Urban waste water treatment per province and river basin district

Urban waste water treatment per province and river basin district

Regions Periods Urban waste water treatment plants Numbers by type Total number (number) Urban waste water treatment plants Numbers by type Mechanical treatment (number) Urban waste water treatment plants Numbers by type Trickling filters (number) Urban waste water treatment plants Numbers by type Aeration tanks (number) Urban waste water treatment plants Numbers by type Oxidation tanks (number) Urban waste water treatment plants Numbers by type Oxidation ditches (number) Urban waste water treatment plants Numbers by type Carrousels (number) Urban waste water treatment plants Numbers by type Discontinuous systems (number) Urban waste water treatment plants Numbers by type Parallel installations (number) Urban waste water treatment plants Numbers by type Multi-stage installations (number) Urban waste water treatment plants Numbers by type Compact installations (number) Urban waste water treatment plants Numbers by type Membrane bioreactor (number) Urban waste water treatment plants Numbers by type Nereda granular sludge reactor (number) Urban waste water treatment plants Numbers by type Hybrid Nereda - active sludge system (number) Urban waste water treatment plants Capacity pollution equivalents by type Total capacity pollution equivalents (1 000 pollution equivalent) Urban waste water treatment plants Capacity pollution equivalents by type Mechanical treatment (1 000 pollution equivalent) Urban waste water treatment plants Capacity pollution equivalents by type Trickling filters (1 000 pollution equivalent) Urban waste water treatment plants Capacity pollution equivalents by type Aeration tanks (1 000 pollution equivalent) Urban waste water treatment plants Capacity pollution equivalents by type Oxidation tanks (1 000 pollution equivalent) Urban waste water treatment plants Capacity pollution equivalents by type Oxidation ditches (1 000 pollution equivalent) Urban waste water treatment plants Capacity pollution equivalents by type Carrousels (1 000 pollution equivalent) Urban waste water treatment plants Capacity pollution equivalents by type Discontinuous systems (1 000 pollution equivalent) Urban waste water treatment plants Capacity pollution equivalents by type Parallel installations (1 000 pollution equivalent) Urban waste water treatment plants Capacity pollution equivalents by type Multi-stage installations (1 000 pollution equivalent) Urban waste water treatment plants Capacity pollution equivalents by type Compact installations (1 000 pollution equivalent) Urban waste water treatment plants Capacity pollution equivalents by type Membrane bioreactor (1 000 pollution equivalent) Urban waste water treatment plants Capacity pollution equivalents by type Nereda granular sludge reactor (1 000 pollution equivalent) Urban waste water treatment plants Capacity pollution equivalents by type Hybrid Nereda - active sludge system (1 000 pollution equivalent) Urban waste water treatment plants Capacity inhabitant equivalents by type Total capacity inhabitant equivalents (1 000 inhabitant equivalents) Urban waste water treatment plants Capacity inhabitant equivalents by type Mechanical treatment (1 000 inhabitant equivalents) Urban waste water treatment plants Capacity inhabitant equivalents by type Trickling filters (1 000 inhabitant equivalents) Urban waste water treatment plants Capacity inhabitant equivalents by type Aeration tanks (1 000 inhabitant equivalents) Urban waste water treatment plants Capacity inhabitant equivalents by type Oxidation tanks (1 000 inhabitant equivalents) Urban waste water treatment plants Capacity inhabitant equivalents by type Oxidation ditches (1 000 inhabitant