Developing Inoculum to Increase Anaerobic Digestion Efficiency in Winter Months

Project Overview

Project Type: Graduate Student
Funds awarded in 2011: $14,974.00
Projected End Date: 12/31/2013
Grant Recipient: University of Maryland
Region: Northeast
State: Maryland
Graduate Student:
Faculty Advisor:
Stephanie Lansing
University of Maryland

Annual Reports


  • Animal Products: dairy


  • Animal Production: manure management
  • Education and Training: extension
  • Energy: bioenergy and biofuels
  • Natural Resources/Environment: biodiversity, wetlands

    Proposal abstract:

    In Maryland, milking cows on dairy farms produce approximately 4.92×106 lbs of manure daily. Anaerobic digestion offers a system that can treat the manure while producing methane as a source of renewable energy. However, the efficiency of methane production in anaerobic digesters decreases when the temperature decreases. This poses a problem in temperate climates such as Maryland. To counter this problem, digesters in temperate climate are designed with internal heating systems that use the biogas produced as the source of heat. This is not a cost-effective method, especially in the winter when there is a greater need for the energy produced and on small to medium-scale farms where co-generation systems, which use waste heat from a generator to supplement digester heating, are too expensive. Freshwater wetlands and landfills contain methane-producing microorganisms (methanogens) that have adapted to the seasonal fluctuations and low temperatures. These systems have a higher diversity of methanogenic microorganisms adapted to colder temperatures than dairy manure, which is normally used as an inoculum source for digesters operating at 35°C. Inoculating cold season digesters with inoculum from these natural systems could improve the digestion process in temperate climates and reduce the internal heating needs of the digester. In this project, laboratory experiments will be conducted to determine the best inocula for low-temperature digestion of dairy manure. In addition, the ideal incubation period needed for microorganisms in the inoculum, and the ideal inoculum to substrate ratio will be determined. Results from this project will be applied to future field–scale studies.

    Project objectives from proposal:

    Due to the lack of research on environmentally derived inoculum and the need for increasing biogas production in the winter using cost-effective digesters, the PI will conduct a laboratory experiment in which inoculum from local sources, such as landfills and freshwater marshes, will be used for digesting dairy manure obtained from a farm in Beltsville, Maryland. The study will be conducted at three temperatures: 5°C and 15°C, and 25°C, which are the approximate average temperatures for the four coldest, moderate, and hottest months in Beltsville, Maryland (, accessed 2011). Conducting the experiment at these three temperatures will allow the PI to estimate the most cost-
    effective inoculum for temperature range when running future field-scale digesters in the future.

    Inoculum from a mesophilic anaerobic digester, which is readily available, from the Beltsville farm digester, will also be compared to these environmentally derived inocula. Successful results from this study will be applied to future studies involving low-cost field-scale anaerobic digesters, which are located at this farm.

    The main objective can be divided into two objectives:
    1.)Obtain suitable inoculum from two landfills, two freshwater marshes, and a mesophilic anaerobic digester and determine the quantity of methane produced from inoculum source when digested with dairy cow manure at 5°C, 15°C, and 25°C.

    Hypothesis: The inocula from landfills and freshwater marshes will produce more methane at 5°C and 15°C than the inoculum obtained from mesophilic anaerobic digester due to of their exposure to seasonal fluctuations and low temperatures during the winter months resulting in higher diversity of methanogenic microorganisms from the environmentally derived inoculum sources.

    2.)Determine the optimal incubation period and inoculum to substrate ratio at 5°C, 15°C, and 25°C. This experiment will be conducted only with the ideal inoculum source at each of the temperature determined in Objective 1. These specific inoculum details (optimal incubation period and inoculum quantity needed) will allow for farmer recommendations to be made.

    Research Hypothesis: Higher inoculum to substrate ratio will result in higher amount of methane generated per gram of dairy manure added due to the presence of a larger quantity of microorganisms. Longer incubation periods will also result in a higher production of methane due to the microbial adaptation to the temperature and the substrate.

    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.