The works of maintenance and upkeep of sanitation facilities represent major activities for the operation units. These works include in particular:
clearing of pumping stations sumps;
maintenance of the equipment installed in pumping stations;
operation and maintenance of treatment plants.

The maintenance of the sewerage network is conducted by the use of advanced mechanical equipment and machinery. Indeed, the ONAS equipment and machinery fleet comprises:

 107 suction and water pressure clearing trucks (of which 11 small-size);
 10 giant suction trucks
 66 mud-removal trucks
37 suction-trucks (of which 8 small-size);
 5 mobile units for camera inspection

In order to carry out the activities above, the operation units draw up every year an annual programme for clearing the networks and annexed facilities, as well as for preventive maintenance of the wastewater and pumping facilities, and this in view of the human resources and equipment available and also of the profitability of the equipment and periodicity of the clearing operations. The intervention zones are listed in priority order and in terms of the relevant schedule. The annual programme is updated at the end of each month in view of the progress of the works.

Components of the operated network as of December 2009

Total network length: 14 630,811 km;
Inspection manholes:  486 538 units
Storm water gutters:  54 968

Connection boxes: 1 006 140 units
Pumping stations: 663

Besides, ONAS has entrusted private developers with the activities of operating part of the network and its annexed facilities as follows:

Total network length: 2267 km (15,5 % of the total network);
Inspection manholes: 64 728 units (13.3 % of the total inspection manholes);
Storm water gutters: 10 100
Connection boxes: 155363 units
Pumping stations: 103
Wastewater treatment plants 17.

Clearing of sewerage networks as of December 2009

ONAS services have undertaken as of December 2009, together with the private sector, the clearing of :
 8050 km of networks (58 % of the total network length);  457758 connection boxes and inspection manholes. 

Operation and maintenance of wastewater treatment plants

As of end of 2009, the number of wastewater treatment plants (WWTPs) amounted to 106 WWTPs, including the plants constructed in rural environment.
   These are the treatment processes used:
Activated sludge  
Oxidation ditch
  Natural ponds
Biological clarifiers
  Filtration sewer  

Modern technologies are used in all wastewater treatment plants constructed by ONAS, which allow automatic operation of these plants. The latter are managed by specialised staff and technicians with expertise in wastewater treatment and maintenance of the electro-mechanical equipments. The quality of treated wastewater is regularly controlled in the laboratories installed at the plants or in private laboratories. Every year, some 180 000 laboratory analysis operations are performed in this regard.