equivalents) Urban waste water treatment plants Capacity inhabitant equivalents by type Carrousels (1 000 inhabitant equivalents) Urban waste water treatment plants Capacity inhabitant equivalents by type Discontinuous systems (1 000 inhabitant equivalents) Urban waste water treatment plants Capacity inhabitant equivalents by type Parallel installations (1 000 inhabitant equivalents) Urban waste water treatment plants Capacity inhabitant equivalents by type Multi-stage installations (1 000 inhabitant equivalents) Urban waste water treatment plants Capacity inhabitant equivalents by type Compact installations (1 000 inhabitant equivalents) Urban waste water treatment plants Capacity inhabitant equivalents by type Membrane bioreactor (1 000 inhabitant equivalents) Urban waste water treatment plants Capacity inhabitant equivalents by type Nereda granular sludge reactor (1 000 inhabitant equivalents) Urban waste water treatment plants Capacity inhabitant equivalents by type Hybrid Nereda - active sludge system (1 000 inhabitant equivalents) Influent waste water Quantities Volume waste water (1 000 m3) Influent waste water Quantities Pollution Equivalents (1 000 pollution equivalent) Influent waste water Quantities Chemical oxygen demand (COD) (1 000 kg) Influent waste water Quantities Biochemical oxygen demand (BOD) (1 000 kg) Influent waste water Quantities Nitrogen compounds as N (total) (1 000 kg) Influent waste water Quantities Phosphorus compounds as P (total) (1 000 kg) Influent waste water Quantities Copper (kg) Influent waste water Quantities Chromium (kg) Influent waste water Quantities Zinc (kg) Influent waste water Quantities Lead (kg) Influent waste water Quantities Cadmium (kg) Influent waste water Quantities Nickel (kg) Influent waste water Quantities Mercury (kg) Influent waste water Quantities Arsenic (kg) Discharge of waste water (effluent) Quantities Volume waste water (1 000 m3) Discharge of waste water (effluent) Quantities Pollution Equivalents (1 000 pollution equivalent) Discharge of waste water (effluent) Quantities Chemical oxygen demand (COD) (1 000 kg) Discharge of waste water (effluent) Quantities Biochemical oxygen demand (BOD) (1 000 kg) Discharge of waste water (effluent) Quantities Nitrogen compounds as N (total) (1 000 kg) Discharge of waste water (effluent) Quantities Phosphorus compounds as P (total) (1 000 kg) Discharge of waste water (effluent) Quantities Copper (kg) Discharge of waste water (effluent) Quantities Chromium (kg) Discharge of waste water (effluent) Quantities Zinc (kg) Discharge of waste water (effluent) Quantities Lead (kg) Discharge of waste water (effluent) Quantities Cadmium (kg) Discharge of waste water (effluent) Quantities Nickel (kg) Discharge of waste water (effluent) Quantities Mercury (kg) Discharge of waste water (effluent) Quantities Arsenic (kg) Sewage sludge Wet sewage sludge by destination Total wet sludge (1 000 kg) Sewage sludge Wet sewage sludge by destination Agriculture (1 000 kg) Sewage sludge Wet sewage sludge by destination Wet oxidation (1 000 kg) Sewage sludge Wet sewage sludge by destination Composting (1 000 kg) Sewage sludge Wet sewage sludge by destination Landfill (1 000 kg) Sewage sludge Wet sewage sludge by destination Incineration (1 000 kg) Sewage sludge Wet sewage sludge by destination Cement industry (1 000 kg) Sewage sludge Wet sewage sludge by destination Co-incineration at power plants (1 000 kg) Sewage sludge Wet sewage sludge by destination Other destinations (1 000 kg) Sewage sludge Dry solids by destination Total dry solids (1 000 kg) Sewage sludge Dry solids by destination Agriculture (1 000 kg) Sewage sludge Dry solids by destination Wet oxidation (1 000 kg) Sewage sludge Dry solids by destination Composting (1 000 kg) Sewage sludge Dry