Phytotechnology applied to municipal wastewater treatment on irrigated fields of Gdansk (Poland) (1872-1992)

Abstract

By I 863 the population of Gdansk was about I 00000 people and the water consumption was
predicted on the level of 100 litres per person a day, which meant about 10000 m3
/day of
wastewater. The water supply and sewerage systems were completed in I 869-1871 and the
wastewater treatment plant built in I 872 (it was situated 3 km from the city), The wastewater
treatment plant consisted of the 320 ha of the irrigation fields of Sianki, These fields were
never used for agriculture. Sand dunes were levelled and ditches were constructed on 2 levels.
Ditches on the upper level received wastewater, while those at the lower level served to drain
treated wastewater. From the upper ditches wastewater was distributed to flood and irrigate
sandy soils covered by grass. The hydraulic load was above 3000 mm per year in I 872,
increasing year after year and ending with 8000 mm per year in 1972. Efficiency of pollution
removal was 80%, The irrigation fields on sandy dunes served well until the 1970s, when the
plant was overloaded, neglected and included into the industrial area of harbour. Fields were
covered by grass monoculture for hay production of couch-grass (Agrophyrum repens). In the
locations of local sedimentation of sewage sludge the monoculture of nettle (Urtica) was
developed. Due to the poor management, more and more wastewater was flowing on the
surface of the fields, instead of infiltrating and percolating through the sandy soil, which
reduced their purification efficiency from 80 to 10%. During the period of 1992-1994 the
plant was closed after 120 years of continuous use.