NITROGEN REMOVAL FROM DIGESTED SLUDGE
SUPERNATANT LIQUOR USING ATTACHED
AND SUSPENDED GROWTH SYSTEMS
T. B. S. Prakasam, Project Manager
W. E. Robinson, Sanitary Chemist
C. Lue-Hing, Director
Department of Research and Development
The Metropolitan Sanitary District of Greater Chicago
Chicago, Illinois 60611
INTRODUCTION
Over the past five years the Metropolitan Sanitary District of Greater Chicago has
been conducting both pilot and full-scale experiments on the control of nitrogen in its
wastewater streams such as the wastewater received at its three major sewage treatment
plants and in digested sludge supernatant (SLS) from sludge holding basins.    Studies
relating to nitrogen control in domestic wastewater were conducted with the specific
objective of developing design criteria for nitrification systems that would produce effluents with NH4-N concentrations complying with Illinois Pollution Control Board (IPCB)
standards.   On the other hand, the objective of controlling nitrogen in the ammonia-rich
SLS has been to conserve or eliminate nitrogen so that the land application of this supernatant, if practical, will be beneficial to plant growth and will not cause any significant
ground water contamination by nitrate.   In addition, strategies of nitrification and denitrification of SLS permit greater land application of sludge and recycling of the nitrified
SLS through the treatment plant or its discharge to receiving waters, depending on its
quality.   The feasibility of nitrifying sludge lagoon supernatant liquor containing up to
about 800 mg NH4-N-N/1 with a pilot-scale rotating biological disc has been reported
earlier [ 1 ].   Currently, the feasibility of denitrifying the nitrified mixed liquor with a
pilot-scale submerged rotating biological disc unit (attached growth unit) is being studied.
In addition, the feasibility of nitrifying and denitrifying the sludge supernatant liquor
simultaneously in a single suspended growth system (slurry system) is also being investigated.   The objective of this report is to present and discuss the results obtained thus far
in these studies.
MATERIALS AND METHODS
Attached Growth Nitrification-Denitrification Pilot Plant
A schematic of the attached growth pilot plant system is given in Figure 1.   The nitrification reactor in Figure 1 is a rotating biological disc unit manufactured by the Autotrol
Niretncerio*,   erecToe
Figure 1.   Nitrogen removal using
submerged rotating
biological contactors.
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