solids by destination Landfill (1 000 kg) Sewage sludge Dry solids by destination Incineration (1 000 kg) Sewage sludge Dry solids by destination Cement industry (1 000 kg) Sewage sludge Dry solids by destination Co-incineration at power plants (1 000 kg) Sewage sludge Dry solids by destination Other destinations (1 000 kg) Sewage sludge Nutrients and heavy metals Ashes (1 000 kg) Sewage sludge Nutrients and heavy metals Nitrogen compounds as N (1 000 kg) Sewage sludge Nutrients and heavy metals Phosphorus compounds as P (1 000 kg) Sewage sludge Nutrients and heavy metals Copper (kg) Sewage sludge Nutrients and heavy metals Chromium (kg) Sewage sludge Nutrients and heavy metals Zinc (kg) Sewage sludge Nutrients and heavy metals Lead (kg) Sewage sludge Nutrients and heavy metals Cadmium (kg) Sewage sludge Nutrients and heavy metals Nickel (kg) Sewage sludge Nutrients and heavy metals Mercury (kg) Sewage sludge Nutrients and heavy metals Arsenic (kg)
Nederland 2023 313 0 1 61 49 45 119 2 12 11 1 0 10 2 29,995 0 54 10,011 4,362 1,197 9,990 91 1,492 1,502 91 0 843 363 23,630 0 60 8,091 3,260 958 7,738 72 1,124 1,320 60 0 692 255 2,245,264 26,036 1,003,290 409,401 92,983 12,757 . . . . . . . . 2,245,264 2,114 76,385 8,590 15,157 1,773 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Noord-Nederland (LD) 2023 61 0 1 9 10 5 28 1 3 2 1 0 0 1 3,369 0 54 651 375 81 1,318 40 322 97 91 0 0 340 2,531 0 60 501 288 59 970 32 250 74 60 0 0 237 260,645 2,692 105,180 44,603 9,278 1,368 . . . . . . . . 260,645 252 9,922 957 1,383 175 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Oost-Nederland (LD) 2023 81 0 0 12 13 20 24 0 4 3 0 0 4 1 6,812 0 0 1,522 1,684 404 2,318 0 585 115 0 0 162 23 5,170 0 0 1,178 1,218 319 1,749 0 464 95 0 0 130 18 447,106 5,998 233,702 92,162 20,813 2,869 . . . . . . . . 447,106 436 15,271 1,464 3,191 441 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
West-Nederland (LD) 2023 121 0 0 25 21 6 56 1 5 5 0 0 2 0 13,382 0 0 4,582 1,860 98 4,811 51 585 927 0 0 468 0 10,344 0 0 3,548 1,421 77 3,683 40 410 779 0 0 386 0 984,537 11,363 430,439 183,371 42,037 5,425 . . . . . . . . 984,537 910 32,267 3,792 6,839 723 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Zuid-Nederland (LD) 2023 50 0 0 15 5 14 11 0 0 1 0 0 4 0 6,432 0 0 3,255 443 615 1,543 0 0 363 0 0 212 0 5,586 0 0 2,865 334 503 1,336 0 0 372 0 0 176 0 552,976 5,982 233,968 89,264 20,855 3,094 . . . . . . . . 552,976 516 18,925 2,377 3,744 434 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Groningen (PV) 2023 22 0 0 4 4 2 8 1 1 1 0 0 0 1 1,017 0 0 180 110 13 260 40 17 56 0 0 0 340 741 0 0 130 80 11 195 32 15 41 0 0 0 237 85,784 826 33,052 13,647 2,673 406 . . . . . . . . 85,784 94 3,699 460 571 58 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fryslân (PV) 2023 27 0 1 0 4 1 18 0 1 1 1 0 0 0 1,336 0 54 0 170 16 828 0 136 41 91 0 0 0 1,006 0 60 0 120 10 604 0 119 33 60 0 0 0 106,597 1,093 41,869 18,382 3,931 585 . . . . . . . . 106,597 94 3,938 281 446 77 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Drenthe (PV) 2023 12 0 0 5 2 2 2 0 1 0 0 0 0 0 1,016 0 0 471 95 51 230 0 169 0 0 0 0 0 784 0 0 371 87 38 172 0 116 0 0 0 0 0 68,264 773 30,259 12,574 2,674 377 . . . . . . . . 68,264 64 2,285 216 366 40 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Overijssel (PV) 2023 32 0 0 9 6 10 2 0 1 2 0 0 1 1 2,196 0 0 899 632 290 218 0 21 90 0 0 22 23 1,740 0 0 703 508 223 182 0 14 75 0 0 17 18 146,451 1,803 69,947 26,868 6,306 868 . . . . . . . . 146,451 145 5,430 455 1,023 126 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flevoland (PV) 2023 5 0 0 0 1 0 4 0 0 0 0 0 0 0 765 0 0 0 65 0 700 0 0 0 0 0 0 0 612 0 0 0 52 0 560 0 0 0 0 0 0 0 31,339 630 23,657 10,560 2,375 313 . . . . . . . . 