The effect of treating farm dairy effluent with varying rates of poly-ferric sulphate on reducing phosphorus leaching through simulated pipe-drain systems

The application of farm dairy effluent (FDE) to land is a significant source of phosphorus entering waterways. Studies have shown that treating FDE with 250 mg Fe/L poly-ferric sulphate (PFS) reduced phosphorus (P) leaching, however it remains unknown if this can be achieved at lower rates of PFS. This study investigated the efficacy of three PFS rates (250, 167, and 83 mg Fe/L) to treat effluent and reduce P leaching compared to untreated FDE, relative to background leaching levels (given as the ‘leaching loss factor’). The application of PFS 250 and PFS 167 proved equally effective, reducing the dissolved reactive phosphorus (DRP) leaching loss factor by 111.1% and 107.8%, respectively. The total dissolved phosphorus (TDP) leaching loss factor reductions from the PFS 250 and PFS 167 were 115.5% and 112.9%, respectively, and the total phosphorus (TP) leaching loss factor reductions were 85.0% and 90.7%, respectively. Reductions greater than 100% indicate that treatments reduced leaching losses to levels below those of the control. The PFS 83 reduced the DRP and TDP leaching loss factors by 80.6% and 80.2%, respectively. This suggests that P leaching can be significantly reduced using a lower rate of PFS than previously reported.