Performance Testing of Screw-press Solid Separators: Comprehensive Solids Analysis and Nutrient Partitioning

A standard performance testing protocol for mechanical manure solids separators has been developed and tested. The protocol measures separator press-liquor throughput and dry-mass capture efficiency across a range of input total solids (TS) concentrations. This protocol was used to test two commercially available screw-press manure solids separators, a Vincent KP-6L and a PressTech Agri-Press with dairy manure slurries. The dry-mass capture efficiency of the Vincent KP-6L ranged from 17 % to 60 % as input TS was changed from 1% to 7%. Press-liquor flow rates for the KP-6L ranged from 34 gallons per minute (gpm) to 8 gpm as input TS was changed from 1% to 7%. The press-cake TS concentration averaged 29% during the testing. The PressTech Agri-Press was evaluated as a total system that used a Bauer hydro-sieve static screen as a pre-thickener. The overall capture efficiency of the static-screen and the PressTech Agri-Press as a system ranged from 39% to 40% as the system input TS was changed from 1% to 7%. Press-liquor flow rates for the static-screen and the PressTech Agri-Press as a system ranged from 44 to 10 gpm as input TS was changed from 1% to 7%. The press-cake TS concentration averaged 30% during the testing. Direct comparisons cannot be made between the two screw-presses because the Agri-Press was not tested as a stand–alone unit. For both the KP-6L and the Agri-Press systems, nutrients were preferentially partitioned into the solid or liquid phase, depending on the nutrient and the input slurry TS content.