Inst.of Advanced  
Studies, UN University
Integrated Bio-Systems in Zero Emissions Applications
Proceedings of the Internet Conference on Integrated Bio-Systems  
Editors: Eng-Leong Foo & Tarcisio Della Senta. 1998
http://www.ias.unu.edu/proceedings/icibs		  

Manure surplus processing at the farm level and in coordinated groups of farms

G. Bonazzi, S. Piccinini. Centro Ricerche Produzioni Animali - CRPA 

(Research Center for Animal Production). C.so Garibaldi, 42 - 42100 Reggio Emilia - ITALY

Tel. +39/522/436999 - Fax +39/522/435142  E-mail: S.Piccinini@crpa.it  

*The paper has already been presented at the International Workshop 
"Environmentally friendly management of farm animal waste", 25-29 november 1997, Sapporo, Japan 
.
.
Abstract:
Manure surpluses in pig farms can be reduced by separation of the solid fraction from the slurry. The solid fraction can be exported to long-distance areas with a high demand for fertilizers, thus reducing the farm surplus. To make the offer of solid fractions more attractive to the farmers outside the surplus areas, composting could be a solution.

The fertilizing value is increased despite the volatilization of the ammonia fraction during the composting process. Nitrogen loss can be limited by means of adding suitable bulking materials, for instance straw or shredded pieces from trimming. To further reduce nitrogen surplus, an aerobic treatment of the liquid fraction resulting from the solid separation can be adopted.

This paper reports the results of trials on a pilot plant performing nitrification, denitrification and enhanced biological phosphorus removal. Results on a farm-scale purification plant specifically designed for pig slurry treatment are also reported.

As regards the group operations, we report the case of a consortium system of pig slurry management in an area with a high livestock density. In about 25 farms with 87,000 places for 80 kg pigs, about 808,000 kg of surplus N per year are produced, with reference to the available agricultural land of the area.

Seven of the largest farms agreed to take part in a coordinated programme of slurry management which aims to reduce about 80% of the N surplus. All the farms carry out raw slurry centrifuging and solid fraction composting, and a cooperative service for collecting and transporting the resulting compost out of the area has been established.

1. INTRODUCTION

Manure surpluses on pig farms can be reduced by means of different slurry treatments. Coarse solid separation by rotating or vibrating screens is the most common treatment, and the solid fraction obtained can be exported to distant areas with a high demand for organic fertilizers, thus reducing the farm surplus. By centrifuging, a more significant volume of solid fraction can be separated from the raw slurry (Piccinini et al., 1987). To make the offer of solid fractions more attractive to the farmers outside the surplus areas, composting could be a solution.

At the farm level, with the aeration of the liquid fraction resulting from the solid separation, a 40% reduction of N can be achieved (Copelli et al., 1985) which, in addition to the export of the solid fraction outside the production area, enables a total N reduction of up to 70%.

A higher N reduction can be achieved by aerobic treatment plants with predenitrification, oxidation-nitrification, and sedimentation, with discharge of the treated effluent into a municipal sewer. In fact, plants designed to discharge in water bodies are not appropriate for animal wastes due to the difficulties in meeting the severe restrictions of the environmental regulations.

In the coordinated group operations, projects have been developed to create centralized treatment plants in the high pig density areas of northern Italy. These projects, however, have not been successful because of the high environmental impact resulting from the polluting residual load of the treated effluent. Greater success seems to be achieved by cooperative services for on-farm treatment and subsequent long-distance transport and distribution of animal wastes or their solid fractions.

This paper presents the results of experiments carried out by CRPA on composting and purification of animal wastes, as well as the description of a cooperative service of waste management in an area with high pig density.
 
 

 
 
Figure 1 - Flow sheet of the experimental composting plant of Soliera (Modena, Italy)
Figure 2
Figure 3
Figure 2 - A view of the experimental composting plant of Soliera (Modena, Italy).
Figure 3 - A view of the turning machine moving on rails.
2. COMPOSTING SOLID FRACTIONS OF PIG SLURRY AND OTHER ANIMAL WASTES
 
By composting these materials, the fertilizing value is increased, despite the volatilization of the ammonia fraction during the process. Nitrogen loss can be limited by means of adding suitable bulking materials, for instance straw or shredded pieces from trimming. The tests on different organic materials were conducted at an experimental composting plant located in an organic waste treatment facility (Piccinini et al., 1995) (Figure 1, 2, 3). The plant comprises a horizontal pit reactor closed inside a greenhouse and equipped with a turning machine moving on rails. The pit is 3 m wide and 60 m long and the maximum height of loaded material is 1 m.
 
 Significant differences can be seen among manure of different origin, which have a different ammoniacal nitrogen content. Figure 4 shows the N share between organic N and NH4-N, and N losses at the start and at the end of a composting process of solid fraction separated from cattle and pig slurry, of poultry (laying hens) manure and of sewage sludge from animal slurry purification.

