Effect of Spray Irrigation of Municipal Wastewater on Nitrogen Transformations in Soil

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Title: Effect of Spray Irrigation of Municipal Wastewater on Nitrogen Transformations in Soil
Creators: Miller, R. H., 1933-; Brar, S. S.; Logan, Terry J.
Contributors: United States. Office of Water Research and Technology; Ohio State University. Water Resources Center
Subjects (LCSH): Land treatment of wastewater
Sewage -- Purification -- Nitrogen removal
Sewage irrigation
Issue Date: 1977
Publisher: Ohio State University. Water Resources Center
Series/Report no.: Project completion report (Ohio State University. Water Resources Center) ; no. 495X
Abstract: The overall objective of this research was to respond to the obvious need for more information on nitrogen mineralization and denitrification in soils receiving secondary treated wastewater. The soil-vegetation systems of the Pennsylvania State University Wastewater Management areas (Reed Canarygrass, Old Field, Hardwood Forest and Gameland) used throughout the study. The use of these soils provided a unique opportunity, since the extensive background research data and experiences on these research sites during the past decade were available to assist us in the experimental design and in data interpretations. One parameter necessary for the calculation of soil nitrogen balances in soils receiving wastewater is nitrogen mineralized from soil organic nitrogen. Plots of nitrogen mineralized using the Stanford and Smith (1972) long term incubation method vs the square root of the time of incubation (t 1/2) were linear for soils from the 0-7.5 cm depth of all the soil vegetation systems over the entire 26 week incubation period, but only for eight weeks for soils from the 7.5-15 cm depth. This lack of continued mineralization in this soil zone undoubtedly reflects the depletion of mineralizeable organic N compounds early in the incubation period. Nitrogen mineralization in the wastewater treated soils was generally higher than the control soils and represented about 3.0-3.5% of the pool of soil organic N in all vegetation systems on the Hublersburg soil series. Mineralization of nitrogen was about 5-9 times greater in the coarse textured Morrison soil from the Gameland area and represented about 8.0% of the soil organic N in this soil. This high N mineralization rate could contribute excess nitrogen capable of leaching downward into groundwater. The possibility that organic N from sites on coarse textured soils mineralizes more rapidly should be investigated since it would make these soils less useful for renovation than previously assumed. Nitrification was found to be rapid in all wastewater treated soils incubated at a variety of temperatures. Nitrification did not occur in the control soils of the Old Field or Gameland sites and was slow in the Hardwood Forest area. This lack of nitrification can readily be explained by the low pH of the control areas compared to the wastewater treated areas. Population estimates of nitrifying bacteria using an MPN method were made but showed no relationship to actual rates of nitrification. Denitrification losses have generally been assumed to be higher in wastewater treated soils than normal agricultural soils because the higher hydraulic loading associated with wastewater treatment keeps the soil saturated for longer time periods. Denitrification potential measurements in this study have provided evidence that this assumption may not be true. Soils from all of the experimental areas had little denitrifying activity regardless of season and depth, and in both the wastewater treated and control soils. Low denitrifying activity was expected in soil samples below 15 cm because of a low organic carbon content of these soils, but not in the surface soil zone. Rapid denitrification in both surface soils and those from lower depths when amended with glucose suggests that a lack of available carbon was limiting denitrification. A comparison of the quantities of soluble carbon and mineralizable carbon found in the experimental soils with data reported by Burford and Bremner (1975)supported this conclusion. Plant residues from the various types of vegetation on the Penn State University Wastewater Management area were found to supply available carbon for denitrification for about two to four weeks after incorporation. These annual additions of carbonaceous residue probably enhance denitrification during the spring before plant growth commences, but the effect will be of short duration and of limited value to total nitrogen renovation of applied wastewater. Measurements were made of the seasonal differences in total root mass and root organic matter, organic carbon, and organic nitrogen in the wastewater treated Reed Canarygrass area during 1974-75. Definite seasonal changes in all parameters were evident with a maximum in summer during the period of maximum growth and a decrease to a minimum in spring before active growth begins. The decrease in root mass, organic matter and organic carbon from July till April would indicate a root turnover rate of about 44-48%. The change in root organic nitrogen from July to April is much less and represents only a 25% decrease.
URI: http://hdl.handle.net/1811/36343
Other Identifiers: OCLC #16861449 (print)
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