development of a mobile process to extract phosphorous from livestock waste as a valuable fertilizer...
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Development of a Mobile Process to Extract
Phosphorous from Livestock Waste as a Valuable
Fertilizer
Gene HoilmanBioresource Engineering Dept.
Oregon State University
Defining the Problem Manure spreading is traditional method of
disposing of wastewater from confined animal feeding operations (CAFO’s) Wastewater application supplies N and P
Applications typically account for uptake of nitrogen; usually applying phosphorous in excess
Environmental and regulatory concerns arise
Environmental Concerns
P unused by crops can enter water bodies via runoff
Extra P in water bodies can increase algal growth
Aesthetic and recreational detriment during algal bloom
Increased oxygen demand when algae senesce
Regulatory Concerns EPA is requiring comprehensive nutrient
management plan as part of CAFO permitting process
Accounting for P will increase land needed for application – may not be an option
A method of P removal directly from the waste may be of help
Identifying a Solution
As pH of a solution increases, some phosphorus-containing compounds precipitate from solution
Struvite: MgNH4PO4+6H2O N removed, but small percent of total Supplemental Mg2+ usually needed
Hydroxylapatite: Ca5(PO4)3OH
Identifying a SolutionEnd-Product Reusability
Struvite identified as a slow-release fertilizer (Bridger et al, 1962)
Wide crop applicability Non-burning Currently sold as fertilizer amendment in Japan
Hydroxylapatite mentioned as potential fertilizer (Momberg and Oellermann, 1992)
Research not available on actual useage
Identifying a SolutionThe Mobile Process Concept
Many smaller CAFO’s may not have money to invest in permanent P removal plant
Mobile nutrient removal service could help these farms
Removal as struvite creates Double income
Existing methodsOverview Several precipitation processes currently
exist Reviewed these for potential adaptation to
mobile process All reviewed processes intended for
permanent, on site installation Several types of wastewaters treated
These include municipal and livestock wastewaters
Existing MethodsReactor Types
Fluidized Bed Reactors Provide seed material
Spontaneous Nucleation Reactors Seed material not provided
Both used to make struvite, hydroxylapatite, or mixture of both
Adaptation to Mobile Process – Reactor Style Minimize hydraulic retention times (HRT’s)
Minimize necessary materials
Provide for ease of harvest
Spontaneous Nucleation Reactor Chosen Low HRT’s Possible (Munch & Barr, 2000)
Flowrate
VolumeHRT
Adaptation to Mobile Process – Chemicals
Sodium Hydroxide for pH Adjustment High solubility allows quick pH adjustment
Magnesium Chloride for supplemental Mg2+
Also highly soluble
Adjusting pH and Mg2+ with separate chemicals allowed full control of optimization
Jar Tests Mg2+:O-PO4 molar ratio and
pH adjusted with control Jar tests investigated
chemical dosing and reaction time
Suggested: High solids content can
interfere No supplemental Mg2+
Maximum necessary HRT = 30 min
Reactor pH = 8.5 Control group jars showed
O-PO4 removal during tests
Control Group O-PO4 Removal Aeration of wastewater increases pH by
driving out CO2 (Battistoni, 2002)
Long time needed to achieve pH comparable to chemical adjustment
Chemical adjustment of pH remains best way to achieve low HRT
Pilot Plant – General Information
Adapted from design of Munch & Barr (2000)
Built with cone-bottomed rapid mix tank and PVC sewer pipe
Cost to build: ~ $1000
Pilot Plant Process
Pilot Plant Operation Flow rates of chemicals calculated based
on flow rate of waste
Waste and chemical flow into reactor initiated simltaneously
Waste flows in and out of the reactor continuously until reactor shut down precipitate settled and harvested after shut
down
Pilot Tests Pilot plant tested at Rickreall Dairy in
Rickreall, Oregon Acceptable solids content
Hydraulic Retention Times Tested: 5 min 10 min (supplemental Mg2+) 20 min 50 min
Experiments ran for 3 to 24 hours
Pilot Plant Results
O-PO4 removal did not significantly vary with HRT ranged between 60%-70%
5 min HRT produced poor quality precipitate
10, 20 and 50 min HRT’s all provided adequate precipitate qualities
Pilot Plant Results (cont.)
Hydroxylapatite formed in tests not supplementing Mg2+
Struvite formed in test that supplemented Mg2+
Product suspended in effluent even at high HRT’s (low flow rates) Prompted redesign of mobile process
“Curve Balls”
No difference in NH4 removal when struvite formed vs. hydroxylapatite
Most NH4 removal due to volatilization Struvite-NH4 comparably small
“Curve Balls” Mg2+:O-PO4 Ratio
Ratio of removed Mg2+:O-PO4 was not 1:1 in the test forming struvite
Other Mg2+ containing precipitates may have formed Bobierrite and magnesite are possibilities
(Dempsey, 1997; Wentzel, 2001)
“Curve Balls”Calcium Carbonate
Product was predominantly calcite (calcium carbonate) Total P only about 0.7% by weight
Diet of cows heavily supplemented with calcium carbonate Serves to buffer stomach acid
Implications for Full Scale Mobile Process
Design modification: Rapid mix reactor Design flow rate and rapid mix tank volume to
achieve 10 min HRT Additional long, wide settling basin may
provide conditions for suspended product to settle
Wastewaters originating from livestock being fed calcium carbonate present problems
Conclusions Project successful in removing a large
portion of soluble phosphorus from a livestock wastewater
With design modifications, a mobile process to remove phosphorus from wastewater could be successful
Further tests with modified design and different wastewater are needed to confirm feasibility of the process
Acknowledgements Louie Kazemier, Jim Cole,
and the staff of Rickreall Dairy
Graduate Committee: Dr. J. Ronald Miner, Dr. Fred Ramsey, Dr. John Bolte, Dr. Prasad Tadepalli
Sandy Lovelady, Yan Ping Liu Qian, and the staff of the CAL
Dr. Mohammed Azizian, Enviro. E. Dept.
Dr. John Selker, Bioengineering Dept.