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.