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Sewage sludge nitrogen : a field study of sludge nitrogen dynamics and a laboratory study of ammonia and nitrous oxide gas evolution

University of British Columbia

Two studies using sewage sludge were conducted to examine the forms of nitrogen in the field and the potential for nitrogen gas loss in the laboratory. A study using biosolids was initiated on Island 6 in the Fraser River to determine sludge mass loss and to characterize nitrogen forms: NH₄⁺, NO₃⁻ and organic N. Sewage sludge was used alone and in combination with wood pulp clarifier fines and deinked recycled paper waste. The pulp plus sewage lost the most mass, followed by the deinked plus sewage mix. Sewage sludge alone showed no statistically significant mass loss over the 8 month period. Inorganic N concentrations (NH₄⁺ and NO₃⁻) exhibited similar fluctuating patterns for all three sludge preparations, first decreasing then increasing and finally decreasing. The major loss of inorganic N may have been due to the loss of NH₄⁺ during the first 3.5 months. In addition, declines in NO₃⁻ indicate that denitrification likely occurs. Both these losses cannot be explained solely in terms of NO₃⁻ production, leaching, and immobilization as measured over the 8 months. All forms of N leached. However, NO₃⁻ concentrations were very low, and thus, leaching and denitrification were not major loss pathways. Ammonia volatilization may have accounted for the majority of the N lost. A second study using sewage sludge was initiated in the laboratory to determine sludge loss of N in the gas phase through the processes of volatilization of NH₃ and the reduction of NO₃⁻ (denitrification) over a 38 day period. On day 19 the sludge chambers were vented and the balance of the study represents a second phase of the study. Sewage sludge was controlled at a low temperature (5°C) simmulating the cool conditions of winter in southwestern British Columbia, and at a high temperature (25°C) emulating the warmer conditions of summer. Irrespective of temperature influences, denitrification occurred at relatively low rates in contrast to NH₃ volatilization which initially exhibited a high loss rate of NO₃⁻N that decreased to levels approaching zero towards the end of the study period. Temperature had a statistically significant effect on both denitrification and volatilization. Denitrification was discontinuous and more variable at the high temperature whereas, at the low temperature, it was continuous and more uniform for the first 18 days. Volatilization was more variable under low temperature conditions than under high temperature conditions for the first 18 days, but during days 7 to 18, the loss of NH₃ was significantly greater at the higher temperature. The loss of gaseous N leads to the conclusion that sludge N loading rates should be increased in compensation. This would lead to an improvement in the efficiency of sludge fertilization operations because managers would come closer to meeting the plant's requirements for N and simultaneously dispose of larger volumes of biosolid waste materials.

Thesis/Dissertation

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2009-03-09

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http://hdl.handle.net/2429/5771

Forestry

University of British Columbia

UBCV

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