Land Application Of Biosolids In A Deep Row Hybrid Poplar Trench System
Open Access
- Author:
- Gogno, Jacob Brophy
- Graduate Program:
- Agricultural and Biological Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- October 30, 2015
- Committee Members:
- Herschel Adams Elliott, Thesis Advisor/Co-Advisor
- Keywords:
- Land Application
Biosolids
Hybrid Poplars - Abstract:
- Biosolids are an organic and nutrient rich material that is derived from wastewater treatment plant sewage sludge. When the material is properly digested and stabilized, it can meet state regulations to be land applied. Increasing the volume of biosolids that are land applied is the only practical option to reduce the likelihood of the material being landfilled or incinerated. Land application is the only disposal method that sustainably recycles the material. A typical application rate for agriculture ranges from 9.1 to 18.2 Mg/ha and the one-time application rate for site remediation allowed in Pennsylvania is 136.4 Mg/ha. Higher application rates which would require a smaller land area for a given mass of biosolids have not been widely investigated in Pennsylvania. This research project evaluated land applying biosolids in a deep-row hybrid poplar trench system at an application rate of 386.5 Mg/ha on a 1.62 ha (4 ac) site in Schuylkill County, Pennsylvania. Because this rate results in application of nitrogen (N) far in excess of that required annually by any vegetation on the site, potential leaching of nitrates into groundwater is the major concern. The fate of the N in the biosolids and how much of it goes through the nitrification process to form nitrate will likely determine if the Pennsylvania Department of Environmental Protection will permit biosolids trenching. This research project was conducted to monitor the fate and transport of the biosolids N and track the establishment and initial growth of the poplars. Preliminary sampling and tests were conducted to determine if the biosolids met state regulations to be land applied and the extent of N loss through volatilization during the stabilization process. Groundwater was monitored to determine if nitrate-nitrogen levels remained under 10 mg/L (the state drinking water standard) and lysimeters were installed in the research area to sample soil water around the trenches. Gas was sampled at the soil surface to determine if N was being lost as nitrous oxide. About 6 mo after being entrenched, biosolids redox conditions were measured and samples were analyzed to assess compositional changes in the material. Chlorophyll readings and a tree assessment were used to determine if poplars were assisting in N removal. All water samples collected from the lysimeters and groundwater monitoring wells had nitrate levels below detection. Redox measurement indicated that the biosolids were extremely anaerobic and therefore conditions were not suitable for nitrification to occur. Previous trenching research found that nitrate in pan lysimeter water beneath trenches was essentially zero for 3-yr (Felton et al., 2008). The tree assessment indicated that the research poplars were, on average, larger than the control poplars. Chlorophyll readings were used to estimate N content. Out of the 139 poplars sampled in both the research and control area only 5 and 6 poplars, respectively, were considered N deficient (foliar N content below 3.5%). From the poplar data, it was concluded that the root system of the poplars had not yet reached the biosolids. However, biosolids samples pulled 6-7 mo after entrenchment indicate that N content in the entrenched biosolids has been reduced. Data collected from pre/post-liming emissions supports the conclusion that the majority of the N lost was in the form of ammonia after the stabilization process. After about 1 year from the initial entrenchment, it appears that land applying biosolids at an application rate of 386.5 Mg/ha has had no negative impacts on groundwater. However, as the soil structure evolves around the biosolids and the poplar roots begin to transport oxygen down to the biosolids, nitrates may begin to form. This research needs to be continued for several more years to conclusively determine the extent to which biosolids entrenchment with poplar production will impact underlying groundwater nitrate levels. For future trenching operations it is recommended that a better soil surface management plan be implemented. Soil pH and nutrient levels in the root zone should be altered. Both pH elevation and fertility improvement can be accomplished by amending the surface soil with an appropriate mixture of lime and lime-stabilized biosolids. This would stimulate early growth of the poplars and allow volunteer vegetation growth between poplar rows to reduce soil erosion which contributed to poplar mortality in the research area.