1. Introductory remarks

To gain a full understanding of a wastewater disposal project is it vital to determine the underlying conditions and constraints of the project, against the background of its ecological and economic effects. The project description may be based on the following criteria:

• previous history of the plan.

• water legislation and standards.

• current wastewater situation (wastewater volume, existing works and their function).

• actual condition of the receiving bodies of water (discharge, quality, self-purification capacity, uses etc.).

• target condition of the receiving bodies of water (management aims: ecological function, uses, expansion requirements etc.; quality targets: characteristics, limits).

• previously established wastewater objectives e.g. based on existing general sewerage plans or other evidence of demand.

• incorporation into regional, national and countryside planning objectives and also the regional/supraregional disposal system.

• reasons for choice of planned works and its main components (pumping stations, storm basins, storm overflows, wastewater treatment plant(s), sludge polders etc.).

• alternatives (e.g. sewerage processes such as dual/combined system, wastewater pumping, sludge recycling/storage, extension or expansion of existing works) as well as baseline state.

Further components of the environmental impact assessment of a wastewater disposal project are descriptions of

• the location-finding process for relevant alternatives, including any necessary socio-economic analyses of sex- and group-specific questions of the population settled in the surrounding area or area covered by the wastewater treatment works in question.

• the location comparison and results.
  - the relevant works and their failure risks.

• factors of the project adverse to the environment and those plants or plant components which should eventually form the object of an environmental impact survey.

Major environmental impacts result from the construction and operation of the sewage treatment plants referred to below with minimum size/capacity as follows:

• pumping stations, output Q_p > 4 500 m³/2h¹⁾

• rainwater basins (rainwater retention basins, rainwater overflow basins etc.), dry weather discharge Q_t > 1 500 m³/2h in the sewer before the rainwater basin system

• rainwater overflows, dry weather discharge in the sewer before the overflow Q_t > 1 500 m³/2h

• wastewater treatment plants, which are designed for (see (1)):

Q_in > 1 500 m³/2h1) (intake) or

B_d,x > 3 000 kg/d BOD₅ (org. daily load in intake) or

P_c > 50 000 PE (connected load in population equivalents with a sewage load per inhabitant of 0.060 kg/d)

The above values should be regarded as guideline figures; in addition, the scope of the assessment must be decided on a case-to-case basis, depending on the environmental relevance of the plant components. This applies particularly, for example, to rainwater retention basins which are installed underground and so are "invisible".

Domestic sewage mainly comprises:

• lavatory wastewater

• kitchen wastewater

• wastewater from baths/showers

• cleaning wastewater (from house cleaning).

It therefore has a varied structure, but as a rule its quality is not such that the existence, operation and safety of the sewage plants or the health of the operating personnel could be endangered. Moreover it lacks properties which could result in adverse changes to the environment, provided the sewage works are designed correctly, the bodies of water managed appropriately and the sewage sludges produced disposed of and recycled properly.

However, here one should note that special attention should be paid to the correct operation of "domestic" sewage plants and hence water conservation, if the volume of wastewater is subject to large variations (sudden loads or temporary and sometimes complete absence of wastewater). This applies particularly to hotels, highway service areas, campsites, convalescent homes and similar installations with individual drainage. Special planning and operating methods are required here to prevent avoidable pollution of bodies of water (33), (34).

The following Sections 3.2 to 3.4 therefore deal only with the analysis and evaluation of the environmental impact of commercial or industrial wastewater, primarily as a component of municipal wastewater (indirect discharges) rather than in terms of discharges from commercial and industrial establishments (direct discharges). For guidance, refer to the German regulations.

2. Wastewater collection and removal area

The direct discharge of commercial or industrial wastewater is safe if as a result

a) the health of the staff employed in public sewage works is not adversely affected,

b) the state and operation of public sewage works are not adversely affected,

c) the bodies of water which take the wastewater from the public sewage works cannot be polluted beyond the permitted level or otherwise adversely affected,

d) no lasting odour nuisance occurs at the sewage works and

e) the sludge treatment, sludge recycling and sludge disposal are not seriously hindered.

If adverse effects of the type described above are anticipated, then the discharge of the wastewater into a public sewage works should be conditional on pre-treatment at the point of production or other suitable measures (see German ATV Arbeitsblatt A 115 (35)).

Safety is generally assured if the figures given in Annex I of (35) for the composition and constituents of wastewater are not exceeded. Permissible concentrations of substances not listed in Annex I must be decided on a case-to-case basis.

