New research conducted by Lincoln University on a farm dairy effluent (FDE) treatment system in Canterbury has shown the system could have significant environmental benefits for river, lake and groundwater quality.

Professor Keith Cameron and Professor Hong Di, of Lincoln University's Centre for Soil and Environmental Research, say field lysimeter trials have shown significant reductions in leaching losses of total phosphorus (TP), dissolved reactive phosphate (DRP) and E. coli from treated FDE applied to pasture soil when compared with losses from untreated FDE.

The system produces both clarified water and treated effluent. The clarified water can be recycled back to wash the dairy yard, or, like the treated effluent, can be irrigated out on to the land.

Cameron said the Ravensdown ClearTech technology had been shown to produce treated effluent with significantly lower concentrations of dissolved reactive phosphate and E. coli.

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"The reductions in DRP and E. coli indicated that land application of the treated FDE would be less likely to cause adverse environmental impacts on water quality than the current practice of land application of untreated FDE; and this has now been confirmed by the lysimeter study."

Ravensdown said in a statement that similar to drinking water treatment methods used all over the world, ClearTech used a coagulant to bind effluent particles together in order to settle them out from the water. This clarifying process resulted in the formation of slow-release phosphate compounds, reducing the risk of P transfer to water via runoff or drainage.

As a third part of the research programme, a pasture field trial was conducted to test whether treated and untreated effluents applied to pasture affected plant production or plant chemical composition.

Di said: "We found there was no significant difference between pasture dry matter yield following land application of treated effluent compared to the untreated FDE, which indicates that these environmental benefits can be achieved without sacrificing current pasture production potential.

"We also found no significant difference in plant P concentration or P uptake by pasture plants grown on the treated effluent plots compared to the untreated FDE plots. This indicates that using ClearTech to treat FDE did not cause a reduction in the amount of P available to plants, despite reducing the DRP concentration in the treated effluent."

There was a 99 per cent reduction in the average DRP concentration of the treated effluent compared to the concentration in the untreated FDE.

The lysimeter study also showed the significantly lower risk of bacteria such as E. coli leaching through the soil profile. This is because the treatment process significantly reduces the number of E. coli microorganisms present in the treated FDE compared to the untreated FDE.

The E. coli concentrations measured in the clarified water were also significantly reduced (by around 99.9 per cent) and the average concentration of E. coli in the clarified water was 83 per cent lower than the critical value that is often used to designate water as being suitable for recreational purposes in New Zealand.

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Three peer-reviewed research papers have recently been published in an international journal and the first one is titled 'A new method to treat farm dairy effluent to produce clarified water for recycling and to reduce environmental risks from the land application of effluent' (Cameron and Di: Journal of Soils and Sediments, January 3, 2019).

The research programme was funded by Ravensdown and Lincoln University.