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A comparison of three types of slurry sampling device
J. agric . Engng Res. (1980) 25, 279-286
A Comparison
of Three
Types of Slurry Sampling
Device
G. G. MARTZOPOULOS*; V. C. NIELSEN?
A simple and reliable method of taking samples of slurry from settled farm slurry stores by means of a tube and piston sampling device is described and compared with 2 other methods of sampling. The results of a statistical analysis of the total solids (TS) content of the samples obtained by the 3 methods indicates that the tube and piston device has advantages over the other methods.
1.
Introduction
The literature contains few references to the method of collection of slurry samples from farm storage systems. The obtaining of accurate samples of livestock slurry from farm storage systems was reviewed by Van der Hock’ in which he concluded that the lack of a representative sampling technique was a serious handicap for laboratory experiments and the interpretation of results. Farm slurries consist of mixtures of faeces and urine from cattle, pigs or poultry, often diluted with rainwater, washing down and cleaning water, bedding materials and wasted fodder. Slurries vary in content depending on the amount of dilution caused by these additional constituents. Livestock slurries are frequently stored for periods ranging from a few days to 12 months in a variety of structures. Stores range from below ground concrete or metal lined tanks, or compounds excavated out of the soil and subsoil and unlined, to metal, concrete or wooden panelled above ground structures. Volumes stored may range from 100 m3 to well over 3000 m3. The contents may be allowed to settle to form 3 distinct layers. A dense layer of sludge on the base, with a liquid layer above and a top layer consisting of a surface crust of light floating material. The depth of each layer is dependent on the composition of the original slurry and there appears to be ,movement of material between the base and the surface crust depending 011 the degree of anaerobic activity present. For management reasons some slurry storage systems required the contents to be regularly mixed to prevent crust formation. All these factors contribute to ,make the collection of a series of representative samples extremely difficult. One of the first attempts to obtain a representative sample was by Stewart.2 He compared a system of shallow trays randomly placed over a given area, to which slurry was applied by tanker, with that of collection by means of 9 1 buckets suspended behind and beneath the spreader device on a slurry tanker. Samples from each technique were collected, bulked, mixed and a representative sample obtained. These were analysed for pH, TS, Total N, Soluble N, P,O, and K,O and the results were compared. It was found that the bucket method of collection was as accurate as the field trays and was more convenient to use. Tunney and Molloy3 described a sampling device which they used to obtain slurry samples from farm stores. This consisted of a rigid 6 cm diameter p.v.c. pipe which was inserted into the stored slurry vertically until it reached the base. The end of the pipe was then sealed and a column of slurry withdrawn. Sealing was achieved by attaching a rubber ball to a length of nylon string which passed down through the pipe; the ball was pulled tight against the end of the pipe and held there while the sampler was withdrawn from the store. A number of random samples were taken and then placed in a plastic bucket and after mixing a 1 1 aliquot was transferred to a polythene bottle. No comparisons were made with other sampling systems. * Prese!lt + Farm Keceived
address:
Department
Waste Unit,
ADAS,
I2 October
1979;
of Agriculture Ministry accepted
and
Horticulture,
of Agriculture,
Reading
I” revised
form
24 January
University
of Readrny
1980
279 0t1~1-8634’80/010279
i 08
;02.Ot1,‘0
‘I 1980 The
British
Society
for
Research
I” Agricultural
Enginrerlng
280
SLURRY
SAMPLING
LItVICES
Van der Hock’ reviewed sampling techniques in use in the Netherlands for aerated, well mixed farm slurries and for settled stored slurries. The first method of sampling aerated slurries consisted of attaching a small bore hollow tube to the frame of an aeration device and connecting this to a small hand pump. Samples from a predetermined depth were withdrawn when required. No results are given for this method. The second method made use of a 1 1 cylindrical container with sealed base attached to a metal support rod. This rod had 2 struts to hold a second rod which was attached to the lid of the container. It was thus possible to open and close the lid of the container when it was immersed in a slurry tank at any depth. Four sampling positions were chosen within a store and sampled at varying depths, for TS, COD, ash and Kjeldahl N. The means of these results indicated that there was variation between sampling points, but no statistical assessment was made. The third method consisted of taking a fixed volume of slurry from each tanker load removed until the store was emptied. Each sample was mixed and a representative aliquot taken and analysed for TS, COD, ash and Kjedahl N. The mean of these results was taken as the analysis of the store of mixed aerated slurry. However, it was expected that there would be a settled layer which remained in the store and was not analysed. Van der Hoek’ then reviewed sampling methods for settled stored pig slurry, which included the container with opening lid, the method used by Tunney and Malloy3 and a method used by the Manure Bank of Limburg. This last method consisted of 2 cylinders, one fitting closely inside the other. The outer cylinder had a series of ports set down its length. The internal cylinder was divided into a series of compartments and by rotating the outer cylinder it was possible to open and close the ports into the internal cylinder. Sampling consisted of lowering the device vertically into the store until it reached the base. The sampling ports were opened and when the container was full the ports were closed, the device was withdrawn and the contents emptied into a bucket and well mixed. This system obtained representative samples through all the layers within the store. Several random samples were taken around the store. The means of the analytical results were taken as the composition of the store contents. The fourth method consisted of taking a representative sample from each slurry tanker load Examples of analysis were given. removed from a store until the storage tank was emptied. Van der Hock’ recommended that this last system was the most reliable provided that the storage tank was completely emptied. However, these conclusions were not based on a statistical comparison of the results of the analysis with other systems using the same slurry, but on practical experience.