The solid fraction separated from cattle slurry, with a starting NH4-N content as low as 7% of TKN, showed N loss of 12%; the solid fraction of pig slurry, with a higher starting NH4-N content, equal to 28%, had N loss of 25%; the poultry manure, with 34% NH4-N, reached N loss as high as 54%, while sewage sludge from animal slurry had 37% N loss.
 
 

Figure 4
Figure 5
Figure 6
Figure 4 - Composting of different animal manures: percentage of TKN, NH4-N and Organic N at the start and at the end of the process.
Figure 5 - Composting of pig slurry solid fraction: percentage of TKN, NH4-N and Organic N at the start and at the end of the process.
Figure 6 - Temperature trend in composting of SFC alone and in mixture with two bulking agents.
Trials were carried out on the solid fraction obtained by means of centrifuging raw pig slurry (SFC). This solid fraction is of shovelling consistency, has a 22-29% dry matter content, constitutes an average of 10-20% of the initial quantity of slurry treated, and contains 20-35% of the total N and 60-70% of the P present in the raw slurry. The solid fraction was tested alone and in a mixture with various bulking agents (straw and shredded pieces from trimmings from public parks); the added quantity was 10% (straw) and 20% (shredded pieces) of the weight of the solid fraction. The physical-chemical characteristics of the various starting mixtures were more or less homogeneous. The materials remained in the reactor for about two months (thermophilic phase), during which they were turned frequently (from 1 to 3 times a week depending on the season and the stage of the process). The materials were subsequently placed in windrows (not turned) under a shed, for a further two-month period which is considered necessary for proper maturation of the product. Figure 5 shows the reduction of N loss resulting from the use of bulking agents. The N loss decreased from 28% with the raw solid fraction to 20-21% with bulking agents. The persistence in the windrow of temperatures in the thermophilic range over a long period of time (Figure 6) was an indicator of a successful composting process.

The humification parameters indicate a good agronomic quality of the resulting compost. As regards the heavy metal content, the resulting values were particularly low with the exception of copper and zinc, parameters that must be kept under control (Table 1).
 

Table 1 - Composting of the Solid Fraction from Centrifuging of pig slurry (SFC): composition of the SFC alone and of the mixtures at the start and at the and of the process.
SFC alone
SFC + straw
SFC + shredded wood pieces
 Parameters
Start
End
Start
End
Start
End
pH  
8.1
8.3
7.9
7.7
8.0
7.9
TS (%)
31.3
32.2
32.4
57.4
34.2
37.9
VS (% TS)
69.4
56.7
74.7
56.8
71.9
58.6
TKN (% TS)
3.27
3.92
2.73
3.30
2.89
4.18
NH4-N (% TKN)
16.7
14.8
16.9
6.3
16.6
8.9
C/N  
11
8
14
11
18
11
P (% TS)
4.75
6.11
3.27
6.12
3.61
5.74
K (% TS)
0.28
0.53
0.96
1.27
0.20
0.66
Cu (mg kg-1 TS)
202
462
219
366
312
466
Zn (mg kg-1 TS)
481
1169
431
1047
580
1119
HI
2.6
0.7
0.7
0.5
0.7
0.6
DH (%)
27.6
60.0
58.5
66.5
59.7
63.1
HR (%)
12.7
32.6
25.6
30.2
27.3
29.5
Note: HI: humification index (NH/(HA+FA)); DH: degree of humification ((HA+FA)/TEC*100); HR: humification rate ((HA+FA)/TOC*100); TEC: total extractable carbon; 
HA+FA: humified organic carbon; NH: not-humification organic carbon (TEC-(HA+FA))

3. PURIFYING THE PIG SLURRY LIQUID FRACTION

Purification plants specially designed for slurry with a high N content such as that of animal wastes did not exist in Italy until just a few years ago. Since 1987, CRPA has been working toward developing an effective process for these animal wastes.

A pilot plant was operated according to a modified "Bardenpho" (JHB) process, performing nitrification, denitrification and enhanced biological phosphorus removal (Figure 7). Tanks were built in stainless steel and were divided into sectors by means of baffles. The hydraulic level in the tanks could be adjusted to different heights. The waste used was anaerobically pre-treated pig slurry. One quarter of the influent flow rate was fed to the slugde denitrification reactor. In this way, more COD was made available for sludge denitrification in order to protect, at the same time, P-release from the negative influence of nitrates. The results are reported in Figure 8a e 8b.

 

Figure 7
Figure 8
 Figure 8b
Figure 7 - Schematic flow-sheets of the pilot plant for the combined nitrogen and phosphorus removal.
Figure 8a - Nutrient removal of the pilot plant operated according to a modified JHB process.
Figure 8b - COD removal of the pilot plant operated according to a modified JHB process.
 
