List of largest wastewater treatment plants

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
Jean-R.-Marcotte Wastewater Treatment Plant[1]	Montreal	Canada	1984	2 780 000	7 600 000	0.67	Secondary treatment planned for 2021.[2]
Detroit Wastewater Treatment Plant[3]	Detroit	USA	1940	2 460 000	6 435 000	0.53	Wet-weather secondary treatment capacity limited to 3 520 000 m³/day.
Stickney Water Reclamation Plant[4]	Chicago	USA	1930	2 665 000[5]	5 450 000[6]	1.67
Deer Island Waste Water Treatment Plant	Boston	USA	1968	1 438 000	4 542 000	0.6[7]	Full secondary treatment since 1995.
Blue Plains Advanced Wastewater Treatment Plant[8]	Washington D.C.	USA	1937	1 450 000	4 073 000	0.62	Secondary treatment since 1959.
Atotonilco de Tula Plant[9]	Mexico City	Mexico	2015	2 000 000	3 000 000
Hyperion Sewage Treatment Plant[10]	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[11]	Moscow	Russia	1950	2 200 000
Lyuberetskiye wastewater treatment facilities[12]	Moscow	Russia	1963	3 000 000
Seine Aval Wastewater Treatment Plant[13]	Paris	France	1940	1 460 000	2 900 000	8
Beijing Huaifang Water Plant	Beijing	China	2017				A Newly Built WWTP, having a capacity to recycle water of 200 million m3/yr.
Shanghai Zhuyan I Wastewater Treatment Plant[14]	Shanghai	China	2004	1 700 000
Stonecutters Island Sewage Treatment[15]	Hong Kong	China	2001		2 765 000[16]
Bailonggang Wastewater Treatment Plant	Shanghai	China	1999	2 000 000
Gabal el Asfar Wastewater Treatment Plant	Cairo	Egypt		1 700 000	2 500 000[17]	1.63
Beckton Sewage Treatment Works	London	UK	1864		2 330 000	1
Morigasaki Water Reclamation Center[18]	Tokyo	Japan	1966		1 540 000	0.41
Western Treatment Plant	Melbourne	Australia	1897	485 000		105[19]

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.