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GERMAN ATV RULES AND STANDARDS
W A S T E W A T E R - W A S T E
STANDARD ATV A 200E
Principles for the Disposal of Wastewater in Rurally Structured Areas
May 1997 ISBN 3-934984-32 0
Marketing: Gesellschaft zur Förderung der Abwassertechnik e.V. (GFA) Theodor-Heuß-Allee 17 D-53773 Hennef Postfach 11 65 . 53758 Hennef
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This ATV Standard has been produced by ATV Working Groups 1.2.7 "Wastewater Discharge in the Rural Area" and 2.10.2 "Wastewater Treatment in the Rural Area". Members are: Working Group 1.2.7 Dipl.-Ing. Riedl, München (Chairman)
Dipl.-Ing. Coppik, Mainz Dipl.-Ing. Kobrow, Düsseldorf Dipl.-Ing. Martinko, Stadtlohn Dipl.-Ing. Otto, Aachen Dipl.-Ing. Reinhardt, Sondershausen Dipl.-Ing. Scharenberg, Hövels-Wingertshardt Dipl.-Ing. Spellier, Salzgitter Dipl.-Ing. Welter, Aachen Dipl.-Ing. Dipl.-oec. Prenger, Paderborn (Guest)
Working Group 2.10.2 Dipl.-Ing. Bucksteeg, München (Chairman)
Dipl.-Ing. Grosche, Radebeul Dipl.-Ing. Kollatsch, Halle Prof. Dr.-Ing. habil. Lützner, Dresden Dipl.-Ing. Maus, Arnsberg Dipl.-Ing. Tiedtke, Minden Dipl.-Ing. Schröder, Aachen Dipl.-Ing. Schweizer, Rottweil Dipl.-Ing. Voß, Kiel Dr.-Ing. Zerres, Stuttgart Dipl.-Ing. Linder, Stuttgart (Guest)
The Standard presented here has been prepared within the framework of the ATV committee work, taking into account the ATV Standard A 400 "Principles for the Preparation of Rules and Standards" in the Rules and Standards Wastewater/Waste, in the January 1994 version. With regard to the application of the Rules and Standards, Para. 1 of Point 5 of A 400 includes the following statement: "The Rules and Standards are freely available to everyone. An obligation to apply them can result for reasons of legal regulations, contracts or other legal grounds. Whosoever applies them is responsible for the correct application in specific cases. Through the application of the Rules and Standards no one avoids responsibility for his own actions. However, for the user, prima facie evidence shows that he has taken the necessary care". The Rules and Standards are not the sole but rather an important source of knowledge for technically correct solutions for the tasks of wastewater and waste engineering in normal cases. For these the ATV Standards form a yardstick for correct technical conduct. They cannot, however, deal with all possible special cases, in which extensive or limited measures are offered. In special cases it is possible to deviate from the definitions of the Rules and Standards, if the same effectiveness with the same security can be achieved in a different fashion.
All rights, in particular those of translation into other languages, are reserved. No part of this Standard may be reproduced in any form by photocopy, microfilm or any other process or transferred or translated into a language usable in machines, in particular data processing machines, without the written approval of the publisher.
Gesellschaft zur Förderung der Abwassertechnik e.V. (GFA), Hennef 1997 Produced by: JF.CARTHAUS GmbH & Co, Bonn
Contents
ATV A 200E
May 1997 3
Direction and objective 4
1. Area of Application 4
2. General planning principles 5
3. Wastewater discharge 7 3.1 Types of wastewater 8 3.1.1 Domestic and industrial wastewater 8 3.1.2 Precipitation water 8 3.1.3 Sewer infiltration water 8 3.2 Planning principles 8 3.3 Drainage systems 9 3.3.1 Modified separate system 9 3.3.2 Modified combined system 9 3.4 Discharge of domestic and industrial wastewater 9 3.4.1 Gravity drainage 10 3.4.2 Pressure drainage 10 3.4.3 Vacuum drainage 11 3.5 Disposal of precipitation water 11 3.5.1 Precipitation water not requiring treatment 11 3.5.2 Precipitation water requiring treatment 13 3.6 Potential for savings 15
4. Wastewater treatment 15 4.1 Selection of the sewage treatment plant 15 4.1.1 Small sewage treatment plants or local sewage treatment plant? 15 4.1.2 Local sewage treatment plants or group sewage treatment plant? 17 4.2 Requirements under Water Law 17 4.3 Special features of small sewage treatment plants and planning principles 18 4.4 Choice of treatment process 18 4.4.1 Wastewater lagoons 19 4.4.2 Technical sewage treatment plants 20 4.4.3 Plants with vegetation beds 23 4.5 Potential for savings 23 4.5.1 General 23 4.5.2 Potential for savings with limited interim solutions 24 3.5.3 Potential for savings with permanent solutions 25
5. Notes for cost comparison calculations 26 5.1 Costs determination 27 5.2 Finance mathematical processing of costs 28 5.3 Effects of costs on wastewater charges 28 5.4 Overall assessment 29
6. Technical Rules and Standards and sources 29
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Direction and Objective This Standard indicates possibilities for the economic realisation of an ordered disposal of wastewater in rurally structured regions. However, with all the currently discussed measures for cost reduction, the actual aims, protection of lakes and rivers and safety of local hygiene may not be placed in jeopardy.
Wastewater treatment plants in rurally structured areas should not be planned, built and operated in accordance with the same principles and requirements as for urban areas, as otherwise the specific costs (DM/inhabitant) would be disproportionately high.
It is the objective of this Standard to simplify the application of relevant Standards specially for rural areas and to promote creative solutions. In this respect proposals for cost reduction, which have often not been taken into account, have been summarised without restricting the design possibilities through new detailed prerequisites. is the preparation and listing. With this, the reduction of the annual costs stands at the forefront, and not only the today propagated investment cost reductions, through divergence from quality ensuring standards. The latter cause, as a rule, considerable follow-on costs in the middle and long-term and/or premature reinvestments. Through this, the required effect of the lowering of charges - if at all - is only achieved in the short-term. Also, cost savings with public sewerage systems, may have not disproportionate costs for additional installations on private property.
The aim of the ATV Standard is not to so reduce standards that, through this, plant operators are in danger of not being able to maintain legal requirements and thus have to face the consequences of criminal and taxation law.
Equally the Standard cannot interfere with the following important cost, contribution and charge relevant factors:
- legal regulations; - promotion practice of the Federal States; - formulation of the communal contribution and charge regulations.
Task of this Standard is, in accordance with the given details in ATV Standard A 400 "Principles for the Revision of Rules and Standards" [11] to provide recommendations for the cost favourable solution of planning, construction and operating problems. It should show how the dimensioning bandwidths and planning latitude can be used in the rurally structured regions and, through this , how savings can be made., In particular the statements in the Standard, do not replace the necessary creative service of the engineer with conceptual planning and the constructive implementation in accordance with the requirements of the individual case.
1. Area of Application The following listed criteria can serve as orientation for the term "rurally structured" within the sense of this Standard:
- small, often widely separated villages and localities;
- large property areas due to more widely spaced, open building, individual farmsteads, hamlets, scattered settlements;
- small settlement density, up to some 25 I/ha settlement area;
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- small proportion of hard surfaces, up to some 20 % of the settlement area including roads and paths;
- no continuous , possibly incomplete, sewer network;
- few available technical drainage systems, frequently small sewage treatment plants; sewers often only as stormwater sewers to nearest lake or river, however, frequently with discharges from small sewage treatment plants;
- primarily agricultural structure and, as a rule, little industry and commerce;
- frequently small and low performance surface waters, often preloaded by diffuse inputs;
- often recreational facilities with seasonally heavily varying wastewater production.
The immediate surroundings of towns also counts as rurally structured area, insofar as the above-given criteria apply.
