Municipal wastewater

Annual cost is the sum of operating and capital costs.

Biological oxygen demand (BOD5) and chemical oxygen demand (COD) are parameters which indirectly measure the level of organic material in wastewater. BOD5 measure the amount of oxygen consumed biochemically in water after 5 days (standard test is 20 degrees celcius over 5 days). COD also measure the amount of oxygen consumed, but this time a strongly oxidising agent is added to the water (usually containing sulphur acid and potassiumdicromat (K2Cr2O7)).

COD will normally show a higher level than BOD5, since more organic compounds will be oxidised and degraded by the added chemicals, as compared to a BOD5-test.

Capacity and load. The capacity of a treatment plant is the amount of wastewater it is designed to handle, while the load is the amount of wastewater a wastewater plant actually receives. The unit of both capacity and load is provided in population equivalents (pe).

Capital cost consists of the following two costs: Depreciation of earlier annual investments and a calculated interest cost for capital goods.

Contribution margin ratio refers to, in percent, how big a share of the annual wastewater related costs the municipalities actually cover by wastewater fees. Municipalities are not entitled to claim more than actual costs, neither are they obliged to claim full cost coverage.

Fee basis

Full cost ratio reflects the relationship between the income from fees and the fee calculation basis, and includes fund provisions and purchases from funds.

High-grade wastewater treatment plants are those that provide a biological and/or chemical treatment phase. Biological treatment mainly removes readily degradable organic material using microorganisms. The chemical phase involves the addition of various chemicals to remove phosphorus. Certain treatment plants also have with special phases for nitrogen removal. High-grade plants reduce the amounts of phosphorus and other pollutants in the effluent more effectively than mechanical plants.

Income from fees

Individual wastewater treatment facilities are designed to handle wastewater equivalent to the amount, or composition, of no more than 50 pe (generally, private plants in areas with scattered settlements). Individual wastewater treatment facilities also include those facilities, which until 2000 was named "separate wastewater facilities". Since the term "individual wastewater facilities" comprise a larger population than "separate wastewater facilities", the two cannot readily be compared.

Investments are gross investments, omitted possible revenues on investment and sale of capital goods. County and state subsidies is included, the same applies to previous surplus from the wastewater sector. Data are derived from the investment account number 350 and 353. Investment is the sum of the following sub-accounts: 010:500, 690, 790. In order to make the calculations comparable with previous years (complete the time series), sub-account 700 and 810 (state contributions) and 730 and 830 (county contributions) is omitted here.

Municipal wastewater facilities include all wastewater facilities and treatment plants with a capacity of 50 pe or more, also including those with no municipal ownership (for example privately owned). The facilities are generally divided into six groups: direct discharge, mechanical, chemical, biological, chemical-biological, and natural purification processes/other treatment.

Mechanical wastewater treatment plants include sludge separators, screens, strainers, sand traps and sedimentation plants. They remove only the largest particles from the wastewater, thus treatment efficiency in regards to nitrogen and phosphorus is relatively low.

North Sea Agreements/OSPAR convention refers to the joint declarations made by the countries around the North Sea to reduce inputs of nutrients to this sea-area. One of the targets was to halve the total inputs of nitrogen and phosphorus during the period 1985 to 1995. Since Norway did not reach the nitrogen target by the end of 1995, the national time limit was extended to 2005. The North Sea Agreements applies to the areas south of the 62o N. As for the nutrient reduction targets, only the counties with drainage into the Skagerak and North Sea, from the Swedish boarder to Lindesnes, are bound by the agreement.

North Sea counties entail the following counties: Viken (30), Oslo (03), Innlandet (34), Vestfold og Telemark (38) og Agder (42). Practically all land areas in these counties drain into the Skagerak and North Sea.

Operating costs constitutes the sum of administrative-, management- and maintenance costs. Data is derived from KOSTRA-form number 23: Cost absorption in water-, waste water and waste-sector’.

Population equivalent (pe) is defined as the amount of oxygen consumed in 5 days when organic material is decomposed in water. When 1 pe is defined as 60 g BOD5, it means that 1 pe will bring in daily the amount of organic material that microorganisms need 60 g of oxygen to decompose within 5 days.

