Removal of Nitrogen and Phosphorus
ROLF ELIASSEN, Professor
GEORGE TCHOBANOGLOUS, Acting Assistant Professor
Department of Civil Engineering
Stanford University
Stanford, California
INTRODUCTION
The removal of nitrogen and phosphorus compounds from wastewaters is receiving worldwide attention because of the adverse effects caused by the discharge
of these contaminants as manifested in the growth of algae and aquatic plants.
Unless steps are taken to control the discharge of these contaminants, overferti-
lization will continue to increase with the multiple reuse of water. The purpose
of this paper is to present and discuss unit operations and processes which are applicable to the removal of nitrogen and phosphorus compounds from wastewaters.
NITROGEN AND PHOSPHORUS IN THE ENVIRONMENT
The presence in the environment of compounds containing available nitrogen
and phosphorus results from the contributions of both natural and man-made
sources. Natural sources which contribute significant quantities of these compounds include runoff and rainfall. Man and man-made sources of nitrogen and
phosphorus include both domestic and industrial wastes, runoff from agricultural
land, farm animal wastes, and urban runoff. The estimated contribution of each
of these sources has been summarized and is presented in Table I.
The forms of nitrogen which are of major importance in water and treated
wastewater are ammonia nitrogen (NHq-N), nitrite nitrogen (NO^-N), and nitrate nitrogen (NO3-N). These forms of nitrogen are of importance because they
are water soluble and are readily available for plant growth. Other forms of nitrogen include atmospheric nitrogen in the form of nitrogen gas (N2)and terrestial nitrogen, usually in the form ofstable organic nitrogen or complexed compounds.
Compounds of phosphorus which are of importance in wastewater may occur in
a variety of different forms, including organic phosphorus (as complex inorganic
phosphates, such as the polyphosphates used in detergents) and soluble inorganic
phosphates (ortho-phosphates and meta-phosphates).
NITROGEN AND PHOSPHORUS REMOVAL PROCESSES
Since a large percentage of the nitrogen and phosphorus compounds found in
wastewater is not removed by conventional treatment processes, advanced wastewater renovation methods and modifications of existing processes have been applied to the problem of removal of these nutrients.
Removal Processes
Processes used for the removal of nitrogen and phosphorus have been summarized and are presented in Table II.   These processes have been grouped into
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