EFFECT OF WASTE-WATER SLUDGE ON GROWTH AND HEAVY-METAL BIOACCUMULATION OF 2 SALIX SPECIES

Fast-growing tree species, such as willows, can benefit from sludge ap plication. While sludges are good fertilizers, they may contain heavy metals which could reduce productivity and cause environment risks. Th e aims of the present research were to: i) determine the biomass produ ction of Salix discolor Muhl. and Salix viminalis L. when supplied wit h various amounts of dried and pelleted sludge and ii) assess the upta ke and accumulation of heavy metals. Trials were carried out using unr ooted cuttings that were planted in large plastic pots containing sand y soil and grown outdoors for a 20-week period. Five doses of sludge w ere applied: the equivalents of 0 (T0), 40 (T1), 80 (T2), 120 (T3), 16 0 (T4) and 200 (T5) kg ''available'' N ha(-1). Trees which received th e highest dosage of sludge showed the best growth. Stem biomass was si gnificantly greater for S. viminalis which had received sludge treatme nts. The relationship between the total biomass yield Y (g) and the ra te of fertilization X (equivalent to kg of ''available'' nitrogen prov ided per hectare) is linear. Regression equations of predicted biomass production were established as follows: S. discolor, Y = 28.36 + 0.56 X and S. viminalis, Y = 39.95 + 0.64X. For both species, the greatest stem biomass per g of N applied was produced with treatments 4 and 5. Amounts of nitrogen per leaf area (N/LA) and per dry leaf mass (N/DL) were higher for S. viminalis. The metal transfer coefficient did not v ary between the species but was significantly different for Cd and Zn. Plants were able to absorb Cd and Zn, but were less able to absorb Ni , Hg, Cu, and Pb. It was concluded that the dried and pelleted sludge is a good fertilizer. S. discolor and particularly S. viminalis can be used as filters for the purification of wastewater sludge as well as for biomass production purposes.