The largest wastewater treatment plants can be defined in several ways.
The largest in term of capacity, both during dry and wet-weathers, is the Jean-R.-Marcotte Wastewater Treatment Plant in Montreal. With full secondary treatment of effluents it would be the Deer Island Waste Water Treatment Plant of Boston. In terms of area occupied it is by far Melbourne's Western Treatment Plant.
| Plant name | City | Country | Opening Year | Dry-weather capacity (m³ per day) | Wet-weather capacity (m³ per day) | Area (km2) | Notes | |
|---|---|---|---|---|---|---|---|---|
| New Delta Wastewater Treatment Plant [1] | El Dabaa |  Egypt | 2023 | 7 500 000 | 0.32 | Holds four Guinness World Records. | ||
| Bahr El-Baqar Wastewater Treatment Plant [2] | Port Said | Egypt | 2021 | 5 600 000 | 0.65 | |||
| Jean-R.-Marcotte Wastewater Treatment Plant [3] | Montreal |  Canada | 1984 | 2 780 000 | 7 600 000 | 0.67 | Secondary treatment planned for 2023. [4] | |
| Detroit Wastewater Treatment Plant [5] | Detroit |  USA | 1940 | 2 460 000 | 6 435 000 | 0.53 | Wet-weather secondary treatment capacity limited to 3 520 000 m³/day. | |
| Passaic Valley Sewerage Commission | Newark | USA | 1902 | 1 320 000 | 2 700 000 | Full secondary treatment since 1982. | ||
| Stickney Water Reclamation Plant [6] | Chicago | USA | 1930 | 2 665 000 [7] | 5 450 000 [8] | 1.67 | ||
| Blue Plains Advanced Wastewater Treatment Plant [9] | Washington D.C. | USA | 1937 | 1 450 000 | 4 073 000 | 0.62 | Secondary treatment since 1959. Enhanced nutrient removal in 2014. | |
| Deer Island Waste Water Treatment Plant | Boston | USA | 1968 | 1 438 000 | 4 542 000 | 0.6 [10] | Full secondary treatment since 1995. | |
| Abu Rawash Wastewater treatment plant | Giza | Egypt | 2021 | 1 600 000 | 1.39 | Secondary treatment since 2021. | ||
| Atotonilco de Tula Plant [11] | Mexico City |  Mexico | 2015 | 2 000 000 | 3 000 000 | |||
| Hyperion Water Reclamation Plant [12] | Los Angeles | USA | 1925 | 1 041 000 | 3 000 000 | 0.81 | Wet-weather secondary treatment (since 1950) capacity limited to 1 821 000 m³/day. | |
| Kuryanovo wastewater treatment facilities [13] | Moscow |  Russia | 1950 | 2 200 000 | ||||
| Lyuberetskiye wastewater treatment facilities [14] | Moscow | Russia | 1963 | 3 000 000 | ||||
| Seine Aval Wastewater Treatment Plant [15] | Paris |  France | 1940 | 1 460 000 | 2 900 000 | 8 | ||
| Shanghai Zhuyan I Wastewater Treatment Plant [16] | Shanghai |  China | 2004 | 1 700 000 | ||||
| Stonecutters Island Sewage Treatment [17] | Hong Kong | China | 2001 | 2 765 000 [18] | ||||
| Bailonggang Wastewater Treatment Plant | Shanghai | China | 1999 | 2 000 000 | ||||
| Gabal el Asfar Wastewater Treatment Plant | Cairo | Egypt | 1 700 000 | 2 500 000 [19] | 1.63 | |||
| Beckton Sewage Treatment Works | London |  UK | 1864 | 2 330 000 | 1 | |||
| Morigasaki Water Reclamation Center [20] | Tokyo |  Japan | 1966 | 1 540 000 | 0.41 | |||
| Vienna wastewater treatment plant | Vienna |  Austria | 2005 [21] | 680 000 [22] | 1 500 000 | 0.39 | ||
| ETE Barueri [23] | Barueri |  Brazil | 1988 | 1 382 400 | 0.86 | |||
| Beijing Huaifang Water Plant | Beijing | China | 2017 | 600 000 [24] | 0.16 [25] | Built underground. | ||
| Crossness Sewage Treatment Works | London | UK | 1859 | 564 000 | 0.7 | Home to Sir Joseph Bazelgette beam engine house, victorian engineering.(beam engine trust), The engine was started by HRH The Prince of Wales, Albert Edward, who subsequently became King Edward VII. | ||
| Western Treatment Plant | Melbourne |  Australia | 1897 | 485 000 | 105 [26] | |||
| Jebel Ali Wastewater Treatment Plant | Dubai |  UAE | 2019 | 375 000 [27] | 6.7 | |||
| Dasherkandi Sewage Treatment Plant | Dhaka |  Bangladesh | 2023 | 350 000 | 500 000 | 0.26 | Largest sewage treatment plan in South Asia. [28] | |
| McAlpine Creek Wastewater Treatment Plant | Charlotte, N.C. | USA | 1966 | 290 950 |
Wastewater treatment capacities are expressed in cubic meters per day. 1000 cubic meters is 1 ML (mega liter). The area occupied by the plants are in square kilometers.