2. General Planning Principles Basis of all planning of wastewater disposal facilities in rurally structured regions should be a wastewater action plan (WAP). This corresponds with the wastewater disposal concepts or plans legally laid down in some Federal States.
Drainage and wastewater treatment systems form one unit and are always to be so considered also with regard to the lakes and rivers into which discharges are to take place.
All characteristics of the disposal area are to be surveyed and investigated separately for stability and prognosis. They must also be included in the general development planning of a community and particularly in the construction management planning.
The sewerage system catchment area and the capacity of the sewage treatment plant are to be determined according to the actual built-up area and existing population as well as existing population equivalents from commerce. Development forecasts and blanket statements with high safety reserves are to be examined critically. With the determination of basic data one should, as far as possible, refer to existing data material (e.g. water consumption). Falling back on general recommendations must, as far as possible, be limited in order to be able to achieve the planning aims (no over-dimensioning, no unnecessary safety factors, cost optimisation).
The wastewater action plan contains:
- definition of the area of application, primarily according to water management and techno-economic criteria and not according to administrative limits and/or local political aspects;
- determination and techno-economic assessment of all existing wastewater systems (sewers, small sewage treatment plants, local sewage treatment plants), in order, as far as possible, to continue to use these;
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- definition of the measures, necessary from the point of view of water pollution control, taking into account the legal data given;
- preparation of possible alternatives and variants with the same depth of planning, in order to find cost favourable solutions;
- preparation of short and mid-term transitional solutions according to priority and with cost details for the step-by-step approach to the planning aim. With this, immediate basic treatment at as many locations as possible is more important than extensive treatment at a few places.
The measures should be arranged in the WAP approximately according to the following timings:
- to be disposed of publicly in the short-term (< 5 years) - to be disposed of publicly in the mid-term (5 - 10 years) - to be disposed of publicly in the long-term (> 10 years) - no public disposal planned.
Due to the requirement for topicallity, the WAP is to be updated at intervals of approximately 5 years.
The following are to be taken into account with regard to water management interests:
- water quality management situation in the area of the discharge;
- influence of discharges on downstream usage, protection of groundwater, detrimental effects on protected areas;
- local discharge into surface waters should be sought rather than long discharge sewers;
insofar as particular water management reasons for water pollution control do not stand in the way;
if an existing critical condition in a lake or river can be improved through the rehabilitation of the wastewater disposal system;
if the interests of priority use (e.g. drinking water) do not stand in the way;
- discharges into the sub-soil (e.g. chalk formation) always require separate consideration in individual cases due to the particular protection requirement of the groundwater.
Improvements to the quality of waters sought by requirements beyond the minimum requirements can, in individual cases, be achieved also with measures in the lake or river; for this procedure there are, however, currently no instructions on how to act.
Due to the vast extent of the drainage area in rurally structured regions the cost emphasis lies in the area of sewerage system/precipitation water treatment so that the greatest savings potential is to be expected here. Planning objective is a solution optimised with regard to investment and follow-on costs. Solutions which solely transfer
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costs from public drainage systems to private drainage facilities do not correspond with the principle of cost minimisation.
Economic disposal solutions can only be achieved if the elaboration is based on well-founded conceptional planning and this planning is carried out independently, i.e. free from delivery and production interests. The greatest savings potential is in the planning stage (see Fig. 1).
Possible saving of project costs (DM)
Fehler! Keine gültige Verknüpfung.
General development and concept planning
Project planning
Implementation
Diag. 1: Possibilities of influencing the project costs dependent on project stage
With planning, technical regulations are to be examined and interpreted taking into account the special features of rurally structured regions. With regard to savings potential the flexibility in standard specifications and rules and standards are to be applied consistently. Those responsible for measures, planners of wastewater systems and responsible authorities must discuss these possibilities and the resultant consequences together.
The tendering for construction projects is to be directed towards the possible capacity of the commercial economy, a favourable time for tendering and as wide a possible competition. Consideration is to be give, already within the scope of planning, as to how far cost saving organisational structures/mergers can be created for operational tasks which have to implemented together.
The use of all savings potential presupposes the tasking of an experienced, qualified planner.
3. Wastewater Discharge Discharge covers the collection and the transport of water. With this, measures for the avoidance and reduction of percolation are dealt with in particular.
With the economic considerations to be carried out for connection of a rurally structured region to a wastewater system, the various possibilities for collection and transport are to be investigated and compared with the respective possibilities for wastewater treatment.
3.1 Types of Wastewater
3.1.1 Domestic and Industrial Wastewater
In rurally structured regions, in addition to domestic wastewater, wastewater is produced from agricultural operations.. Wastes and residues from agricultural operations, e.g.
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liquid manures and silo seepage liquor, may not be fed into the communal wastewater sewer.
Domestic wastewater originates from households and small businesses which serve to supply the region. Wastewater from restaurants, hotels, barracks is counted with domestic wastewater
Commercial wastewater (e.g. from food businesses, agriculture (see ATV Advisory Leaflet M 702) [12] is to be taken into account according to quantity and kind.
3.1.2 Precipitation Water
Water which runs off and is collected from precipitation in built-up or hard surface areas also counts as wastewater.
The surface water from outside areas is to be kept away from the sewerage system.
Depending on the usage of the surface area on which the precipitation falls one differentiates between:
- precipitation water requiring treatment, and - precipitation water not requiring treatment.
It is to be established whether the precipitation water, due to the degree of its pollution, must be fed to a treatment system, may be transported into a receiving water or allowed to percolate into the subsoil (see also Sect. 3.5).
In rurally structured regions the greatest part of the precipitation water produced is seen as not requiring treatment. An accurate demarcation of the catchment areas is to be carried out and, for every area, it is to be established whether the precipitation water requires treatment or this requirement can be avoided.
With agricultural operations heavily soiled areas such as washdowns, manure aprons or runoff areas separated from the normal yard surfaces are to be drained into liquid manure pits. Yard surfaces are to be treated, from a drainage aspect, as public traffic areas.
3.1.3. Sewer Infiltration Water
Sewer infiltration water covers groundwater (leakage), illicit water introduced via bad connections (e.g. drain water, stormwater) as well as surface water running into a wastewater sewer (e.g. via a manhole cover).
3.2 Planning Principles
The technical Rules and Standards for the discharge of wastewater, stormwater treatment and combined wastewater treatment with the respective, determined specific inflow values also apply in rural areas.
The regulations for communal drainage and the charges must be agreed for the drainage solution (hard surfaces, stormwater usage, measure of divided charges, etc.).
The planning concepts must orient themselves to the requirements of the rural area. With this the following principles are to be assumed:
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- priority is to be given to the collection and discharge of wastewater;
- no water is to be fed to a sewage treatment plant whose degree of pollution is lower than that required for the effluent of the sewage treatment plant;
- precipitation water is to be percolated immediately where it arises, wherever the subsoil conditions and the degree of pollution of the precipitation water allow;
- if a discharge of precipitation water, which does not require treatment, is necessary it should take place, as far as possible, via trenches, flumes or depressions;
- sewer infiltration water is to be avoided.
3.3 Drainage Systems
In general one differentiates between combined and separate systems. With the combined system the wastewater is collected and discharged in a sewer together with the precipitation water.
With the separate system wastewater and precipitation water are collected and discharged separately. In addition to the combined and separate systems there are the following drainage systems, in particular for the separation of qualitatively differing partial flows:
- modified separate system - modified combined system.
3.3.1 Modified Separate System The modified separate system consists of one wastewater sewer; domestic, commercial and industrial wastewater only are fed to it. Precipitation water not requiring treatment is irrigated, percolated or discharged into a surface water immediately at its origin or after diversion.
So far as wastewater requiring treatment is unavoidable this is fed into a stormwater sewer.
