One of my favorite school field trips was to the Hornsby Bend Biosolids Management Plant in Austin, Texas. I found the processes of turning sludge and wastewater into useful products fascinating. For instance: Dillo Dirt™.
Dillo Dirt™ is a unique Texas product created in 1989 and recognized with a first-place award by the United States Environmental Protection Agency (EPA) for Biosolids Recycing. It was the first program in the state of Texas and one of the oldest in the nation.
Using gravity belt thickeners, the sludge is thickened and then sent it to an anaerobic digestion phase, where the oxygen is removed. This reduces the amount of human and plant pathogens by 90%. A by-product of this process is methane gas, which is used to power electric generators on site.
Once this digestion process is complete, biosolids are re-thickened and are almost ready for landscaping. The water separated from these processes is used to irrigate 150 acres of a 550-acre hay and feed crop farm, for which the City of Austin receives revenue from the contracted farmer.
This is recycling at its finest, using every part of the system, combining the re-thickened sludge with yard trimmings collected curbside from Austin residents and using a several-month curing process to make sure the dirt is usable for gardens and landscapes.
There have been concerns about whether to use the Dillo Dirt™ for growing vegetables and fruits, but it adheres to strict guidelines from the EPA and has been labeled with “unrestricted use.”
In 2009 at Austin City Limits Music Festival, there were alarming issues with people covering themselves in mud, which was partially Dillo Dirt™ and rain, and they had symptoms of rashes. According to Austin Water, the EPA and the State of Texas have established acceptable levels of metal to protect the public.
Although I would not cover myself in any type of mud, I have had great success using Dillo Dirt™ in my garden, and have never suffered any ill effects from handling it with bare hands.
Dillo Dirt™ also donates most of its product to parks and organizations for their landscaping and agricultural endeavors.
Title Department Program Manager