Figure 9
Figure 9 - Flow sheet of the monitored pig slurry purification plant.
Figure 10
Figure 10 - A view of the pig slurry purification plant; on the right side the oxidation-nitrification tank and on the left side the pre-denitrification tank.
As the good performance was replicated, the process appears to be reliable. In spite of the low redox potential in the anaerobic tank, release of phosphorus was not observed, though it may have been masked by biologically induced chemical precipitation.
In fact, P-removal was effective when the plant was operated according to the JHB process, achieving up to 95% removal, with effluent P concentration of 10 to 20 mg l-1 (Cossu et al., 1990).

Following this experience, a farm level plant was built at a large piggery. The aim was not to discharge into the surface water, but to obtain an effluent with a less rigid standard of quality that would be suitable for secondary treatment in municipal treatment plants or for landspreading with low nutrient content.

This farm, which is included in the cooperative manure management system described further on, has a capacity for 610 sows and an average live weight of about 750 tons.
The slurry treatment plant (Figure 9, 10) has been operating since 1991 and comprises a solid/liquid separation section with two centrifuges, one for raw slurry and one for surplus sludge, and an aerobic treatment section with predenitrification, oxidation-nitrification, sedimentation and discharge into the municipal sewer.

The performance of the plant, monitored for about two years (Piccinini et al., 1996), is shown in Table 2.
 
Table 2 - Performance of the monitored farm-scale purification plant for pig slurry.
Influent
Effluent
Removal %
 Parameters
x
s
n
x
s
n
x
s
n
TS (g·kg-1)
20.71
7.20
23
---
---
---
---
---
---
TSS (g·kg-1)
15.73
7.49
23
0.12
0.10
23
99
1
23
COD (mg·l-1)
22,089
8,257
23
467
124
23
98
1
23
TKN (mg·l-1)
1,990
623
23
34
43
23
98
2
23
NH4-N (mg·l-1)
1,420
419
23
15
32
23
99
2
23
NO3-N (mg·l-1)
---
---
---
48
33
23
---
---
---
P (mg·l-1)
656
239
23
31
10
23
95
4
23
BOD5 (mg·l-1)
---
---
---
132
83
23
---
---
---
x = Mean; s = Standard deviation; n = number of sample.
 
More recent experiments have been carried out in Italy on Sequential Batch Reactor technology (SBR) (Bortone et al., 1992). SBRs offer the possibility of treating piggery clarified liquid fraction in an easier and cheaper way than the traditional biological treatment plants. Moreover, the possibility of changing the reaction and settling periods can be useful when problems occur, such as wastewater variability and changes in sludge settling properties. A farm-scale SBR is now operating on one of the farms of the cooperative manure management system described in the following section.

4. A COOPERATIVE SYSTEM OF PIG EFFLUENT MANAGEMENT

In about 25 farms located within a 3,000 ha area with 87,000 places for 80 kg pigs, approximately 808,000 kg N per year are produced in excess of the demand for crop cultivation in this area. Seven of the largest farms agreed to take part in a coordinated programme of slurry management which aims to reduce the N surplus. All the farms carry out raw slurry centrifuging (Figure 11) and compost the solid fraction under a shed by turning the windrows with a front-end loader (Figure 12). A cooperative service has been established for collecting and transporting the resulting compost out of the surplus area to farms with a demand for organic fertilizers. One of the tasks of the cooperative service is to make sure that the centrifuges and the other plants are operating correctly.
 

Figure 11
Figure 12
Figure 11 - A centrifuge for solid/liquid separation of raw pig slurry.
Figure 12 - a view of a farm covered plantform for centrifuging and composting.
   
Figure 13
Figure 13
Figure 13 - Flow sheet of the cooperative system of pig slurry treatment to reduce N surplus.
Figure 14 - A view of the SBR plant.
 

 The characteristics of the cooperative system and the results of the monitoring programme carried out in 1996-1997 are reported in Figure 13 and in Table 3.

In 3 of the 7 farms, the liquid fraction is stored up to 180 days and then spread in the surrounding land area. Considering the losses due to removal of the fresh slurry from the housings, to the storage and landspreading of the liquid fraction, together with the export of the solid fraction, the total N reduction in these farms is about 60%. In 2 other farms, the liquid is purified in an aerobic treatment plant, stored in lagoons, and then utilized in the fields. In these farms, N reduction is about 90%. In the remaining 2 farms, the liquid is purified, then for the largest part discharged in a public sewer for the final treatment in a municipal wastewater treatment plant. One of the purification plants is the one monitored by the authors as described above; the other is an SBR plant (Figure 14). In these farms, an N reduction level of 95% can be achieved. The total N reduction in the cooperative system represents about 78% of the N surplus of the area.

