Filtration System Helps Landfill Meet Water Quality Requirements

by Chris Shuster

Located off Highway 64 in Bradenton, FL, the Lena Landfill in Manatee County has faced many obstacles in an effort to control waste. With a population of over 310,000 residents, Manatee County collects over 350,000 tons of trash per year. Occupying over 330 acres of land, the landfill must bury the trash while preserving and protecting the environment in the surrounding area.

One way of protecting the environment and the surrounding population is to keep leachate, or potentially hazardous liquids containing contaminants from decomposing trash within the landfill, from entering groundwater or surrounding rivers and ponds. To accomplish this, the landfill has a system to direct all runoff water and stormwater to a 120-acre holding/settling pond. However, in 2005, Manatee County's Lena Landfill was facing fines and penalties if some water quality issues were not addressed.

The Florida Environmental Protection Agency requires that all water discharged to stormwater ditches and drains meet a quality standard of 29 nephelometric turbidity units (NTU) or less. The Lena Landfill was operating with a turbidity of 35–40 NTU.

There were limited options to remedy the problem. One was to build an additional holding pond, which would occupy an additional 60 acres of the landfill's valuable land, and obtaining a permit from the Department of Environmental Protection for a new hazardous waste site takes many years and can be very difficult to get. Another option was to filter the water in the existing settling pond while preserving the unused acreage for future use to bury trash from the county's rapidly growing population.

In an effort to avoid millions of dollars in lost revenues, Manatee County contracted with the engineering firm PBS&J (Post, Buckley, Schuh & Jernigan) to develop a solution. There are many factors to consider when choosing a filtration system, including the capital cost, efficiency, and maintenance. David Weber, an engineer at PBS&J, specified the installation of an automatic disc filter system capable of handling two million gallons of water per day (MGD).

Manatee County Lena Landfill

The automatic Turbo-Disc Filter system was designed and manufactured by Miller-Leaman Inc. of Daytona Beach, FL. The system consists of two 24-pod systems, complete with booster pumps. As the water in the leachate, or settling pond, rises to a predetermined level, submersible pumps activated by a float switch are engaged. The water is then directed through the fully automatic, self-cleaning filter systems and discharged into adjacent waterways, meeting the Florida EPA requirements. The automatic filters were designed to accommodate 1,400 gpm of water contaminated with particles, sediment, and organic contaminants.

The cost of the filter system was substantially less than other techniques being considered for the project. In addition, the filter uses a fraction of the backwash water used by sand filters, a feature that was of particular interest in this case.

In an effort to validate the technology and familiarize landfill personnel with the Turbo-Disc Filter, Miller-Leaman transported its fully operational demonstration trailer to the site. The demo trailer has the ability to pump water from the actual water source to determine the solids loading (PPM), the particle distribution size, NTU level, and other important variables. The filter housings in the demo trailer are transparent, allowing the customer to visualize the effectiveness of the filter, both in filtration and backwash modes.

Each micron size was tested and water samples were taken to check the NTU level. Once the appropriate micron size was determined in order to satisfy the NTU requirement specified, the information was extrapolated to properly size the filter system.

Intake water piping to Turbo-Disc System with booster pumps.

System maintenance is performed approximately once a year, depending on the water quality of a given application, and is relatively simple.

For the Lena Landfill project, where land availability was extremely limited, filtering the existing stormwater retention pond proved to be a cost-effective solution for meeting environmental requirements.

About the Author:

Chris Shuster is Vice President of Sales & Marketing for Miller-Leaman.