Dillo Dirt
Dillo Dirt is Austin's homegrown compost.
Dillo Dirt™ is made at Austin Water's Hornsby Bend Biosolids Management Plant, the first program of its kind in Texas and one of the oldest in the nation. Brush from City departments and residents is mixed with treated biosolids and composted to create a rich, recycled soil product, with composting temperatures between 130 and 170 degrees Fahrenheit virtually eliminating pathogens. After active composting for more than a month, Dillo Dirt is cured for several more months and screened to produce a finished compost.
Dillo Dirt meets all Texas Commission on Environmental Quality (TCEQ) and Environmental Protection Agency (EPA) requirements and can be used for landscaping and flower beds. It reduces watering requirements and enriches the soil while diverting waste from the landfill. Our compost has been awarded the U.S. Composting Council Seal of Testing Assurance.
You can drop off brush at Hornsby Bend to be used in making Dillo Dirt.
Where to Find Dillo Dirt
Dillo Dirt is marketed and sold by Austin Water's biosolids reuse contractor, Synagro. To purchase, contact Synagro sales at sales@synagro.com or 800-370-0035.
Several thousand tons of Dillo Dirt are available each year for donation to programs benefiting Austin residents, including public schools, parks, nonprofits and other charitable organizations. The material is donated at no cost, but recipients are responsible for transportation. Email dillodirt@austintexas.gov for more information.
Resources
Dillo Dirt can be used for a variety of soil improvement applications. Use the rates below as a guide.
To calculate cubic yards needed: length (ft.) × width (ft.) × depth (inches) ÷ 324 = cubic yards
| Use | Lbs per 1,000 sq ft (depth) | Instructions |
|---|---|---|
| Turfgrass — Establishment, Soil Incorporated | 1,500–4,000 lbs (½"–2") | Mix with top 4"–6" of soil. Use lower rate on fertile soil, higher rate on infertile soil. |
| Turfgrass — Surface Mulch | 700–4,000 lbs (¼"–2") | Spread evenly on surface before seeding small species (Bermuda) or after seeding large-seeded species (fescues). |
| Turfgrass — Maintenance | 300–700 lbs (⅒"–¼") | Spread evenly on surface. For cool-season grasses, apply higher rate in fall or split between fall and spring. |
| Nursery Crops and Ornamentals — Establishment | 1,500–4,300 lbs (½"–2¼") | Mix with top 6"–8" of soil. Do not use where acid-soil plants (azalea, rhododendron, etc.) are to be grown. |
| Nursery Crops and Ornamentals — Maintenance | 300–600 lbs (⅒"–⅕") | Spread evenly on surface. Can be mixed into soil or used as mulch. |
| Tree Balling | 50% rate | Mix compost with bark or soil. |
| Potting Soil Mixes | No more than ⅓ by volume | Water and drain mix several times before planting to prevent salt injury. Blend with peat, sand, perlite, vermiculite or bark. |
1,500 lbs per 1,000 sq ft is approximately ½" depth of compost. Compost has a bulk density of about 1,000 lbs per cubic yard at 40% moisture. Source: USDA publication ARM-NE-6, August 1979.
Dillo Dirt meets all EPA and TCEQ requirements for unrestricted use. Biosolids naturally contain small quantities of metals that travel through the sewer system. EPA and TCEQ have established acceptable levels to protect public health and the environment, and Dillo Dirt contains far less than the allowable maximums.
Some of these metals, including zinc, molybdenum and chromium, are essential plant nutrients. Austin Water's pretreatment program monitors wastewater quality and controls industrial discharges to keep metals levels low.
Originally established in the 1950s as stabilization ponds, the Hornsby Bend Biosolids Management Plant has become a nationally recognized, award-winning biosolids recycling facility situated on 1,200 acres along the lower Colorado River about eight miles east of downtown Austin. Biosolids from Walnut Creek and South Austin Regional wastewater treatment plants are pumped to Hornsby Bend, where centrifuges thicken them to reduce volume before treatment.
Anaerobic Digestion
Thickened biosolids are stabilized through anaerobic digestion in eight two-million-gallon tanks. Digestion destroys more than 90% of pathogens. Methane produced during digestion powers onsite generators. After digestion, biosolids are thickened again by belt presses before composting.
Composting and Water Reuse
Water separated from the biosolids is treated in a 180-acre pond system. The treated water irrigates an onsite farm where hay is harvested by a contract farmer, with a portion of revenue returned to the City.
Dewatered biosolids are combined with chipped brush and composted in windrows more than 500 feet long. Yard trimmings collected by Austin Resource Recovery (ARR) are ground into mulch at Hornsby Bend and mixed with biosolids for composting. The biological heat of composting produces a stable, safe organic product.
Austin Water holds a long-term contract with Synagro of Texas-CDR, Inc. for biosolids composting at Hornsby Bend. In addition to Dillo Dirt, Synagro produces AllGro® compost, which meets all regulatory specifications for biosolids compost.
Guidance Documents
These documents are for public information and for use by contractors working at Hornsby Bend.
Hornsby Bend is nationally recognized for its biodiversity and is one of the best birding sites in Texas. Learn more about birding and other events at the Center for Environmental Research.
For general questions about Dillo Dirt, email dillodirt@austintexas.gov or call 512-972-1956.