Domestic wastewater systems handle high-volume waste streams with relatively low concentrations of nutrients and other components of the waste. Every toilet, shower, washing machine, and dishwasher contributes significant amounts of water to the waste stream. For example, the Metropolitan St. Louis Sewer District (population 1,400,000) handles 360 million gallons of wastewater each day, or about 255 gallons per person per day.

In contrast, manure production on hog finishing operations is predominantly feces and urine generated by the animals. Added water in the buildings is limited to cleaning activities and wasted drinking water. Total manure and wastewater production averages about 1.4 gallons per animal per day for grow-finish operations. Volumes are higher on operations that have open manure storages in regions where annual rainfall exceeds annual evaporation. On these operations, manure and wastewater production still typically runs less than 3 gallons per animal per day.

To put these differences in perspective, the city of St. Louis generates more than 22 times the waste volume of all the grow-finish pigs in Missouri.

The high volume of human waste systems typically requires domestic wastewater systems to discharge treated water into surface waters. The treatment objective is to lower nutrients, organic matter, and pathogens in wastewater to a point that the wastewater can be released into a river or other water body without exceeding the assimilation capacity of the water body for those pollutants.

The limited added water in animal manure systems makes it feasible to contain the manure in storage structures or waste treatment lagoons and then land-apply the manure as a fertilizer source. Permits for almost all animal feeding operations make routine discharge of manure to waters of the state illegal; the permits are called "no-discharge" permits. All manure must be land-applied in a manner that prevents overflow of manure storages or treatment lagoons and runoff during manure application. The rates of manure applied to fields are dictated by the productivity of crops. Failure to comply with these standards typically results in a notice of violation and fines from regulatory agencies.

For more information on the difference between the objectives of human waste and animal manure, see the publication Hog Manure and Domestic Wastewater Objectives.

John A. Lory
Associate Professor of Extension
University of Missouri