3.3.2 Modified Combined System The modified combined system is a special case combined system. Only domestic, commercial and industrial water and precipitation requiring treatment are fed to the combined wastewater sewer; this combined wastewater is diverted and treated. The precipitation water not requiring treatment is irrigated, precipitated or discharged into a surface water immediately at its origin or after diversion.
3.4 Discharge of Domestic and Industrial Wastewater
At the forefront of wastewater disposal in the rural area is the discharge of domestic and industrial wastewater.
A pre-treatment of commercial and industrial wastewater can be necessary.
Further information can be found in the respective drainage regulations and in ATV Standards A 102 [4] and A 115 [6].
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3.4.1 Gravity Drainage With a gravity drainage system the depth of the sewer is of considerable economic significance. The depth is influenced by the topography, the existing supply pipelines and, possibly, necessary crossover structures (e.g. crossings of lakes and rivers).
However, the connection of cellar gravity drainage systems is not a compelling necessity. The security against backflow in deep lying cellars is ensured in accordance with the provisions of DIN 1986.
An often cost favourable model of transport pipelines is represented by the gradient pressure pipeline. With this the wastewater is transported via a pressure pipeline (with or without pumping station) even if sufficient gradient is available. In comparison with the gravity pipeline, pipes with small nominal widths can be laid, whereby maintaining an even gradient is not necessary. High and low points below the hydraulic pressure line are permitted. Separation between shafts are larger as only monitoring and cleaning openings are to be provided (see Fig. 2).
Fig. 2: Example of a gradient pressure pipeline with and without pump
Further information can be taken from ATV Standards A 110 [5] and A 116 [7] as well as the Working Report of the ATV Working Group 1.1.2 (1.1.6) (KA 1/87) [13]. In addition, the dimensioning principles for pressure pipelines apply.
3.4.2 Pressure Drainage The pressure drainage system is a special drainage system extensively used for the discharge of wastewater from rurally structured regions.
This technique allows the economic connection of large areas with low population density and the connection of individual houses, farms or small groups of houses with pipe diameters even smaller than DN 50.
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With pressure pipelines smaller than DN 80 pumps with cutter devices (not to be confused with the banned kitchen waste comminutor) must be employed, whereby, if required, their effect on the sewage treatment plant is to be taken into account. The combination of several houses with one pumping station is possible.
Further information can be taken from ATV Standard A 116 [7], prEN 1091 [1] and prEN 1671 [2].
3.4.3 Vacuum Drainage Vacuum drainage systems can be considered for the discharge of wastewater. Foreseeable later network extensions are to be taken into account due to the tight limitations for the pipeline dimensioning. In addition, the vacuum drainage system requires particular care with the laying and operation of the pipelines.
Further information can be taken from ATV Standard A 116 [7] and prEN 1091 [1].
3.5 Disposal of Precipitation Water
There are no Federal German countrywide rules for the treatment of precipitation water in the separate system.
The boundary between precipitation water requiring and not requiring treatment is based on the principle of feeding no water to a sewage treatment plant whose degree of pollution is less than is required in the effluent of the sewage treatment plant. As a rule not requiring treatment are runoffs from roof and courtyard surfaces as well as residential roads and pathways. Further information can be taken from the Working Report of ATV WG 1.4.3 (KA 2/94 [14] and KA 8/96 [17]) and the ATV WG 1.4.1 (KA/ 5/95) [16].
3.5.1 Precipitation Water not Requiring Treatment The disposal of water not requiring treatment is made up from the technical measures of retention, percolation and discharge. With the planning of the disposal of precipitation water implementation is to be examined in this order. Frequently combinations of these measures are applied.
Retention
Retention systems can be necessary before discharge into a lake, river or percolation system, if a discharge acceleration compared with the natural surface run-off over the ground and/or an overloading of the peculation system or lake or river is to be avoided with larger, connected hard surface areas.
One has to differentiate between
- natural retention areas; - artificial retention installations.
The following come into consideration as retention facilities
- terrain depressions; - chambers, pipes, ditches; - lagoons, garden ponds; - cisterns.
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Percolation
Priority is to seek percolation via a sufficiently covered, active layer of soil is in order to exploit its good cleaning capacity.
From a conceptional aspect one must differentiate between:
Percolation on private property (Decentralised percolation)
By extensive avoidance of impermeable surfaces and, if necessary possible breaking of the sealing and subsequent new permeable surfacing, percolation systems, if necessary in combination with retention systems matched to the local conditions, are to be installed on private property. The functioning of such systems, in comparison with other drainage systems, depends to a high degree on the acceptance by the landowner; servicing and maintenance of such systems are of considerable significance.
Further information on the selection and dimensioning of decentralised percolation systems can be taken from ATV Standard A 138 [10].
Percolation for a large catchment area (Central percolation)
If the subsoil conditions do not permit decentralised percolation and there is no receiving water within an economic distance, centralised percolation should be selected. The precipitation water is fed, as far as possible via open ditches, to the centralised percolation system, whereby a percolation in the ditches is also desired. Central percolation can take place via depressions or into a tank.
Possibilities for percolation listed in order of water management value are:
Surface percolation
Percolation on permeable hard surfaces or on flat side areas of impermeable surfaces.
Percolation in terrain depressions
Percolation in flat, usually grass covered ground hollows. Special form of surface percolation. Hollow also serves for short-term retention.
Percolation basins
Open earth basin covered at least with thin grass with large percolation surface and high storage volume.
Pipe and ditch percolation
Percolation in a perforated pipe section bedded in gravel, above ground percolation in a gravel filled ditch. Combinations of both types and also combination with depression percolation as depression-ditch-system are possible.
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Shaft percolation
Intermediate storage of precipitation water in a shaft /chamber with permeable walls and delayed percolation into the subsoil.
Discharge
If the subsoil conditions do not allow a decentralised or centralised percolation and there is a lake or river in the vicinity, the precipitation water should be fed to the lake or river, where possible via an open ditch, whereby possibilities of retention should be used, e.g. via the depression - ditch system.
With small lakes and rivers attention is to be paid to the material and hydraulic effects of an introduction of precipitation water. Information on this can be taken from the report of the ATV WG 1.4.3 (KA 8/96) [17] and ATV WG 2.1.1 (KA 5/93) [18].
3.5.2 Precipitation Water Requiring Treatment
Insofar as precipitation water requiring treatment cannot be avoided it is, as a rule, to be discharged and treated via a pipeline system.
The combined system always requires treatment of the stormwater.
Stormwater overflow discharges are necessary upstream of the sewage treatment plant depending on the type of sewage treatment plant and on local conditions.
Dimensioning and design of stormwater treatment systems are in accordance with ATV Standard A 128 [9] and/or the Directives of the Federal States.
Stormwater overflow discharges, stormwater tanks with overflow, stormwater sedimentation tanks and percolation systems via the active soil can be considered for employment as stormwater discharge or treatment plants.
Combined wastewater overflow discharges could possibly be dispensed with if wastewater ponds are employed and suitably designed for wastewater treatment (see Sect. 4.2.1).
For rural areas the following is to be observed with the employment of a combined system;
- with small catchment areas and the thus small wastewater run-offs, throttling and discharge of the combined wastewater discharge to the sewage treatment plant can be problematic;
- stormwater overflow systems in the form of enclosed tanks are to be avoided for reasons of cost;
- stormwater overflow systems should, as far as possible, be equipped with adjustable throttle devices in order, on one hand, to reduce the danger of blockages with small throttle discharges and, on the other hand, to use the storage volume optimally;
- with the employment of a mechanical sewage treatment plant with a capacity below ca. 500 IPE the parallel treatment of stormwater in the sewage treatment plant is barely possible as these sewage treatment plants have only a small buffer for the
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large pollutant loads and water quantities which run off in rainy weather (see also Sect. 4.4.2).