31,339 29 1,053 83 216 21 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Gelderland (PV) 2023 44 0 0 3 6 10 18 0 3 1 0 0 3 0 3,851 0 0 623 986 113 1,400 0 564 25 0 0 140 0 2,818 0 0 475 658 96 1,007 0 450 20 0 0 113 0 269,316 3,566 140,099 54,734 12,132 1,689 . . . . . . . . 269,316 262 8,788 926 1,952 294 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Utrecht (PV) 2023 23 0 0 3 4 0 14 0 0 1 0 0 1 0 2,110 0 0 185 108 0 1,365 0 0 19 0 0 432 0 1,680 0 0 145 79 0 1,082 0 0 14 0 0 360 0 142,163 1,790 68,523 28,400 6,455 815 . . . . . . . . 142,163 112 4,220 429 850 78 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Noord-Holland (PV) 2023 30 0 0 8 5 3 8 1 3 2 0 0 0 0 4,565 0 0 1,930 1,038 82 785 51 433 246 0 0 0 0 3,696 0 0 1,713 781 63 581 40 305 213 0 0 0 0 315,490 3,937 148,089 68,846 14,767 1,923 . . . . . . . . 315,490 337 11,596 1,411 2,348 228 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Zuid-Holland (PV) 2023 53 0 0 3 12 3 32 0 1 2 0 0 0 0 5,908 0 0 1,833 714 16 2,618 0 65 662 0 0 0 0 4,405 0 0 1,242 561 13 1,989 0 46 552 0 0 0 0 467,107 5,127 195,941 78,582 18,638 2,444 . . . . . . . . 467,107 403 14,374 1,643 3,213 357 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Zeeland (PV) 2023 15 0 0 11 0 0 2 0 1 0 0 0 1 0 799 0 0 634 0 0 43 0 86 0 0 0 36 0 563 0 0 447 0 0 31 0 59 0 0 0 26 0 59,777 508 17,886 7,543 2,177 243 . . . . . . . . 59,777 59 2,077 309 428 60 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Noord-Brabant (PV) 2023 33 0 0 11 2 14 5 0 0 1 0 0 0 0 4,386 0 0 2,772 16 615 620 0 0 363 0 0 0 0 3,933 0 0 2,501 11 503 547 0 0 372 0 0 0 0 384,884 4,182 164,280 64,398 14,419 2,280 . . . . . . . . 384,884 335 12,705 1,412 2,440 315 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Limburg (PV) 2023 17 0 0 4 3 0 6 0 0 0 0 0 4 0 2,046 0 0 484 427 0 922 0 0 0 0 0 212 0 1,653 0 0 365 323 0 790 0 0 0 0 0 176 0 168,091 1,800 69,688 24,866 6,436 814 . . . . . . . . 168,091 181 6,219 965 1,303 119 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The river Eems 2023 16 0 0 7 3 0 4 0 0 1 0 0 0 1 1,134 0 0 366 102 0 270 0 0 56 0 0 0 340 819 0 0 267 73 0 201 0 0 41 0 0 0 237 91,423 911 36,425 15,219 2,953 438 . . . . . . . . 91,423 105 4,070 508 628 62 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The river Rijn (North Rijn) 2023 38 0 1 0 5 4 23 1 2 1 1 0 0 0 1,521 0 54 0 178 45 918 40 153 41 91 0 0 0 1,157 0 60 0 127 33 678 32 134 33 60 0 0 0 122,917 1,237 47,444 20,700 4,435 662 . . . . . . . . 122,917 109 4,478 336 537 90 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The river Rijn (East Rijn) 2023 73 0 0 13 14 15 23 0 2 2 0 0 3 1 6,863 0 0 1,515 1,742 385 2,825 0 190 90 0 0 92 23 5,178 0 0 1,174 1,284 299 2,137 0 130 75 0 0 61 18 438,362 5,930 230,557 90,572 20,697 2,819 . . . . . . . . 438,362 412 14,865 1,183 2,865 341 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The river Rijn (Central Rijn) 2023
The river Rijn (West Rijn) 2023 114 0 0 15 22 10 51 1 7 6 0 0 2 0 13,096 0 0 4,241 1,896 145 4,247 51 1,062 952 0 0 502 0 10,209 0 0 3,338 1,442 116 3,244 40 802 799 0 0 429 0 968,258 11,359 432,817 184,481 41,482 5,447 . . . . . . . . 968,258 906 31,695 3,843 6,914 781 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The river Maas 2023 52 0 0 14 3 14 16 0 0 1 0 0 4 0 6,079 0 0 2,784 427 606 1,686 0 0 363 0 0 212 0 5,242 0 0 2,428 323 496 1,448 0 0 372 0 0 176 0 519,904 5,651 220,978 84,732 19,722 2,904 . . . . . . . . 519,904 478 17,404 2,281 3,413 376 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The river Schelde 2023 20 0 0 12 2 2 2 0 1 0 0 0 1 0 1,302 0 0 1,105 16 16 43 0 86 0 0 0 36 0 1,024 0 0 884 11 13 31 0 59 0 0 0 26 0 104,399 949 35,069 13,697 3,694 486 . . . . . . . . 104,399 104 3,873 438 800 124 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Source: CBS.
Explanation of symbols

