thus the process of the anaerobic treatment starts.

Aerobic treatment

The technological design provides an innovative construction for the biological treatment: the "combi-pool", consisting of a set of concentric tanks: an outer annular aeration tank and a circular clarifier, centrally located. Each of the two technological lines include/s such a system, being able to operate independently.

Aeration

The aeration system provides three high-efficiency blowers, one for each of the technological lines, the third being the reserve. The aeration equipment, located at the base of the aeration tanks (ring shaped), contains a fine-bubble aeration system with membrane diffusers. Due to the oxygen sensors from inside the aeration tanks, the assembly provides the amount of oxygen required for the biological treatment, fulfilling the condition of reducing energy consumption.

Final Clarification

Following the steps of the biological treatment, in the final clarifier (the central circular tank) the activated sludge settles and then is transported to the distribution chamber to the anaerobic tanks, for ensuring a new cycle of treatment. Treated wastewater is discharged through a circular pipe, located at the top of the tank and subsequently discharged to the emissary.

Sludge treatment

Excess sludge and the floating sludge collected at the surface of the final clarifier are transported and stored in a circular tank - thickener tank for activated sludge in excess. When the sludge concentration from inside this tank reaches a threshold value, the sludge is transported to the dewatering station. Using a polymer solution, automatically dosed by a special equipment, the sludge is dewatered using 2 belt filter presses and then stored on drying platforms.