2.
Methods and analysis
Three methods of sampling stored slurry were examined: 1. Three cylindrical containers 160 mm high and 60 mm in diameter with the top ends open were attached to a metal rod and set at 3 positions, to obtain samples of the 3 layers of unmixed slurry simultaneously (see Fig. 1). 2. Three cylindrical containers of similar size to method 1, with opening lids were set at the same positions on the metal rod as in method 1. The lids were opened once the rod had been placed in the slurry in a vertical position, at the required depth (see Fig. I), but could not be closed while submerged in the slurry. 3. A piston and tube sampler was made from a Perspex tube 50.8 mm in diameter and attached to a metal support rod. The piston device consisted of a metal rod (the same length as the tube and support rod), which had attached to the bottom end a rubber bung which just fitted into the tube and closed it after the sample had been taken. The piston was constructed by using a similar rubber bung set on the rod so that when the end of the tube was closed, this bung closed the top end. To maintain the position of the rod within the tube when sampling, the top end of the tube was fitted with a gland through which the rod passed (see Fig. 2(a)). Sampling was
G.
G.
MARTZOPOULOS:
V.
C.
NIELSEN
Top
1
-Covered
Open ended conioiner
container
/
Centre
I Piston + tube A contomer
1
Base
F&. 1. The arrangement of the 3 samplers for .simultaneorrs sampling
(b)
Fig. 2. The tube and piston slurry sampling clepice. The tube and piston components: (b) the .rumpler in the closed position: (c) the piston extended read) (a)
,fiw
carried
strn7pling
out by extending the rod beyond the tube until the piston reached the end of the tube, The sampler was then carefully inserted into the slurry store vertically until the end bung on the rod rested on the base of the store. The tube was then pushed down the rod until it enclosed the end bung and the sampler was then withdrawn from store (see Fig. 2(b)). The sample thus retrieved contained a vertical cross section of the slurry store contents from the top to the base. For comparative sampling tests, the 3 methods were mounted on a single central rod (see Fig. I), thus allowing all 3 samples to be taken from the same position in the store. Four sampling points were chosen to permit 4 replications from each store. A TS analysis was used for comparison of the sampling methods. Whole samples of the 2 container methods were taken, while for the piston and tube method a 250 ml aliquot was taken from a well-mixed bulk sample. Four stores at the National Institute for Research in Dairying were tested respectively containing: Fig. Z(c).
282
SLURRY
SAMPLING
DEVICES
1. Slurry from dairy cows fed on maize silage. The covered store appeared to be well mixed and non-stratified. However, when it was emptied a settlement of thick sludge was found on the base of the store. 2. Slurry which had been left to settle and stratify from dairy cows fed on a diet of lucerne. The store was covered. 3. Slurry from youngstock on a conventional diet. The uncovered store had been left to settle and stratify. 4. Slurry put into a single uncovered store from various sources around the site, with a variable straw content and consistency. Sampling took place during a thaw in the winter when melting ice had caused the surface crust to sink. 3.
Results
The data on the samples taken at the 4 sampling points A, B, C and D in each of the 4 stores are presented in Table I. For the 2 cylinder samplers, samples were taken at 3 positions in each of the stores, top, centre and base. The piston and tube sampler took a sample which included all 3 positions. These data were used as the basis for statistical comparisons. The first comparison in Table II related only to the 2 container methods of sampling, and the following 4 situations were examined : 1. Differences between the 4 sampling position in each store. 2. Differences between mean samples obtained by the 2 sampling methods. 3. Comparison of the TS between the 3 layers within the store (a) top. 4. Comparison of the 2 sampling methods when used in each of the 3 layers. These 4 sets of comparisons were repeated for each of the 4 stores. The results indicate that for the first comparison that of the sampling position, there were significant differences in stores 3 and 4. In the second comparison, sampling method, there were significant differences in the samples from store 4 and that the open top container had a significantly lower TS concentration. In the third comparison there were significant differences in the TS concentration in all 4 stores between the 3 sampling depths. In the fourth comparison there were only significant differences between the 2 sampling methods in the fourth store and these occurred in the centre and base samples. Comparison of the 2 sampling methods indicated that the mean TS content of the open containers was always lower in each of the stores than the TS content obtained by the covered containers. The second basis of comparison was to examine the differences between all 3 sampling methods within each store, taking the mean values of the TS of the samples in each sampling position. The results are presented in Tables 111and 1V. The results of the comparisons made in Table III indicate that the TS content of the tube and piston samples were significantly higher than those obtained by the other 2 methods. In Table IV the results indicate that the variation of TS of the samples from the tube and piston method was very small and relatively consistent compared with the other 2 sampling methods. 4.
