Reuse of water from the wastewater treatment plant in Thessaloniki
4 June, 2050
Waste water source
In Thessaloniki, the secondary effluent of the wastewater treatment plant (165,000 m³/day) is used for agricultural irrigation of the Halastra-Kalohori area. Approximately 2,500 ha of spring crops are irrigated with a mixture of fresh water and effluent in the Halastra-Kalohori area. In this implementation, the effluent is mixed with freshwater from the Axios River at a maximum ratio of 1:5. The mixed water values of SS, COD and BOD were less than 12, 18, and 2 mg/L. This is much below the norms deemed satisfactory by several regulations and guidelines around the world as well as of those considered safe by the specific regulations for this practice.
Part of the wastewater effluent of 165,000 m³/day from the Thessaloniki wastewater treatment plant is mixed with river water from the Axios and eventually reused to irrigate approximately 2,500 ha of rice, corn, alfalfa, sugar beet and cotton. Water requirements varied from 60 to 111 m³/ha/day, for cotton and rice. In the traditional surface water irrigation methods, the efficiency is less than 70%. The effluent is mixed with freshwater from the Axios River at a maximum ratio of 1:5. The Land Reclamation Institute is in charge of the surveillance of the system, checking the quality characteristics of the effluent delivered to the irrigation network and the possible effects of its use.
Rice is the principal crop cultivated in the plains west of Thessaloniki, followed by cotton, sugar beet & corn. The area is characterized as an area of intensive agriculture and has significant infrastructures for irrigation (open channels), drainage (open channels) and flood prevention (extensive levies). Also the shoreline is used for intensive aquaculture (mussels). Farmers of the area often practice both cultures (rice, mussels). The crops irrigated with reclaimed water are rice, alfalfa, corn and cotton.
Waste water treatment description
Nutrient removal : Conventional municipal wwtp techniques
Pesticide removal : none
Disinfection : Chlorine
Suspended solids removal : Primary treatment in wwtp
The installed capacity is 1,333,000 population equivalents. The total incoming load is 155,135 m³/day. The majority of the incoming load is wastewater supply (154,470 m³/day) from the sewerage network, supplied with water from cesspools (665 m³/day). The reuse of the wastewater treatment plants effluent for irrigation is 2,275,000 m³ yearly.
Extent of the agricultural beneficiaries
The reuse of wastewater is implemented since 2007 at the Halastra-Kalohori irrigation network. Total extent of the irrigated area is 2,500 ha, with following superficies across the crops:
Rice : 1677 ha (68.5%)
Alfalfa : 111 ha (4.5%)
Corn : 559 ha (22.8%)
Cotton : 104 ha (4.26%)
Type of agreement
Ilias, A., Panoras, A., & Angelakis, A. (2014). Wastewater Recycling in Greece: The Case of Thessaloniki. Sustainability, 6(5), 2876–2892. https://doi.org/10.3390/su6052876
The evaluation of the results of crop yield and soil data in relation to the water quality and the irrigation method shows that the municipal wastewater of Thessaloniki city treated by activated sludge and chlorination can reinforce the water resources of the Thessaloniki plain. The treated effluent is discharged to the neighboring Halastra-Kalohori irrigation network, and reused after mixing with river water from the Axios. The mixing of the two waters is essential because of the effluent's increased salinity due to seawater intrusion into the sewerage system.