Intensive, housed pig farming systems, and dairy cow feedpads, standoff areas and calf rearing units are suited to pre-treatment of effluent using a two-stage pond system because they typically produce effluent high in organic matter and, in the case of piggeries, high in nitrogen and phosphorus levels.
Anaerobic or First Pond
Raw effluent or waste enters the anaerobic pond. Bacteria that do not require oxygen break down organic matter, releasing carbon dioxide, ammonia and methane (visible as ‘bubbling’). Solid materials, such as undigested and non-degradable solids, sink to the pond floor forming sludge, which is removed mechanically once or twice a year. A crust of solids also typically forms on the surface.
These processes act to reduce the organic and nutrient levels before partially treated effluent enters the second, aerobic pond.