Table explanation


This table presents the most significant results of the annual survey Public treatment of urban waste water. The results are presented per province and river basin district (Rijn, Maas, Eems and Schelde) and include:
- number and capacity of the urban waste water treatment plants by type of treatment;
- the volume and concentration of organic matter, nutrients and heavy metals in the waste water running into waste water treatment plants (influent) and the volume of treated waste water (effluent). As of 2017, data on heavy metals are only inventoried for even years.
- the volume and destination of the sludge released, with nutrients and heavy metals. As of 2017, sludge data are only inventoried for even years.
Additional data on urban waste water treatment plants, process technology, energy consumption, generation of energy and sludge dewatering can be accessed on the Dutch version of StatLine.

Data available from: 1981

Status of the figures:
The figures in this table are definitive.

Changes as of 21 March 2025:
The figures of 2023 has been added.

When will new figures be published?
New figures on 2024 will be published by March 2026.

Description topics

Urban waste water treatment plants
The number and capacity of urban waste water treatment plants in the Netherlands where nearly all domestic waste water and waste water from the private sector is treated. The plants are all operated by regional water quality control authorities.
Numbers by type
Number of sewage water treatment plants broken down by method of treatment.
Total number
The total number of urban waste water treatment plants in the Netherlands.
Mechanical treatment
Installation where suspended matter is extracted from waste water by settlement.
Trickling filters
Waste water is sprinkled over a layer of porous stones covered with bacteria (biofilm). Thus, organic compounds in the waste water are degraded.
Aeration tanks
Pre-settled waste water runs through an intensively aerated basin containing active sludge (bacteria). Organic pollutants are degraded by oxygen and active sludge. The treatment process takes up only a short period of time and the sludge load is high which is typical of aeration basins.
Oxidation tanks
Operates by the same principle as the aeration tank but the sludge load is significantly lower. The resulting sludge is highly mineralised and will therefore decompose more slowly.
Oxidation ditches
In oxidation ditches, waste water is directed through a aeration circuit several times. The process takes up 2 or 3 days. Consequently, the sludge load is extremely low.
Carrousels
This technology is chiefly applied in large installations. Typical of carrousels are the depth (between 2 to 4 metres) and the aeration method.
Discontinuous systems
Oxidation basins and oxidation ditches. Waste water is let in batch-controlled.
Parallel installations
Various combinations of treatment systems (so-called 'streets') are applied in one installation.
Multi-stage installations
A serial process consisting of two systems, for instance, a trickling filter and an aeration basin. The waste water runs through both stages.
Compact installations
A system consisting of a basin subdivided into four segments. Waste water flows into the aeration segment. Subsequently, the sludge is separated in the central aeration zone. Then part of the sludge is conditioned in the reaeration zone and led back into the aeration zone. The other part (surplus sludge) is stabilised in the sludge mineralisation zone and subsequently removed.
Membrane bioreactor
A system where the sludge is separated from the waste water by using a membrane.
Nereda granular sludge reactor
In the Nereda granular sludge reactor the wastewater is purified by micro-organism clogged in natural granular structures of high density. These granules have a high biological activity and make it easy to separate the micro-organisms from the treated wastewater.

