Table 7.
Heavy metal concentrations in individual fractions of sewage sludge.
| Metal | Fraction | S1 | S2 | S3 | S4 | S5 | S6 | S7 |
|---|---|---|---|---|---|---|---|---|
| mg·kg−1DM | ||||||||
| Cd | F1 | BDL | BDL | BDL | BDL | BDL | BDL | BDL |
| F2 | 0.9 ± 0.0 | 1.1 ± 0.0 | 1.2 ± 0.1 | 0.9 ± 0.1 | 1.1 ± 0.0 | 1.3 ± 0.0 | 1.1 ± 0.1 | |
| F3 | 1.2 ± 0.3 | 1.1 ± 0.2 | 1.2 ± 0.1 | 1.3 ± 0.1 | 1.1 ± 0.3 | 1.9 ± 0.1 | 2.2 ± 0.2 | |
| F4 | 0.8 ± 0.1 | BDL | 1.1 ± 0.4 | 1.4 ± 0.2 | 0.7 ± 0.0 | 1.8 ± 0.0 | 1.5 ± 0.1 | |
| R, % | 106.8 | 124.4 | 112.2 | 114.1 | 126.7 | 123.6 | 119.2 | |
| Cr | F1 | BDL | BDL | BDL | BDL | 0.6 ± 0.0 | BDL | 1.2 ± 0.0 |
| F2 | BDL | BDL | BDL | BDL | BDL | BDL | BDL | |
| F3 | 19.7 ± 8.2 | 17.0 ± 4.5 | 23.5 ± 1.4 | 22.1 ± 0.4 | 17.7 ± 1.6 | 25.2 ± 0.5 | 25.5 ± 0.7 | |
| F4 | 16.0 ± 0.6 | 8.0 ± 0.8 | 15.3 ± 1.3 | 19.0 ± 2.6 | 12.6 ± 0.5 | 24.8 ± 0.7 | 22.2 ± 0.2 | |
| R, % | 62.3 | 71.6 | 70.9 | 65.5 | 58.0 | 73.3 | 73.0 | |
| Cu | F1 | 0.7 ± 0.1 | 2.3 ± 0.1 | 0.8 ± 0.1 | 0.9 ± 0.0 | 1.9 ± 0.0 | 0.5 ± 0.1 | 1.4 ± 0.1 |
| F2 | 4.8 ± 1.2 | 6.9 ± 2.4 | 1.6 ± 0.2 | 1.1 ± 0.1 | 3.5 ± 05 | 0.7 ± 0.1 | 1.7 ± 0.1 | |
| F3 | 118.3 ± 30.4 | 110.8 ± 23.1 | 141.1 ± 7.0 | 151.7 ± 5.6 | 126.9 ± 14.8 | 210.5 ± 3.8 | 198.8 ± 6.3 | |
| F4 | 13.4 ± 2.1 | 4.9 ± 0.5 | 11.1 ± 1.6 | 12.1 ± 0.4 | 7.6 ± 0.5 | 16.5 ± 0.4 | 14.5 ± 0.5 | |
| R; % | 110.9 | 120.0 | 111.8 | 116.0 | 118.8 | 120.8 | 111.5 | |
| Ni | F1 | 5.4 ± 0.2 | 5.4 ± 0.2 | 5.8 ± 0.9 | 5.6 ± 0.2 | 7.6 ± 0.1 | 9.4 ± 0.0 | 11.2 ± 0.1 |
| F2 | 3.6 ± 0.1 | 1.8 ± 0.0 | 3.7 ± 0.2 | 3.6 ± 0.2 | 2.6 ± 0.1 | 4.7 ± 0.1 | 2.9 ± 0.0 | |
| F3 | 8.3 ± 8.9 | 4.2 ± 2.8 | 8.2 ± 1.1 | 9.5 ± 0.1 | 3.7 ± 0.1 | 7.3 ± 0.3 | 7.1 ± 0.4 | |
| F4 | 13.9 ± 1.1 | 10.9 ± 4.0 | 13.2 ± 2.3 | 15.2 ± 3.3 | 11.1 ± 0.4 | 19.1 ± 2.4 | 18.0 ± 0.8 | |
| R; % | 56.9 | 43.7 | 49.9 | 52.9 | 42.5 | 41.4 | 41.1 | |
| Pb | F1 | BDL | BDL | BDL | 1.1 ± 0.7 | BDL | BDL | BDL |
| F2 | BDL | 1.2 ± 0.1 | BDL | BDL | BDL | BDL | BDL | |
| F3 | 18.0 ± 14.8 | 19.5 ± 10.0 | 7.9 ± 1.0 | 3.8 ± 0.3 | 10.2 ± 0.6 | 13.3 ± 0.4 | 19.4 ± 1.0 | |
| F4 | 65.3 ± 4.8 | 24.3 ± 2.0 | 74.5 ± 10.7 | 80.3 ± 14.2 | 52.8 ± 4.9 | 107.9 ± 1.1 | 93.9 ± 5.5 | |
| R; % | 67.4 | 46.1 | 59.5 | 60.4 | 50.9 | 64.1 | 60.3 | |
| Zn | F1 | 123.0 ± 6.6 | 308.1 ± 10.2 | 137.4 ± 17.0 | 94.1 ± 4.8 | 220.9 ± 3.5 | 230.5 ± 7.4 | 252.5 ± 4.9 |
| F2 | 538.1 ± 11.3 | 334.2 ± 10.8 | 555.6 ± 23.1 | 568.9 ± 20.6 | 482.1 ± 15.4 | 600.5 ± 6.7 | 545.1 ± 10.4 | |
| F3 | 304.7 ± 187.2 | 256.2 ± 135.0 | 377.3 ± 28.8 | 455.6 ± 34.6 | 285.5 ± 30.9 | 560.1 ± 20.3 | 571.3 ± 44.2 | |
| F4 | 57.5 ± 6.7 | 14.3 ± 2.5 | 59.1 ± 10.0 | 70.0 ± 12.2 | 34.6 ± 3.0 | 96.5 ± 1.9 | 81.8 ± 3.2 | |
| R; % | 71.6 | 83.6 | 68.8 | 76.3 | 72.7 | 80.5 | 78.3 | |
Results are expressed as the mean ± standard deviation in mg kg−1 of dry matter; R—heavy metal recovery rate calculated by comparing the sum of the four fractions with the total concentrations of heavy metals in the sludge samples; BDL—below detection limit.