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1.1 Definitions
1.2 Problems
1.3 Objectives
1.4 Stages of wastewater disposal
2. Environmental impacts and protective measures
2.1 Introductory notes
2.2 Typical environmental impact
2.2.1 Impact of wastewater collection and removal
2.2.2 Impact of wastewater treatment
2.2.3 Impact of disposal of faecal matter
2.2.4 Impact of wastewater discharge
2.2.5 Impact of sludge disposal
2.3 Avoidance and safety measures
2.3.1 Wastewater avoidance
2.3.2 Safety measures
2.3.2.1 Introductory notes
2.3.2.2 Safety measures in wastewater collection and disposal
2.3.2.3 Safety measures in wastewater treatment
2.3.2.4 Safety measures in sludge disposal
3. Notes on the analysis and evaluation of environmental impacts
3.1 Introductory remarks
3.2 "Wastewater collection and removal" area
3.3 "Wastewater treatment" area
3.4 "Sludge disposal" area
4. Interaction with other sectors
5. Summary assessment of environmental relevance
1.1 Definitions
Wastewater is water whose properties have been changed by domestic, industrial, agricultural or other use and water (sewage) discharged with it during dry weather as well as the run-off and collected water (rainwater) from built-up or paved areas due to rainfall. Sewage also includes the liquids discharged and collected from waste treatment and storage plants.
Community water management, a division of water resources management, comprises the sum of all targeted environmental-protection measures to supply communities, trade and industry with satisfactory drinking or industrial water as well as the disposal of domestic, commercial and industrial wastewater from these areas.
Wastewater disposal, a division of community water management, essentially comprises the collection, removal, treatment and disposal of wastewater.
The generally accepted rules of the art comprise those rules which have been tested in practical applications, such that the majority of the people working in this specialist field regard the processes, plant, facilities or operating methods in question as correct (3). The technical nature of the rules may vary according to the requirements in individual countries.
The state of the art is the state of development of advanced processes, plant, facilities or operating methods, guaranteeing the practical suitability of such technical measures. To determine the state of the art, an assessment must be made in particular of comparable processes, plant, facilities or operating methods which have been successfully tested in operation (4). The technical nature of the state of the art may vary according to the requirements in individual countries.
1.2 Problems
The world-wide industrial development of recent decades, with its effects on the manufacture of goods and on the consumption patterns and health habits of the population, has led to an appreciable increase in the volume of wastewater. In this respect, targeted wastewater disposal (WWD), involving careful analysis and taking into account not only the local conditions and options but also the environmental aspects of the relevant plant, can bring about the necessary improvements. As a rule, these relate to measures not only in the fields of wastewater technology, but also in the fields of law, administration, business management and organisation.
The necessary improvements should also aim to achieve reasonable representation for women, as one of the target groups, in the institutions and bodies responsible for wastewater disposal. This is the best way to guarantee that their legitimate interest in participating in the development and implementation of administrative, business and environmental monitoring regulations will be served.
1.3 Objectives
The controlled disposal of sewage and rainwater forms a vital part of the infrastructure of human settlements built on principles of hygiene and hence is fundamental to efforts to improve the quality of life. Furthermore it is an essential component of water quality management, whose aim should be:
- to maintain the ecological equilibrium of
bodies of water and - where it has been disturbed - to restore it
- to ensure a water supply of guaranteed quantity and quality for
the general public as well as for trade and industry - with
particular emphasis on long-term sustainability - and
- to enable all other water uses which serve both the well-being
of the general public and the legitimate needs of individuals in
the long term (5).
Figures show that in many countries there is a marked imbalance between water supply and wastewater disposal. This is because, in the countries in question, clear priority has been given to the matter of water supply, without paying at least equal attention to the necessary development of wastewater disposal facilities. The same also applies to the relationship between water supply and wastewater disposal in commercial and industrial establishments.
Within this environmental brief, questions of municipal wastewater disposal also take high priority. Questions of commercial and industrial wastewater disposal - in view of their complexity and scope - can only be dealt with selectively.
1.4 Stages of wastewater disposal
The area of municipal wastewater disposal may in particular comprise the following disposal stages:
- wastewater collection
- wastewater removal
- wastewater treatment
- wastewater discharge
- disposal of faecal matter (from latrines and similar installations)
- sludge treatment.
The disposal stages mentioned may refer both to sewage (domestic, trade, industrial) and to rainwater. In this respect one should not forget percolating water, which includes e.g. groundwater which penetrates sewers through leaks, or drainage water which results from groundwater lowering and is removed via the drainage network.
In the individual disposal stages the following wastewater processes take place:
- wastewater collection: collection of wastewater at source using connection, down and soil pipes as well as by wastewater collection pits, cesspits, latrines etc.
- wastewater removal: conveying of wastewater through sewers (in the case of rainwater also through open channels) using separate, combined or sewage-only systems (the latter without central removal of rainwater).
- wastewater treatment: application of physical, biological (aerobic or anaerobic) and chemical processes with the aim of minimising the substances contained in the wastewater which are harmful to the environment, and in particular to water, or of reducing their harmful effect to the necessary degree.
- wastewater discharge: return of the wastewater (usually after treatment) to the natural water cycle (e.g. using clarification basin overflows for counter-overflow basins in the combined system, rainwater overflows in separate systems or effluent channels in sewage treatment works).
- sludge treatment: processing sludge for recycling or disposal (see DIN 4045, (6)).
The environmental impact of the disposal stages described should first be considered individually in order to assess their importance. An integrated assessment, also taking into account any significant interactions, should then be carried out for the project.
In the case of commercial and industrial wastewater disposal, one should proceed in a similar way on the basis of the above-mentioned disposal stages, for both directly discharging and indirectly discharging wastewater producers. However, there is one further decisive disposal stage which must be considered first, namely the stage involving the avoidance or reduction of wastewater, taking into account the quantity (volumetric flow) and the pollutant load (mass flow). In this respect questions of the material input of production as well as that of production itself, i.e. its process-side, are particularly important.