Sewage overflows includes overflows in sewage pipelines and manhole covers that may cause wastewater to accumulate in unwanted places, with the potential to cause material damage or to be released untreated into water recipients

Sewage pipeline system includes both separate sewage pipelines and combined sewer (pipelines carrying both sewerage and storm water).

Treatment efficiency refers to the relative change in weight of a particular chemical substance between the measuring points in and out of the wastewater treatment plant. E.g. 30 per cent treatment efficiency means the 30 per cent of the amount going in to the wastewater treatment plant are removed before discharge into the recipient.

Wastewater facilities without treatment refer to discharges originating from wastewater facilities without treatment, also commonly referred to as direct discharges. The discharge is connected to municipal pipelines, but it doesn't take place any form of treatment.

Wastewater facility is defined in the Pollution regulation (FOR 2004-06-01 nr 931) as any plant handling wastewater consisting of one or more components: wastewaterpipelines, wastewater treatment plant or a discharge device (unofficial English translation).

Wastewater fees, claimed by the municipality, consist of a connection fee and an annual wastewater fee. The connection fee is collected once only - during installation - while the wastewater fee is collected every year.

Wastewater pipelines comes into three main groups:

1. Combined sewer (both sewerage and storm water)
2. Separate sewage
3. Separate storm water

What is referred to as a sewage pipeline system in the statistics only includes the first two categories, while separate storm water systems and private house connections are excluded.

Wastewater treatment plants are generally divided into three main groups according to the type of treatment they provide: mechanical, biological or chemical. Some plants incorporate combinations of these basic types. In addition, combinations of these basic types also exist.

Municipalities: Classification of municipalities

Counties: Classification of county

Grouping of municipalities ("KOSTRA-groups"): Norway's municipalities are grouped according to population and economic comparable groups. The clafssification is based on the report (in Norwegian only) Gruppering av kommuner etter folkemengde og økonomiske rammebetingelser 2020

Name: Municipal wastewater
Topic: Nature and the environment

Division for Energy, Environmental and Transport Statistics (425)

The figures are primarily published on national, county level and municipality level.

The statistics is published annually, normally in October, with an additional and summarising report - Municipal wastewater: Expenditures, investment, municipal fees, discharges, treatment and disposal of sewage sludge - relseased in December (based on the same data material; in Norwegian, english summary only).

The statistics is reported to EUROSTAT/OECD as part of their Joint Questionnaire on inland waters (JQ-IW).

Collected and revised data are stored securely by Statistics Norway in compliance with applicable legislation on data processing.

Statistics Norway can grant access to the source data (de-identified or anonymised microdata) on which the statistics are based, for researchers and public authorities for the purposes of preparing statistical results and analyses. Access can be granted upon application and subject to conditions. Refer to the details about this at Access to data from Statistics Norway.

The Norwegian Environment Agency (Miljødirektoratet) have a duplicate of the same data.

The purpose with the statistics is to give an overview of the status and development in the municipal wastewater sector.

Data collection was carried out sporadically in the 1980s, however since 1990 there's been a data collection on an annual basis. First it was administered under the name SSB-avløp, a co-operation between county administrations and Statistics Norway; secondly there was SESAM (1998-2001); thirdly the Municipality-State-Reporting (KOSTRA) (2002-2014), and last by the Norwegian Environment Agency (2015 and onwards).

KOSTRA which is a separete but also in part integrated with the official wastewater statistics started up as a project in 1995 with the intention to provide relevant and up-to-date information about resources spent, priorities and meeting targets in municipalities and counties. The goal is to collect data in a co-ordinated way, and make the information flow a one time delivery per year for all steering-information needed by municipality. The number of municipalities and counties was gradually increased until the reporting year of 2001, then all municipalities were included in the KOSTRA.

The data sources of KOSTRA wastewater and the remaining wastewater statistics are close to identical, although KOSTRA statistics comprise only the municipally organised part of the wastewater sector.

Important user groups of the wastewater statistics are the different national and regional public administrations/governments, mainly the Ministry of Environment, Norwegian Environment Agency, the different county administrations and municipalities. To various degrees, other potential user groups are science, media, business and industry and NGOs.

KOSTRA statistics provide control information to the municipalities and counties, and works as a benchmarking attemt for the municipal administration.

