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The Speciation and reactivity of wastewater-derived organic nitrogen
David L. Sedlak, University of California, Berkeley
Elif Pehlivanoglu, University of California, Berkeley
Technical Completion Report W-972
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ABSTRACT: Nitrogen often is the limiting nutrient for the growth of algae and
phytoplankton in estuaries and surface waters in California. To control cultural
eutrophication (i.e., excessive growth of algae and plankton related to
anthropogenic sources) regulatory agencies often focus on the control of point
source discharges, including municipal wastewater effluent. Recent attempts to
control cultural eutrophication in nitrogen-limited systems have focused on the
simultaneous control of all forms of inorganic nitrogen with the underlying
assumption that inorganic and organic nitrogen are equally bioavailable. To
assess the validity of this assumption, algal growth bioassays were conducted
using denitrified wastewater effluent samples that contained mainly organic
nitrogen. The growth assays were performed with a species of algae (Selenastrum
Capricornutum) that is commonly used for regulatory compliance monitoring.
Results of the study indicate that the wastewater-derived dissolved organic
nitrogen (DON) is not bioavailable to the algae in the absence of bacteria.
However, approximately half of the wastewater-derived organic nitrogen was
available to the algae in the presence of bacteria during a two-week incubation.
In conjunction with the experiments on bioavailability, the nature and
properties of wastewater-derived organic nitrogen was characterized by
measuring concentrations of free and combined amino acids and by subjecting
wastewater effluent samples to ultrafiltration. Results of these experiments
indicate that most of the wastewater-derived organic nitrogen was associated with
unidentified compounds that are capable of passing through a 1 kDa ultrafilter.
Wastewater-derived organic nitrogen also plays an important role in the
formation of the carcinogenic disinfection byproduct, N-nitrosodimethylamine
(NDMA). NDMA is formed when wastewater effluent is disinfected with
chlorine. It also can be formed when surface water or groundwater that has been
impacted by wastewater effluent discharges undergoes disinfection in drinking
water treatment plants. Recently, concerns associated with NDMA have caused
great concern among utilities that practice indirect potable water reuse. Most of
the attention to date has focused on the removal of NDMA from the treated
wastewater effluent. However, the presence of NDMA precursors also could be a
problem if the NDMA precursors in drinking sources are stable after they are
discharged because they could result in NDMA formation during drinking water
treatment. To assess the stability of NDMA precursors associated with
wastewater-derived organic nitrogen, NDMA precursor concentrations were
measured in effluent samples before and after incubation with bacteria under
aerobic conditions. Results of the experiments indicate that the NDMA
precursors are stable for at least 30 days.
These results suggest that wastewater-derived organic nitrogen consists of
complex compounds that are not very reactive. However, under certain
conditions, wastewater-derived organic nitrogen species can serve as a source of
nutrients in nitrogen-limited systems and as disinfection byproduct precursors.
The results of this research will be useful in the development of indirect potable
water reuse systems and the design of watershed protection plans designed to
protect aquatic ecosystems from the effects of cultural eutrophication.
SUGGESTED CITATION:
David L. Sedlak and Elif Pehlivanoglu,
"The Speciation and reactivity of wastewater-derived organic nitrogen"
(September 1, 2004).
University of California Water Resources Center.
Technical Completion Reports.
Paper sedlak.
http://repositories.cdlib.org/wrc/tcr/sedlak
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