Substances which block the sewerage network, form poisonous, foul-smelling or explosive vapours and gases or attack buildings and building materials to a significant degree must not be discharged into a public sewage works.

The German ATV Arbeitsblatt A 115 does not yet contain any specific regulations for indirect discharge of hazardous materials within the meaning of 7a WHG (German Federal Water Act (11)), e.g. of certain chlorinated hydrocarbons such as hexachlorobenzene, pentachlorophenol, trichloroethene etc. Basically, 7a WHG and the relevant follow-up regulations of the Federal States required that the state-of-the-art be assessed in order to determine the permissibility of indirect discharge of such substances.

In Germany, the wastewater in question must be monitored and analysed in accordance with the relevant DIN standards (DIN 38400 ff.) (36).

3. Wastewater treatment area

In the Federal Republic of Germany, under 7a WHG (11), binding emission standards for the discharge of wastewater into surface waters are given in the appendices to the "Allgemeine Rahmenverwaltungsvorschrift über Mindestanforderungen an das Einleiten von Abwasser in Gewässer" (General Administrative Framework Regulation on Minimum Requirements for the Discharge of Wastewater into Waters) (12). A summary of the relevant administrative regulations is given in (37).

For discharges from municipal sewage works, the standards are defined in appendix 1 of (12). According to this document, the following limit values apply for different size classes of sewage works in Germany in accordance with the generally recognised rules of the art:

Table 2 - Minimum standards for discharges from municipal sewage works

Size class1)	BOD5 (mg/l)	COD (mg/l)	NH4-N (mg/l)	Ptot(mg/l)
1 (< 60) 2 (> 60 < 300) 3 (> 300 < 1200) 4 (> 1200 < 6000) 5 (> 6000)	40 25 20 20 15	150 110 90 90 75	--- --- 10 10 10	--- --- --- 2 1

1) Figures in brackets: intake values BOD₅ (raw) [kg/d]

With increasing plant size (connected load), the standards become more stringent as a result of the greater operational reliability of the sewage works.

Here too, the monitoring analysis is based on the relevant assessment procedures according to the German DIN standard 38400 (36). The same applies to analysis of wastewater from commercial and industrial establishments. The method and scope of sampling also very largely depend on the relevant administrative regulations.

If it is apparent in a particular case that despite the application of relevant emission standards, an unacceptable burden may be imposed on the bodies of water (insufficient capacity of the receiving water), it may be necessary to lay down stricter standards for the condition of the wastewater to be discharged, if other measures, such as transfer of part of the volume into another river basin, are not possible. As regards discharge monitoring (analysis), the same regulations are to be applied as already mentioned above.

4. Sludge disposal area

The environmental implications of (municipal) sewage sludge are primarily in relation to its disposal in the form of agricultural fertiliser. Important criteria have been defined in Germany under the Klärschlamm-Verordnung (sewage sludge ordinance) (16) which establishes permitted values for the concentrations of selected heavy metals in the soil and in the sewage sludge itself; in addition, restrictions are imposed on the quantities which may be applied. See Table 3 below.

Table 3 - Permitted concentrations of heavy metals in accordance with the Klärschlamm-Verordnung (sewage sludge ordinance)

Heavy metals(HM)	Generally permitted concentrations in sewage sludge	Quantity permitted to be applied	Maximum permitted heavy metal concentration upon application of sewage sludge
	mg/kg1)	t/(ha·3a)1)	g(ha·3a)	g/(ha·3a)
Cadmium Mercury Nickel Lead Chromium Copper Zinc	20 25 200 1200 1200 1200 3000	5 5 5 5 5 5 5	100 125 1000 6000 6000 6000 15000	33.3 41.7 333.3 2000 2000 2000 5000

1) related to dry sludge residue

At least in temperate zones, if the regulations contained in the sewage sludge ordinance are complied with, no long-term harm will be inflicted on soil, plants, animals or humans through the use of sewage sludge in agriculture; moreover, in particular, the health of people or animals will not be harmed by consumption of foodstuffs or fodder produced on land to which the sludge is applied (15).

When actually constructing a sewerage system, it may be advisable to determine the heavy metal concentrations which a sewer network may discharge to the central sewage works so as to ensure that the permissible heavy metal concentrations of the sewage sludge can be maintained in accordance with the sewage sludge ordinance. Suitable procedures are indicated in publication (38).

For the sewage sludge analysis, reference should again be made to the relevant regulations in accordance with DIN 38400 ff. (36).