Wastewater treatment plants (WWTPs) can be an option in some towns and cities for repurposing pet waste only if the facility decides to accept the waste stream.
In the U.S. and Canada, WWTP managers and municipalities decide if dog waste can be flushed or if large quantities of dog waste can be taken to their facilities for treatment. Whether a material is accepted depends on a facility’s processes, policies and capacity.
Toilet waste flows into sanitary sewers – to be distinguished from storm sewers which collect runoff from streets and other sites that don’t require septic treatment to control dangerous pathogens. Storm sewer runoff flows directly into public waterways. Sanitary sewer runoff is sanitized at WWTPs and can be reused. The processed residual is sometimes repurposed as agricultural fertilizer.
Many newer animal shelters routinely hose loose dog waste into septic sewage drains. These drains are designed when the facilities are built for that specific purpose.
In past years the EPA recommended flushing dog poop but that advice has been largely withdrawn from online public statements. WWTPs are designed and built for human waste. Facilities are understandably wary that too much pet waste might result in systemic problems.
A number of Canadian cities, including Vancouver have banned dog waste from regular garbage bins. That city now streams dog waste from designated bins to the water treatment plant.
To determine the suitability of adding pet waste into systems that end up at WWTPs, you need to contact your local water treatment service.