Section Six
INDUSTRIAL WASTES
C. INDUSTRIAL WASTE CASE HISTORIES
64    NITROGEN EFFECTS ON GROUNDWATER FROM
ANAEROBIC DAIRY-SHED WASTE PONDS
Gilbert T. Tellez, Graduate Student
Zohrab Samani, Associate Professor
Ricardo Jacquez, Professor
Department of Civil, Agricultural and Geological Engineering
New Mexico State University, Las Cruces, New Mexico 88003
INTRODUCTION
As livestock operations in the U.S. continue to grow, liquid manure waste applied to the land is
becoming a major environmental concern. Many dairy operations employ anaerobic ponds as a means
of final waste disposal. Anaerobic ponds have a relatively low construction cost, with a minimal
maintenance requirement. Nitrogen is the major nutrient in manure which is of particular concern in
terms of its water pollution potential.
The various microbiological reactions in an anaerobic environment result in the breakdown of
complex organic materials without molecular oxygen. The microbial population derives energy for
cell synthesis by utilizing chemically bound oxygen in the form of carbon dioxide, nitrates, sulfates
and organic molecules as the electron acceptor. Resulting products include methane, carbon dioxide,
ammonia, hydrogen sulfide and reduced organic molecules.
Dairy-shed wastewater consists mainly of dung, urine, and wash water from plant cleaning. When
disposed of by pond storage, potential ground water pollution may occur through seepage of the
nitrogen species. Most mammals excrete the bulk of their nitrogen in the form of urea. This compound is highly soluble, and being electrically neutral, does not affect the pH when it accumulates, as
does ammonia.1 Once nitrogen from liquid manure has infiltrated and become incorporated in the soil
profile, its movement is primarily in the nitrate form.2 Since the primary mechanism for nitrate
migration downward is the mass flow of the soil solution, and relatively high infiltration rates,
nitrates are a major ground water pollution constituent. Nitrate pollution is a concern mainly because
of the implications for human health, and when ingested, can cause methemoglobinemia. This is a
toxicity resulting from the fact that in the blood stream nitrate changes ferrous iron, which is capable
of transporting and releasing oxygen, to ferric iron which is incapable of supplying oxygen. Therefore, this toxicity is a shortage of oxygen in tissues where it is needed. The resulting illness is called
methemoglobinemia.3
Investigations were conducted to determine the amount and distance of pollutant movement from
animal waste lagoons.4 Ammonium and nitrate concentrations in the ground water samples indicated
seepage from each of three tested lagoons. Rupture of lagoon seals (clay) leading to seepage was
attributed to drying of exposed subsoil or embankment soil during recession of lagoon liquid levels
and to gas release from microbial activity in soil beneath the seal.
For the conditions studied in the laboratory on a Plainfield sand column, nitrogen immobilization,
ammonification, and nitrification were the primary transformations found to occur in the soil system.
The two dominant forms of inorganic nitrogen found in these soil systems were ammonium and
nitrate. When the liquid manure was added to the soil profile, ammonium moved downward through
the soil until it was adsorbed on exchange sites of soil particles. The ammonium was temporarily held
in a zone near the soil surface where nitrification completely dominated all other nitrogen transformations.2
48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
637