No external users have access to statistics before they are released at 8 a.m. on ssb.no after at least three months’ advance notice in the release calendar. This is one of the most important principles in Statistics Norway for ensuring the equal treatment of users.

The statistics here is related to other statistics, e.g. Municipal water supply.

The statistics is also related to other statistics concerning discharge and pollution of water. The discharge figures of the wastewater sector, together with the similar figures from agriculture, industry and aquaculture, add up to a national account on nitrogen and phosphorous discharges for Norway, the socalled Comprehensive Study on Riverine Inputs and Direct Discharges (RID) (mijodirektoratet.no, PDF) (in Norwegian only).

The statistics are developed, produced and disseminated pursuant to Act no. 32 of 21 June 2019 relating to official statistics and Statistics Norway (the Statistics Act).

KOSTRA data are collected by Statistics Norway on behalf of the Climate and Pollution Agency with legal basis in the Pollution Control Act (lovdata.no). Statistics Norway can make use of the collected data for official statistical purposes with legal basis in the Statistics Act (lovdata.no).

The Climate and Pollution Agency collect their data solely with legal basis in the Pollution Control Act (13th Mars, 1981, no. 6).

Council Directive of 21 ^st May 1991 concerning urban wastewater treatment (91/271/EEC).

Wastewater statistics also indirectly provide input data to other EU reportings like waste and climate statistics.

Data are collected annually for all existing wastewater facilities and slugde treatment plants (complete data collection).

For wastewater facilities less than 50 pe and wastewater pipeline system, KOSTRA is the datasource, thus every municipality report aggregated data in KOSTRA form 26A.

Data on municipal fees and self cost is reported by the municipalities in KOSTRA form 22 and 23.

Physical data: Complete data collection. Wastewater facilities 50 pe or larger and sludge treatment plants report individually to Altinn/Directorate of Environment, while wastewater facilities less than 50 pe report aggregated data on municipality level through the KOSTRA data collection and form 26A.

Economic data: Complete data collection. Annual reporting to KOSTRA for all municipalities.

Notably, since 2001, all municipalities have reported their accounts electronically with KOSTRA, and this created, together with the new account scheme, a way of utilizing the accounts as a powerful information source to financial statistics within municipal wastewater sector.

However, by collecting data directly from the municipality’s accounts, information from various organisation structures will not be collected because they are not visible in the account for the municipality. Therefore data for cost absorption since 2006 is collected via KOSTRA questionnaire 23 (Kostnadsdekning i vann, avløps- og avfallssektoren). The data reported must be limited to the instruction for calculation of full cost.

Editing is defined here as checking, examining and amending data.

Data is collected electronically once every year. KOSTRA data to Statistics Norway have deadline 15 th of February, while data reported to the Directorate of Environment is due 30th of February.

The electronic forms all contain built-in consistency checks and logical tests. When the data arrive Statistics Norway, they will be checked again, both automatically and manually.

The most updated and detailed theoretical framwork and methodology applied in wastewater statistics is published in Norwegian language only (English summary), see the report Municipal wastewater: Expenditures, investment, municipal fees, discharges, treatment and disposal of sewage sludge.

A brief summary of the referenced methodology in English is however presented below here:

Calculation of discharges of phosphorous and nitrogen
Due to the fact that only part of wastewater facilities undertake direct analysis of pollution loads and discharges, some level of estimation and the use of standard factors needs to be applied in the calculations. Thus, total discharge and treatment efficiency figures of nitrogen and phosphorus are in part based on estimations (see below for further details).

The following calculation procedure has been applied to municipal wastewater facilities, capacity of 50 population equivalents (pe) or more:

1. If information on discharge quantity, expressed as kilogram per year, has been reported, then this information will be used directly.
   
