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.

Discharges into water and burden on surface water in the Netherlands, 1990, 1995, 1999 and 2000

Technical note

The influent is the incoming wastewater; the effluent is the treated wastewater that is discharged to surface water.

The figures shown for treatment efficiency are weighted averages for all types of wastewater treatment plant. Inaccuracies in the measurements associated with detection thresholds can lead to fluctuations in the loads and efficiencies, especially for cadmium, mercury and arsenic.

References

CBS (2003). Statline. Zuivering van afvalwater. Statistics Netherlands, Voorburg/Heerlen.

Relevant sections and indicators in the Environmental Data Compendium

Relevant information outside of the Environmental Data Compendium

More information about the discharge of oxygen-demanding substances and the burden on surface water can be found on Statline (Statistics Netherlands).