Effluent ponds and storage tanks are a significant part to any effluent management system, after all, they’re storing all those essential nutrients that will later be used for fertilisation of crops and pastures. However, to truly maximise the value of the stored effluent there’s a few things to keep in mind…
Stir well, achieve more
If effluent is left sitting in a pond or tank the solids will inevitably sink to the bottom and crust and debris will form on the top, separating out the essential nutrients. To maximise the value of your effluent it is vital the effluent is thoroughly mixed prior to pumping to ensure a consistent mix of nutrients is being pumped out and spread evenly over pasture. For farmers monitoring the level of nitrogen and other nutrients in the effluent it also ensures more accurate results for testing and analysis.
Additionally, with a well stirred pond you will also achieve these benefits:
No solids accumulation at the bottom of the pond
There are a number of issues with solids accumulating at the bottom of the pond/tank:
- As the solids sit at the bottom of the pond/tank they lose their nutrient value, meaning by the time you dig them out to spread you are getting a lot less value from your resource.
- The accumulation of solids reduces the volume of storage available. In some cases this can become a council compliance issue as most councils will have minimum requirements for effluent storage.
- You will eventually need to drain the pond and get a contractor in, or spend time digging out the solids yourself. This can be costly, inefficient, and is less effective than simply stirring well.
Prolongs the life of your pump & irrigator
Thoroughly mixed effluent reduces strain on your pump, and you’ll be far less likely to experience blockages. So your entire system is more likely to run smoothly.
Reduced odour
Aerating the pond gets the biology of the pond working which will greatly reduce the odour.
Aesthetics
Everybody wants to have an enviable looking farm, and a well stirred pond is a much better look than crust and vegetation!
Tip: It is essential to stir BEFORE pumping so the sediment can be mixed with water. It can be difficult to tell just how much is accumulated at the bottom, and it is too late to mix if you’ve already pumped down to the sludge.
How to get a good mix
To create a stirring action that will get the entire pond swirling, you need to create a strong horizontal flow of water with sufficient velocity to carry the suspended solids. A consistent speed of approximately 0.8 metres per second will stop solid particles from dropping out of suspension, and the only way to do this is by creating a strong horizontal thrust. This is where a shore mounted electric stirrer is recommended as they are able to provide the right combination of angle, power and speed to churn up the entire pond.
In the past, floating vertical stirrers were promoted for having low power requirements, however these are not recommended for the following reasons:
- Having a vertical shaft the solids are merely pushed away from the propeller, and will then slow down and drop out of suspension in the water, so they never end up being effectively mixed. Moving the stirrer around the pond will only shift the solids from one area to another, so nutrients are not getting mixed in and therefore don’t end up leaving the pond.
- While some floating effluent stirrers may have low power requirements, a lot of the time these need to be run constantly to achieve any results.
- In terms of safety it is always better to keep electricity out of water, and not have the need for anyone to venture out onto an effluent pond should the stirrer require maintenance.
Another option which has been suggested in the past is using a pump type stirrer. In theory these stirrers should work, however in reality you would need a massive pump, or even several pumps to even come close to what a shore mounted stirrer can achieve. In fact, independent studies have proven Nevada electric stirrers to be 10x more efficient than a pump type stirrer.