Hurst Creek MUD has a total wastewater treatment capacity
of 500,000 gallons per day (gpd), with the ability to treat
four times this volume on a short term basis. The treatment
plants are of the complete mix variety, with duplicate
aeration basins, clarifiers, chlorine contact basins and
tertiary filters. Treated wastewater, termed effluent,
is stored in a 110,000 gallons in-ground tank and pumped
to a 50 million gallon effluent storage pond located just
east of Flintrock Falls. From there the effluent is applied
to The Hills and Flintrock golf courses.
Raw sewage is 99% water and one percent of liquid and
solid human wastes, scrap food, paper, soap and medical
waste – plus whatever else people flush down their drains.
These wastes consist of proteins, fats, carbohydrates,
cellulose, bacteria and viruses. Without treatment, these
materials are highly putrisable and will rapidly decompose
with strong odor production. During heavy rainstorms
runoff and ground water enter the collection system and
dilute the sewage but increase the overall volume of flow.
A complete mix wastewater treatment plant purifies sewage
by feeding it to bacteria; this takes place in a large
tank, the aeration basin, to which is bubbled a large volume
of compressed air. Bacteria of the genus Aerobacter –
which means air bacteria – thrive in the broth, consume
the putrisable matter and grow more bacteria. Periodically,
the excess bacteria must be wasted out of the system and
hauled away to a State- licensed land application farm.
After aeration, the wastewater flows by gravity to a settling
basin, called the clarifier; here, the water is quiescent
and still and the heavy particles slowly settle to the
bottom, where they are raked up as sludge and returned
to the head of the plant. The sludge consists of
concentrated bacteria which are added to the incoming raw
sewage flow to start the whole process over again. Clear
water is skimmed off the surface of the clarifier, disinfected
with chlorine and filtered to become effluent.
Hurst Creek’s effluent is of a high quality, comparable
to water from Lake Travis, with two exceptions: concentrations
of phosphorus and nitrate are several orders of magnitude
higher than lake water. These compounds act as fertilizer
for plant growth, hence the ban on wastewater discharges
in the Highland Lakes area. Instead, effluent is stored
and applied to golf courses as needed, and the phosphorus
and nitrogen promote the growth of grass rather than algae.