Due to these problems decisions on a combined system in rural areas are to be examined critically.
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Table 1: Potential for savings with the discharge of wastewater
Measures: Remarks: - Indication of new construction areas
primarily where a cost favourable disposal is possible
- If required, indicate and take into consideration effects on an existing drainage system
- Critical limitation of the area where disposal is to be under public arrangements
- Removal of remote individual properties;release from connection and usage obligation
- Sewerage system only for collection and discharge of wastewater
- Decentralised percolation of precipitation water at place of occurrence or discharge into surface water
- Combined drainage systems within a disposal area for collection and transport
- e.g. pressure or gravity drainage
- Reduction of stormwater runoff - Unsealing of hard surfaces; disconnection of all surface areas which can be drained by percolation or direct discharge into a lake or river
- Reduce precipitation water requiring treatment
- Proved measures for the avoidance or treatment at location of occurrence
- Retention of precipitation water - Use natural retention volumes, if necessary also create artificial facilities
- Separate surface water from external areas of the sewerage system
- Consequent reduction of the amount of sewer infiltration water
- Discharge of precipitation water not requiring treatment via open ditches
- Laying of sewers in soft surface verges of public paths
- Particularly useful for transport sewers; take into account existing supply pipelines
- Reduction of the pipeline length of collection and transport sewers by line selection, also through private property (gardens, meadows and arable land)
- Record easements; assure access; avoid overbuilding
- Reduction of laying depth of collector sewer - As a rule lifting systems necessary
- Use of existing drainage systems - Examine and assess carrying capability and structural condition with regard to future use
- Undercutting of previously demanded minimum pipe nominal widths
- Examine in individual cases
- Structural reduction of monitoring and pump shafts/chambers to the operationally necessary level
- Pay attention to the efficiency of inspection and cleaning equipment
- Common pipeline trenches for supply and disposal pipelines
- Ensure timely agreement
- As far as possible backfilling of the open cut with in-situ soil
- Allow settlement in open ground
- Employment of new laying techniques - Examine the economy and applicability of alternative construction methods and closed construction in accordance with ATV Standard A 125, drain ploughs, trench cutting machines or small excavators with trench bucket
- Agreement of road construction measures with sewer construction measures
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3.6 Potential for Savings
For wastewater discharge it can be established that the potential for savings in the conceptual field is greater that that for the constructional design and method of construction. The preparation and assessment of alternatives with different drainage solutions (local sewage treatment plant or group sewage treatment plant) and drainage systems (comp. Sect. 3.3 with 3.5) are essential prerequisites for this.
The measures listed in Table 1 should be examined for applicability both for the construction of new plants and for rehabilitation projects, whereby, along with investment costs also the operational costs, as well as the life of the systems must be taken into account.
4. Wastewater Treatment The capacity of sewage treatment plants in rural areas lies, as a rule, below 5000 IPE (so-called small sewage treatment plants) and thus within the area of application for Size Classes 1 and 2 of Appx. 1 of the Basic Wastewater Administration. Ordnance (Rahmen-AbwasserVwV) in accordance with §7A of the Water Management Law (WHG). For small sewage treatment plants in accordance with DIN 4261 - these are plants for a capacity up to 8 m3/d wastewater inflow - there are no generally valid minimum requirements laid down.
This section goes into detail for the „small sewage treatment plant“. The statements made can, to a limited extent, be carried over to plants with larger design capacities.
The valid Standard Specifications and Directives for sewage treatment plants considered are summarised in Table 2.
4.1 Selection of the Sewage Treatment Plant
4.1.1 Small Sewage Treatment Plants or Local Sewage Treatment Plant? The wastewater engineering connection of a built-up area with sewage treatment plants individual to a private property and subsequent discharge contradicts the concerns of local hygiene and water management. The disposal here of sludge is, to a large extent, unsolved and, without large communal sewage treatment plants in the neighbourhood, barely possible. Such an extensive decentralisation can be verified as saving no costs if almost equal treatment services, such as with local or group sewage treatment plants, are required and really all costs (operation, servicing, monitoring, sludge disposal, depreciation) are recorded in real cost terms.
Small sewage treatment plants can be erected if a proper wastewater disposal by means of public sewerage systems incur disproportionately high costs and the proper disposal within and outside the property as well as the faecal sludge disposal are assured. Small sewage treatment plants only come into consideration - independent of the treatment process employed - for scattered buildings, local adjustments, gaps in buildings or similar or as rehabilitation element for interim solutions.
Each community has, within the scope of its planning jurisdiction and in agreement with the water authorities, the freedom of choice as to whether it pursues keeping scattered buildings and the smallest localities as such or whether it defines residential or
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commercial areas. If it wishes to have the latter ,there results the necessity for a correct disposal in the form of a central local connection.
4.1.2 Local Sewage Treatment Plants or Group Sewage Treatment Plant?
With the search for the correct wastewater engineering solution one must assume various assessment criteria. The sequence below at the same time reflects the order of precedence with decision making.
Lakes and rivers
Wastewater engineering rehabilitation measures serve for local hygiene and water pollution control. With regard to the latter, the following question has to be at the forefront: can a lake or river fundamentally and in particular with regard to downstream usage, at all accept the treated wastewater at all? This question is a matter for the responsible water authority.
The question of location
If a lake or river is suitable for the acceptance of treated wastewater there arises the question of seeking a location for a local sewage treatment plant acceptable to all those involved and affected. Local political groups, project management planning and planners of wastewater systems must work together regarding the decision on location.
Wastewater treatment processes
Due to the differences of the wastewater treatment processes offered it is often attempted, with system specific arguments, to influence the decision "capable of acceptance by lake or river yes/no" and thus also the decision "local sewage treatment plant yes/no". With the correct selection of a tested technical process the necessary decisions with regard to "lakes and rivers" and "location" can be made with certainty. High technology, extremely automated plants on the one hand or particularly nature-near sewage treatment plants on the other provide no fundamentally new arguments for the decision. Small sewage treatment plants which can be operated long-term without servicing do not exist.
Economy
If a lake or river with acceptance capability, a nearby site for a sewage treatment plant and a location for the group solution are available, alternatives for local and group sewage treatment plants are to be investigated. In addition to the cost comparison calculations in accordance with Federal States Working Team, Water (LAWA) Guide lines [15] the non-financial assessable factors are to be evaluated in accordance with Sect. 5.
4.2 Requirements under Water Law
With sewage treatment plants with a design capacity below 5000 IPE the minimum requirements apply only for the organic pollutant parameters BOD5 and COD, none for the nutrient parameters nitrogen and phosphorous.
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Advanced requirements can, however, come into consideration if they are, from a water management aspect, necessary in order to achieve or maintain the planned quality in the lake or river and if, at the same time, it is also expected that the desired target can be actually achieved by reduction of the diffuse loads.
Thus the sewage treatment plant size of 5000 IPE also marks a limitation from the dimensioning and technical process aspect which is reflected in ATV Standards of the ATV series of Rules and Standards (see Table 2).
The requirements under Water Law for the discharge of treated wastewater must be agreed between and laid down well in time by those responsible for the measures, planners and responsible authority.
If time-staged requirements under Water Law are predetermined the planner is in a position to present a design for appropriately fitting expansion stages.
4.3 Special Features of Small Sewage Treatment Plants
Planning and operation of small sewage treatment plants often prove to be more difficult than with larger plants. The essential reasons for this are:
- the wastewater flow with small catchment areas has larger specific pollutant load surges and higher hydraulic peaks than with larger drainage networks;
- small machines and technical processing installations are basically more liable to faults than large units;
- the provision of qualified operating personnel for small sewage treatment plants in practice often meets with the greatest difficulties: even automation cannot offer any equivalent alternative.
