Effluent pond treatment systems

What

Farm effluent is commonly treated using a two-pond system combining both an anaerobic and facultative pond. The combination of an anaerobic and aerobic pond efficiently removes sediment and biological oxygen demand (BOD). Pond systems, however, are not primarily designed to remove nutrients, such as nitrogen and phosphorus, or microbes resulting in high concentrations in the effluent.

Treatment of farm effluent beyond the current two-pond system and land application has potential to significantly reduce nitrogen, phosphorus, and microbial risk to waterways. New treatment options include the use of a coagulant to flocculate and settle the colloidal particles in the farm effluent and produce clarified water for recycling.

Why

The two-pond treated effluent represents a significant improvement when compared to the nutrient concentrations of raw farm effluent, however, the concentrations of nitrogen and phosphorus in discharges from a two-pond treatment system are still more than three orders of magnitude greater than levels considered likely to promote aquatic weed growth.

Land application of farm effluent became the preferred treatment option for many Regional Councils in the 1990s, allowing the water and nutrients applied to land in FDE to be utilised by the soil-plant system.

Lincoln University researchers from the Centre for Soil and Environmental Research developed 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. This treatment has a lower potential risk of environmental impacts when applied to land than untreated farm effluent and traditional pond systems. Land application of the clarified water or the treated farm effluent had no adverse impact on plant growth. Read more about their research here.

A limitation of further effluent treatment is the farm does not receive the benefit of the nutrient value of the effluent. Treatment is most suited to areas where there is no natural ability of the land to remove nitrate beyond the root zone, such as the Oxidising Soil and Aquifer Physiographic Environment where groundwater nitrate concentrations are elevated, or where differed irrigation is limited by a high water table.

DairyNZ has ’A Farmers Guide to Managing Farm Dairy Effluent’ document and many resources and tools for effluent management available at the following link.

References