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
For the pollution load per-capita and day , mean values for Europe are:
Table 6.1: Pollution load per-capita and day (in g)
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)
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)
Pop. Connected to sewers
% tot. pop.***
|Pe from industry connected to sewers
% tot. pe
Total pe to sewers
|* 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:
- 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
discharges by industry
Direct discharges by industry
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
Paper & paper products
Chemical products and refined
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:
- 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