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In this study, the separation and drying efficiency of the excreta, separated into solid and liquid fraction by a flat conveyor belt under a partial slatted floor in a facility for fattening pigs, was determined. Two transverse slope angles (4
° and 6
°) for the flat belts were used, in a trial with pigs from 20.61 to 117.83 kg of live weight (LW), and the sample size was 7 pigs per pen, 42 pigs per room. The flat belt was more efficient with 6
° than with 4
° slope angle (32.65% vs. 29.91% dry matter content of solid fraction during the whole fattening period, respectively;
*P* < 0.0001). The separation and drying efficiency of the excreta, defined as the ratio of dry matter content of the solid fraction to dry matter content of fresh faeces, were significantly higher for the angle of 6
° than for the 4
° (1.4137 vs. 1.3030, during the whole fattening period;
*P *< 0.0001). With a slope angle of 6
°, this efficiency was not improved in finishing period -83.40 to 117.83 kg LW (two extractions per day) with regard to the growth period -20.61 to 83.40 kg LW (one extraction per day). Meanwhile, with 4
° it did improved. The ventilation system underneath slat seems to play a key role in the obtained results.

Traditionally, the pig wastes are collected in pits under the slatted floor in which are stored. An improvement to this method was the replacement of the pit by canals also under the partial slatted floor. These canals collect and run off the slurry to a pit outside the livestock. The slurry collected by both systems has low dry matter content and produces large volumes of waste. These systems increase the management cost of the waste. Otherwise, the European Union Directive 91/676/CEE limits the permissible dose of nitrogen for agricultural soil to 170 kg/ha. This means that for every 100 fattening pig places, a surface area of 4.5 - 6.0 ha of land is necessary to disperse slurry without risk of contaminating soil and water tables.

Pig slurry over-application carries the risk of environmental pollution [

Several research groups [

Our previous studies [

The aim of this study was to determine the influence of slope angle of the flat belt system proposed by [

The experiment was carried out at 2014 in the Pig Welfare Laboratory (Universidad Politécnica de Madrid) (

In this experiment we only have used two (A, B) of the four rooms of the building. In rooms A and B, the manure separation system with a flat belt under slats was installed.

The two rooms have a mechanical exhaust ventilation system with the fans located under the space occupied by the animals; as such the ventilating air circulates over the flat belt [

The flat belts were 0.60 m wide and could be adjusted crossways from 0˚ - 8˚ (0% - 14.5% slope) and on one side has a gutter to collect the liquid fraction separated (

84 pig barrows were used, (7 pigs per box, 42 per room): available surface per pig was 1.05 m^{2} (40% slatted floor) during the whole fattening period in compliance with European Union space requirements. Live weight at the start of the fattening period was 20.61 ± 2.75 kg, then being fattened up to a final weight of 117.83 ± 11.75 kg and they were fed ad libitum (

The slope angles on the flat belts in rooms A and B were 4˚ and 6˚, respectively, during the whole fattening period. Those angles were chosen according to our previous studies [

Excreta (faeces and urine) fell onto the belts through the slats. The belts in both rooms were emptied once a day from the start of fattening period to a live weight of 83.4 kg―growth period, and twice a day until the end of the fattening period―finishing period (

Solid fraction and liquid fraction were stored in containers and, respectively, measured and emptied weekly and daily. Solid fraction samples were taken weekly during the fattening cycle: once the container was empty and after the belts were in operation, the solid fractions were homogenized and three samples were taken per room. Also, three fresh faeces samples per room were taken from the pens slatted floor every week. Once day per week, also three liquid fraction samples per room were taken from the liquid fraction container.

Chemical composition | Growth period^{a} | Finishing period^{a} | ||
---|---|---|---|---|

Starter | Grower A | Grower B | Finisher | |

Crude protein, % | 17.70 | 17.40 | 16.80 | 15.50 |

Crude fat, % | 3.80 | 4.50 | 5.00 | 4.20 |

Crude fiber, % | 4.70 | 3.90 | 4.00 | 4.40 |

Ash, % | 6.00 | 5.30 | 5.10 | 4.50 |

Lysine, % | 1.07 | 0.99 | 0.90 | 0.76 |

^{a}Growth period: 20.61 - 83.40 kg live weight; finishing period: 83.40 - 117.83 kg live weight.

Room | Belt | Slope | Periods | Slope angle | Extractions day^{−1 } |
---|---|---|---|---|---|

A | Flat | Transverse | Growth^{a}^{ } | 4˚ | 1 |

Finishing^{a}^{ } | 2 | ||||

B | Flat | Transverse | Growth^{a}^{ } | 6˚ | 1 |

Finishing^{a}^{ } | 2 |

^{a}Growth period: 20.61 - 83.40 kg live weight; finishing period: 83.40 - 117.83 kg live weight.

To determine the percentage of dry matter of solid fraction and liquid fraction (total solids), the samples were oven dried at a temperature of 105º C until a constant weight was reached.

Separation and drying efficiency of the excreta (SDEE) was defined as the ratio of dry matter content of the solid fraction to dry matter content of fresh faeces.