2. If no information as specified in point 1 above has been reported, but outflow concentrations and average water quantities have been provided, then discharge quantity is calculated in kilos per year from the following equation:
   
   Concentration (mg/l) x average water quantity (m ³ /year) / 1000
   
3. If neither point 1 nor 2 above can be calculeted, then discharge quantities will be estimated by multiplying the number of people connected to the wastewater facility with a standard factor for average discharge per person and another factor for standard treatment efficiencty. These factors are listed below:

• 1.8 gram (phosphorus)
• 12 gram (nitrogen)

Discharge of nitrogen and phosphorous per year at the outlet of wastewater facility can then be estimated from the following equations:

• Phosphorous: ((number of persons connected x 1.8 x 365) / 1000) x average treatment efficiency
• Nitrogen: ((number of persons connected x 12 x 365) / 1000) x average treatment efficiency

Small wastewater treatment facilities (less than 50 pe), usually individual plants, make use of the same set of standard factors on average discharge of nitrogen and phosphorous per person per day, as mentioned above. However catogories for type of treatments and treatment efficiencies differs somewhat. Therefore, treatment efficiencies for small wastewater treatment plants, in percentage, are specified below:

_{* Wastewater from sealed tanks are normally delivered to other wastewater plants and treated elsewhere, thus, discharge and treatment efficiency calculations are included with them.}

_{** Standard factor set up in collaboration with Bioforsk.
*** Standard factor set up in collaboration with Norsk Vann.}

Calculation of discharges of organic material, heavy metals and persistant organic pollutants

The calculations are mainly built on the method suggested by Blytt og Storhaug (2008).

The method was originally designed for heavy metals and persistant organic pollutants, but it has now also been extended to cover also organic material (biological oxygen demand (BOD ₅ ) and chemical oxygen demand (COD)). The statistics presented here covers only discharges from treated wastewater to the water recipient. In addition the statistics, so far, only covers discharges from wastewater treatment facilities 50 pe or larger.
The following parameters are included in the statistics:
- Arsenic (As)
- Cadmium (Cd)
- Crom (Cr)
- Copper (Cu)
- Mercury (Hg)
- Nickel (Ni)
- Lead (Pb)
- Zink (Zn)
- DEHP
- Biological oxygen demand (BOD ₅)
- Chemical oxygen demand (COD)

A. Annual discharge from wastewater facilities reporting annual discharge data
Calculation of discharges from these wastewater facilities are relatively straight forward. The discharges constitute the total sum of calculated discharges from all these facilities (either reported as (1) kg discharge per year or (2) the combination of the volume of water treated and average concentration of the parameter).
According to the Pollution Regulation (lovdata.no) (norwegian: Forurensningsforskriften), chapter 11, wastewater treatment plants larger than 20 000 pe are required to do water sampling and analyse for content of heavy metals, while wastewater treatment plants larger than 50 000 pe in addition are required also to analyse for a selection of organic pollutants. That means large wastewater treatment plants directly or indirectly report actual discharge data which can be used for statistical purposes, while discharges from smaller treatment plants are largely unknown.

B. Annual discharge from wastewater treatment plants with no reported discharge data
Calculation of discharges which are not covered by the Pollution regulation, or for some other reason are missing, will be estimated for. The estimations are based on standard factors - discharge per person connected. The data source to establish these factors are based on actualy data from treatment plants in "point A" above. Data on people connected to wastewater facilities exist in most cases, even if they don't carry out analyses, and thus, this informatio is the used to upscale discharges to national level.

Thus, for every wastewater facility in "point A" above with reported discharge data, we will first calculate a specific discharge for each chemical component (unit: microgram / person connected):

Spesific discharge = microgram discharge per year / number of people connected

This is carried out on every wastewater facility containing actualy data for every component being analysed. Then these wastewater facilities are divided into two categories based on their type of treatment:

• Treatment category I: direct discharges, mechanical and other treatment
• Treatment category II: chemical, biological, chemical-biological and natural purification

For each of these treatment categories, the median value for each heavy metal and each organic pollutant will become the overall specific discharge factor. "People connected" in the sense applied here means permanent residents who are being served by the wastewater facility through their pipeline system.

For example cadmium, there will be two spesific discharge factors, one for treatment category I and another for treatment category II. The same applies to all the other components in the statistics. The factors are updated each year based on the most recent data reported.

Please note! For BOD ₅ and COD, a 5 per cent trimmed average instead of median value has been used when establishing the spesific discharge factors. This deviates from the original method suggested by Blytt and Storhaug (2008). The reason for this adjustment in method is that this better explains the variation in discharges for these particular components. Spesific discharge factors for the different chemical components:

_{Source: `2023-data (reported Spring 2024 to Altinn/Directorate of Environment ).}

When the spesific factores have been established, they are then applied to the wastewater facilities with no discharge data (in point B). For example if a treatment facility belonging to treatment category I has 1 500 people connected, the estimated discharge is then 1 500 people multiplied with the discharge factor for treatment category I.

