Management of slurry in Gran Canaria Island with full-scale natural treatment systems for wastewater (NTSW). One year experience in livestock farms.

The aim of this work is to describe the performance of three full-scale natural treatment systems for wastewater, which operated in an integrated manner in livestock pig farms (1000-1500pigsintotal) over one year. Slurry management was performed with these natural treatment systems operating under the normal waste loading conditions of the livestock farms in which were integrated. The systems were comprised of elements such as first generation digesters, subsurface flow constructed wetlands and facultative ponds. The facilities, located on the island of Gran Canaria (Spain), enabled the study of viable alternatives for effluent management characterized by low-cost treatments. The systems were evaluated in terms of chemical oxygen demand removal efficiency, operating with variable organic loading. Values of between 80% and 90% were obtained. A comparison was also made of first-generation cascade flow digester operation (<70% removal efficiency), with complete-mix digesters (<20% removal efficiency), and finally with facultative ponds combined with subsurface flow constructed wetlands (<91% removal efficiency). It was also verified that when natural treatment systems for wastewater combine different elements they have better removal efficiency and better response to load and/or flow changes.