HAZWASTE: Microbes Clean Contaminated Green Waste

Tony Minna

Bugs can be man's best friend, especially during a major contaminated green waste cleanup. Microbes can offer a cost-effective alternative to landfilling or burning by turning this contaminated debris into compost. They also can help generate revenue by creating a marketable product.

Green waste can become contaminated when operators start accepting additional materials, such as tar, oil and creosote-laden railroad ties, waste mixed with paint thinners and solvents, and in many cases, by the foam firefighters use to extinguish green waste fires. Additionally, moisture and heat encourage harmful bacteria to thrive and multiply.

Depending on the circumstances, microbe technology may prove to be more economical than dumping contaminated debris. With microbe technology, anaerobic microbes breed and multiply, breaking down organic material by consuming bacteria as long as there is a constant temperature of 120 degrees to 132 degrees Fahrenheit and sufficient air, water and food. Microbes also can reduce the firefighting foam's petroleum distillates to acceptable levels so that the material can be resold as erosion control material or mulch and compost.

For example, earlier this year the city of Santa Clarita, Calif., had to clean up green waste contaminated by fire-fighting foam. Although the tipping fees at the local Browning-Ferris Industries (BFI) landfill was only $25 per ton and the site was located only 3.5 miles from the debris, the fees for disposing of the 50,000 cubic tons would total approximately $1,250,000.

After investigating microbe technology, the city hired Van Nuys, Calif.-based TM Enterprises to clean up the debris. Using a Peterson Pacific trommel with 2-inch capabilities, the contractor screened the pile and ground the overs with another Peterson Pacific machine with a 4-inch capacity. The microbes were sprayed as the materials came off the belt, which insured a uniform application.

The Los Angeles County Health Department required that the compost or fines off the screen be treated in 2,000-ton piles. Here, controlling the pile's temperature became critical not only to prevent fires but also to limit the heat's affect on the microbes.

Using specially cultured microbes, at a cost of $2,400 per pile, initial tests showed a slight increase in bacterial counts of fecal coliform and salmonella, but the microbes soon began lowering the harmful bacteria counts.

By rolling the piles daily and adding more microbes using a sprinkler, the fecal coliform dropped from 450,000 parts per million (ppm) to minus 3 in eight weeks. The salmonella count dropped from 350,000 ppm to zero in four weeks. Reaching the required threshold of 1,000 ppm, the materials were moved off the city's property and sold for $4 per yard.

Microbe technology worked quickly, met all regulatory requirements and saved the city money. What more can you ask from a bunch of bugs?