Table 3 shows the investment and management costs. Given the environmental importance of this demonstration project, the government granted a subsidy of 70% of the investment for the centrifuges and the composting facilities, and 50% of the investment for the purification plants.

The manure management costs are very high and, when liquid fraction purification is added to solid/liquid separation and composting, the total cost of pork production rises to levels that exceed the pork market prices. In such cases, only farmers who have their own financial resources and are more efficient, thus keeping average pork production costs low, can sustain the cost of the complete line of treatment, including purification. For the others, this only becomes possible if they receive public subsidies. A market opportunity for selling the compost produced, however, could help farmers sustain the costs.
Table 3 - Characteristics and performance of the cooperative system of pig manure management.
Pig places in the 3,000 ha area (average weight of one pig = 80 kg)
87,000
Nitrogen produced by all pigs of the area (kg·y-1)
1,099,688
Nitrogen surplus with respect to crop demand of the area (kg·y-1)
808,000
N° of pig places in the 7 largest farms involved in the cooperative manure management
61,300
Nitrogen produced in the 7 largest farms (kg·y-1)
769,450
Nitrogen reduced by treatment in the 7 largest farms (kg·y-1)
630,000
Reduction of surplus (%)
78
Investment costs for centrifuges and on-farm composting facilities (US $ per pig place)
36,9
Investment costs for the purification plants (in 4 of the 7 farms) (US $ per pig place)
64,7
Manure management costs, capital interest and depreciation not included:(a) 
  • - for C, Co, T, L (US $ per kg of pork produced);
  • - for C, Co, T, P, L (US $ per kg of pork produced);
  • - for C, Co, T, P, D (US $ per kg of pork produced).
    •
     
    • 0,03
    • 0,08
    • 0,09
    Average costs of pork production without the above costs, interest and depreciation included (1996) (US $·kg-1)
    1,60
    Market price of pork (Oct. 1997) (US $·kg-1)
    1,65
    (a) C = Centrifuging; Co = composting; T = transport of compost produced; L = landspreading of liquid fraction inside the surplus area; P = purifying; D = discharging of the effluent into a municipal sewer.
     

    5. Conclusions

    Composting of the solid fraction from centrifuging is possible on the farm scale where turning of windrows can be accomplished with a front-end loader under a shed. To reduce NH3 loss, bulking agents such as straw or shredding wood trimmings can be added.

    The liquid fractions after solid separation can be treated using on-farm purification systems specifically designed for animal wastes. The resulting liquid fraction is outside the limits for water bodies but can be discharged into the public sewer system or used on agricultural land in high volumes, as the nitrogen and phosphorous content is reduced.

    The creation of centralized treatment plants is not suitable because of the opposition of the residential population and the high environmental impact due to the residual load of treated effluent. Cooperative systems of pig slurry management have greater chances for success. The treatments are carried out on the single farms, while the management of the systems is carried out by the cooperative service.

    The costs of centrifuging, composting, transport of compost out of the area and landspreading of the liquid fraction within the surplus area are sustainable.

    Liquid fraction purification, followed by landspreading or discharging in the public sewer, can lead to a significant reduction in N surplus, but given the present market prices of pork in Italy, the costs are only sustainable by those farmers who have their own financial resources and more efficient operations.

     

     

    6. REFERENCES

    Bortone, G., Gemelli, S., Rambaldi, A. and Tilche, A. (1992) Nitrification, denitrification and biological phosphate removal in sequencing batch reactors treating piggery wastewater. Water Science and Technology, vol. 26, no. 5-6, 977-985.

    Copelli, M., De Angelis, S. and Bonazzi, G. (1985) Aeration of pig slurry to control odours and to reduce nitrogen levels. Proceedings of a seminar held in Silsoe, UK, 15-19 April 1985. Elsevier Applied Science Publishers, 251-257.

    Cossu, R., Bortone, G., Canziani, R., Andreottola, G. and Piccinini, S. (1990) Nutrient removal from anaerobically pre-treated piggery wastewaters. Proceedings Conference IAWPRC, Kyoto, Japan, August.

    Piccinini, S. and Cortellini, L. (1987) Solid-liquid separation of animal slurry. Proceedings of the 4th International CIEC Symposium on Agricultural Waste Management. Braunschweig (Germany) 11-14 May.

    Piccinini, S., Rossi, L., Bonazzi, G. and Dall'Orso, G. (1995) The Emilia-Romagna experiment in animal manure composting. Proceedings of the International Conference "The Science of Composting" Bologna, 30 May - 2 June.

    Piccinini, S., Bonazzi, G. (1996) The current situation of the management and disposal of livestock wastes in Italy. Ingénieries - EAT - Animal Manures in Europe, 73-80.