Polish experience with sewage sludge dewatering in reed systems

Macrophyte plants e.g. reed, cattails, bulrush, can be applied to sewage sludge utilisation. One of the first facilities of this type in the Gdansk region (Northern Poland) was established in Darzlubie in 1995 and primary sludge has been utilised in reed beds there. The objective of the undertaken research was evaluating the influence of sewage sludge storage on its chemical and biological properties. A total of 5.5 m thick layer of primary, anaerobically stabilised sludge (moisture 90-96%) was loaded to the reed bed during 6 years of operation. As a consequence of dewatering and biochemical transformation, the sludge layer decreased to 30 cm. Moisture, organic matter, total nitrogen and total phosphorus contents, as well as coli index, Clostridium perfringens index and the number of Ascaris lumbricoides ova were measured. Also the contents of heavy metals (Cu, Pb, Zn, Ni, Cr and Cd) were determined in sludge samples. The study showed that sludge storage in reed beds results in dewatering and partial stabilisation. In the reed lagoons in Swarzewo and Zambrow, dewatering of secondary sludges was investigated. The results of measurements of the quality of sludge and effluent from the reed lagoon in Zambrow are also presented.