As from 2019 this new treatment type is distinghuished separately in Statline. In the period 2011-2018 already 4 Nereda systems became operational. Until 2019, these installations were classified as oxidation tanks and/or discontinous systems.
Hybrid Nereda - active sludge system
System consisting of a parallel operated Nereda granular sludge reactor and activated sludge system.

In the Nereda granular sludge reactor the wastewater is purified by micro-organism clogged in natural granular structures of high density. These granules have a high biological activity and make it easy to separate the sludge from the treated wastewater.

In activated sludge systems the wastewater is treated in bassins with flocculated sludge . This sludge clumps exists of microorganisms that feed on the the organic pollution in wastewater.

As from 2019 this new treatment type is distinghuished separately in Statline. In the period 2013-2018 already 2 hybrid Nereda - activated sludge sytems became operational. Until 2019, these installations were classified as parallel installations.
Capacity pollution equivalents by type
Capacity urban waste water treatment plant:
A value that indicates how much organic pollution theoretically can be treated by a waste water treatment plant.

The pollution equivalent is the official unit that quantifies the pollution in waste water; one pollution equivalent = 150 g TOD (Total Oxygen Demand).
One pollution equivalent is the daily quantity of oxygen-demanding material in the waste water of one person. The degree of pollution in the waste water produced by the private sector is also expressed in pollution equivalents.
This unit is used as of 2010, so for previous years no values are available.
Total capacity pollution equivalents
Mechanical treatment
Installation where suspended matter is extracted from waste water by settlement.
Trickling filters
Waste water is sprinkled over a layer of porous stones covered with bacteria (biofilm). Thus, organic compounds in the waste water are degraded.
Aeration tanks
Pre-settled waste water runs through an intensively aerated basin containing active sludge (bacteria). Organic pollutants are degraded by oxygen and active sludge. The treatment process takes up only a short period of time and the sludge load is high which is typical of aeration basins.
Oxidation tanks
Operates by the same principle as the aeration tank but the sludge load is significantly lower. The resulting sludge is highly mineralised and will therefore decompose more slowly.
Oxidation ditches
In oxidation ditches, waste water is directed through a aeration circuit several times. The process takes up 2 or 3 days. Consequently, the sludge load is extremely low.
Carrousels
This technology is chiefly applied in large installations. Typical of carrousels are the depth (between 2 to 4 metres) and the aeration method.
Discontinuous systems
Oxidation basins and oxidation ditches. Waste water is let in batch-controlled.
Parallel installations
Various combinations of treatment systems (so-called 'streets') are applied in one installation.
Multi-stage installations
A serial process consisting of two systems, for instance, a trickling filter and an aeration basin. The waste water runs through both stages.
Compact installations
A system consisting of a basin subdivided into four segments. Waste water flows into the aeration segment. Subsequently, the sludge is separated in the central aeration zone. Then part of the sludge is conditioned in the reaeration zone and led back into the aeration zone. The other part (surplus sludge) is stabilised in the sludge mineralisation zone and subsequently removed.
Membrane bioreactor
A system where the sludge is separated from the waste water by using a membrane.
Nereda granular sludge reactor
In the Nereda granular sludge reactor the wastewater is purified by micro-organism clogged in natural granular structures of high density. These granules have a high biological activity and make it easy to separate the micro-organisms from the treated wastewater.

As from 2019 this new treatment type is distinghuished separately in Statline. In the period 2011-2018 already 4 Nereda systems became operational. Until 2019, these installations were classified as oxidation tanks and/or discontinous systems.
Hybrid Nereda - active sludge system
System consisting of a parallel operated Nereda granular sludge reactor and activated sludge system.

In the Nereda granular sludge reactor the wastewater is purified by micro-organism clogged in natural granular structures of high density. These granules have a high biological activity and make it easy to separate the sludge from the treated wastewater.

In activated sludge systems the wastewater is treated in bassins with flocculated sludge . This sludge clumps exists of microorganisms that feed on the the organic pollution in wastewater.