Discussion and conclusions
The results of the first group of comparisons given in Table II indicate that the consistency of the samples was very irregular between and within the stores. This was probably due to the
following factors affecting the depth of each layer within the stores. 1. The length of time the slurry had been stored: experience indicates greater stability of the layers with increasing time. 2. The effect of whether the store is open or covered. Again experience indicates that covering a store reduced evaporation from the surface, therefore keeping the crust damp.
I
(sdf
(~0
fsd)
TOP Centre Base Average
TOP Centre Base Average
(sd)
TOP Centre Base Average
TOP Centre Base Average ---____
16.96 17.70 18.92 17.94 (1.36)
17.10 17.90 IQ.46 18.15 (1.20)
10.84 13.14 14.12 12.70 (1.68)
10.62 12.74 13.87 12.41
(t 45)
12.16 6.95 12.98 10.70 (3,27) __~~.
11.98 1.27 12.35 10.53 (2.83)
_-__.
11.72 11.70 12.06 11.83 (0.20)
Top covered con?ai~er
A
1164 Il.82 Il.98 Il.81 (0.17) _---
shmpling point:, ---____- .-__~-Sampler Open Depth condainet position _~__ _-_______
-
‘-Jr
/
-
--
I
stores
-
_
11.84 11.79 12.04 11.89 (0.13) ---
~I_-
Top covered container
c
The
small
16.87 1747 18.45 17.60 (0.80)
10.27 13.28 8.49 (5.88)
1.93
_
IQ.25
19.25
14.42 -_
14.42
13.94 --..
13.94
14.07
14.07
piS?Ol
-
‘I
Ttrbt und
area chosen for sampling
16.84 17.86 IQ.18 17.96 (1.17)
2.01 12.Q5 14.18 9.71 (6.70) _I-__~--
11.82 8.85 12.77 1 I.15 (2.041 11.03(l-67) ______..~ ____~~~_
Il.75 9.12 12.21
11.80 11.76 11.97 1 I-84 (0.12)
Open container -__ -.
rrplication.
19.12
19.12
14.58
14~58
13-82
13.82
14.05
14.05
and p&or f
Tube
.___.~
to permit
16.73 17.53 18.97 17.74 (1.14)
12.72 12.90 14.26 13.29 (0.84)
11.92 8.70 12.93 Ii,18 (2.21)
11.73 11.77 11.87 11.79 (0.07)
--_
conr~i~er
TOP covered
B
-_ ------”
of the 4 slurry
16.86 17.38 18.71 17.65 (0.95)
12.75 12.68 14.18 13.20 (0.85)
11.86 8.97 12.27 f1,03 (l-80) .I________
11.70 11.73 11.92 11.78 (0.12)
Open cun~ajaer
I 111~ in rach
19.39
19.39
14.52
14.52
13.73
13.73
14.11
14.11
Tube and pis~ot
t$d): Standard deviation Sampling points A, B, C and D were chosen from within an area of causrd by uneven distribution of material within each store
-
-
TABLE
Data on the composition of samples in terms of percentage total solids
slurry
(i ,28) inthe
16.32 17.51 18-88 17.57
13-07 12.98 14.62 13.56 (0.92)
11.52 6.07 12.95 IO.18 (3.63) -----
11-72 11.78 11.90 11.80 (0.09)
was to avoid variation
16.26 17.17 18.36 17.26 (1.05)
12.87 12.68 14.22 13.26 (0.84) _._._.
11.64 6.25 12.11 IO.00 (3.26)
11.68 11.74 11.89 11.77 (0.11)
containet
Open
D ---I TOP covered conlaitzer -~--
content
19.07
19.07
14.64
14.64
13.65
13.65
14.02 ---
14.02
-;b; and pisfon
Sampling position
* PzO.05
d.f. = I5
IV (D) *I(M)
III Depth (D)
____~_
II Sampling method 00
I
Source
2
Store
253 90,315 6332 25,261
1,834,686
833,219
1,067,974
-
0.46 0.91 0.05 8.40
608
6.70
N.S.D. N.S.D. N.S.D. S.D.
S.D.
SD.
S.D.
107
N.S.D. N.S.D. N.S.D. S.D.
S.D.
_
S.D.
N.S.D. N.S.D. SD.
