ENVIRONMENTAL ASSESSMENT OF TOXIC METALS OCCURRENCE IN URBAN SEWAGE SLUDGE FOR ITS POTENTIAL LAND APPLICATION.

The quantity of produced sewage sludge (SS) from wastewater treatment plants (WWTPs) is growing daily and the proper disposal of biosludge became a serious environmental issue worldwide. The socio-economic and legislative criteria have to be taken into consideration in order to proper manage and control the storage of these bio-wastes. One of the proposed solutions in European countries for the management of huge amounts of SS is land application in agriculture and for this purpose, the potentially toxic metal composition of SS should be assessed by employing accurate analytical techniques. In this work a strategy of environmental assessment is presented and a comparison is made for SS originated from WWTPs in Northern Greece serving two large municipalities (Kavala and Drama) as regards the occurrence of potentially toxic elements (PTE), the coefficients of variation of their concentrations during various periods of time and the appropriateness for their use as soil amendment. A comparison is made regarding the toxic metal levels from similar reports for various WWTPs in Greece and other countries in the world with the synthetic results obtained by us (expressed in mg kg-1 dry matter in the form: mean±SD, median and range, respectively): Kavala-Cd 1.46±0.60, 1.24, 0.8-2.5; Cr 40.6±27.7, 32, 14-85; Cu 119.7±37.8, 108, 69-198; Ni 17.9±8.7, 16.1, 8.8-34; Pb 61.0±16.1, 58, 37-96; Zn 978.2±91.8, 994, 810-1095 & Drama-Cd 2.28±1.90, 1.7, 1.3-7.3; Cr 108.9±89.2, 42, 24-239; Cu 126.8±39.5, 122, 53-191; Ni 33.9±18.2, 33, 14-64; Pb 48.1±15.1, 43, 33-74; Zn 1057.6±203.9, 1080, 798-1340. Although the sludge PTE concentration results demonstrate a large variability, the Kavala/Drama coefficients of variations (%) (Cd: 41.3/83.3; Cr: 68.1/81.9; Cu: 31.6/31.2; Ni: 48.3/53.6; Pb:26.3/31.4; Zn:9.4/19.3), are lower than those obtained in other wastewater works. [ABSTRACT FROM AUTHOR]