PHYTOREMEDIATION OF A SLUDGE DEPOZIT PROCEEDED FROM A CITY WASTEWATER TREATMENT PLANT

It is presented the possibility to reduce contents of heavy metals (cadmium, zinc) in a sludge proceeded from the wastewater treatment plant of Iasi Municipality. The sludge was deposited, for over 10 years, in a mud pond with a surface about 15 ha, placed on a calcareous and salinised alluvial soil. For this purpose, it is proposed using the spontaneous flora, which has been settled in a period of four years after closure of the deposit. The flora has been predominantly composed of Phragmytes australis, and also other species such as Rumex acetosela, Chenopodium album, Aster panonicum, Solanum nigrum and others. These plants accumulated in their roots and in the aerial part cadmium (Cd) quantities, which exceed up to 60, respectively 14 times the normal values. Similarly, zinc (Zn) has been concentrated in the roots and aerial parts 33 times, 18 times respectively. The transfer (TF) and bioaccumulation (BAF) factors' values highlight the plants' feature to accumulate heavy metals from the sludge. The plants can be arranged in a decreasing series of the accumulated heavy metals (cadmium, copper, lead, zinc), thus Rumex acetosela, Solanum nigrum, Chenopodium album, Aster panonicum and Phragmytes australis. Applying phytoextraction of polluting heavy metals only by annual harvesting of aerial part of the spontaneous flora now existing, will bring the sewage sludge to a normal content level of these heavy metals in a period of up to 450 years. If the harvest will include also the roots, the time necessary to decontaminate the sludge could be reduced with 50-60 %. In addition, the change of floristic composition so that Rumex and Solanum genus are becoming dominant, could lead to a significant reducing of phytoremediation period.