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