As from 2019 this new treatment type is distinghuished separately in Statline. In the period 2013-2018 already 2 hybrid Nereda - activated sludge sytems became operational. Until 2019, these installations were classified as parallel installations.
Capacity inhabitant equivalents by type
Capacity urban waste water treatment plant:
A value that indicates how much organic pollution theoretically can be treated by a waste water treatment plant.

The capacity expressed in Inhabitant Equivalents is determined on basis of: one inhabitant equivalent = 54 g BOD (Biological Oxygen Demand).
One inhabitant equivalent is the daily quantity of oxygen-demanding, organic substances in the waste water of one person.
Nowadays, the use of the unit inhabitant equivalent is decreasing. The most common unit is the pollution equivalent.
Total capacity inhabitant equivalents
The total capacity of all urban waste water treatment plants.
Mechanical treatment
Installation where suspended matter is extracted from waste water by settlement.
Trickling filters
Waste water is sprinkled over a layer of porous stones covered with bacteria (biofilm). Thus, organic compounds in the waste water are degraded.
Aeration tanks
Pre-settled waste water runs through an intensively aerated basin containing active sludge (bacteria). Organic pollutants are degraded by oxygen and active sludge. The treatment process takes up only a short period of time and the sludge load is high which is typical of aeration basins.
Oxidation tanks
Operates by the same principle as the aeration tank but the sludge load is significantly lower. The resulting sludge is highly mineralised and will therefore decompose more slowly.
Oxidation ditches
In oxidation ditches, waste water is directed through a aeration circuit several times. The process takes up 2 or 3 days. Consequently, the sludge load is extremely low.
Carrousels
This technology is chiefly applied in large installations. Typical of carrousels are the depth (between 2 to 4 metres) and the aeration method.
Discontinuous systems
Oxidation basins and oxidation ditches. Waste water is let in batch-controlled.
Parallel installations
Various combinations of treatment systems (so-called 'streets') are applied in one installation.
Multi-stage installations
A serial process consisting of two systems, for instance, a trickling filter and an aeration basin. The waste water runs through both stages.
Compact installations
A system consisting of a basin subdivided into four segments. Waste water flows into the aeration segment. Subsequently, the sludge is separated in the central aeration zone. Then part of the sludge is conditioned in the reaeration zone and led back into the aeration zone. The other part (surplus sludge) is stabilised in the sludge mineralisation zone and subsequently removed.
Membrane bioreactor
A system where the sludge is separated from the waste water by using a membrane.
Nereda granular sludge reactor
In the Nereda granular sludge reactor the wastewater is purified by micro-organism clogged in natural granular structures of high density. These granules have a high biological activity and make it easy to separate the micro-organisms from the treated wastewater.

As from 2019 this new treatment type is distinghuished separately in Statline. In the period 2011-2018 already 4 Nereda systems became operational. Until 2019, these installations were classified as oxidation tanks and/or discontinous systems.
Hybrid Nereda - active sludge system
System consisting of a parallel operated Nereda granular sludge reactor and activated sludge system.

In the Nereda granular sludge reactor the wastewater is purified by micro-organism clogged in natural granular structures of high density. These granules have a high biological activity and make it easy to separate the sludge from the treated wastewater.

In activated sludge systems the wastewater is treated in bassins with flocculated sludge . This sludge clumps exists of microorganisms that feed on the the organic pollution in wastewater.