The following planning principles derive from the special features of small sewage treatment plants:
- small sewage treatment plants may not be designed as smaller copies of large plants;
- buffering and balancing of the wastewater inflow are more important than highly technical treatment stages;
- simple multipurpose construction is more advantageous than complicated multi-stage technology;
- clearly arranged, easily serviced, robust mechanical installations are to be provided. A high performance automation is to be avoided;
- operational safety and easy serviceability have priority over exaggerated volume and energy savings;
- as a rule, sludge treatment can be put down as agricultural utilisation.
ATV Standards, Advisory Leaflets and Guides for small sewage treatment plants (see Table 2) already take account of the above planning principles.
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May 1997 19
4.4 Selection of Treatment Process
Technical sewage treatment plants and wastewater lagoons as well as combinations of these two processes are available. In addition new developments are always coming into discussion. The following come into question as treatment process:
- oxidisation ponds;
- aerated lagoons;
- wastewater lagoons with inserted biological contactors or biological filters;
- biological contactor or biological filter plants;
- activated sludge plants with joint aerobic sludge stabilisation;
- plants with hydrophyte beds as biological treatment element.
Table 3 contains a summary and assessment of the wastewater treatment processes for connection sizes up to 5000 IPE. With this a preselection of the treatment process/type of sewage treatment plant can be made. The most purposeful and economic solution can then be made from investigations of alternative solutions. With this the main aspects are:
- efficiency and stability of the treatment process as well as the assurance of maintaining the required discharge values;
- robustness and simplicity of the process technology;
- easy servicing and accessibility in order to be able to carry out the necessary operations and the laid down self-monitoring measurements;
- assurance of sludge disposal;
- treatment and disposal of residues (screenings, grit chamber residue, sewage sludge);
- extension possibilities for staged expansion.
4.4.1 Wastewater Lagoons Wastewater lagoons, due to their large buffer capacity, are to be more favourably rated than small volume technical sewage treatment plants for the treatment of wastewater in rural locations. They can dampen the knock-on effect of hydraulic and material pollution surges on lakes and rivers and offer, through retention, the most simple possibility of joint treatment of stormwater in small localities with combined sewer systems. (For possible solutions see ATV Standard A 201). Further advantages are:
- possibility of near natural configuration;
- simple, cost saving construction;
- no or only small mechanical expense;
- in addition to a regular control of operation only small servicing task;
ATV A 200E
May 1997 20
- sludge clearance only necessary in one or two year intervals.
Wastewater lagoons have a relatively high surface area requirement. Odour emissions from the first pond of an oxidation pond series are possible. The development of algae and thus algae drifting can also be disruptive. With permeable subsoil a possible expensive sealing of the bottom could be come necessary.
The following lagoon systems were differentiated:
Large volume oxidation ponds have the largest buffer capacity against pollution and hydraulic surges. In particular, with existing or unavoidable new combined sewerage systems of smaller rural areas, it represents the only viable solution for wastewater treatment. Due to the large surface area requirement its main employment area is with connection values below 1000 IPE.
Aerated lagoons are advantageous, due to their smaller specific surface area requirement, with connection values of more than some 1000 IPE and, above all, with the connection of seasonal operations, in particular such as those in the food industry.
Combination of lagoons with biological contactors or biological filters can be shown to be a practical solution for connection sizes below some 3000 I, in particular with the expansion of existing plants of one or another process and/or for planned staged expansion.,
4.4.2 Technical Sewage Treatment Plants
Technical sewage treatment plants are available for residential areas, in particular if separate drainage exists, i.e. stormwater is not jointly treated. However, it must be ensured that only little sewer infiltration water ensues. The joint treatment of stormwater in accordance with the principles of ATV Standard A 128 [9] leads, with localities with connection values of less than 500 IPE, to constructional difficulties and operational problems due to the necessary throttling down to small inflows, appropriate stormwater tank emptying times (see also Sect. 3.5.2) as well as the design of the secondary sedimentation installations. Sludge storage space is necessary for technical sewage treatment plants with independent sludge disposal.
Activated sludge plants with joint sludge stabilisation are, as a rule, cheaper in construction and more expensive in operation, at least for energy costs, than biological contactor and biological filter plants. Due to the longer retention times of the wastewater in the aeration tanks a larger buffer capacity is ensured. Furthermore, with flat large aeration tanks, already considerable space for the acceptance of stormwater inflow is available through small impoundage.
Biological filter plants regenerate themselves after a short period without any operational intervention should there happen to be damage to the fixed biological film. Problems with the sludge stirred up in the secondary sedimentation stage seldom occur. However, the treatment method of the digestible sludge arising in the primary sedimentation stage must be well thought out in biological filter plants.
Biological contactor plants are assessed as being similar to biological filter plants if and when the mechanical installations are delivered in a robust design. Biological contactors are, in any case, to be protected against the effects of weather by an overhead construction.
Prefabricated compact plants/container sewage treatment plants, according to the above described methods are, as a rule, cheaper to produce. However, they are more
ATV A 200E
May 1997 21
inflexible in their design for individual requirements and in method of operation. In many cases they are for wastewater inflow only, i.e. not conceived for the joint treatment of stormwater.
System sewage treatment plants, varied by component, can be equivalent to dispersed construction..
New developments with special combination of methods and process variants, e.g. SBR process, fixed bed technology and special constructions are to be assessed separately case by case with regard to operational safety, scope of servicing, treatment performance and sludge treatment in comparison with the normal, proven operational processes. There are already ATV Working Groups formed for the processes given above as examples. Suitable solutions for the joint treatment of stormwater and for sludge treatment are often lacking. ATV Guide H 254 gives important information on the assessment of such plants.
4.4.3 Plants with Vegetation Beds For plants with vegetation beds there have been, up until now, only provisional definitions in an ATV Standard A 262 (Draft) which, however, still does not represent generally accepted dimensioning, planning and construction principles. Nevertheless, practice has shown that, with careful planning, design and operation on the basis of ATV Standard A 262 and feeding with pre-treated domestic wastewater of normal concentrations, the minimum requirements for sewage treatment plants up to 1000 IPE can be maintained.
Discontinuous (alternating) bed feeding improves the treatment performance and contributes to the longer retention of the permeability of the soil matrix. The use of cohesive soils is unsuitable for reasons of soil hydraulics.
Should vegetation beds be employed for biological treatment of wastewater, the following is recommended:
- observation of the details laid down in ATV Standard A 262 (Draft) with regard to location, dimensioning, construction and operation as well as primary sludge treatment and disposal;
- construction of vegetation beds at ones own expense with the objective of cost saving only under the direction of a specialist;
- cost comparison calculations taking into account all peripheral installations.
Vegetation beds have a comparatively high requirement for surface area. Odour emissions can occur. With permeable subsoil possible expensive sealing of the bottom is possible.
4.5 Potential for Savings
4.5.1 General
Precondition for the utilisation of all the following potential savings is the agreement between the person responsible for the measures, the planner and the responsible authority.
In the specific pollutant loads for the inhabitants there are already contingencies for locally oriented small commercial concerns such as, for example, the butcher and the village inn. General growth rates must be justified and should only exceed 10 - 15 % if concrete developments with dates are known. The establishment of growth rates to be
ATV A 200E
May 1997 22
included in the planning must take place taking into account other reserves, e.g. in the area of data assessment and dimensioning. An addition of growth rates and other reserves and/or safety factors to give an inflated total reserve is to be avoided.
Insofar as a group sewage treatment plant is to be sought in the long-term, necessary interim local sewage treatment plants are to be so designed and constructed that, if required, the solution which goes beyond the local area can be developed by stages from these plants.
- existing earth or concrete tanks, for example, can be refunctioned later for stormwater treatment/storage.
- mechanical equipment and other plant components can possibly be used further at other locations.
- activated sludge plants with joint sludge stabilisation can be modified later with digesters.
