ACTIVATED SLUDGE TREATMENT
OF A HIGH STRENGTH NITROGENOUS WASTE
Richard O. Mines, Assistant Professor
Department of Civil Engineering
Virginia Military Institute
Lexington, Virginia 24450
Joseph H. Sherrard, Professor
Department of Civil Engineering
Virginia Polytechnic Institute and State University
Blacksburg, Virginia 24061
INTRODUCTION
Discharge of high concentrations of ammonia in wastewater effluents can have an adverse impact
on receiving streams. Combined carbon/nitrogen biological oxidation systems such as the activated
sludge process have long been recognized for their capability of elimination of ammonia and providing a nitrified effluent. Most nitrification studies that have been conducted have focussed on
municipal and low strength ammonia wastewaters. Relatively few studies have been performed on
the fate of ammonia in wastewaters from the fertilizer, coking, petroleum and refining, and organic
chemical industries wastewaters containing a high concentration of ammonia. This laboratory research investigation was undertaken to evaluate the fate of nitrogen when treated in an activated
sludge process at a high initial ammonia concentration.
LITERATURE REVIEW
Nitrification
Nitrification involves a group of aerobic, chemoautotrophic bacteria, collectively known as nitrifi-
ers, which oxidize ammonium nitrogen (NH*4-N) to nitrate nitrogen (NO"3-N) in a two-step sequential reaction. The first reaction involves the oxidation of NH +4 — N to nitrite nitrogen (NO "2 — N)
by the genus Nitrosomonas. In the second step, Nitrobacter oxidizes NO"2-N to NO"3-N. Both
autotrophs utilize inorganic carbon to include carbon dioxide (C02), bicarbonate (HCO ",), and carbonates (CO "3) for synthesis of biomass. Both reactions are thermodynamically favorable with estimates of free energy of release from 58-84 kcal/mole for ammonium oxidation and from 15.4-20.9
kcal/mole for nitrite oxidation [1,2]. Each individual step and the overall nitrification equation is
presented below:
2NH+4 + 302 Nitrosomonis 2NO"2 + NH+ + 2H20 (1)
2NO -2 + 02 Nitrobactf 2NO ", (2)
NH+4 + 202 Nltr'fler.s NO", + 2H+  + H20 (3)
Rarely has a buildup or accumulation of nitrites occurred in aerobic treatment systems since Equation
2 yields less energy than Equation 1. As a result, the Nitrobacter must process 3 to 4 times as much
substrate (based on thermodynamic considerations) and a nitrite buildup seldom occurs. Therefore,
nitrification kinetics are governed by Equation 1.
837