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United Nations Environment Programme
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Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>

6.1 Wastewater characteristics (Topic a)

The characteristics of wastewater and stormwater in Europe has been recorded extensively in the literature. EUROSTAT, the Statistical Office of the European Communities is now in the process of assembling additional information from countries with a particular focus on volumes, characteristics and loads, and the degree of treatment. Sources in addition to the domestic sector include agriculture, mining, manufacturing industries (e.g. metals, transport equipment, textiles, paper and paper products, chemicals products and refined petroleum), energy, and construction.

For the domestic (sanitary) sewage, the most convenient source of reference on wastewater characteristics in Europe is Imhoff's "pocket" - book which is now in its twenty-sixth edition (Imhoff 1985). Imhoff has recorded mean values in Europe since the beginning of the Century and provided generations of European engineers with the basic information they need to study the characteristics of wastewater in a specific circumstance taking into account variations in living conditions, indirect discharges of industrial and commercial wastewater (including cooling water), infiltration of groundwater and discharges of surface water into sewer networks, and both diurnal and seasonal fluctuation. Of course, a basic variable is the amount of water consumed (in households) and the amount of human waste carried away.

As a general guideline, the mean flow of sanitary sewage in Europe is generally assumed to be 200 liters per-capita and day not counting any of the other inflows listed above (Imhoff, 1985). In larger cities, this figure tends to be higher. However, this amount is not used as a design criteria for specific projects it serves as a general guideline but for each individual case, careful measurements and/or an estimation is carried out before a project can be planned.

For the pollution load per-capita and day , mean values for Europe are:

Table 6.1: Pollution load per-capita and day (in g)

Parameter mineral organic total BOD

settleable solids
Non-settleable solids
Dissolved solids

20
5
75
30
10
50
50
15
125
20
10
30
Total 100 90 190 60
Source: Imhoff, 1985

Based on an assumed per-capita daily flow of 200 liters, the average strength of sewage in Europe is accordingly:

Table 6.2: Average strength of sewage in Europe (in m/L)

Parameter mineral organic total BOD

Settleable solids
Non-settleable solids
Dissolved solids

100
25
375
150
50
250
250
50
150
100
50
150
Total 500 450 950 300
Source: Imhoff, 1985

Other average values have been determined for European conditions with respect of daily peak flows and seasonal fluctuations but are recorded here since they are not intended, nor used, for planning and design. As pointed out before, planning and design are always based on prior study of the quantity and quality of the sewage produced in the given location; the averages quoted above are intended to indicate the likely order of magnitude and guide the specialist in the planning of the study.

Western Europe is one of the most highly and most densely industrialized regions of the world and the variety of industrial wastewater discharged into the environment either directly or indirectly via municipal sewers is very great The quantity and quality of the wastewater is normally expressed per ton of raw material processed or per ton of finished product though are often converted to person equivalents (pe) on the basis of BOD. Variations are very great both as regards quantity and quality depending on the type of industry but also the process applied by each individual enterprise of an industrial sector: variations of between 2 to 5, or even 10 are common.

Table 6.3 exhibits information on the discharges from households and industry. The most representative sample are the so-called EU10 countries which have a population of 333.6 million or 90% of the population of the EU population. They comprise Germany (DE), Spain (ES), France (FR), Greece (GR), Italy (IT), Luxembourg (LU), The Netherlands (NL), Portugal (PT), Finland (FI) and the United Kingdom (UK). Table 5 shows that in the terms of person equivalents, the distribution of wastewater from sewered household and industry is as follows:

  • Sewered households: 269.8 million pe or 57.3% of the total load discharged into/via public sewerage systems by households and industry. This represents 36.6% of the total combined domestic and industrial load of 738.4 million pe.
  • Industry discharges a total of 468.6 million pe. This represents 63.4% of the combined domestic and industrial load.
  • Indirect discharges by industry: 201.5 million pe or 43.7% of the total load discharged into/via public sewerage systems by households and industry.
  • Indirect discharges by industry: 267.1 million pe or 43%% of the total load of 468.6 million pe discharged by industry.

Table 6.3: Domestic and industrial discharges in EU10 countries (in million pe)

  DE ES FR GR IT LU NL PT FI UK EU10 AT* BE** DK IR* SE*
Total population 81.6 38.5 57 10.5 56.8 0.42 15.4 10.8 5.1 57.5 333.6 7.9 10.1 5.1 3.5 8.8

Pop. Connected to sewers
 
% tot. pop.***

75.2
 
92%
31.6
 
82%
29
 
51%
6.1
 
58%
46.8
 
82%
0.415
 
99%
15
 
97%
6.2
 
57%
4
 
78%
55.5
 
97%
269.8
 
81%
5.9
 
75%
  4.6
 
90%
2.4
 
68%
7.7
 
88%
Pe from industry connected to sewers
% tot. pe
47.5
 
39%
46.6
 
60%
19.5
 
40%
2
 
25%
48
 
51%
0.2
 
33%
9
 
38%
4.7
 
43%
1.5
 
27%
22.5
 
29%
201.5
 
43%
    3.9
 
46%
   

Total pe to sewers
 

122.7
 
78.2
 
48.5
 
8.1
 
94.8
 
0.615
 
24
 
10.9
 
5.5
 
78
 
471.2
 
    8.5
 
   
* Inhabitants (not person equivalents) - missing industrial discharge. ** no data for Belgium. *** Some of this information is at variance with Table 9 for statistical reasons.
Source: EEA, 1999