- lagoons can be expanded later with biological contactors/filters.
The solution which extends beyond the local area must therefore already be planned early, at least for the main features, in order to take into account the location and the later function can be taken into account in the planning of local sewage treatment plants.
Locations for sewage treatment plants are to be so selected that they are, as far as possible, free from construction problems. Unfavourable site conditions, flooding protection measures, noise and nature conservation conditions as well as measures for the reduction of odour emissions have considerable influence on the construction and operating costs.
Fundamentally, expansion phases staged by time must, in planning forecasts, be provided with a minimum time interval (some 5 years) in order to guarantee economic efficiency and to avoid continuous construction sites. In general not only the effects of measures for savings on investment costs but also on the operating costs as well as on operational safety are to be estimated and taken into account in decision making.
4.5.2 Potential for Savings with Limited Interim Solutions With limited interim solutions there are the following possibilities for savings, dependent on the later further usage of the sewage treatment plant:
- with technical sewage treatment plants and lagoons the dimensioning latitude given by ATV Rules and Standards for the reduction of volume is to be fully utilised;
- the selection of material must, in the long rune, be matched to the interim solution (e.g. for short term operating duration, railings and gratings in galvanised normal steel and not in special steel);
- local plants should be so constructed that components can later continue to be used on site (e.g. for stormwater tanks);
- the technical safety standard is, in agreement with the Municipal Accident Insurers (GUV) and the professional association, to be limited to the absolutely necessary;
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May 1997 23
- traffic areas are to be made as simple as possible (e.g. water bound cover);
- with wastewater lagoons one can dispense with an automatic screen and grit chamber, with technical plants with a grit chamber clearance device;
- operational buildings should be constructed simply (e.g. container or wooden hut), integration of laboratory and workshop facilities outside the local area can be used in order to reduce the requirement for space;
- with the agricultural utilisation of sewage sludge one can dispense with a stationary sludge dewatering plant. If a sludge dewatering is necessary, a mobile dewatering, or better, a dewatering together in a larger neighbourhood sewage treatment plant fitted with appropriate facilities is to be planned observing the reloading due to sludge liquor;
- emergency circulation pipelines are to be limited to the absolutely necessary level and, with regard to the very infrequent usage, are to be of simple design;
- to a large extent one should do without stationary emergency power equipment. Instead of this, exchange units should be held ready as neighbourhood aids or emergency plans should be agreed with the Fire Service or Technical Aid Service (THW);
- protection against flooding should be matched to the duration of the interim solution taking into account the effects of flooding;
- sludge containers should be constructed in simple form (e.g. based on the construction of liquid manure containers in agriculture);
- expensive measurement, control and regulation technology is to be dispensed with.
4.5.3 Potential for Savings with Permanent Solutions - Selection of location as well as considerations on central regional solutions should be
made according to water management and technical-scientific aspects and not to administrative boundary or local political aspects.
- In addition to the general statistical basic data, primarily locality oriented, realistic values are to be used in the planning. Where measurements for the substantiation of dimensioning data are practical, these should be carried out.
- The efficiency of existing plant components is to be determined carefully and sensibly included in the overall concept.
- Commerce is only to be taken into account according to the actual loading and, as far as possible, not according to theoretical rates or unproven details from commercial operators.
- A load-dependent, staged expansion should be included in the planning (e.g. wastewater lagoons which can later be supplemented by technical plant).
- Technical and measurement equipment of the sewage treatment plant should be carried using sound judgement. Furthermore, a simple circuit diagram is sufficient in place of a mosaic circuit diagram.
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May 1997 24
- Sewage sludge is as far as possible to be utilised in agriculture, whereby direct acceptance by the farmers is to be sought.
- Sludge lagoons, in which a good dewatering with even return loading of the sewage treatment plant is achieved with the employment of a suitable conditioning agent, can be practical with necessary intermediate storage of sewage sludge.
- Delivery of faecal sludge with small sewage treatment plants presumes the holding of large reserves as well as extensive additional facilities and is therefore to be avoided.
- Plant components can be placed on the ground or erected on shallow foundations, should local conditions allow.
- In addition to normal construction the employment of prefabricated containers can be taken into consideration taking account of lifetime.
- Necessary superstructures should be combined and/or so planned, through appropriate design of the plants, that only small areas have to be overbuilt.
- If seasonal businesses are connected, the sewage treatment plant should be so designed that, outside the season, components or indeed complete lines can be taken out of operation.
- Quality standards are to be reduced to the absolutely necessary (material, wall thickness, equipment).
- Attention should be paid to standardisation (holding of spare parts) with the organisational combination of several sewage treatment plants.
5. Information for Cost Comparison Calculations Investment and subsequent costs are essential for reaching a decision on a project or possible variants/alternatives. In particular, the complete concept and total costs must also be identifiable where an all-embracing and complete disposal can be carried out by stages only.
The procedure in accordance with the Federal States Working Team Water (LAWA) [15] "Guideline for the Carrying Out of Cost Comparison Calculations" has proved itself for cost comparison. The aim of this Guideline is the cost associated assessment of water management measures within the framework of investment decisions. It provides a statement on the cost associated advantage of an alternative with the comparison of various possibilities. It does not correspond with a business management cost comparison. Prognoses on rates and contributions must be put together from the communal tax laws of the Federal (German) States.
The cost comparison calculation divides into the following steps:
- costs determination;
- financial processing of the costs including cost comparison of cost cash values and/or annual costs and sensitivity tests/sensitivity analyses;
- overall assessment.
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May 1997 25
The application of this procedure, however, only makes possible a comparison of the monetarily appraisable cost associated effects of alternatives with the same level of planning without useful lives entering the comparison. Thus the application of this method theoretically assumes the same useful life for the alternatives and , therefore, can only verify the relative cost advantage capability of the alternatives.
Below are given notes and supplements from previous experiences on the individual work steps.
Before starting planning, wastewater system planners, those responsible for the measures, responsible authorities and, possibly, the affected citizens must agree on the assessment of the non-monetarily calculable planning aspects. This is necessary as the assessment of these factors is naturally also liable to subjective estimations.
For example, the following are designated as non-monetarily assessable aspects:
- intrusions into nature and landscape; - consideration of the overall water resources; - capability for timely realisation; - reduction of the ease of drainage for customers; - operational safety.
5.1 Cost Determination
The accuracy of cost determination depends on the planning stage (see Table 4). The further the planning advances the more detailed and accurate the costs can be estimated. The determination of the costs must be based on region specific up-to-date prices and as far as possible on technical experiences from local projects. Cross-region statistical details can offer an idea for the establishment of future price changes; they must be matched to the regional conditions.
With the implementation of cost comparison calculations contributions from third parties are not taken into account. The depreciation of properties is not to take place.
The cost determination for alternative solutions must always be comprehensive, i.e. include all costs which occur at all points of origin, even those on private property.
Cost determination
Planning stage/ point in time
Accuracy % (without
developmentof construction
costs) Provisional cost assumption
On awarding planning task
Rough estimate ± 50
Cost assumptions Study Estimation based on values from experience DM/km, DM/I, DM/ha
Cost estimation Initial planning Estimated on the basis of values from experience DM/m, DM/m2, DM/m3
Cost calculation Draft planning Determined on the basis of roughly allocated construction quantities per component DM/m3 soil, DM/m3 reinforced concrete
Cost estimate Placing of construction services
Exact determination on the basis of contract conditions with the unit prices offered by the bidder
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May 1997 26
Establishment of costs
Settlement of measures
Precise determination according to site measurements and contractual agreements
0
Table 4: Accuracy of cost determination dependent on the planning stage
The following types of cost are to be taken into account in the cost comparison calculation:
Investment costs
- costs for purchase of land, damages, easements - costs for preparation (planning, survey, expert opinion) - costs for development and infrastructure - construction costs - reinvestment costs.
