A six-month experimental study was conducted to evaluate the agricultural use of the sludge produced at Psyttalia after completion of secondary biological treatment. Based on the results obtained from a bench scale activated sludge system the average biological sludge production for the year 2000, is estimated to be approximately 111 tn DS/day. Using the values of heavy metals measured in Psyttalia primary dewatered sludge and in the biological sludge obtained from the laboratory scale unit, the approximate heavy metal concentrations of the sludge produced in Psyttalia after the construction of the Biological Treatment Plant were determined: 327 mgCu/kg DS, 4140 mgZn/kg DS, 981 mgCr/kg DS, 264 mgPb/kg DS, 228 mgNi/kg DS, 1.6 mgCd/kg DS and 7 mgHg/kg DS. According to the above results the use of sludge in agriculture is unfeasible at present given the high zinc concentrations that exceed EC Regulations, but also considering the high concentrations of other heavy metals that exceed the more stringent regulations of several European countries.

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