As from 2019 this new treatment type is distinghuished separately in Statline. In the period 2013-2018 already 2 hybrid Nereda - activated sludge sytems became operational. Until 2019, these installations were classified as parallel installations.
Influent waste water
Data on concentrations and quantities of pollutants in the waste water running into urban waste water treatment plants (influent).
Quantities
Volume waste water
The annual volume of influent waste water.
Pollution Equivalents
The pollution equivalent is the official unit that quantifies the pollution in waste water; one pollution equivalent = 150 g TOD (Total Oxygen Demand).
One pollution equivalent is the daily quantity of oxygen-demanding material in the waste water of one person. The degree of pollution in the waste water produced by the private sector is also expressed in pollution equivalents.
This unit is used as of 2010, so for previous years no values are available.
Chemical oxygen demand (COD)
Chemical oxygen demand (COD). Measure of the amount of oxygen consumed when a substance is degraded chemically.
Biochemical oxygen demand (BOD)
Biological oxygen demand (BOD). Measure of the amount of oxygen consumed when a substance is biodegraded.
Nitrogen compounds as N (total)
The total amount of nitrogen in organic compounds (e.g. proteins) and inorganic compounds (e.g. nitrate and ammonium)
Phosphorus compounds as P (total)
The total amount of phosphates and other phosphorus compounds in waste water, measured as phosphorus (P).
Copper
Chromium
Zinc
Lead
Cadmium
Nickel
Mercury
Arsenic
Discharge of waste water (effluent)
Data on concentrations and quantities of pollutants in treated waste water (effluent) discharged from urban waste water treatment plants.
Quantities
Volume waste water
The annual volume of effluent waste water.
Pollution Equivalents
The pollution equivalent is the official unit that quantifies the pollution in waste water; one pollution equivalent = 150 g TOD (Total Oxygen Demand).
One pollution equivalent is the daily quantity of oxygen-demanding material in the waste water of one person. The degree of pollution in the waste water produced by the private sector is also expressed in pollution equivalents.
This unit is used as of 2010, so for previous years no values are available.
Chemical oxygen demand (COD)
Chemical oxygen demand (COD). Measure of the amount of oxygen consumed when a substance is degraded chemically.
Biochemical oxygen demand (BOD)
Biological oxygen demand (BOD). Measure of the amount of oxygen consumed when a substance is biodegraded.
Nitrogen compounds as N (total)
The total amount of nitrogen in organic compounds (e.g. proteins) and inorganic compounds (e.g. nitrate and ammonium).
Phosphorus compounds as P (total)
The total amount of phosphates and other phosphorus compounds in waste water, measured as phosphorus (P).
Copper
Chromium
Zinc
Lead
Cadmium
Nickel
Mercury
Arsenic
Sewage sludge
Residue of treated waste water consisting of suspended solids and excess active sludge (biomass). Sewage sludge is measured including water (see Total wet sludge) or as dry solids.
Wet sewage sludge by destination
The volume of wet sewage sludge, i.e. including water by destination (processing method).
Total wet sludge
Total wet sludge discharged.
Agriculture
Application of manure or soil improver in agriculture. Due to rigid legislation impossible since 1995.
Wet oxidation
Wet oxidation of sludge in so-called VerTech installations: the sludge is oxidised under high pressure in a deep shaft.
Composting
Landfill
Dumping of sludge on regional landfill sites or special sludge depots.
Incineration
Incineration of sludge in special sludge incineration plants or in household waste incinerators.
Cement industry
Co-incineration in cement ovens.
Co-incineration at power plants
Sewage sludge used as a secondary fuel at a power plant.
Other destinations
Mainly reuse.
Dry solids by destination
Discharged sewage sludge in kilogrammes of dry solids by destination (processing method). Dry solid is the residue of sewage sludge after evaporation at 105 degrees centigrade.
Total dry solids
Agriculture
Application of manure or soil improver in agriculture. Due to rigid legislation impossible since 1995.
Wet oxidation
Wet oxidation of sludge in so-called VerTech installations: the sludge is oxidised under high pressure in a deep shaft.
Composting
Landfill
Dumping of sludge on regional landfill sites or special sludge depots.
Incineration
Incineration of sludge in special sludge incineration plants or in household waste incinerators.
Cement industry
Co-incineration in cement ovens.
Co-incineration at power plants
Sewage sludge used as a secondary fuel at a power plant.
Other destinations
Mainly reuse.
Nutrients and heavy metals
The total weight of nutrients and heavy metals removed with the sludge. Most heavy metals adsorb strongly to the sludge particles.
Ashes
The residue of non-inflammable, inorganic matter after incineration.
Nitrogen compounds as N
The total amount of nitrogen in organic compounds (e.g. proteins) and inorganic compounds (e.g. nitrate and ammonium).
Phosphorus compounds as P
The total amount of phosphorus in sewage sludge is analysed as P205 (diphosphorus pentoxide) converted to P total.
Copper
Chromium
Zinc
Lead
Cadmium
Nickel
Mercury
Arsenic