Construction Company


Address : 10 Germanikis Sholis Athinon str. (Ex Ziridi), Gr 15123 Marousi, Athens, Greece
Tel : +30 210.6100500
Fax : +30 210.6857094
E-mail :

Environmental Projects


1. Operation and Maintenance of Sewage Treatment Plant for Major Thessaloniki (Stage II)

The plant is designed according to the following inlet and outlet data. The incoming sewage concerns municipal sewage, septic sewage and industrial pre-treated liquid waste.
Currently it operates at an average daily flow of 150.000-160.000m3/day.

The plant consists of the following units:


- Inlet works, consisting of (3) chambers in operation and (1) for future expansion
- Inlet Pump station consisting of Archimedean Screws 2,3m3/s each.
- Screening, (5) lines equipped with mechanical screens of 10mm, screw conveyors and (2) screenings dewatering units.
- Grit-grease removal, in (2) rectangular aerated tanks equipped with reciprocating bridge carrying submergible sand pumps and scum scraper. Sand washing and dewatering unit.
- Rain water storage tanks, two of D=47m and V=5.000m3 each
Septic Sewage reception and pre-treatment units
- (3) Venturi channels for flow measurement
- Primary circular clarification, (3) of D=47m and V=5.000m3 each.
- Intermediate pump station of sewage and sludge recirculation, (8) Archimedean pumps of 1,77m3/s each and excess sludge pump station
- Bioreactors, consisting of (8) rectangular tanks each of 17.500 m3 and 6m deep, with anoxic and aerated zones. Aeration by fine bubble diffusers with tapered density, for organic load and nitrogen removal. Submergible mixers and submergible axial pumps for internal recirculation. Provision for extension with (2) additional bioreactors.
- Air Blowers, (5) each of 28.500Nm3/h air accommodated within a building.
- Secondary Circular Clarifiers of D=54m each
- Disinfection by hypochlorite solution in a contact tank
- Outlet Pump Station, including (4) of 1,58m3/s each to charge the off-shore discharge pipeline.
- Off-Shore Discharge Pipeline the inland part has a length of 7.800m, consisting of (2) reinforced concrete pipes of diameter 1600mm and thickness 20mm
The off-shore part has a length of 2.600m consisting of (2) reinforced concrete pipes of diameter 1600mm and thickness 20mm and (2) branches at an angle of 30º to feed the diffusers. The diffusers consist of uprisers of HDPE and ductile iron.


- Primary Sludge pre-thickening, consisting of (4) circular tanks of D=15,6m and V=600m3 each and (2) Mohno pumps (55m3/h each) for sludge feeding to digesters.
- Anaerobic Digestion of Sludge, mesophilic 35ºC, consisting of (2) tanks each 7.700m3, and provision for a third one. Sludge Preheating and biogas mixing (HEATAMIX).
- Gas Holders, (2) circular floating roof of 2.000 m3 each, and biogas flare
- Sludge Post-thickening, consisting of (6) circular tanks of D=15,6m and V=600m3 each, plus (3) Μohno pumps variable flow max 95m3/h each.
- Mechanical Thickening of excess Sludge, consisting of (2) drums of 107m3/h each.
- Sludge Homogenization tanks (dual chamber)
- Sludge dewatering, consisting of (5) Belt-presses each 35m3/h, producing cake of 22% dry solids content.
- Advanced Treatment of Sludge (Sanitation), by means of lime powder addition to produce a cake of at least 35% dry solids content

The “CONSTRUCTION COMPANY CHRISTOPHER D. CONSTANTINIDIS S.A.” has also been awarded the “Operation and Maintenance” contract of the complete Plant.


2. Operation & Maintenace of Major Athens (Psittalia) Wastewater Treatment Plant (Stage I)

The plant treats all sewage produced in the Greater Athens drainage basin, except a minor quantity of sewage that is treated in Metamorfosi’s WWTP.

The incoming sewage is initially pre-treated at the Akrokeramos facilities (main land) and is subsequently directed, via an inverted siphon (underwater) to the facilities on the island of Psittalia, where primary treatment and sludge treatment take place. Afterwards, through an off-shore disposal pipeline, it is expelled at a satisfactory depth and diffused into the Saronicos bay with an organic load reduced by 35-40%.

The plant’s sewage-treatment 1st STAGE consists of the following:
- Sewage screening and degridding (a procedure carried out at the Akrokeramos facilities)
- Primary sewage settlement (with an average removal rate of 63% for suspended solids and 38% for the organic load),
- Primary Sludge pre-thickening,
- Primary Sludge anaerobic digestion,
- Sludge Post-thickening and
- Sludge Dewatering to 30% Dry Solids, for disposal to a Sanitary LandFill
- Power Production Plant to utilize the biogas produced by sewage treatment.

The 7,4 MW - electrical power covers the wastewater treatment plant’s energy needs, while excessive energy is sold to the Hellenic Public Power Corporation.

The Psittalia Wastewater Treatment Plant treats daily with 750.000 m3 of sewage and has a nominal daily capacity of 1.000.000 m3. Recently the plant was expanded for secondary (biological treatment) of sewage.