Significam
43.34
I.28 0.28 0.22 27.8
350 14,106 13,443 41,870
23,663
23.6
3.22 2.79 3.93
106.831
2638 415,843 132,482
I
TABLE II
D*
9.60 16,742
2,657 0,131
Open Co veretl
11.831
0.752
0.185
Top 1 I.729
17.59
9.10
16.74 16.75
17.417
18.61 19.12
Base
18.866
14.09
12.571
1I.954
Base
17.86
17.43 17.70
D
13.41
Covered container
Centre
17,565
12.54
7.77:
11.761
Top
C
“/,)
17.778
Centre
17.697
13.25
B
(TS
methods
Means
Open container
0.055
0.107
18.016
0.151
_____
12.55
A
3.068
LSD,.
Significant differences within each stormontainer
Only in the top layer the two samplers gave samples with N.S.D. TS Y<,
TS 7; in the base significantly higher TS % in the centre significantly lower Top layer had significantly lower TS concentration S.D. TS “1 ‘0 between all the layers _______ ____.-
Significant lower TS concentration in samples from open container
C position had significantly lower TS concentration Only in B and C positions N.S.D. TS % _
-
Remarks
C;.
G.
MARTZOPOULOS;
V.
C.
285
NIELSEN
TABLE III
Significant differences in sampling between the 3 sampling methods
Samplers Store
CMeun TS : c;of’the snmples) _ Tube + container piston _- -__ 14.06 11.82 13.79 10.80 12 39 14.54
contniner Il.89 IO.66 Il.84
17.61
19.21
17.86
-
* P=OO5
F
Significance*
12x103 269 6,35
S.D. SD. S.D.
0.396 0.372 1,979
Container methods not different. Higher TS concentration tube + piston sampler
317
S.D.
0.167
All the methods were different. Higher TS concentrations in tube+ piston sampler.
Remarks
LSDo.5
Covered
Open
____
in
-
-
d.f.-6
TABLE IV
Variation of samples within the methods
-
Uncovered container ___-.11.80 0.032
Store
-_____ Mean S.D. Coefficient of variation (“//,) 0.27 --__ Mean 10.65 S.D. 0.492 Coefficient of variation (%) 4.92 ___~ Mean 11.84 S.D. 2.266 Coefficient of variation (%) 19.14 ___Mean 17.61 S.D. 0.279 Coefficient of variation (‘JJ 1.58
2
3
4
-
Covered container
Tube + piston
Il.82 0.045
14.06 0.038
0.38
0.27
10.80 0.0469
13.79 0.124
462
0.90
12.32 I.773
14.54 0.094
14.40
0.65
17.86 0.253
19.21 0,143
1.42
0.75
-
3. The type of slurry stored, that is the effect of additional quantities of bedding materials or of dilution water. 4. The effect of the weather on the formation of a surface crust in uncovered stores. The covered sampling containers were able to collect a more representative sample from the base of the store as is indicated in Tables I and 11, but in the other positions there was not very much difference between the 2 methods. This may have been caused by the fact that the open container became partly filled with less dense material as it was lowered to the desired sampling position and therefore was unable to collect a representative sample. The covered container also produced significantly lower TS contents than the tube and piston method. This may have
286
SLURRY
SAMPLING;
DEVICES
been due to the composition of the slurry sampled, in that the more liquid fractions of the slurry moved more readily into the space left by the escaping air, while the more viscous fractions flowed less easily into the container. The covered container was also limited by the height of the opening 160 mm above the base of the store. It was therefore not possible to obtain a truly representative sample of the dense base layer. The results of the second group of comparisons given in Tables III and IV in which the 3 sampling methods are compared, indicate that the tube and piston method collected significantly more TS than the other 2 methods. It was not possible to obtain a definitive TS content for each store, so that the accuracy of the tube and piston sampler cannot be verified. However, the consistency of the TS contents by the tube and piston method in each of the four samples taken in each store were significantly better than those obtained by the other 2 methods. This has been attributed to (i) the sampling technique, which consists of causing the minimum disturbance to the contents of the slurry store during the sampling operation and (ii) that variation in the depth of the 3 layers of slurry within the store will automatically be compensated for. Both the other methods cause considerable disturbance by displacement of the store contents as the sampling container is lowered to the required sampling depth. The position of the sampling containers on the handling rod were fixed arbitrarily and may not have conformed to the layers within a particular store. REFERENCES
Van der Hoek, K. W. Utilisation of manure by land spreading. CEC Eur. 5672c, 1977 ’ Stewart, T. A. The collection of slurry samples on a field scale and their subsequent storage for chemical analysis. Rec. agric. Res., 1968 17 (1) 97-100 ’ Tunney, H.; Molloy, S. Variations between farms in N, P, K, mg and dry matter composition of cattle, ’
pig and poultry manures. Ir. J. agric. Res., 1975 14 71-79
A Comparison
of Three
Types of Slurry Sampling
Device
G. G. MARTZOPOULOS*; V. C. NIELSEN?
A simple and reliable method of taking samples of slurry from settled farm slurry stores by means of a tube and piston sampling device is described and compared with 2 other methods of sampling. The results of a statistical analysis of the total solids (TS) content of the samples obtained by the 3 methods indicates that the tube and piston device has advantages over the other methods.
