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Dealing With Solids In Dairy Shed Effluent

Weeping Wall

Solids in effluent (manure) from dairy sheds create many management challenges for farmers.

By Department of Primary Industries - 2nd December 2005 - Back to News

Solids in effluent (manure) from dairy sheds create many management challenges for farmers. Dairy effluent consists of both a watery component as well as a solid component (fibrous material and gravel). Some of the management challenges for the solid portion include the sludging up of ponds, blocking of pipes, blocking of irrigation nozzles and a need for an ‘effluent pump’ to handle the fibre rather than a ‘water pump’.

There are two ways in which solids in dairy effluent can be managed. Firstly, it can be managed by separating the solids from the liquid component, such as a two-pond system, or by managing the solids and liquid as one by keeping the solids in suspension as in a single pond system.

Separation of the solid component from the liquid component can be undertaken using a weeping wall, static screen, anaerobic pond or an extruder pump.

A weeping wall is used in conjunction with a trafficable solids trap. It uses slats of wood with gaps to allow the liquid to weep through while preventing the fibrous material from entering the sump. The weeping wall has had mixed success, as a small gap filters more of the solids, however smaller gaps are easier to block which prevents anything from passing through. Consequently a weeping wall needs to be continually managed by cleaning the wall with a broom, shovel or spraying the wall with water after every milking.

A static screen uses a wire mesh face to separate solids and liquid. The effluent is collected in a sump and is then pumped up and over the screen where it acts as a sieve and separates the solid fibrous material from the liquid. The solids are collected on an impervious pad and the liquid is piped to a storage pond. The screens can potentially become blocked with dry effluent and should therefore be hosed at the end of each milking to keep it free from fibrous material. Regular maintenance of the pump and stirrer is also recommended as breakdowns can cause a risk to waterways by overflowing.

An anaerobic pond is often used in a 2 or 3 pond system to separate the solids from the liquid. An anaerobic pond operates without oxygen, which is created by a deep pond so microbes can break down the organic matter into gases. All ponds must be constructed to prevent leaching of their content by using low permeable soils. The ponds will periodically need desludging. This may be required every 2 to 5 years depending upon sediment build-up.

The emptying method for anaerobic ponds will vary from farm to farm, depending upon pond management. Prior to any pumping the sludge will need to be stirred into a suspension. If the system is going to be managed via a pump and irrigation system, then an effluent pump (pump that can handle solids) will be required. A slurry tanker or excavator can be used to transport or relocate the solids from the pond and spread them to pasture.

An extruder pump is a piece of equipment that can also be used to separate solid from liquids. This pump needs to be elevated and so the effluent will need to be collected in a sump, then stirred and pumped by a submersible pump up to the extruder pump. The solid portion needs to be collected on an impervious pad and the liquid portion is piped to a storage pond. This system needs to ensure the sump has the capacity to hold enough effluent as a contingency for pump failure.

The second way effluent can be managed it to treat both the solid and liquid component together. A single pond system stores effluent for a predetermined period before is applied onto pasture or crops. Effluent is conveyed from the dairy, preferably by gravity, to the storage pond. The size of the pond is related to water usage in the dairy, rainfall and the storage period. The pond needs to be emptied over the drier season, without the risk of run-off, so the pond is empty for the storage period.

Management of a single pond can be quite challenging, as equipment needs to be able to manage the solid components. Application for a single pond system needs to ensure that pumps, fixed sprinklers and travelling irrigators are able to handle raw effluent. Slurry and vacuum tankers and muck spreaders are another application alternative. Advantages of a single pond system include less space required and they generally have a lower capital cost. The negative aspects of single ponds include fewer pump options, reduced ability to recycle water from the single pond and solids are hard to manage in large rectangular ponds.

For further information please contact the Gippsland DPI Nutrient Extension Team at Ellinbank on (03) 5624 2222 or at Maffra on (03) 5147 0800.

Source: http://gippsland.com/

Published by: news@gippsland.com

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