To calculate the properties of the air in the rooms and the exhaust air, six sensors HOBO (Hobo Pro v2 U23-001) were used. In each room, one of the sensors was situated center in the room and 1.10 m high; the other two sensors were 0.40 m before the fans. These equipment records temperature (operation range: −40˚C to +70˚C; accuracy: 0.2˚C between 0˚C and 50˚C; resolution: 0.02˚C at 25˚C) and relative humidity (operation range: 0% to 100%; accuracy: 2.5% between 10% and 70%; resolution: 0.03%) every two minutes. With those values, humidity ratio of the air in the rooms and the exhaust air were calculated.

The data of variables: dry matter content of the solid fraction and fresh faeces, total solids content of the liquid fraction, average production of solid and liquid fraction, and separation and drying efficiency of the excreta were subjected to analyses of variance by the ANOVA process of the Statgraphics Centurion. The statistical model included the effect of flat belt slope angle.

The effect of the slope angle on the dry matter content and the average production of the solid fraction are shown in

The data analysis shows that the slope angle had a significant effect on the percentage of dry matter content (% DM) of the solid fraction, whether during all fattening cycle (P < 0.0001) as for each of the two periods considered (growth period: P = 0.0081; finishing period: P < 0.0001). This indicates the different separation efficiency of faeces and urine on the belt. Separation efficiency is always improved with the greater slope angle of 6˚. These results confirm previous observations of [

Slope angle | Periods | |||||
---|---|---|---|---|---|---|

Whole fattening | Growth^{a}^{ } | Finishing^{a}^{ } | ||||

N^{ } | % DM^{ } | N^{ } | % DM^{ } | N^{ } | % DM^{ } | |

4˚ | 39 | 29.91 | 21 | 28.24 | 18 | 31.87^{ } |

6˚ | 39 | 32.65 | 21 | 31.01 | 18 | 34.57 |

SEM | 0.326 | 0.639 | 0.291 | |||

P | <0.0001 | 0.0081 | <0.0001 | |||

Slope angle | N^{ } | APSF^{ } | N^{ } | APSF | N^{ } | APSF^{ } |

4˚ | 15 | 0.022401 | 8 | 0.025210 | 7 | 0.019185 |

6˚ | 15 | 0.021391 | 8 | 0.022995 | 7 | 0.019557 |

SEM | 0.001308 | 0.00212 | 0.000614 | |||

P | 0.5897 | 0.4733 | 0.6759 |

^{a}Growth period: 20.61 - 83.40 kg live weight; finishing period: 83.40 - 117.83 kg live weight. N = number of observations. % DM = dry matter content of the solid fraction (%). APSF = average production of solid fraction (kg∙kg LW^{−1} day^{−1}). LW = live weight. SEM = standard error of mean. P = probability values resulting from the analysis of variance.

The system of [

The dry matter content of the solid fraction was higher in the finishing period than in the growth period with both slope angles studied, and the differences of the DM content between periods was similar for the two slope angles considered (3.63% and 3.56% for 4˚ and 6˚, respectively). The possible cause of this difference is a more favourable surface-volume ratio for water evaporation of droppings on the belt with two extractions per day (finishing period) than with one extraction (growth period), because the clusters of solids on the belt were smaller in the finishing period.

In absolute values, the differences among slope angles for dry matter content of solid fraction were slightly higher in growth period than in the finishing period (2.77 vs. 2.70, respectively); however, the differences in relative values between periods for dry matter content of solid fraction were higher for 4˚ than for 6˚ (112.85% vs. 108.47%, respectively), so it may be more advantageous to carry out two extractions per day in the finishing period for 4˚ slope angle than for 6˚.

The slope angle had no effect on the average production of solid fraction per kg of live weight and day (APSF) neither at the whole period (growth and finishing periods together) nor at each period separately (growth and finishing) (^{−1} day^{−1}; 56.16 kg LW: 39.38 g∙kg LW^{−1} day^{−1}; 88.74 kg LW: 36.09 g∙kg LW^{−1} day^{−1}; 111.12 kg LW: 32.19 g∙kg LW^{−1} day^{−1}.

Always the % DM of the solid fraction produced was clearly greater than the % DM of the fresh faeces collected from the slat. The results of the variance analysis of the dry matter content of the fresh faeces are showing in

The difference between % DM of fresh faeces and % DM of the solid fraction

Room | Periods | |||||
---|---|---|---|---|---|---|

Whole fattening | Growth^{a}^{ } | Finishing^{a}^{ } | ||||

N^{ } | % DM^{ } | N^{ } | % DM^{ } | N^{ } | % DM^{ } | |

A | 39 | 22.76 | 21 | 22.21 | 18 | 23.38 |

B | 39 | 23.11 | 21 | 22.74 | 18 | 23.54 |

SEM | 0.225 | 0.304 | 0.166 | |||

P | 0.2004 | 0.3202 | 0.5187 |

^{a}Growth period: 20.61 - 83.40 kg live weight; finishing period: 83.40 - 117.83 kg live weight. N = number of observations. % DM = dry matter content of the solid fraction (%). SEM = standard error of mean. P = probability values resulting from the analysis of variance.

indicates a considerable drying of the droppings on the belt. For a particular day,

That is, the results of % DM of the solid fraction were due to both the separation efficiency of faeces-urine as the drying efficiency of the droppings on the belts.