1.
Introduction
The literature contains few references to the method of collection of slurry samples from farm storage systems. The obtaining of accurate samples of livestock slurry from farm storage systems was reviewed by Van der Hock’ in which he concluded that the lack of a representative sampling technique was a serious handicap for laboratory experiments and the interpretation of results. Farm slurries consist of mixtures of faeces and urine from cattle, pigs or poultry, often diluted with rainwater, washing down and cleaning water, bedding materials and wasted fodder. Slurries vary in content depending on the amount of dilution caused by these additional constituents. Livestock slurries are frequently stored for periods ranging from a few days to 12 months in a variety of structures. Stores range from below ground concrete or metal lined tanks, or compounds excavated out of the soil and subsoil and unlined, to metal, concrete or wooden panelled above ground structures. Volumes stored may range from 100 m3 to well over 3000 m3. The contents may be allowed to settle to form 3 distinct layers. A dense layer of sludge on the base, with a liquid layer above and a top layer consisting of a surface crust of light floating material. The depth of each layer is dependent on the composition of the original slurry and there appears to be ,movement of material between the base and the surface crust depending 011 the degree of anaerobic activity present. For management reasons some slurry storage systems required the contents to be regularly mixed to prevent crust formation. All these factors contribute to ,make the collection of a series of representative samples extremely difficult. One of the first attempts to obtain a representative sample was by Stewart.2 He compared a system of shallow trays randomly placed over a given area, to which slurry was applied by tanker, with that of collection by means of 9 1 buckets suspended behind and beneath the spreader device on a slurry tanker. Samples from each technique were collected, bulked, mixed and a representative sample obtained. These were analysed for pH, TS, Total N, Soluble N, P,O, and K,O and the results were compared. It was found that the bucket method of collection was as accurate as the field trays and was more convenient to use. Tunney and Molloy3 described a sampling device which they used to obtain slurry samples from farm stores. This consisted of a rigid 6 cm diameter p.v.c. pipe which was inserted into the stored slurry vertically until it reached the base. The end of the pipe was then sealed and a column of slurry withdrawn. Sealing was achieved by attaching a rubber ball to a length of nylon string which passed down through the pipe; the ball was pulled tight against the end of the pipe and held there while the sampler was withdrawn from the store. A number of random samples were taken and then placed in a plastic bucket and after mixing a 1 1 aliquot was transferred to a polythene bottle. No comparisons were made with other sampling systems. * Prese!lt + Farm Keceived
address:
Department
Waste Unit,
ADAS,
I2 October
1979;
of Agriculture Ministry accepted
and
Horticulture,
of Agriculture,
Reading
I” revised
form
24 January
University
of Readrny
1980
279 0t1~1-8634’80/010279
i 08
;02.Ot1,‘0
‘I 1980 The
British
Society
for
Research
I” Agricultural
Enginrerlng
280
SLURRY
SAMPLING
LItVICES
Van der Hock’ reviewed sampling techniques in use in the Netherlands for aerated, well mixed farm slurries and for settled stored slurries. The first method of sampling aerated slurries consisted of attaching a small bore hollow tube to the frame of an aeration device and connecting this to a small hand pump. Samples from a predetermined depth were withdrawn when required. No results are given for this method. The second method made use of a 1 1 cylindrical container with sealed base attached to a metal support rod. This rod had 2 struts to hold a second rod which was attached to the lid of the container. It was thus possible to open and close the lid of the container when it was immersed in a slurry tank at any depth. Four sampling positions were chosen within a store and sampled at varying depths, for TS, COD, ash and Kjeldahl N. The means of these results indicated that there was variation between sampling points, but no statistical assessment was made. The third method consisted of taking a fixed volume of slurry from each tanker load removed until the store was emptied. Each sample was mixed and a representative aliquot taken and analysed for TS, COD, ash and Kjedahl N. The mean of these results was taken as the analysis of the store of mixed aerated slurry. However, it was expected that there would be a settled layer which remained in the store and was not analysed. Van der Hoek’ then reviewed sampling methods for settled stored pig slurry, which included the container with opening lid, the method used by Tunney and Malloy3 and a method used by the Manure Bank of Limburg. This last method consisted of 2 cylinders, one fitting closely inside the other. The outer cylinder had a series of ports set down its length. The internal cylinder was divided into a series of compartments and by rotating the outer cylinder it was possible to open and close the ports into the internal cylinder. Sampling consisted of lowering the device vertically into the store until it reached the base. The sampling ports were opened and when the container was full the ports were closed, the device was withdrawn and the contents emptied into a bucket and well mixed. This system obtained representative samples through all the layers within the store. Several random samples were taken around the store. The means of the analytical results were taken as the composition of the store contents. The fourth method consisted of taking a representative sample from each slurry tanker load Examples of analysis were given. removed from a store until the storage tank was emptied. Van der Hock’ recommended that this last system was the most reliable provided that the storage tank was completely emptied. However, these conclusions were not based on a statistical comparison of the results of the analysis with other systems using the same slurry, but on practical experience.
