A standard performance testing protocol for mechanical manure solids separators has ... The press-cake TS concentration averaged 30% during the testing.
PERFORMANCE TESTING OF SCREW-PRESS SOLID SEPARATORS: COMPREHENSIVE SOLIDS ANALYSIS AND NUTRIENT PARTITIONING Robert T. Burns and Lara B. Moody The University of Tennessee, Biosystems Engineering & Environmental Science Dept. P.O. Box 1071, Knoxville, TN 37901-1071 ABSTRACT 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. INTRODUCTION Dairies using hydraulic-flush manure collection systems routinely rely on solids separation in order to achieve an effluent that is low enough in solids to recycle as flush water. Mechanical solids separators are routinely used on dairy farms to assist in the provision of a low TS effluent for use as recycled flush water. The performance of mechanical manure solids separators varies as the total solids content of the input manure changes. Generally higher press-liquor flow-rates increase and dry-mass solids capture efficiencies decrease as manure TS is lowered in the input manure slurry processed by the separation unit. To properly size and install mechanical manure solids separation units, the separators’ performance characteristics must be known for the specific manure slurry found at the farm in question. A protocol for testing mechanical solids separation devices has been developed at the University of Tennessee (UT). This protocol tests manure solids separator performance across a wide range of input manure slurry TS concentrations. This provides useful information to engineers selecting manure separation equipment. By testing all devices using one protocol at one location, equality between equipment tests is increased. The results of the separator performance testing is a comprehensive analysis of the unit, including; pressliquor flow rates over a range of influent total solids (TS) concentrations and the resulting press-cake TS concentration, dry-mass capture efficiency, and nutrient partitioning of total kjeldahl nitrogen (TKN), total phosphorus (TP), soluble phosphorus (SP), and potassium (K). MATERIALS AND METHODS To date, two brands of mechanical screw-press separators have been tested using the UT testing protocol. A Vincent KP-6L (Vincent Corp., Tampa, FL) and a PressTech Agri-Press (Press Technology & Manufacturing, Inc., Springfield, OH) were tested with dairy manure slurries. The KP-6L was tested with a screw having a 3/8” notch every 3/8” along the flight. The press had a 0.050” screen. The Agri-Press was
preceded by a Bauer Hydro-sieve static screen (Springfield, OH). The Agri-Press used a 6” continuous flight screw with a 0.006” wedge-wire screen. The performance tests were conducted at the University of Tennessee Dairy Experiment Station in Lewisburg, TN. It is a 175-cow facility using a scrape waste collection system. For the performance tests, manure and bedding (approximately 20% TS) were scraped and stored for two days prior to testing. The dairy uses recovered manure solids for bedding material. Each performance tests began with a 500 gal (1890 L) tank containing waste with approximately 10% TS. To make 10% TS, the collected manure was mixed with dilution water for 30 minutes using an electric paddle stirrer. Then, manure was pumped from the tank to the separator. For the Vincent testing, the dairy manure slurry was pumped to the separator at a rate exceeding the input capacity of the unit. Overflow piping carried excess manure slurry back to the waste sump. The Agri-Press unit input rate was limited by the maximum flow-rate that the static-screen could process. All test runs with the Agri-Press were made with the associated static-screen at full capacity. Samples were collected from the influent and each effluent point. Effluent solids are referred to as presscake, and effluent liquids are referred to as press-liquor. Duration was based on the time required to recover approximately 50 gal (190 L) of press-liquor. Resulting press-cake and press-liquor volumes were weighed using two Tru-test load cells (Models #703 and PROII, Tru-test, Mineral Wells, TX). After testing the separators at 10% TS, the mix in the tank was diluted to approximately 8% TS, the separator was again tested. Subsequently, tests were performed at approximately 6, 4, 2 and 1% TS. Samples were analyzed for total and volatile solids using Standard Method 2540. G (Standard Methods, 1998), SP