Nitrogen-containing compounds were
also analyzed through the soil column
system. In the vadose column, any remaining ammonia from the DCTWRP effluent
was quickly consumed while nitrate
levels increased by a similar mass basis.
This indicates that nitrification is occurring throughout the vadose zone, not a
surprising finding as the cyclic nature of
surface spreading reintroduces oxygen
into the aquifer and promotes oxic conditions. Through the saturated columns the
nitrate and total nitrogen concentrations
were predominantly consumed, as less
than 1 mg/L as N was consistently found in
the six-month saturated column effluent.
THE RESULTS OF project #4600 show
that the SAT process is a powerful natural purification process with the ability to
effectively remove most of the indicators
of human waste within the recycled water.
The soil columns’ operation is a gradual
process that occurs over the course of
months, years, or even possibly decades,
as the biological community seems to
adapt to the changing water quality. The
soil columns continue to
increase in their effectiveness
over both retention time and
overall operation time. This
research project provides
our industry and regula-
tors alike with an increased
understanding of the SAT
process, which in turn pro-
vides an increased comfort
with tapping into this natu-
ral treatment process. While
there is much to be learned
from this study, there is still
much more to understand
about this sustainable and
natural treatment process.
Utilities investigating new
ways to develop sustainable
water sources would be well
served to consider the use
of SAT where groundwa-
ter basins are already used for drinking
water and land is available to allow for
the percolation of water into the ground.
Publication of the final project deliver-
ables is anticipated in early 2017.
CDPH (CALIFORNIA DEPARTMENT of
Public Health). 2016. “DPH-14-003E
Groundwater Replenishment Using
Recycled Water.” http://www.cdph.
TRUSSELL, R. S., and C. B. Trussell.
Forthcoming. Soil Aquifer Treatment
Characterization with Soil Columns
for Groundwater Recharge in the San
Fernando Valley. Project #4600. Denver,
Colo.: Water Research Foundation.
Table 1. Summary of CEC removal using soil columns
(90 to 50%)
(50 to <25%)