Sand Separation using Laboratory Scale Column Diffuser
for Sand Laden Manure
J. Alex Maxwell
Clarkson University 2008 Summer REU
Advisor: Stefan J. Grimberg
Introduction
With the rise in energy prices across the nation and the average retail cost of whole milk at only $3.75 per
gallon, dairy farmers are looking for more ways to become environmentally and economically
sustainable. In an effort to save costs on energy expenses, farmers are starting to invest in the idea of
anaerobic digestion to convert their excess manure into useful biogas. The biogas, mostly comprised of
around 60% methane (CH4) and 40% carbon dioxide (CO2), can be burned to provide heat energy or be
used to produce electrical energy by means of a biogas-fueled engine-generator. By using cow manure to
fuel anaerobic digesters, dairy farmers can greatly reduce or eliminate purchased sources of heat and
power, reduce wastewater treatment and environmental compliance costs, and ease exposure to
fluctuating power prices.
The Clarkson University Biomass Group (CBG) was started three years ago in 2005 in an
interdisciplinary effort to better investigate and promote the conversion of dairy manure and other wastes
into biogas in the North Country of New York State. In partnership with local farms, the United States
Department of Agriculture (USDA), and other government agencies, Clarkson Engineering faculty and
students have been researching and collecting data to answer the questions surrounding the reliability and
economic/environmental value of anaerobic digester-energy recovery. Hoping to increase the
implementation of anaerobic digestion within the region, the CBG has developed pilot and laboratory
scale systems for the digestion of manure, the recovery of heat and power, the environmental emissions,
and the separation and recycling of sand of sand-laden manure.
Many modern dairy farms, especially those located in the North Country, use sand as a bedding material
for their cows. Sand is chosen over other materials such as concrete or hay for its cleanliness and comfort
that it provides the cows. Increased comfort leads to increased milk production, and the cleanliness of
sand prevents disease vectors to spread and grow. However, sand-laden manure does have some
drawbacks.
The most significant challenge in dealing with sand-laden manure is that it can easily settle in the
anaerobic digester and limit the volumetric size of the reactor. As shown in previous research by Clarkson
graduate students, anaerobic digestion of sand-laden cow manure was achievable in laboratory-scale
digesters. However, when applied in the pilot scale, sand-separation within the digester did not perform as
expected. As a result, it was determined that a separate sand-separation apparatus would need to be
constructed to achieve sand-separation outside of the anaerobic digester. The research completed as part
of the 2008 Clarkson Summer REU program in conjunction with the CBG aims at developing a valid
procedure for the separation of sand from dairy manure in a laboratory-scale apparatus so that it can be
reused in the dairy barn as bedding. In removing sand from manure, the size of the reactor will not be
greatly affected, and anaerobic digesters will become more beneficial to dairy farmers.
Gonzaga University – Class of 2009
Civil Engineering
REU
Dr. Stephan Grimberg
Experimental Approach
Before being able to determine the best procedure/model for gas separation of sand from manure the
following objectives were set in place:



Determine the parameters for testing and analysis
Determine the procedure for testing and analysis
Produce results that illustrate the effectiveness of the column diffuser
Parameters
Before running the laboratory-scale column experiments certain parameters, such as gas flow rates,
diffuser pore size, volume of sample size, dilutions, etc., were defined and better apparatuses were
designed in order to extract more meaningful data. After constructing a new apparatus for column
experiments, it was determined that all experiments would be run at a one-to-one dilution ratio of sandladen manure to water/digester effluent (three liters of each). Gas flow rates varied depending on the
medium being used for separation, but values ranged from 0.7 liters per minute (LPM) to 5 LPM. And,
the diffuser pore size selected for testing was one millimeter.
Procedure
After the parameters for testing were determined, the experimental procedure was then formulated to test
the effectiveness of the laboratory scale column diffuser.
Results
The cumulative results of the experimental runs are still being determined; however, preliminary results
indicate that the column diffuser is effectively removing sand from manure on the laboratory scale.
Qualitatively, the sand removed in the column experiments has proven to have a reduce content of
organic material, and the material left in suspension shows limited traces of fines sand particles. More
quantitative and qualitative analysis will follow.
Sources
"Optimum sand recycling during anaerobic digestion of dairy manure." REU Environmental Sciences and
Engineering Project Summaries. Clarkson University. 2 Jul 2008
<http://web2.clarkson.edu/reu/project_summaries.php#rp2008002>.
"CBG Home." OptimuClarkson Biomass Group (CBG). Clarkson University. 2 Jul 2008
<http://web2.clarkson.edu/cbg/index.html>.
USDA. "Table 2--Retail prices for whole milk, average of three outlets, selected cities, by months, 2008."
02 Jul 2008 1. 2 Jul 2008
<http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5066867>.
Kevin L., Hickey. "Laboratory Scale Anaerobic Digestion of Sand Laden Dairy Manure." A Thesis by
(2007).
Gonzaga University – Class of 2009
Civil Engineering
REU
Dr. Stephan Grimberg