Piggery effluent polluting stream
Waikato Regional Council has sought an interim Enforcement Order from the Environment Court to stop piggery effluent from entering a waterway north of Te Aroha.
Effluent has become a big topic over the last few years, with major pressure being put on farmers by their regional authorities to clean up their act.
While there has been major investment in effluent ponds and storage tanks, what are the mechanics of getting ‘harvested’ effluent out onto paddocks to unlock its full potential?
There is a common misconception that to pump effluent over any reasonable distance from a storage area you will need a pump with high flow rates and high pressure.
Anyone who has sweetened the missus up by creating a water feature in the garden will know that the flow over the waterfall needs lots of water to create the desired effect – it’s advisable to use larger diameter hose.
The physics of the matter is quite simply friction. When pumping with a 150mm delivery hose, the pressure drop resulting from frictional losses will be only about 25% of that in a system using a 100mm hose.
Looking at a typical 100mm set-up with a flow rate of 150m3/hr pumped over 1000m, the likely pressure drop is about 12.6 bar, and the effluent will travel at 4.5m/sec.
Upsizing to 150mm hose with a corresponding set-up will see a system pressure drop of only 4.8 bar, and the effluent travels in the pipe at a speed of 3.04m/sec.
So it stands to reason that if you can reduce your overall system requirements for very high pressures by fitting bigger diameter hoses, there is huge potential saving fuel for the pumping tractor and a corresponding reduction in wear and tear on the pump and the pipeline, while delivering the required volumes of effluent during the working day.
We can look at the mechanics in more detail by comparing four typical set-ups, all trying to deliver 170m3/hr:
System 1
600m of 150mm supply hose; pressure loss 1.52 bar
400m of 125mm drag hose; pressure loss 2.41 bar
Total pressure required 3.93 bar
System 2
600m of 150mm supply hose; pressure loss 1.52 bar
400m of 100mm drag hose; pressure loss 6.34 bar
Total pressure required 7.86 bar
System 3
600m of 125mm supply hose; pressure loss 3.62 bar
400m of 100mm drag hose; pressure loss 6.34 bar
Total pressure required 9.96 bar
System 4
1000m of 100mm supply hose; pressure loss 15.86 bar
Total pressure required 15.86 bar
Note that in examples 1 and 2 the output requirement of 170m3/hr was achieved with a tractor running at 1450 engine rpm, and the pressure requirement in example 4 is not achievable even with the best products in the marketplace.
So while it’s sensible to do some homework and find the best pump and spreader system for your particular operation, don’t overlook the need for a pipe that can deliver the volumes with low pressure drops.
A 150mm pipe might show a reduced effluent speed in the pipe, but that pipe has a 50% greater carrying capacity and is the easy way to get high daily delivery rates and reduced fuel/power costs.
Third-year student Cady Burns has won the Waikato Regional Council Prize in Water Science for 2024.
The Rural Change programme, providing free private mental health professional sessions to the rural industry, is set to continue its next chapter within Rural Support Trust from 1 July 2024.
Beef + Lamb New Zealand chief executive Sam McIvor will step down in July.
A new report shows farm employers across the dairy, sheep and beef, and arable sectors have continued to invest strongly in one of their greatest assets – their staff.
The country’s 4200 commercial fruit and vegetable growers will vote from May 14 on a new HortNZ levy.
OPINION: Talking about plant-based food: “Chicken-free chicken” start-up Sunfed has had its valuation slashed to zero by major investor Blackbird…
OPINION: Synlait's financial woes won’t be going away anytime soon.