Oxygen-demanding substances and nutrients in wastewater at Dutch urban wastewater treatment plants, 1981-2001

The amount of substances and nutrients in the effluent from wastewater treatment plants has fallen considerably since 1985, mainly due to improvements in the efficiency of the plants.

		1981	1985	1990	1995	1999	2000	2001
		million kg
Influent	COD	695	800	933	921	915	921	937
(= inflow)	BOD	285	304	349	331	346	354	354
	Total N	61	70	81	84	88	85	85
	Total P	17.5	18.6	14.2	13.8	13.3	13.3	13.8
Effluent	COD	145	134	131	100	98	91	94
(= outflow)	BOD	40	29	24	13	14	11	12
	Total N	33	38	39	36	31	29	30
	Total P	10	11	6.2	3.5	3.0	2.8	2.9
		%
Treatment	COD	79	81	85	89	89	90	90
efficiency	BOD	87	88	92	96	96	97	97
	Total N	45	46	52	57	64	66	65
	Total P	36	39	56	74	77	79	79
Source: CBS (2003).						CBS/EDC/June03/0152
BOD: Biochemical Oxygen Demand COD: Chemical Oxygen Demand

Fall in burden on surface water

Between 1985 and 2001 there was a fall of more than 75% in the phosphorus load on surface water from UWWTP effluent. This is a result of the introduction of phosphate-free washing powders and improved phosphate removal during the wastewater treatment process. A start is now being made on far-reaching measures for nitrogen removal. The objective is to achieve treatment efficiency for the country as a whole of 75% in 2005 (2001: 65%). Better wastewater treatment processes have improved treatment efficiency for oxygen-demanding substances.

• Discharges into water and burden on surface water in the Netherlands, 1990, 1995, 1999 and 2000
• Capacity of wastewater treatment plants, 1980-2001

Terminology

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 (CBS, 2003).

• The Biochemical Oxygen Demand (BOD) indicates how many kilogrammes of oxygen are needed for the bacterial breakdown of organic - as well as certain inorganic - pollutants in wastewater.
• The Chemical Oxygen Demand (COD) shows how much oxygen is needed for the complete chemical breakdown of these compounds. The table includes the annual amounts of oxygen required for both parameters. As concentrations, both parameters are measures for the level of contamination of the wastewater.
• The pollution value (expressed as inhabitant equivalents) is the quantity of oxygen-demanding substances for which the oxygen demand in aerobic degradation equals that of the wastewater of one inhabitant per day.

References

• CBS (2003). Statline. Zuivering van afvalwater. Statistics Netherlands, Voorburg/Heerlen.
• Lievense, A., R.H. Huwaë and C.M. Baas (2000). Verwijdering van stikstof en fosfor op rioolwaterzuiveringsinrichtingen 1998. Kwartaalbericht Milieustatistieken 2000/3. Statistics Netherlands, Voorburg/Heerlen.

Relevant sections and indicators in the Environmental Data Compendium

• Guide to societal developments relating to Actors in the water chain
• Discharges into water and burden on surface water in the Netherlands, 1990, 1995, 1999 and 2000
• Guide to Environmental theme of Eutrophication

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).