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Handling of waste in intensive pig production units

In the previous article, the health aspects in intensive pig production units were discussed.  In this article, as well as in the following one, an overview of the handling of waste in intensive pig production units is discussed. When planning and building a pig production unit, a strategy should be devised to handle its waste of by-products in such a way that it could be put to use, or to treat it in such a way that it does not become a nuisance.  At the same time, the national and provincial health regulations have to be obeyed, while useful applications of the waste material should be investigated.
The amount of waste produced by a 100-sow production unit has the same pollution potential as a town with
2 800 inhabitants.  A 100-sow unit which markets say 20 piglets per sow per year, will produce about 1 710 tons of undiluted waste per year.  Add to this the waste of washing water, and the total annual waste production of a 100-sow unit could exceed 6 000 tons.
Positioning of new units
The following considerations are important, regardless of which method is used, to handle manure:

  • The prevailing wind direction in relation to residences
  • The proximity of water sources that can be polluted by the flow-off from the unit
  • The availability of a suitable site for erecting a manure handling system
  • The gradient of the site, which should be flat enough for a building, but steep enough to ensure proper drainage
  • The availability of sufficient water encourages proper cleaning.

Methods for handling waste

  • Handling of solid manure

The handling of solid manure, that is to say manure and bedding, requires a lot of labour.  The following are usually needed: Solid concrete floors with a slope; a large enough concrete floor outside the building where the mixture of manure and bedding can be scattered for long-term storage or composting; front-end loaders to transport, mix and turn the manure; and different types of scrapers pulled by a chain or cable, mounted on a tractor.
The solid manure, which is usually mixed with some bedding, can be stacked in wind-rows.  It should be constructed and positioned to allow water to drain from the wind-row, without collecting effluent water.  Treatment of solid manure, which is being stored for long periods, is essential to avoid stench and flies.  The most common method to aerate the material is to regularly turn the wind-row, or to blow air mechanically through the wind-row by means of a centrifugal fan.

  • Handling of liquid manure

Liquid manure is a combination of all the excreta of the pigs and the water coming from leaking drinking nipples, flushing water for floors and water used for flushing other areas.  The handling of liquid manure is preferred for one or more of the following reasons:  It is less labour intensive than the handling of solid manure; no bedding material is needed; flies do not breed in liquid manure; slatted floors limit direct contact between animals and their manure; wasted manure water from lagoons can be recycled for cleaning purposes and aerated and odourless liquid manure with a low viscosity can be recycled as flushing water.
Liquid manure can be handled by deep storage channels under slatted floors which are seldom emptied; shallow channels under slatted floor which are regularly flushed clean; open channels which are flushed clean regularly; or wide concrete alleys which are regularly flushed clean.

  • Slatted floors

Slatted floors leave the pens dry and relatively clean and require less labour.  Concrete slats are the most common and durable kind, but they also are the heaviest, demanding sturdy support.
To avoid contact between the animal and his manure, the feeding places have to be far away from the manure accumulation areas to prevent contamination of what he feed; drinking places must be put over the slatted area because animals tend to urinate while they drink; and partitions that enable animals in adjoining pens to communicate, have to be placed over the slatted area because pigs defecate and urinate while communicating.
Expanded metal floors are not recommended because they may damage the feet and nipples of the animals and untreated alluminium bars are also not recommended because of possible corrosion damage. Wooden slats are not recommended, as they disintegrate, bend and are chewed by pigs, leading to uneven spacing between the slats.

  • Deep channel storage systems

The deep manure channel (about 1 m deep) underneath slatted floors serves as a storage tank with a storage capacity of between one and three months.  The channel is first filled with water op to a depth of about 70 mm to prevent flies from breeding in the initially semi-solid manure.  The manure slurry should not be allowed to get deeper than 200 mm underneath the slats. Unnecessary leaking from drinking nipples should be avoided.
When large volumes of slurry is moved, for instance when manure is being dumped, toxic and suffocating gases may be released which can even cause the animals to die.  It has become obvious from experience that the deep channel storage system is not recommended for southern Africa.

  • Shallow channel and open channel manure removal systems

These systems are very common in piggeries and is recommended for all buildings and there is no build-up of toxic gases or gases with an unpleasant odour, because the diluted slurry which is created this way, can be flushed to a tank outside the building.  The main disadvantage of flushing open channels and shallow channels is that they require large amounts of water.  The amount of fresh water used can, however, be drastically cut by re-using the slurry, or by using aerated manure with a low flood resistance as flushing medium.
Channel dividers are needed on wide channels to prevent the flushing water from flowing around solid manure.  Experience has shown that when a slope of one to two percent is used together with a smooth channel floor, the channel should not be less than 40 m long.  This will ensure that the flushing water move fast enough to clean effectively.
Flush systems
Flush systems for manure removal are classified as flush tanks with a sluice gate or valve discharge; tipping tanks; siphon tanks, above the ground or at ground level; high volume pumps; and continuous operating systems.
The flushing tank with sluice gate or valve discharge is the most popular system because it is simple and easy to construct.  The advantages of a flush tank are as follows:

  • Building costs are low because the tank can be placed at ground level against one wall joined to the end wall of the building
  • A simple and inexpensive sluice gate may be used
  • The tank may be filled by means of an inexpensive low-powered pump
  • To prevent the tank from accidently overflowing, a floater-control inlet may be installed
  • Because of the large flushing volume, usually about 3 m per flushing, only one flushing per day or one every two days will be necessary.

Disadvantages of a flush tank with a sluice gate discharge are that:

  • Although greasing will help, it is difficult to prevent the sluice gate from leaking when it is in use
  • Steel sluices gates with mechanical linkage are subject to corrosion and
  • Manual labour is required to open the sluice gate for flushing.

Tipping tanks are mainly used for small volume flushings, as at farrowing houses. The advantages of tipping tanks are that the basin can be filled by means of an inexpensive low-power pump or tap and an automatic flushing action.   The disadvantage of tipping tanks are that the size is almost limited to a content volume of 380 to 570 liters; strenuous labour conditions are required for regular maintenance and corrosion of metal construction materials can occur.
It is also impractical for long buildings due to the small volume discharge, and open tank construction does not allow for a controlled release of flushing water.
In the next article the structures and equipment for the handling of manure will be discussed. The manual on Housing for Pigs can be ordered from the Marketing Division of ARC-ILI at tel. 012 842 4000.

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