Current expenses/operating costs - personnel costs - material costs (operating and auxiliary resources) - energy costs - disposal costs - maintenance costs - wastewater charges.
Manufacturer specific dependencies are to be assessed carefully with regard to their effects on the current costs.
5.2 Financial Mathematical Processing of Costs
In this working step the costs of alternatives are converted by finance-mathematical means, at a predetermined point in time, or the purpose of a value. With this, the various cost structures (alternatives with higher investment costs are compared with solutions with high subsequent costs) must be taken into account.
With this, calculation variables are:
- useful life of construction, mechanical and electrical technology; - rate of interest (actual/nominal); - development of construction and operating costs (actual/nominal); - period of consideration for the cost comparison.
The LAWA Guidelines [15] contain proposals for the determination of these parameters. As these variables are decisive for the result of the comparison, they are also prescribed specifically, in part, for a Federal State. The input values for the calculation variables, to be determined beforehand by those involved, are to be traceably documented. Particular attention must be given to the following points:
- determination of the period under consideration; - determination of the individual rates of depreciation; - consideration of reinvestments and determination of payment points;
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May 1997 27
- consideration of residual values; - consideration of the construction time for the start of the flow of capital and the repayment period; - region specific deviations with the determination of the calculation variables; - unified determination of interest rate and price changes (actual/nominal) for all alternatives.
Every planning measure and every comparison is based on assumptions. By the variation of important input parameters (sensitivity analyses) the cost related effects of possible changes to the end result are presented clearly.
5.3 Effects of Costs on Wastewater Charges
Every alternative examined in the cost comparison calculation must subsequently be thoroughly assessed for annual costs which result from this. These - and not the investment costs alone - are relevant for the wastewater charges, which the citizen, in every case, has to bear. A recommendation on the determination of the charges cannot be given, as these are, essentially, dependent on the specific local formulation of the charges bye-law.
Basically the annual costs for wastewater disposal and thus the wastewater charges (see Fig. 3) are made up from the cost groups
- operating costs including personnel costs - wastewater charge - calculated costs (interest and depreciation for expenses).
The expenses for depreciation are, along with the investment costs, essentially determined by the depreciation period, i.e. higher investment costs for high value types of design can, due to the longer depreciation period, be more favourable in annual costs than lower investment costs with reduced standards. Investment and operating costs are often equally opposed.
InterestPersonnel costs
Other operatingcosts
Expenses fordepreciation
Wastewatercharges
Fig. 3: Composition of the wastewater charges in rurally structured regions
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May 1997 28
5.4 Overall Assessment
The overall assessment is a summary of all previous examinations and calculations as well as those of the input parameters upon which the comparison is based. It serves as the final work step which presents the solution which is to be implemented and the decision steps, as well as the considerations, transparently. It must, in addition to the results of the cost comparison, indicate the evaluation of the non-monetarily considered aspects. A summary in the form of a decision matrix has proved successful.
6. Technical Rules and Standards and Sources (References which have no known official translation are given in the original language. A courtesy translation is given in square brackets).
[1] EN 1091 Vacuum Drainage Outside Buildings; Performance Requirements - 2/97
[2] prEN 1671 Vacuum Drainage Systems - 12/94 [3] ATV A 101 Planning of Drain and Sewer Systems New Construction,
Rehabilitation and Replacement - 1/92 [4] ATV A 102 Allgemeine Hinweise für die Planung von Abwasserableitungs-
anlagen und Abwasserbehandlungsanlagen bei Industrie- und Gewerbebetrieben - 11/90 [General Notes for the Planning of Wastewater Discharge Systems and Wastewater Treatment Systems with Industrial and Commercial Concerns]
[5] ATV A 110 Standard for the Hydraulic Dimensioning and Performance Verification of Sewers and Drains - 8/88
[6] ATV A 115 Discharge of Non-Domestic Wastewater into a Public Sewerage System - 10/94
[7] ATV A 116 Special Sewage Systems Vacuum Drainage Service - Pressure Drainage Service - 9/92
[8] ATV A 125 Pipe Driving - 9/96 [9] ATV A 128 Standards for the Dimensioning and Design of Stormwater Structures
in Combined Sewers - 4/92 [10] ATV A 138 Construction and Dimensioning of Facilities for Decentralised
Percolation of Non-Harmful Polluted Surface Water - 1/90 [11] ATV A 400 Grundsätze für die Erarbeitung des Regelwerkes 1/94
[Principles for the preparation of Rules and Standards]) [12] ATV M 702 Wirtschaftsdünger, Abfälle und Abwasser aus landwirtschaftlichen
Betrieben - 8/95 [Manure, Wastes and Wastewater from Agricultural Concerns (in preparation)]
[13] KA 1/87 Arbeitsbericht der ATV-Arbeitsgruppe 1.1.2 (1.1.6) Abwasser-transportleitungen - Planungs Bau- und Betriebs-grundsätze“ [Report of the ATV Working Group 1.1.2 (1.1.6) „Compressed Air Flushed Wastewater Transportation Pipes - Planning Construction and Operation Principles“]
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[14] KA 2/94 Umgang mit Regenwasser - derzeitiger Stand der Regenwasserbehandlung im Trennsystem; Arbeitsbericht der ATV Arbeitsgruppe 1.4.3 [Dealing with Stormwater - Current Status of Stormwater Treatment in the Separate System; Report of ATV Working Group 1.4.3.
[15] LAWA Leitlinien zur Durchführung von Kostenvergleichsrechnungen Ausarbeitung Guidelines des LAWA Arbeits - kreises Nutzen-Kosten-Untersuchungen in der Wasserwirtschaft 1993 [Guidelines for the Carrying out of Cost Comparison Calculations; Elaboration of the LAWA Working Group Usage-Costs Investigations in the Water Industry 1993 [16] KA 5/95 Hinweise zur Versickerung von Niederschlagsabflüssen;
Arbeitsbericht der ATV-Arbeitsgruppe 1.4.1 [Notes on Percolation of Precipitation Runoffs; Report of the ATV Working Group 1.4.1]
[17] KA 8/96 Handlungsempfelungen zum Umgang mit Regenwasser; 2. Arbeitsbericht der ATV-Arbeitsgruppe 1.4.3 [Recommendations for the Handling of Stormwater; 2nd Report of the ATV Working Group 1.4.3]
[18] KA 5/93 Weitergehende Anforderungen an Mischwasserentlastungen; 1. Arbeitsbericht der ATV-Arbeitsgruppe 2.1.1 [Extensive Demands on Combined Wastewater Overflows; 1st Report of the ATV Working Group 2.1.1]
[19] ATV-A105 Hinweise für die Wahl des Entwässerungssystems - 4/97 (Draft) [Information on the Selection of the Drainage System]
Further ATV Standards and Standard Specifications are listed in Table 2 "Summary of the Valid Standard Specifications and Standards for Small Sewage Treatment Plants".