2.
Methods and analysis
Three methods of sampling stored slurry were examined: 1. Three cylindrical containers 160 mm high and 60 mm in diameter with the top ends open were attached to a metal rod and set at 3 positions, to obtain samples of the 3 layers of unmixed slurry simultaneously (see Fig. 1). 2. Three cylindrical containers of similar size to method 1, with opening lids were set at the same positions on the metal rod as in method 1. The lids were opened once the rod had been placed in the slurry in a vertical position, at the required depth (see Fig. I), but could not be closed while submerged in the slurry. 3. A piston and tube sampler was made from a Perspex tube 50.8 mm in diameter and attached to a metal support rod. The piston device consisted of a metal rod (the same length as the tube and support rod), which had attached to the bottom end a rubber bung which just fitted into the tube and closed it after the sample had been taken. The piston was constructed by using a similar rubber bung set on the rod so that when the end of the tube was closed, this bung closed the top end. To maintain the position of the rod within the tube when sampling, the top end of the tube was fitted with a gland through which the rod passed (see Fig. 2(a)). Sampling was
G.
G.
MARTZOPOULOS:
V.
C.
NIELSEN
Top
1
-Covered
Open ended conioiner
container
/
Centre
I Piston + tube A contomer
1
Base
F&. 1. The arrangement of the 3 samplers for .simultaneorrs sampling
(b)
Fig. 2. The tube and piston slurry sampling clepice. The tube and piston components: (b) the .rumpler in the closed position: (c) the piston extended read) (a)
,fiw
carried
strn7pling
out by extending the rod beyond the tube until the piston reached the end of the tube, The sampler was then carefully inserted into the slurry store vertically until the end bung on the rod rested on the base of the store. The tube was then pushed down the rod until it enclosed the end bung and the sampler was then withdrawn from store (see Fig. 2(b)). The sample thus retrieved contained a vertical cross section of the slurry store contents from the top to the base. For comparative sampling tests, the 3 methods were mounted on a single central rod (see Fig. I), thus allowing all 3 samples to be taken from the same position in the store. Four sampling points were chosen to permit 4 replications from each store. A TS analysis was used for comparison of the sampling methods. Whole samples of the 2 container methods were taken, while for the piston and tube method a 250 ml aliquot was taken from a well-mixed bulk sample. Four stores at the National Institute for Research in Dairying were tested respectively containing: Fig. Z(c).
282
SLURRY
SAMPLING
DEVICES
1. Slurry from dairy cows fed on maize silage. The covered store appeared to be well mixed and non-stratified. However, when it was emptied a settlement of thick sludge was found on the base of the store. 2. Slurry which had been left to settle and stratify from dairy cows fed on a diet of lucerne. The store was covered. 3. Slurry from youngstock on a conventional diet. The uncovered store had been left to settle and stratify. 4. Slurry put into a single uncovered store from various sources around the site, with a variable straw content and consistency. Sampling took place during a thaw in the winter when melting ice had caused the surface crust to sink. 3.
Results
The data on the samples taken at the 4 sampling points A, B, C and D in each of the 4 stores are presented in Table I. For the 2 cylinder samplers, samples were taken at 3 positions in each of the stores, top, centre and base. The piston and tube sampler took a sample which included all 3 positions. These data were used as the basis for statistical comparisons. The first comparison in Table II related only to the 2 container methods of sampling, and the following 4 situations were examined : 1. Differences between the 4 sampling position in each store. 2. Differences between mean samples obtained by the 2 sampling methods. 3. Comparison of the TS between the 3 layers within the store (a) top. 4. Comparison of the 2 sampling methods when used in each of the 3 layers. These 4 sets of comparisons were repeated for each of the 4 stores. The results indicate that for the first comparison that of the sampling position, there were significant differences in stores 3 and 4. In the second comparison, sampling method, there were significant differences in the samples from store 4 and that the open top container had a significantly lower TS concentration. In the third comparison there were significant differences in the TS concentration in all 4 stores between the 3 sampling depths. In the fourth comparison there were only significant differences between the 2 sampling methods in the fourth store and these occurred in the centre and base samples. Comparison of the 2 sampling methods indicated that the mean TS content of the open containers was always lower in each of the stores than the TS content obtained by the covered containers. The second basis of comparison was to examine the differences between all 3 sampling methods within each store, taking the mean values of the TS of the samples in each sampling position. The results are presented in Tables 111and 1V. The results of the comparisons made in Table III indicate that the TS content of the tube and piston samples were significantly higher than those obtained by the other 2 methods. In Table IV the results indicate that the variation of TS of the samples from the tube and piston method was very small and relatively consistent compared with the other 2 sampling methods. 4.