Separation and drying efficiency were significantly higher for the angle of 6° than for the 4˚ (

The effect of slope angle on average production of liquid fraction (AVLF) and total solids content (TS) of liquid fraction are presented in

However, TS was greater with 4˚ slope angle than with 6˚ (significant difference only for finishing period -two extractions per day, P = 0.0299). This could be explained because of the different dragging of faeces along the belt by the

Slope angle | Periods | |||||
---|---|---|---|---|---|---|

Whole fattening | Growth^{a}^{ } | Finishing^{a}^{ } | ||||

N^{ } | SDEE | N^{ } | SDEE | N^{ } | SDEE | |

4˚ | 39 | 1.3030 | 21 | 1.2694^{ } | 18 | 1.3421 |

6˚ | 39 | 1.4137 | 21 | 1.4122^{ } | 18 | 1.4155 |

SEM | 0.0123 | 0.0197 | 0.0110 | |||

P | 0.0001 | 0.0106 | <0.0001 |

^{a}Growth period: 20.61 - 83.40 kg live weight; finishing period: 83.40 - 117.83 kg live weight. N = number of observations. SDEE = separation and drying efficiency of the excreta. SEM = standard error of mean. P = probability values resulting from the analysis of variance.

urine, or because of the different rate of water evaporation. The greater calculated production of total residues (solid fraction + liquid fraction) for 6˚ slope angle at finishing period (shown in

Slope angle | Periods | |||||
---|---|---|---|---|---|---|

Whole fattening | Growth^{a}^{ } | Finishing^{a}^{ } | ||||

N^{ } | AVLF^{ } | N^{ } | AVLF | N^{ } | AVLF^{ } | |

4˚ | 15 | 0.018662 | 8 | 0.021057 | 7 | 0.015924 |

6˚ | 15 | 0.023401 | 8 | 0.023392 | 7 | 0.022806 |

SEM | 0.002150^{ } | ^{ } | 0.002386^{ } | ^{ } | 0.003421^{ } | |

P | 0.1094 | 0.4104 | 0.1805 | |||

Slope angle | N^{ } | TS^{ } | N^{ } | TS^{ } | N^{ } | TS^{ } |

4˚ | 39 | 26,075.0 | 21 | 24,477.5 | 18 | 27,938.7^{ } |

6˚ | 39 | 24,105.2 | 21 | 23,929.0^{ } | 18 | 24,310.0 |

SEM | 925.7 | 1,396.6 | 1,131.9 | |||

P | 0.1366 | 0.7826 | 0.0299 |

^{a}Growth period: 20.61 - 83.40 kg live weight; finishing period: 83.40 - 117.83 kg live weight. N = number of observations. AVLF = average production of liquid fraction (L∙kg LW^{−1} day^{−1}). LW = live weight. TS = total solids content of the liquid fraction (mg∙L^{−1}). SEM = standard error of mean. P = probability values resulting from the analysis of variance.

Slope angle | Periods | ||
---|---|---|---|

Whole fattening | Growth^{b}^{ } | Finishing^{b}^{ } | |

4˚ | 0.041287 | 0.046520 | 0.035300 |

6˚ | 0.045026 | 0.046621 | 0.042591 |

^{a}Calculated values from data of the ^{−1}; 6˚ slope angle, 1.010 kg∙L^{−1}. ^{b}Growth period: 20.61 - 83.40 kg live weight; finishing period: 83.40 - 117.83 kg live weight.

with a 4˚ slope angle because of the urine remained more time over the belt than with 6˚.

Finally, note that our AVLF results are quite lower than those reported by other authors that use conveyor belts for faeces-urine separation too, probably because of our ventilation system: [^{−1} day^{−1}, respectively; [^{−1} day^{−1}, respectively; and [^{−1} day^{−1}, respectively.

The flat belts are an appropriate system to separate faeces and urine properly and to dry the remaining faeces with the important help of the exhaust ventilation system underneath slatted floor. A transverse slope angle of 6˚ makes possible to obtain higher values of dry matter content in the solid fraction than a transverse slope angle of 4˚. To increase the % DM of the solid fraction, with a slope angle of 6˚, only one extraction per day is enough along the whole fattening period, but with 4˚, the efficiency of the system is increased in the finishing period with two extractions per day.

This project was financed by TRAGSA; the authors would like to thank this Public Spanish Company.

Alonso, F., Mateos, A., Vázquez, J., Garcimartín, M.A., Sánchez, E. and Ovejero, I. (2018) Flat Belt Separation System under Slat in Fattening Pig Housing: Effect of Belt Slope Angle. Agricultural Sciences, 9, 692-702. https://doi.org/10.4236/as.2018.96048