Application of limestone-bed bioreactors to treat silage leachate

Project Overview

Project Type: Graduate Student
Funds awarded in 2017: $14,957.00
Projected End Date: 04/30/2019
Grant Recipient: Cornell University
Region: Northeast
State: New York
Faculty Advisor:
Tammo Steenhuis
Cornell University


Not commodity specific


  • Animal Production: manure management
  • Natural Resources/Environment: wastewater quality management
  • Soil Management: soil quality/health

    Proposal abstract:

    The occurrence of silage bunker effluent in dairy farms is a challenge for farm owners. Containing elevated concentrations of organic matter (OM), the leachate has high acidity and high biological and chemical oxygen demands (BOD and COD, respectively) and nutrient content. Excess nutrient cause eutrophication in the lakes and water bodies. Silage leachate can cause fish-kill and vegetation burning. The leachate, therefore, is corrosive and hard to manage for the farmers, though it occurs in small volumes. This research will address the silage leachate problems by proposing use of cost-effective limestone-bed bioreactors in the treatment of such potent wastewater. Limestone will increase the pH and thereby, will provide a better environment for anaerobic bacteria. Therefore, the degradation of organic matter and removal of BOD will be facilitated. In lab experiments, we will compare the performance of the limestone-bed bioreactors with the recommended field practice of storage in tanks. Furthermore, an additional step for the treatment of excess nutrients will be included. Moreover, the lab experiments will determine the optimum retention time which is essential for designing the field bioreactors. Finally, the field demonstration examines the in-situ performance of the bioreactors. Since the farmers are the main addressees of this research, the result of this research will be presented in the northeast certified crop advisor’s (NECCA) meetings. The results of this research will also be presented in multiple regional and national conferences and proceedings and will also be published in a peer reviewed journal.

    Project objectives from proposal:

    Our objective is to improve the quality of the silage leachate. In comparison to other agricultural wastewaters, silage bunker leachate has the poorest water quality. Though small in volume, it has a great potential for environmental contamination. This is due to the combined low pH (high acidity), low pE (high electron activity), and high nutrient content, which is unique among wastewaters. Given these facts, this research will target the following objectives in silage leachate treatment:

    1- To remove BOD from the silage leachate
    The pH for the silage bunker leachate ranges from 3.6 to 5.5 (Cropper and DuPoldt, 1995)), far from optimal biological pH, therefore, the current natural removal techniques will not be efficient or sufficient. The optimum pH for anaerobic systems ranges from 6.5 to 7.5, depending on the organic matter content (Liu et al., 2008). This pH can however be achieved by flowing the wastewater through lime bed bioreactor (Barry and Colleran, 1982).

    2- To determine an optimum hydraulic retention time
    Our second goal is to find the relationship between BOD removal and hydraulic retention time (HRT) in the bioreactors. Together with the estimated flow rate from (Cropper and DuPoldt, 1995; NRCS, 2013), this information will provide guidelines to design bioreactor in field settings. To reduce the cost of the constructing such bioreactors, it is important that the size is not overestimated.

    3- Nutrient removal
    This project will investigate the removal of nutrients, specifically P and N, from the wastewater. By increasing pH and the abundance of Ca, P can precipitate out of the solution. Nitrogen (N) will be removed in an anaerobic bioreactor.

    The ultimate objective of this research is to help farmers to avoid fees and penalties by providing an approach to treat the silage leachate, and thereby, reduce the farm’s spending. In general, the current research will address three of five required themes: “the reduction of environmental risks”, “the reduction of costs”, and “the conservation of soil, the improvement of water quality and the protection of natural resources”.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.