Discussion and conclusions
The results of the first group of comparisons given in Table II indicate that the consistency of the samples was very irregular between and within the stores. This was probably due to the
following factors affecting the depth of each layer within the stores. 1. The length of time the slurry had been stored: experience indicates greater stability of the layers with increasing time. 2. The effect of whether the store is open or covered. Again experience indicates that covering a store reduced evaporation from the surface, therefore keeping the crust damp.
I
(sdf
(~0
fsd)
TOP Centre Base Average
TOP Centre Base Average
(sd)
TOP Centre Base Average
TOP Centre Base Average ---____
16.96 17.70 18.92 17.94 (1.36)
17.10 17.90 IQ.46 18.15 (1.20)
10.84 13.14 14.12 12.70 (1.68)
10.62 12.74 13.87 12.41
(t 45)
12.16 6.95 12.98 10.70 (3,27) __~~.
11.98 1.27 12.35 10.53 (2.83)
_-__.
11.72 11.70 12.06 11.83 (0.20)
Top covered con?ai~er
A
1164 Il.82 Il.98 Il.81 (0.17) _---
shmpling point:, ---____- .-__~-Sampler Open Depth condainet position _~__ _-_______
-
‘-Jr
/
-
--
I
stores
-
_
11.84 11.79 12.04 11.89 (0.13) ---
~I_-
Top covered container
c
The
small
16.87 1747 18.45 17.60 (0.80)
10.27 13.28 8.49 (5.88)
1.93
_
IQ.25
19.25
14.42 -_
14.42
13.94 --..
13.94
14.07
14.07
piS?Ol
-
‘I
Ttrbt und
area chosen for sampling
16.84 17.86 IQ.18 17.96 (1.17)
2.01 12.Q5 14.18 9.71 (6.70) _I-__~--
11.82 8.85 12.77 1 I.15 (2.041 11.03(l-67) ______..~ ____~~~_
Il.75 9.12 12.21
11.80 11.76 11.97 1 I-84 (0.12)
Open container -__ -.
rrplication.
19.12
19.12
14.58
14~58
13-82
13.82
14.05
14.05
and p&or f
Tube
.___.~
to permit
16.73 17.53 18.97 17.74 (1.14)
12.72 12.90 14.26 13.29 (0.84)
11.92 8.70 12.93 Ii,18 (2.21)
11.73 11.77 11.87 11.79 (0.07)
--_
conr~i~er
TOP covered
B
-_ ------”
of the 4 slurry
16.86 17.38 18.71 17.65 (0.95)
12.75 12.68 14.18 13.20 (0.85)
11.86 8.97 12.27 f1,03 (l-80) .I________
11.70 11.73 11.92 11.78 (0.12)
Open cun~ajaer
I 111~ in rach
19.39
19.39
14.52
14.52
13.73
13.73
14.11
14.11
Tube and pis~ot
t$d): Standard deviation Sampling points A, B, C and D were chosen from within an area of causrd by uneven distribution of material within each store
-
-
TABLE
Data on the composition of samples in terms of percentage total solids
slurry
(i ,28) inthe
16.32 17.51 18-88 17.57
13-07 12.98 14.62 13.56 (0.92)
11.52 6.07 12.95 IO.18 (3.63) -----
11-72 11.78 11.90 11.80 (0.09)
was to avoid variation
16.26 17.17 18.36 17.26 (1.05)
12.87 12.68 14.22 13.26 (0.84) _._._.
11.64 6.25 12.11 IO.00 (3.26)
11.68 11.74 11.89 11.77 (0.11)
containet
Open
D ---I TOP covered conlaitzer -~--
content
19.07
19.07
14.64
14.64
13.65
13.65
14.02 ---
14.02
-;b; and pisfon
Sampling position
* PzO.05
d.f. = I5
IV (D) *I(M)
III Depth (D)
____~_
II Sampling method 00
I
Source
2
Store
253 90,315 6332 25,261
1,834,686
833,219
1,067,974
-
0.46 0.91 0.05 8.40
608
6.70
N.S.D. N.S.D. N.S.D. S.D.
S.D.
SD.
S.D.
107
N.S.D. N.S.D. N.S.D. S.D.
S.D.
_
S.D.
N.S.D. N.S.D. SD.
