During the period 1982-1992 the works of the first phase were constructed, with a total budget of 11,5 billions of Drs., that included:
- The Central Sewerage Duct (KAA) in a length of 16,2 kilometres, the 11,8 of which consist a culvert.
- The total of the collecting and boosting ducts, collecting sewage, downstream the Central Sewerage Duct, with total length of 6,3 kilometres.
- The five (5) coastal pump stations that pump sewage in the Central Sewerage Duct.
- The four (4) pump stations and the collecting and boosting ducts of the low regions of Western Thessaloniki.
- The First Stage of Installations of Treatment of Thessaloniki Sewage (EELTh) for the total of municipal sewage, with 45% degree of cleaning in the winter and 55% during summertime.
- The twin Duct of Gallikos-Axios Rivers, with a length of 12,5 kilometers, which would lead the processed sewage to Axios River.
At the same time, the Company of Water supply and Sewerage of Thessaloniki (EYATh), working on the construction of new split networks for the sewerage of municipal wastes, the repair of already existing mixed networks for the sewerage of wastes and rain drainage, and their orientation towards the Central Sewerage Duct, took care that all city sewage were channeled towards the installations of treatment, through the Central Duct.
The works of a second phase became necessary due to the strict specifications of the Ramsar convention for the protection of water biotopes over the wider region of Axios River, the reduction of water flow of the river, added to the interest and the concerns of residents of the region. During the transient stage, before the works of phase B, additional works of 330 million drachmas were also constructed, so as in February 1992 the installations of Stage A efficiently processed 40.000 cubic meters of sewage per day. Furthermore, after some improvements on the process of treatment, the capacity was increased to 55.000 cubic meters per day, corresponding to 30 – 40% of total sewage of Thessaloniki, while the degree of treatment was no less than 90%.