Disinfection of secondary effluents by infiltration-percolation

Abstract

Irrigation reuse is an adequate strategy to dispose of the effluents of conventional wastewater treatment plants everywhere a chronic shortage of water resources is experienced. The most attractive usages of reclaimed water are irrigation of public parks, sports fields, golf courses an edible crops. These uses require disinfection of wastewater so as to comply with relevant regulations. Conventional disinfection procedures are fairly effective; but, in Mediteranean countries, low technology techniques, such as lagooning and infiltration-percolation, are often more reliable. The cost of drained infiltration-percolation facilities is highly dependant on the volume of their filtrating sand bed. Therefore, relationship among hydraulic load, sand depth and disinfection efficiency are of great importance. A circular drained dune sand infiltration percolation filter, 1.5 m sand deep, with a surface of 565 m2, was constructed in Vall-Llobrega, Catalonia, Spain. The filter was fed with activated sludge effluent using a pivot irrigation system equipped with low-pressure bubbles. The plant worked for two years, the hydraulic load ranging from 0.165 to 0.35 m per day of infiltrating surface. Physico-chemical parameters, total and faecal coliforms contents were monitored. A pivot irrigation system can be considered a major technological improvement.