3. Results and discussion
3.1 Concentrations of Heavy Metals Contained in Sludge
The sludge collected from Fu-Tien Water Resources Recovery Center contains on average 76% water
content. Analyses of metals contained in the dry sludge are shown in Figure 1. Among these metals,
concentrations of Ni and Cd vary over a wide range. The current limitations on metals contained in farm land
are 200 mg/kg for Cu, 250 mg/kg for Cr, 5 mg/kg for Cd, 500 mg/kg for lead, 200 mg/kg for Ni and 600
mg/kg for Zn in Taiwan. Hence, Cu and Zn contained in all sludge samples have concentrations exceeding the
limitations. All sludge samples contain Zn twice the legal limitation of Zn in soil; half of the samples contain
Ni exceeding the limitation. Cd is the easiest among all metals to be absorbed by plants; rice plant has a
specially capability of absorbing Cd from soil. Although Cd has the lowest concentration in sludge, for some
of the sludge samples, Cd exceeds the limitation. The analysis results show that applying the domestic sludge
on farm land for growing crops has a potential risk of contaminating the soil.