Package plants are pre-engineered and prefabricated wastewater treatment plants using an aerobic activated sludge process typically used for treating blackwater and greywater. Systems treat organic waste but can be modified or expanded to provide nitrogen and phosphorus treatment. They are often designed to achieve specific discharge standards or to yield a product water suitable for non-potable use for agricultural and aquaculture production, industrial uses, water sustainability, and reclamation uses such as irrigation, washdown, and artificial recharge. These scalable plants can serve a range of community sizes, from small towns to medium-sized cities, and are often used for small villages and towns, housing subdivisions, mobile-home parks, marinas, resorts, military installations, schools, manufacturing facilities, and other small facilities; flows can range from 50 gallons per day (gpd) to 5 million gpd (C&M Mining Machinery, 2020). They can be readily built on-site and modified for enhanced degrees of wastewater treatment. They have a compact footprint, are easily transportable, relatively simple to operate, and have low labor requirements.

Package plants combine mechanical and chemical processes for primary treatment and secondary treatment; they may include nutrient control through chemical or biological processes to achieve tertiary treatment. Package plants typically function as cluster systems, satellite systems, or smaller-scale centralized systems intended to serve a broad range of community sizes.