Extract Phosphorous from Livestock

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Nov 12, 2013 (3 years and 9 months ago)

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Development of a Mobile Process to
Extract Phosphorous from Livestock
Waste as a Valuable Fertilizer

Gene Hoilman

Bioresource 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
: MgNH
4
PO
4
+6H
2
O


N removed, but small percent of total


Supplemental Mg
2+

usually needed



Hydroxylapatite
: Ca
5
(PO
4
)
3
OH



Identifying a Solution

End
-
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 Solution

The 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 methods

Overview


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 Methods

Reactor 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
Volume
HRT

Adaptation to Mobile Process


Chemicals


Sodium Hydroxide for pH Adjustment


High solubility allows quick pH adjustment



Magnesium Chloride for supplemental
Mg
2+


Also highly soluble



Adjusting pH and Mg
2+

with separate
chemicals allowed full control of
optimization

Jar Tests


Mg
2+
:O
-
PO
4

molar ratio
and pH adjusted with
control


Jar tests investigated
chemical dosing and
reaction time


Suggested:


High solids content can
interfere


No supplemental Mg
2+


Maximum necessary HRT
= 30 min


Reactor pH = 8.5


Control group jars showed
O
-
PO
4

removal during tests


Control Group O
-
PO
4

Removal


Aeration of wastewater increases pH by
driving out CO
2
(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 Mg
2+
)


20 min


50 min



Experiments ran for 3 to 24 hours

Pilot Plant Results


O
-
PO
4

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 Mg
2+



Struvite formed in test that supplemented
Mg
2+



Product suspended in effluent even at high
HRT’s (low flow rates)


Prompted redesign of mobile process


“Curve Balls”



No difference in NH
4

removal when
struvite formed vs. hydroxylapatite



Most NH
4

removal due to
volatilization


Struvite
-
NH
4

comparably small





“Curve Balls”


Mg
2+
:O
-
PO
4

Ratio


Ratio of removed Mg
2+
:O
-
PO
4

was not 1:1
in the test forming struvite



Other Mg
2+

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.