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

1. Development of a Mobile Process to Extract Phosphorous from Livestock Waste as a Valuable Fertilizer Gene Hoilman Bioresource Engineering Dept. Oregon State University

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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)

11. 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

12. 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

13. 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

14. 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

15. Pilot Plant Process

16. 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

17. 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

18. 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

19. 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

20. “Curve Balls” • No difference in NH4 removal when struvite formed vs. hydroxylapatite • Most NH4 removal due to volatilization • Struvite-NH4 comparably small

21. “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)

22. “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

23. 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

24. 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

25. 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.