using QuikChem method 12-115-01-1-H (Lachat Instruments, Milwaukee, WI), TP using QuikChem method 13-115-01-1-B (Lachat Instruments, Milwaukee, WI), TKN using QuikChem method 13-107-06-2-D (Lachat Instruments, Milwaukee, WI). RESULTS Vincent KP-6 The Vincent KP-6L was evaluated at TS concentrations ranging from 0.4 to 7% TS. The press-liquor flow rate from the screw-press increased as the TS concentration of the influent decreased (Figure 1). At the initial TS influent concentration of 7%, the press-liquor flow rate was 8 gallons per minute (gpm). At the lowest input TS tested (TS of 0.4%), the press-liquor flow rate increased to 53 gpm. The KP-6L maintained a constant press-cake consistency throughout the test. The average TS concentration of the press-cake was 28.9% (± 1.3%) (Figure 1). The dry-mass capture efficiency of the screw press decreased with decreasing TS concentrations (Figure 2). Dry-mass capture efficiency was calculated as follows: Dry-mass capture efficiency (%) =
min (%TS in ) − m PL (%TS PL ) m (%TS PC ) × 100 = PC × 100 min (%TS in ) min (%TS in )
Where min is mass influent, mPL is mass press-liquor and mPC is mass press-cake. When the influent TS concentration was 7%, 60% of the solids were recovered in the press-cake (Figure 2). As the influent TS concentration decreased to 0.4, the dry-mass capture efficiency decreased to 5.3%. As shown in Table 1, TP and TKN were preferentially partitioned into the press-cake. Greater partitioning of these nutrients was noted at lower TS input slurries. Soluble P was seen to partition into the press-liquor; greater movement into the press-liquor occurred at lower TS input slurry concentrations.
Press-Liquor Flow Rate
Press Cake TS 100%
Dry-Mass Capture Efficiency 100%
60
50
90% 50 Press Liquor Flow Rate (gpm)
80% 70%
40
60% 50%
30
40% 20
Press Cake TS
Press Liquor Flow Rate (gpm)
90%
30% 20%
10
80% 70%
40
60% 50%
30
40% 20
30% 20%
10
10% 0
10%
0% 0
1
2
3
4 5 Influent TS (%)
6
7
Dry-Mass Capture Efficiency
Press-Liquor Flow Rate 60
0
8
0% 0
FIGURE 1. Press-liquor Flow Rate (gpm) and Press-cake Total Solids (TS, %) from KP-6L as Affected by Influent TS (%).
1
2
3
4
Influent TS (%)
5
6
7
8
FIGURE 2. Dry-Mass Capture Efficiency by KP-6L as Affected by Influent Total Solids (%).
TABLE 1. Influent and Press-Cake mass of solids (wet basis) and nutrients from the KP-6L Screw-Press, where mass is m, influent to the solid separator is in, effluent press cake is PC, total solids is TS, soluble phosphorus is SP, total phosphorus is TP and total kjeldahl nitrogen is TKN. Influent TS (%) 0.4 0.7 2.0 3.5 4.8 7.0
min (lb) 346.2 420.3 417.6 426.6 450.6 426.8
mPC (lb) 0.237 1.34 6.56 18.58 37.6 64.8
mSP- in (lb) .0088 .012 .017 .017 .024 .027
mSP-PC (lb) 3.0x10-6 2.5x10-5 8.9x10-5 3.1x10-4 6.1x10-4 0.0013
mTP-in (lb) 0.022 0.046 0.1 0.14 0.2 0.3
mTP-PC (lb) 1.7x10-4 0.0014 0.0054 0.014 0.039 0.054
mTKN-in (lb) 0.07 0.19 0.5 0.8 1.2 1.5
mTKN-PC (lb) 1.7x10-4 0.0049 0.02 0.06 0.16 0.27
PressTech Agri-Press Press-Tech provided a manure separation system for testing that utilized a static-screen pre-thickening unit and an Agri-Press screw-press unit. The results listed here are for the overall system performance, not the performance of the screw-press alone. It should be noted in any comparisons between the Vincent and Press-Tech units that the Vincent unit was tested as a stand-alone unit, and was not tested with a prethickener. The Press-Tech side hill/screw-press system was tested at TS concentrations ranging from 1.2 to 8.5%. The press-liquor flow rate through the separator system increased as influent TS concentration decreased (Figure 3). The maximum press-liquor flow rate of 44.1gpm occurred at an influent TS concentration of 1.2%. At 8.5% TS, the system achieved a flow rate of 6.4 gpm. The Press-Tech side hill/screw-press system maintained a constant press-cake consistency throughout the test (Figure 3). The average TS concentration of the press cake was 29.7% (± 5%). The dry-mass capture efficiency of the separator system remained fairly constant over the range of influent concentrations tested. The average dry-mass capture efficiency was 32.1 (± 8.5%) (Figure 4). As shown in Table 2, TP and TKN were preferentially partitioned into the press-cake. Soluble P was not seen to partition into the press-liquor with this unit. A greater percentage of SP was noted to remain with the press-cake at higher TS input slurry concentrations.
