Technology Type - Chemical Flocculation

Technology Strengths,Weaknesses and Critical Indicators

Chemical flocculation technologies remove the non-dissolved particles from the waste stream typically resulting in irrigation quality “tea water”:

  • Produces a clay like cake which is high in phosphorus and with significant amounts of organic nitrogen.
  • Technologies include belt presses, centrifuges, dissolved air flotation systems and others all of these technologies require flocculants to achieve high rates of solids removal
  • There is significant variation of chemical and energy use depending on site and by technology
  • There is significant variation of operational intensity depending on site and by technology
  • There is significant variation of cost depending on site and by technology
  • Proven technology for nitrogen recovery, phosphorous recovery, storage reduction, GHG reduction, and odor control

image/svg+xml Nitrogen Recovery Phosphorus Recovery Storage Reduction GHG Reduction Odor Control Pathogen Reduction Negative Positive NEAT MATRIX - Peer Reviewed P - Documented D - Expert Opinion E P D E P D E

Overall Summary

Primary Application

  • Dairies concerned with recovery/partitioning of phosphorous out of liquid stream.
  • Removing solids from storage lagoons and/or producing liquid suitable for irrigation.
  • No practical limitation on scale of dairy.
  • Systems work on both digested and raw dairy manure—although the higher the solids content the more polymer generally required.
  • No practical limit on geographic or climatic location of the dairy.

Economic/Return on Investment Considerations

  • Installed capital costs can be a concern—with approximate estimates in the medium range of expense, as compared to other fine solids separators.
  • Operating costs are of concern and can be on the high end because of the cost of required daily chemical addition.
  • Important manure management offsets are possible with adoption of this technology.
  • Separated solids contain approximately 35% of total nitrogen and 85% of phosphorous.
  • Liquids can be managed more cost effectively during storage and field application.

Industry Uptake

  • As of 2018, approximately two-dozen centrifuge systems are installed on U.S. dairies
  • Most installations are on larger dairies

Technology Maturity

  • Vendors active within the dairy space are marketing second, third-generation equipment, having learned many lessons from initial installations.
  • The technology is considered mature, but with lessons still to be learned and improvements to be expected.
  • Value-added marketing of the separated solids is not mature, considerable work is still required in this area.
  • Multiple configurations and vendors are active in the dairy space.

Primary Benefits

  • Significant odor reduction due to removal of volatile solids from anaerobic environment.
  • Significant separation of organic material from liquid, resulting in ‘tea water’ that is almost completely removed of suspended solids.
  • Pathogen reduction to liquid is small, limited pathogens stay attached to solids.
  • Because of significant organic matter separation GHG reductions are high.
  • Key benefit is partitioning total nitrogen and total phosphorous into the separated solids, significantly reducing nutrient footprint and NPK ratio of resulting liquid.
  • Organic nitrogen leaves with the solids, leaving mostly inorganic ammonia in liquid.

Secondary Benefits

  • The technology can act as a pre-treatment to further downstream treatment, particularly the use of ammonia stripping, nitrification/denitrification, and membranes, aimed at further partitioning/recovery of nitrogen and/or volume reduction.
  • Manure management offsets are potentially significant, especially on dairies with existing concerns related to nutrient overload and high manure transportation costs.
  • When correctly applied, liquid can result in savings to manure management costs without yield loss.
  • Can translate, under proper manure/nutrient management, into reduced nutrient losses to surface/groundwater and mitigation of concerns related to N/P eutrophication and nitrate in groundwater.

How it works

  • Raw and/or digested manure, after primary separation of bulk/fibrous solids is homogenized and fed to the system at constant rates. Manure is mixed with a site-specific polymer solution so that small, suspended solids are induced to attach. These flocs of attached solids either sink or rise, allowing for their separation from the bulk liquid. Finally, the flocs are dewatered so that a stackable pile can be produced.
  • The products are a phosphorous-rich solids or cake and low solids ‘tea water’.

Pretreatment and/or Post-treatment Required

  • Pretreatment(s) for stable on-going operation is primary solids separation as well as a buffer tank to ensure homogeneous and consistent flow to the system.
  • Post-treatment of solids includes handling/storage and sale/distribution.
  • Post-treatment of liquids includes handling/storage and field application.


  • Most efficient when pre-testing has identified a suitable polymer.
  • Effective performance requires consistent operations and maintenance.
  • Value-added markets for the separated solids are immature.
  • Separated solids may require post-treatment to create a salable product.
  • Sand-laden manure can cause pumps and equipment to wear out quickly.
  • A consequence of the treatment is a solid containing polymer, which has implications for its organic certification as well as the physical properties of the solid (i.e. water holding capacity, degradation, feel/texture, etc.).
  • No renewable energy production.
  • Chemicals and some electricity required for operation.
  • No thermal energy production.

Other Considerations

  • Understanding of the real capital and operating costs, as compared to existing manure management system is important for a successful project.
  • Farm operations will need to adapt manure application approaches to the new products.
  • Roughly ½ hour a day in walk-through oversight with an additional 12 hours per month to do regular maintenance.
  • Additional time is required for the handling, moving, storage, and application of solids.
  • Reduced labor/costs related to lagoon storage agitation/dredging, liquid pumping/trucking and application.
  • Extra time and education are required to effectively operate and maintain the technology
  • Adaptation to the new nutrient characteristics of the product are required for effective use of nutrients to fields and crop yield.
  • Value-added sales of separated solids may require market development.

Bronstad, E., Frear, C., Yorgey, G., Benedict, C (2017). Fine solids, phosphorus recovery from manure digestate. Presentation at Biocycle REFOR17, Portland OR, October 18, 2017.       


Fangueiro, D., Senbayran, M., Trindade, H., & Chadwick, D. (2008). Cattle slurry treatment by screw press separation and chemically enhanced settling: effect on greenhouse gas emissions after land spreading and grass yield. Bioresource technology, 99(15), 7132-7142.


Frear, C., Ma, J., Yorgey, G., (2018). Approaches to nutrient recovery from digested dairy manure. Washington State University Extension, Pullman WA. EM112E.


Garcia, M. C., Szogi, A. A., Vanotti, M. B., Chastain, J. P., & Millner, P. D. (2009). Enhanced solid–liquid separation of dairy manure with natural flocculants. Bioresource Technology, 100 (22), 5417-5423.


Hjorth, M., Christensen, K. V., Christensen, M. L., & Sommer, S. G. (2010). Solid–liquid separation of animal slurry in theory and practice: A review. In Sustainable Agriculture Volume (30) p.153-180.


Holly, M. A., Larson, R. A., Powell, J. M., Ruark, M. D., & Aguirre-Villegas, H. (2017). Greenhouse gas and ammonia emissions from digested and separated dairy manure during storage and after land application. Agriculture, Ecosystems & Environment, 239, 410-419.


Liu, Z., Carroll, Z. S., Long, S. C., Gunasekaran, S., & Runge, T. (2016). Use of cationic polymers to reduce pathogen levels during dairy manure separation. Journal of environmental management, 166, 260-266.


Neerackal, G. M., Ndegwa, P. M., Joo, H. S., Wang, X., Harrison, J. H., Heber, A. J., ... & Frear, C. (2015). Effects of anaerobic digestion and solids separation on ammonia emissions from stored and land applied dairy manure. Water, Air, & Soil Pollution, 226(9), 301.

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