HEAVY-METALS IN WASTE-WATER TREATMENT-PLANT SLUDGES IN THE CZECH REPUBLIC

Since 1987 operators of municipal wastewater treatment plants, having the population equivalent over 5 000, monitor systematically heavy metals in sludges, based on one or two samplings on the average annually. Generally, Cd, Cr, Cu, Ni, Pb and Zn are monitored: since 1989 Hg is becoming the centre of systematic attention. Occasional data are available on concentrated Ag, Co, As and Mo. These data were collected and ordered by the authors of the paper. On their basis lines of exceedance were plotted and sets were prepared, characterizing both localities with the common level of the sludge contamination, and with the extremely low contamination. level reflecting the condition that could be achieved if measures limiting the heavy metal input into public sewerage systems were adopted. The results achieved were compared with heavy metal concentration limits, as determined in the Industrial composts standard,both for raw materials used for the compost production, and for composts of Ist and IInd grades. With a view to the general environmental contamination, and considering the present economic and agricultural use, the input raw materials should meet the demands that are required under the standard for the prepared composts.