Table 2: Summary of valid Standard Specifications and Standards for small sewage treatment plants as at April 1997 Range of 4 IPE to 50 IPE Range of 50 IPE to 500 IPE Range from 500 IPE to 5000 IPE
ATV Standard A 106 of October 1995 Design and Construction Planning of Wastewater Treatment System
ATV Standard A 123 of June 1985 Treatment and Disposal of Sewage Sludge from Small Sewage Treatment Plants
DIN 4261 Part 1 of February 1991 Small Sewage Treatment Plants
DIN 4261 Part 3 of September 1990
ATV Standard A 109 of January 1983 Standards for the Connection of Motorway Services to Sewage Treatment Plants
Plants without Wastewater Aeration Application, Dimensioning and Design
Small Sewage Treatment Plants Plants without Wastewater Aeration Operation and Servicing
DIN drawing approval through DIN CERTCO ATV Standard A 129 of May 1979 Wastewater Disposal from Recreational and Tourist Facilities
DIN 4261 Part 2 of June 1984 Small Sewage Treatment Plants Plants with Wastewater Aeration Application, Dimensioning, Design
DIN 426 1 Part 4 Small Sewage Treatment PlantsPlants with Wastewater Aeration
ATV Standard A 122 of June 1991 Standards for the Dimensioning, Construction and Operation of Small Sewage Treatment Plants with Aerobic Biological Treatment Stage for Connection Values between 50 and 500 Inhabitants and Total Population Equivalents
ATV Standard A 126 of December 1993 Principles for the Treatment of Wastewater in Sewage Treatment Plants According to the Activated Sludge Process with Joint Sludge Stabilisation with Connection Values between 500 and 5,000 Total Number of Inhabitants and Population Equivalents
General engineering supervision approvals by the German Institute for Civil Engineering
ATV Standard A 135 of March 1989 Principals for the Dimensioning of Biological Filters and Biological Contactors with Connection values over 500 Population Equivalents
ATV Standard A 201 of October 1989
Principles for the Dimensioning , Construction and Operation of Wastewater Lagoons for Communal Wastewater
ATV Standard A 257 of October 1989
Principles for the Dimensioning of Wastewater Lagoons and Interconnected Biological Filters or Contactors
ATV Standard A 262 (Draft) of October 1996 Principles for the Dimensioning, Construction and Operation of Plant Beds for Communal Wastewater for Capacities up to 1000 Inhabitants and Population Equivalents
ATV Guide H 254 of November 1986
General Assessment Criteria for Sewage Treatment Plants with Special Process Combinations/Variants for Design Capacities to 10,000 IPE
means: application also outside the limitations of the range
ATV Advisory Leaflet M 258 - in preparation Employment of Fine Screens and Sieves in Small Communal Sewage Treatment Plants
Table 3: Assessment of wastewater treatment processes for connection sizes up to approx. 5000 IPE
Process A B C D E F G Assessment criteria
Plant beds Nonaerated wastewater lagoon
Aerated wastewater lagoon
Lagoon plant with technical
intermediate stage (biological
filter/contactor)
Mechanical-biologicalsewage treatment
plant (open construction)
Mechanical-biologicalsewage treatment plant(compact construction)
Sewage treatment plant with additional or new
technology (compact construction)
1 Treatment processes
Known in part; however, various
mechanisms in the bodies of soil and still
unclear on the influence of plants
Well known Well known Well known Well known Well known Always open questions with new developments
2 Dimensioning Provisional determinations (ATV M
262 - Draft)
Established (ATV A 201)
Established (ATV A 201)
Established (ATV A 257)
Established (ATV A 122, ATV A 126, ATV
A 135)
Established (ATV A 122, ATV A 126, ATV
A 135)
Deviations from normal dimensioning values
often at the expense of process stability and/or operational safety (ATV
H 254) 3 M and E
equipment None to very little None to very little Medium Medium Variably high Mostly high to very
high Very high
4 Constructional characteristics
Pre-treatment necessary,
continuously even wastewater feed and
bed throughflow
None Mutual matching of lagoons, aeration and
stirring
Mutual matching of lagoons and technical
installations
Proven solutions available for all
necessary details
System type unit construction; occasionally
unacceptable space interconnection
System type unit construction; occasionally
unacceptable space interconnection
5 Reaction volumes
Bodies of soil difficult to control; enrichment
of substances, tendency to blockages
Bodies of water controllable at all
times; in some cases algae mass
development
Bodies of water controllable at all times
Process stages controllable individually
Process stages controllable individually
In part difficult access and control possibilities
of individual spaces
In part difficult access and control possibilities
of individual spaces
6 Buffer capacity for pollutant surges
Large Exceptionally large Very large Very large to large Large to medium; long-term activation
more favourable, biological
filter/contactor less so
Often small; long-term activation more
favourable, biological filter/contactor less so
Often very small
7 Storage capacity with regard to combined wastewater inflow
Slight; with additional bed impoundment
medium
Very large Very large Very large to large Small to very small stormwater tanks
necessary, with small design capacities
difficulty with stormwater tank
drainage
Very small; stormwater tanks necessary, with
small design capacities difficulty with
stormwater tank drainage
Usually very small stormwater tanks
necessary, with small design capacities
difficulty with stormwater tank
drainage 8 Treatment
performance Varying long-term
experiences Tested over the long-
term Tested over the long-
term Tested over the long-
term Tested over the long-
term According to the
system more or less No long-term
experience, at least not
- General long-term tested with full load - Organic
substances Minimum
Requirements (MR) maintainable
MR maintainable MR maintainable MR maintainable MR maintainable MR maintainable No details possible
- Nutrients Very variable Moderate Moderate Moderate Slight Slight No details possible
Table 3: Assessment of wastewater treatment processes for connection sizes up to approx. 5000 IPE - continued -
Process A B C D E F G
Assessment criteria
Plant beds Nonaerated wastewater lagoon
Aerated wastewater lagoon
Lagoon plant with technical
intermediate stage (biological
filter/contactor)
Mechanical-biologicalsewage treatment
plant (open construction)
Mechanical-biologicalsewage treatment plant(compact construction)
Sewage treatment plant with additional or new
technology (compact construction)
9 Introductory phase
Several weeks None None Intermediate stage a few weeks
A few weeks A few weeks A few weeks
10 Operational controls, servicing
With inflow facilities and in the single flow
area increased; plant care necessary
Very slight Slight Slight Necessary daily Necessary daily; tasks often more difficult due
to networking; specialist required with
operational defects
Necessary daily; tasks often more difficult due to networking; specialist
required with operational defects
11 Operational safety
Danger of blockage; risks with winter
operation
Very high Very high to high Very high to high Different dependent on location and design
Very different for the various systems
Very different for the various systems
12 Residues Sludge clearance more or less frequent
depending on the system
Sludge clearance in one to several year cycles according to
design
Sludge clearance in one to several year cycles according to
design
Sludge clearance in one to several year cycles according to
design
Frequency of sludge removal according to intermediate storage
possibility
Sludge clearance more or less frequent
according to system; frequency of sludge
removal according to intermediate storage
possibility
Sludge clearance more or less frequent
according to system; sludge removal and disposal often not
sufficiently thought out
13 Operating costs Slight Very slight Considerable electricity costs;
overall moderate
Considerable electricity costs;
overall moderate
High High No details possible
14 Construction costs
Moderate Moderate Moderate to high Moderate to high High Moderate to high No details possible
15 Area requirement Very large Very large Large Large to moderate Slight Very slight Very slight
16 Environmental concerns
Landscaping very easy; development of odours with operating
problems
Landscaping very easy; development of odours with operating
problems
Landscaping still very possible; noise
protection necessary according to aeration
system
Landscaping still very possible
Measures for landscaping and noise protection necessary
Some system dictated buildings urgently
require skilled concealment
Noise and odour problems usually solved
by complete cover; super-structure requires
skilled concealment
17 Area of application
Alternative to normal biological processes
with connection values< 1000 I; suitable as
down-stream stage for wastewater treatment
Preferably for rural sites < 1000 I;
particularly suitable for small locations with
combined wastewater systems
For rural sites > 1000 I; particularly suitable for
locations with wastewater inflows
from seasonal operations
For small sites < 3000 I; in particular with
limited space or for the rehabilitation of smaller
overloaded lagoon plants or of biological
filter or contactor plants with combined wastewater problems
Adaptable to special local conditions
Particular care required with selection from the
numerous manufacturer specific systems with regard to
advantages, disadvantages and
costs
Only after careful answering of questions on which advantages
the new process brings with departure from
tried systems and with acceptance of additional risks
