Originally established in the 1950s as a series of stabilization ponds used to treat wastewater sludge (biosolids) from the City's wastewater plants, the Hornsby Bend Biosolids Management Plant ("Hornsby Bend") has become a nationally recognized biosolids recycling facility winning many awards, including a first-place award by the U.S. Environmental Protection Agency (EPA) for biosolids recycling.

Situated on 1,200 acres of land along the Colorado River, about 8 miles east of downtown Austin, the facility is a national model for innovative approaches to benefit the environment, such as reducing waste, producing compost, and protecting ecosystems.

Biosolids (specifically primary and secondary waste-activated sludge) from the City's wastewater treatment plants are pumped to Hornsby Bend from the City's wastewater treatment plants. They are then thickened by gravity belt thickeners to reduce volume and allow more time for decomposition in the digesters.

Anaerobic Digestion

Once thickened, biosolids are stabilized by a process called anaerobic (without oxygen) digestion. The process occurs in eight large tanks or digesters (with a capacity of 2-million gallons each). Digestion destroys more than 90% of the pathogens present in the biosolids. Methane gas, a by-product of the process, is used to power on-site electric generators. After digestion, biosolids are thickened again by belt presses before they are re-used in composting.

Biosolids Land Application and Water Re-use

Water separated from the sludge flows through a 180-acre facultative pond system. After polishing in a 4-acre greenhouse enclosed aquatic plant facility, the treated effluent is used to irrigate approximately 150 acres of a 550-acre on-site farm. Hay and other feed crops are harvested from this land by a contract farmer, and the City receives a portion of the revenue.

The dried biosolids are combined with yard trimmings collected curbside throughout Austin and composted in 6-foot high rows (windrows) measuring more than 500 feet long. Residential yard trimmings picked up curbside in Austin are mixed with biosolids for composting. The biological activity and heat from composting produces a stable organic product that can be safely used by the public. A portion of this compost is sold under the trade name of "Dillo DirtTM".