Wastewater treatment by infiltration percolation: a case study

A 1700 p.e. pilot infiltration percolation plant treating the sewage of Mazagon, a seaside resort in the South of Spain, is investigated. Primary effluents, intermittently applied over twin 200 m(2) infiltration basins, percolate down to the aquifer through unsaturated dune sands. Each application sequence delivers a volume of 0.25 m(3) per m(2) of infiltration basin. Analyses of the water sampled at five depths ranging from 0.3 to 2.0 m below me infiltration surface show that the oxidation performance of the plant is highly dependent on the applied load. Monitoring the oxygen content in the air phase of the vadose tone allows to determine the kinetics of the oxygen stock recovery and the oxidation capacity of the plant. Disappointing removal of faecal coliforms and streptococci is attributed to high pore water velocities due to infiltration heterogeneity and the high water height applied during each feeding sequence.