Heavy metals in wastewater at Dutch UWWTPs, 1981-2001
Compared to 1985, emissions in effluent at wastewater treatment plants have been cut back considerably for most metals.
| Cadmium | Chromium | Copper | Mercury | Lead | Nickel | Zinc | Arsenic | |
| 1 000 kg | ||||||||
| In influent 1) | ||||||||
| 1981 | 2.7 | 64 | 132 | 0.9 | 141 | 49 | 470 | 2.4 |
| 1985 | 2.4 | 54 | 160 | 0.8 | 144 | 43 | 510 | 3.3 |
| 1990 | 2.0 | 39 | 177 | 1.0 | 96 | 33 | 497 | 4.9 |
| 1995 | 1.5 | 32 | 189 | 0.7 | 81 | 31 | 451 | 5.6 |
| 1999 | 1.0 | 21 | 166 | 0.5 | 56 | 32 | 464 | 6.0 |
| 2000 | 1.0 | 21 | 158 | 0.5 | 53 | 26 | 403 | 5.7 |
| 2001 | 1.0 | 20 | 153 | 0.5 | 58 | 25 | 461 | 6.4 |
| In effluent 1) | ||||||||
| 1981 | 1.1 | 26 | 40 | 0.3 | 57 | 35 | 141 | 1.2 |
| 1985 | 1.0 | 22 | 48 | 0.2 | 58 | 30 | 153 | 1.7 |
| 1990 | 0.8 | 13 | 36 | 0.3 | 25 | 19 | 140 | 2.5 |
| 1995 | 0.4 | 7 | 23 | 0.2 | 10 | 13 | 124 | 2.6 |
| 1999 | 0.4 | 6 | 20 | 0.2 | 9 | 16 | 114 | 3.0 |
| 2000 | 0.4 | 6 | 18 | 0.1 | 10 | 13 | 110 | 2.8 |
| 2001 | 0.4 | 5 | 21 | 0.1 | 13 | 14 | 109 | 3.1 |
| % | ||||||||
| Treatment efficiency | ||||||||
| 1981 | 60 | 60 | 70 | 70 | 60 | 30 | 70 | 50 |
| 1985 | 60 | 60 | 70 | 70 | 60 | 30 | 70 | 50 |
| 1990 | 60 | 66 | 79 | 70 | 74 | 40 | 72 | 50 |
| 1995 | 76 | 79 | 88 | 75 | 87 | 57 | 73 | 53 |
| 1999 | 59 | 69 | 88 | 70 | 85 | 49 | 76 | 51 |
| 2000 | 59 | 73 | 88 | 71 | 82 | 49 | 73 | 51 |
| 2001 | 60 | 74 | 86 | 71 | 78 | 44 | 76 | 52 |
| Source: CBS (2003). | CBS/EDC/June03/0153 | |||||||
| 1) Figures for 1981-1992 are based on the loads in the sludge and on the following assumed treatment efficiencies: copper, mercury and zinc: 70%; cadmium, chromium and lead: 60%; arsenic: 50%; nickel: 30% (CUWVO, 1986). Figures for 1993-2001 are based in part on influent and effluent measurements. | ||||||||
Developments
Despite the increased inflow of wastewater to urban wastewater treatment plants (UWWTPs), the inflow of most metals through the influent and their emission through the effluent are much lower than in 1985. The falls in cadmium, mercury, chromium and nickel are mainly due to clean-up measures at industrial sources. The introduction of lead-free petrol has substantially reduced lead run-off from roads to the sewer system. The inflow of copper and zinc has also fallen slightly. A specific source-based approach to these metals is now in place with a view to reducing the inflow still further. Improved treatment efficiencies have already led to major reductions in discharges in effluent. The higher efficiencies are presumed to be the result of the fact that the residence time for wastewater is longer in the current generation of wastewater treatment plants. This allows the metals to adsorb better to the sewage sludge. There have also been major reductions in total discharges to water.