In this way, by partly using data based on actual analyses and partly by using estimations/factors, the statistics on heavy metals and organic pollutants, one can then calculate a national discharge for the whole wastewater sector.

Additional calculation and adjustments for BOD ₅ and COD
For BOD ₅ and COD there exist an additional calculation compared to what is the case with heavy metals and persistand organic pollutants. It only applies in those cases when it has been reported (1) data on BOD ₅ , but not COD, or (2) data on COD, but not BOD ₅ . Both BOD ₅ and COD measure organic material, and in order to avoid too much estimations, discharges in these instances are calculated from a theoretical BOD ₅ /COD-relationship (source: KOSTRA 2023-data):

• Treatment category I: 0.50
• Treatment category II: 0.27

For example the BOD ₅ /COD-relationship in treatment category I of 0.50 means that the amount of BOD ₅ in average is 50 per cent of what is the case with COD. The BOD ₅ /COD-relationships above have been established based on wastewater facilities that reports both BOD ₅ and COD, and thus makes it possible to establish a more general BOD ₅ /COD-relationship. The relationship is then applied to those wastewater facilities that misses either BOD ₅ or COD in their reporting (but not both!). For example if a wastewater facility belonging to treatment category II is reporting 200 tonnes of BOD ₅ , but data on COD is missing in their reporting, then this facility will have an estimated COD discharge of 200 tonnes / 0.27 = 740 tonnes. Opposite, if a wastewater facility belonging to the same treatment category reports 200 tonnes of COD, then the BOD ₅ discharge will be estimated to 200 tonnes * 0.27= 54 tonnes.

Consequently, discharge from these "one-sided" reportings (wastewater facilities) will be calculated based on part factor (BOD ₅ /COD-relationship) and part discharge data and actual analyses (either BOD ₅ or COD). This is considered a "second best solution" for estimating discharges for these facilities as apposed to a complete factor calculation.

Calculation of use of sewage sludge
The 2005-data-reporting introduced a new way of reporting sewage sludge compared to earlier years. Gross sewage sludge and its associated percentage dry weight are now included in the reporting compared to earlier it was only asked for dry weight of sewage sludge. In order to calculate the dry weight now, the information of percentage dry weight is essential. In cases where percentage dry weight is missing, then the following method has been applied to the data:

1. If percentage dry weight of the produced sludge product has been reported, but not for the amounts of sludge used, then this percentage has been applied.

2. If percentage dry weight of neither the produced sludge product nor the amounts used has been reported, a standard factor of 25 per cent dry weight has been applied.

Calculation of heavy metal content in sewage sludge

The calculation of average heavy metals in sewage sludge constitutes a weighted average of the reported figure; that is the content of heavy metals is weighted based on the amount of sludge reported for the different wastewater treatment plants. Thus, figures reported from larger treatment plants generally influence the final average figures more compared to smaller ones.

In the same way, maximum heavy metal content in sludge constitutes a weighted average figure of the values reported as maximum (as above, weighted against the amounts of sewage sludge disposed).

Calculation of number of small wastewater treatment plants (less than 50 pe) and their corresponding inhabitants connected.
Due to the fact that there is less reliable information available on smaller treatment plants, some estimation is necessary. Two estimation techniques may occasionally be applied:

1. Certain municipalities lack information on the distribution of inhabitants on type of treatment for smaller wastewater treatment plants. If the municipality has provided information on total amount of inhabitants connected, in addition to number of small treatment plants, the inhabitant distribution on type of treatment is estimated. The inhabitants are then distributed proportionally based on the number of treatment plants. For example lets say the municipality reports totally 3000 inhabitants connected to small treatment plants, 400 sludge separators, and 500 sludge separators with infiltration, but no distribution of inhabitants on types of treatment. Then the inhabitants connected is estimated to be 3 000x(400/(400+500)) = 1 333 inhabitants to sludge separator and 3 000x(500/(400+500)) = 1 667 inhabitants to sludge separators with infiltration, totally 3 000 inhabitants.