Press Cake TS
Press-Liquor Flow Rate 100%
Dry-Mass Capture Efficiency 100%
60
50
90% Press Liquor Flow Rate (gpm)
80% 70%
40
60% 50%
30
40% 20
Press Cake TS
Press Liquor Flow Rate (gpm)
90%
30% 20%
10
50
80% 70%
40
60% 50%
30
40% 20
30% 20%
10
10% 0
10%
0% 0%
1%
2%
3%
4% 5% Influent TS (%)
6%
7%
8%
Dry-Mass Capture Efficiency
Press Liquor Flow Rate 60
0
9%
0% 0%
FIGURE 3. Press-liquor Flow Rate (gpm) and Press-cake Total Solids (TS, %) from the Side Hill/Screw-press Separator System as Affected by Influent TS (%).
1%
2%
3%
4% 5% Influent TS (%)
6%
7%
8%
9%
FIGURE 4. Dry-Mass Capture Efficiency by the Side Hill/Screw-press System as Affected by Influent Total Solids (%).
TABLE 2. Influent and Press-Cake mass of solids (wet basis) and nutrients from the Agri-Press system, where mass is m, influent to the solid separator is in, effluent press cake is PC, total solids is TS, soluble phosphorus is SP, total phosphorus is TP and total kjeldahl nitrogen is TKN. Influent TS 1.2 2.4 5.2 6.7 8.5
min (lb) 186.0 322.7 558.0 502.7 472.7
mPC (lb) 6.0 11.0 25.0 27.0 20.0
mSP- in (lb) 4.23 7.42 16.15 13.22 10.86
mSP-PC (lb) 0.37 0.31 0.65 3.13 1.8
mTP-in (lb) 7.6 17.3 51.2 24.6 21
mTP-PC (lb) 0.94 1.6 5.1 5.2 4.4
mTKN-in (lb) 12.4 43.2 88.5 86.3 61.8
mTKN-PC (lb) 3.7 5.8 20.1 19.5 13.8
CONCLUSIONS The testing protocol developed for mechanical manure solids separators was used to quantify the performance of two commercial units across a wide range of input dairy manure slurries. The press-liquor flow-rate and the dry-mass capture efficiencies varied significantly for both units tested as the input manure slurry TS was changed. This illustrates the importance of having performance data specific to the manure that the unit will be operated with. The results of the performance test provide a comprehensive analysis of the unit evaluated. From the analysis, a planner can estimate the expected through put of material, the resulting mass of solids to be removed and the total solids (TS) content of the pressed cake as affected by the influent TS concentration. This is important information when sizing process sumps and solids storage areas; it is critical to selecting a unit that can be operated in the time frame desired by the dairy operator. Information concerning the mass of nutrients expected to remain with the separated solids will be of use to nutrient management planners who require estimates for whole farm planning of new facilities that plan to use mechanical solids separators. REFERENCES Standard Methods for the Examination of Waste and Wastewater Treatment, 20th Edition. 1998. Clesceri L.S., A.E. Greenberg, A.D. Eaton eds. United Book Press Inc., Baltimore, Maryland.
