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)

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.