2. If the municipality lacks information on number of small treatment plants, but has information on the number of inhabitants connected, then this information may be used for estimation purposes. A theoretical connection factor based on the reported material is being applied. In 2023, this factor was 2.2 inhabitants per wastewater treatment plant (median value). For example if a municipality has the following information: 1 000 inhabitants connected to sludge separator, the estimated figure turns out to be 1 000/2,2 = 455 small treatment plants.

Calculation of statistics on country, county and KOSTRA group level (estimations)

Every year there are incidents of non-respondents, and this is visible in the statistics on municipality level as “blank data”. When it comes to figures reported in the plant level - sewage and sludge treatment –Statistics Norway make corrections in order to "neutralise" such deficiencies when calculating figures published on country, county and KOSTRA group level . Normally, this implies direct imputation of figures reported earlier i.e. if it is not reported anything in this year's reporting such missing information is collected from last year or previous years. These earlier reporting thus form the basis for the respective site when you sum up to a country, county or KOSTRA group level. The municipality in question will still come out as missing in the statistics on municipality level in that particular year, since they didn’t reported, but the statistics published for the country, county and KOSTRA group level will be subject to "statistical correction", not directly visible in the published KOSTRA figures. Thus, one can not simply sum up basic figures for all municipalities and expect that total corresponds to published national figures in the statistics. The purpose of such corrections is of course to remedy for non respondents and create more robust and reliable estimates on statistics published by Statistics Norway for the country, counties and KOSTRA groups.

Calculation of pollution load (relevant to KOSTRA only)

Due to the fact that only a minority of wastewater facilities undertake direct measures of pollution load, standard factors needs to be incorporated in the calculations. Thus, total load figures of phosphorus in to the facility are largely based on this set of factors (see below for further details).

The following calculation procedure has been applied to municipal wastewater facilities, capacity of 50 pe or more:

1. If the wastewater facility provides information on load, expressed as kilogram per year, this information will be used directly.

2. If the wastewater facility provides no information, as specified in number point 1 above, but given outflow concentrations and average water quantities, then load is calculated in kilos per year from the following equation:

concentration (mg/l) x average water quantity (m3/day) x 365 / 1000

3. If measurements are not carried out, total load are calculated by multiplying the number of people connected to wastewater facilities with standard factors of average load per person per day (1.6 gram phosphorous per person per day):

number of people connected x 1.8 (g P/ day x person) x 365 / 1000

NB! For the years 2015 and earlier 1.6 g TOT-P/day x person was used as a factor instead of 1.8 as mentioned above, thus here is a “small break in time series".

Not relevant

Employees of Statistics Norway have a duty of confidentiality.

Statistics Norway does not publish figures if there is a risk of the respondent’s contribution being identified. This means that, as a general rule, figures are not published if fewer than three units form the basis of a cell in a table or if the contribution of one or two respondents constitutes a very large part of the cell total.

Statistics Norway can make exceptions to the general rule if deemed necessary to meet the requirements of the EEA agreement, if the respondent is a public authority, if the respondent has consented to this, or when the information disclosed is openly accessible to the public.

More information can be found on Statistics Norway’s website under Methods in official statistics, in the ‘Confidentiality’ section.

In recent years, a few re-calculations and updates of the time series has been carried out in the earlier published statistics. The reason is commonly due to correcting erroneous data in the times series. Note then that the last and current version of the statistics will always be found in its most updated form in Statbank.

For more details, see chapter 2.10 in the report Municipal wastewater: Expenditures, investment, municipal fees, discharges, treatment and disposal of sewage sludge.

The statistics of individual wastewater treatment plants (less than 50 pe) is often more uncertain compared to wastewater treatment plants equal ot or larger than 50 pe.

The data on heady metals and organic pollutions are also generally associated with high level of uncertainty (only lalrge wastewater facilities actually do sampling and analysis on this).

For more details, see chapter 2.9 in the report Municipal wastewater: Expenditures, investment, municipal fees, discharges, treatment and disposal of sewage sludge.

A revision is a planned change to figures that have already been published, for example when releasing final figures as a follow-up to published preliminary figures. See also Statistics Norway’s principles for revisions.