Biological Treatment of Groundwater in Basins with Floating Filters–I. Test Arrangements and General Results

The research project deals with biological treatment of groundwater, in particular, the removal of iron and manganese in basins equipped with, primarily, floating coarse-grained filters that constitute the pre-treatment unit. This unit, which complements the sand filter, is actually the principal treatment unit. In the “pre-treatment unit” water flows recurrently through the floating filter and through the boundary surface between air and water. This promotes chemical oxidation, creates favourable conditions for biological activity and accelerates the sedimentation of the precipitate on the bottom of the basins. In the pre-treatment unit the precipitation process for iron in the different test plants (7 plants) started effectively within 1 to 5 months, the reduction being 82-95%. For manganese the reduction was from 0 to 83 %. After the sand filtration unit iron was almost totally removed and at three test plants also the manganese reduction was at least 80%. At some of the plants the said time was not sufficient to get the precipitation process for manganese going. The groundwater treatment result is influenced, in addition to technical arrangements, in a decisive way by the physico-chemical and microbiological quality of the raw water.