As referred to above, 43.7% of the industrial wastewater load is discharge indirectly in Western Europe. In Section 6.7.1, some of the requirements are listed which must be met. Of paramount importance is that the public sewers and treatment processes are not damaged by the industrial wastewater. In general, the following need particular attention:

  • Temperature.
  • pH-value.
  • BOD/COD.
  • Sludge.
  • Ammonium-nitrogen and phosphorus.
  • Chemicals, especially lead, cadmium, chromium, copper, nickel, mercury, and the halogenated hydrocarbons.
  • Volatile compounds.
  • Petroleum products.

EURPSTAT is in the process of collecting information from EU Member States as regards the volumes of wastewater discharged in Western Europe (in m/day) and the load effected by the discharge on the river systems in the region (in 1000 kg/day). This information, which will become available sometime in the near future, will, inter alia, include the type of data exhibited in Tables 6.4 and 6.5.

Table 6.4: Information assembled by EUROSTAT on volume (m/day), and organic and nutrient loads (1000 kg/day) discharged by the domestic and industrial sectors (selected items)

Type of discharge

Items recorded

Domestic sector
Indirect discharges by industry
Direct discharges by industry

Volume
BOD
Total nitrogen & phosphorus

As regards industrial wastewater, the discharges of heavy metals shown in Table 6.5 are of particular interest.

Table 6.5: Information assembled by EUROSTAT on heavy metals discharged by industrial sectors in 1000 Kg/day (selected items)

Industrial sectors, e.g.

Heavy metals, e.g.

Mining and quarrying
Food processing
Textiles
Paper & paper products
Chemical products and refined
Petroleum

Cd
Cr
Cu
Hg
Ni
Pb

The effects of the amounts and pollution discharged into the rivers and lakes of Western Europe, and ultimately into the sea have been recorded in the two Assessments referred to in Section 6.0.2, and, more thoroughly, the report on Environment in the European Union at the turn of the Century (EEA 1999). Health effects may be caused where water is abstracted for drinking water supplies from polluted groundwater and surface water, the latter especially along the river Rhine. Polluted beaches in all countries of the region are also responsible for health effects. Effects on agriculture are likely, especially in the South of Western Europe; however, ecological effects are more widespread.

The following are but some of the effects reported by the EEA:

  • Organic pollution: From the 1940s onward, the discharge of organic waste has increased but over the past 15 to 30 years, biological treatment of wastewater and radically reduces discharges of oxygen consuming substances from some industries (mainly pulp and paper) have brought down pollution in parts of Europe. Many rivers are now well oxygenated. Information from about 1000 river sites across Europe shows that in mid-1960s, 35% of the sites had an annual average concentration of organic pollution of below 2 mg/L BOD while 11% were heavily polluted with levels greater than 5 mg/L BOD. Now, 6% of the river sites show heavy pollution. In the river Rhine, the concentration of oxygen has increased from an annual average value of around 5 mg/L in the 1970s to current values around 10 mg/L. Figure 6.1 exhibits percent information for rivers with a BOD of more the 5 mg/L, separately for the EU countries in the North, West and South, on the one hand, and, on the other hand, for Eastern Europe. The backlog existing in Eastern Europe is noticeable.

Figure 6.1: Percentage of rivers with a BOD higher than 5 mg/L in the EU (North, West and South) and in Eastern Europe Source: EEA, 1999

  • Nitrate: Nitrates are considered a health problem if occurring at levels above 50 mg/L. In EU countries, the Drinking-Water Directive establishes a guide level of 25 mg./L. Actual levels in many private wells used for drinking water supply are above that level (up to around 30%, in some countries). Reductions can only be achieved if the nitrogen load from agriculture is substantially reduced. In European rives, mean nitrate concentrations in 68% river stations exceeded 1 mg/L. There is no overall indication that the reduced application of nitrogen fertilizer has resulted in lower levels in the 1990s. The impact of nitrate is more significant in coastal and marine water than in rivers. There is increased growth of macrophytes and mass occurrence of filamentous algae and phytoplankton leading to oxygen depletion and kills of animal life.
  • Phosphorous: Information from about 1000 river stations in Europe shows that 90% had a mean concentration of total phosphorous exceeding 50 mg/L which is more than twice the concentration in waters not affected by human activity. The same situation excists in many of the lakes. Decreases in concentration took place during the 1980s and 90s as a result of improved wastewater treatment and reduced content of phosphorous in detergents but in the future, phosphorous discharges from diffused sources may need to be addressed as well.
  • Ecological impact: Oxygen depletion by organic pollution has a strong impact on riverain fauna. After ecological impact has been considerable, improvements have been registered during the past 15 years. Today, most of the countries of the region classify 80% to 95% of the river stretches as having good to fair ecological quality. Rivers with poor or bad quality are generally polluted by wastewater discharges and are in regions of high population density and intensive farming.

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