Significam
43.34
I.28 0.28 0.22 27.8
350 14,106 13,443 41,870
23,663
23.6
3.22 2.79 3.93
106.831
2638 415,843 132,482
I
TABLE II
D*
9.60 16,742
2,657 0,131
Open Co veretl
11.831
0.752
0.185
Top 1 I.729
17.59
9.10
16.74 16.75
17.417
18.61 19.12
Base
18.866
14.09
12.571
1I.954
Base
17.86
17.43 17.70
D
13.41
Covered container
Centre
17,565
12.54
7.77:
11.761
Top
C
“/,)
17.778
Centre
17.697
13.25
B
(TS
methods
Means
Open container
0.055
0.107
18.016
0.151
_____
12.55
A
3.068
LSD,.
Significant differences within each stormontainer
Only in the top layer the two samplers gave samples with N.S.D. TS Y<,
TS 7; in the base significantly higher TS % in the centre significantly lower Top layer had significantly lower TS concentration S.D. TS “1 ‘0 between all the layers _______ ____.-
Significant lower TS concentration in samples from open container
C position had significantly lower TS concentration Only in B and C positions N.S.D. TS % _
-
Remarks
C;.
G.
MARTZOPOULOS;
V.
C.
285
NIELSEN
TABLE III
Significant differences in sampling between the 3 sampling methods
Samplers Store
CMeun TS : c;of’the snmples) _ Tube + container piston _- -__ 14.06 11.82 13.79 10.80 12 39 14.54
contniner Il.89 IO.66 Il.84
17.61
19.21
17.86
-
* P=OO5
F
Significance*
12x103 269 6,35
S.D. SD. S.D.
0.396 0.372 1,979
Container methods not different. Higher TS concentration tube + piston sampler
317
S.D.
0.167
All the methods were different. Higher TS concentrations in tube+ piston sampler.
Remarks
LSDo.5
Covered
Open
____
in
-
-
d.f.-6
TABLE IV
Variation of samples within the methods
-
Uncovered container ___-.11.80 0.032
Store
-_____ Mean S.D. Coefficient of variation (“//,) 0.27 --__ Mean 10.65 S.D. 0.492 Coefficient of variation (%) 4.92 ___~ Mean 11.84 S.D. 2.266 Coefficient of variation (%) 19.14 ___Mean 17.61 S.D. 0.279 Coefficient of variation (‘JJ 1.58
2
3
4
-
Covered container
Tube + piston
Il.82 0.045
14.06 0.038
0.38
0.27
10.80 0.0469
13.79 0.124
462
0.90
12.32 I.773
14.54 0.094
14.40
0.65
17.86 0.253
19.21 0,143
1.42
0.75
-
3. The type of slurry stored, that is the effect of additional quantities of bedding materials or of dilution water. 4. The effect of the weather on the formation of a surface crust in uncovered stores. The covered sampling containers were able to collect a more representative sample from the base of the store as is indicated in Tables I and 11, but in the other positions there was not very much difference between the 2 methods. This may have been caused by the fact that the open container became partly filled with less dense material as it was lowered to the desired sampling position and therefore was unable to collect a representative sample. The covered container also produced significantly lower TS contents than the tube and piston method. This may have
286
SLURRY
SAMPLING;
DEVICES
been due to the composition of the slurry sampled, in that the more liquid fractions of the slurry moved more readily into the space left by the escaping air, while the more viscous fractions flowed less easily into the container. The covered container was also limited by the height of the opening 160 mm above the base of the store. It was therefore not possible to obtain a truly representative sample of the dense base layer. The results of the second group of comparisons given in Tables III and IV in which the 3 sampling methods are compared, indicate that the tube and piston method collected significantly more TS than the other 2 methods. It was not possible to obtain a definitive TS content for each store, so that the accuracy of the tube and piston sampler cannot be verified. However, the consistency of the TS contents by the tube and piston method in each of the four samples taken in each store were significantly better than those obtained by the other 2 methods. This has been attributed to (i) the sampling technique, which consists of causing the minimum disturbance to the contents of the slurry store during the sampling operation and (ii) that variation in the depth of the 3 layers of slurry within the store will automatically be compensated for. Both the other methods cause considerable disturbance by displacement of the store contents as the sampling container is lowered to the required sampling depth. The position of the sampling containers on the handling rod were fixed arbitrarily and may not have conformed to the layers within a particular store. REFERENCES
Van der Hoek, K. W. Utilisation of manure by land spreading. CEC Eur. 5672c, 1977 ’ Stewart, T. A. The collection of slurry samples on a field scale and their subsequent storage for chemical analysis. Rec. agric. Res., 1968 17 (1) 97-100 ’ Tunney, H.; Molloy, S. Variations between farms in N, P, K, mg and dry matter composition of cattle, ’
pig and poultry manures. Ir. J. agric. Res., 1975 14 71-79