National Drinking Water Clearinghouse
West Virginia University
P.O. Box 6064
Morgantown, WV
26506-6064


Tech Trends

Package Plants

by Vipin Bhardwaj
Technical Assistance Specialist

Conventional water treatment systems include steps such as coagulation, flocculation, sedimentation, and filtration. In package water treatment plants, the same steps are combined in one unit. In these plants, the equipment is pre-designed, assembled in a factory, skid mounted, and transported fully assembled to the site, including the control system. At the site, the treatment unit requires only plumbing and electrical hook up to complete installation.

The popularity of package plants increased during the last decade. In 1990, there were approximately 650 to 700 such units in the U.S., according to the U.S. Environmental Protection Agency (EPA). As of 1998, there were more than 2,000 package units in service across the country.

Package Plants Have Advantages
For small communities, package plants offer four distinct advantages:
1. compact size,
2. cost effectiveness,
3. ease of use, and
4. unattended operation.
Because package plants offer savings in the engineering, design, installation, and operation and maintenance costs, they are economical for treating smaller volumes of water.

Package plants can effectively remove turbidity and bacteria from surface water with consistently low to moderate turbidity levels. Package plants can treat water with varying water quality, although such treatment may require more skilled operators and closer attention.

Small system managers typically prefer treatment protocols that require minimal operator skill and attention. Package systems fulfill these requirements. For example, a package system can have an automatic backwash operation in the absence of an operator and can have the filters returned to service on
a pre-programmed basis.

Types of Package Plants
The three basic types of package plants are (1) conventional package plants, (2) tube-type clarification package plants, and (3) adsorption clarifier package plants.

Conventional package plants, as the name suggests, contain the conventional steps of coagulation, flocculation, sedimentation, and filtration. Package water treatment plants are available from several manufacturers in a wide range of capacities. Design criteria used for these modular units vary widely. Some manufacturers adhere closely to accepted conventional design practices, such as 20- to 30-minute flocculation detention time, a 2-hour sedimentation detention time, and rapid sand filters rated at 2 gpm/ft2.

In tube-type clarifier package plants, manufacturers have used new technology, including tube settlers and high-rate dual- and mixed-media filters to reduce the size of a plant and extend the capacity range of single factory-assembled units.
An adsorption-clarifier package plant features an up-flow filter with low density plastic bead media (called the adsorption clarifier), followed by a mixed media filter to complete the water treatment. The flocculation and sedimentation basins have been replaced by the adsorption clarifier bed, thus combining the two steps into one.

Selecting a Package Plant System
Package plant systems are most appropriate for treatment unit sizes ranging from 25,000 to 6 million gallons per day (95 to 23,000 cubic meters per day) of water treated.

Influent water quality is the most important consideration in determining the suitability of a package plant application. Complete influent water quality records should be examined to determine turbidity levels, seasonal temperature fluctuations, and color level expectations.

Both high turbidity and color may require coagulant dosages beyond many package plant design specifications. In cases of consistently high levels of turbidity and color, the package plant capacity must be down-rated or a larger model selected. Where turbidity exceeds 100 to 200 NTU, pre-sedimentation may be required as a pretreatment. Pilot tests may be necessary
to select a package plant for more innovative designs using high flow rates and shorter detention time unit processes.

Highly variable influent water quality requires a high level of operational skill and attention, which tends to negate the package plant advantages of low cost and automation.

Package Plant Image Source: EPA’s Technologies for Upgrading Existing or Designing New Drinking Water Treatment Facilities

Package Units Can Have Varying Applications
Package units can be used to treat water supplies for communities as well as non-community water systems, such as those in factories, schools, recreational areas, state parks, construction camps, ski resorts, remote military installations, and other locations where potable water is not available from a municipal supply.

Several state agencies have mounted package units on trailers for emergency water treatment. Their compact size, low cost, minimal installation requirements, and ability to operate virtually unattended make them an attractive option during emergencies and in locations where revenues are not sufficient to pay for a full-time operator.

Future Applications of Package Plants
When installed correctly and maintained properly, package plants will operate sufficiently. These systems have the potential for helping small systems comply with treatment regulations and the needs of the communities they serve.

Over the years, manufacturers have incorporated new technologies into their designs. But, because many existing state design standards recognize only conventional treatment processes, package plants employing innovative technologies sometimes encounter regulatory barriers. Some states consider package plants to be an “alternative treatment,” which means that manufacturers need to put their equipment through lengthy pilot studies from state to state.

At the national level, at least two organizations are interested in package plants. EPA—in partnership with the NSF International—has initiated an Environmental Technology Verification program for verifying the effectiveness of these package plants. The Association of State Drinking Water Administrators has developed a protocol for approving package plants and treatment modules. With these national initiatives and the many advantages of the plants described above, the use of package plants will undoubtedly continue
to increase.

References:
U.S. Environmental Protection Agency, Office of Drinking Water. 1990. Technologies for Upgrading Existing or Designing New Drinking Water Treatment Facilities. EPA/625/4-89/023. Cincinnati, OH.

HDR Engineering, Inc. 2001. Handbook of Public Water Systems, 2nd Edition. John Wiley and Sons, Inc.: New York, NY.

Goodrich, James et al. 1995. “Package Plants for Small Systems: A Field Study,” AWWA Journal. November 1995, pp. 39–47.

Adams, Jeff and C. Bruce Bartley. 2000. “The EPA’s Environmental Technology Verification Program for Packaged Drinking Water Treatment Systems.” Presented at the Small Drinking Water and Wastewater Systems Conference. January 12–15, 2000. Phoenix, AZ.