Compacted Brazilian soil hydraulic behaviour during the percolation of petroleum-produced water

Abstract

This paper analyses the results of column tests performed on samples of compacted soils permeated by petroleum-produced water from onshore areas in north-east Brazil. It is shown that in almost all of the tested samples, the soil hydraulic conductivity decreased over time. Bioclogging and biofilm formation, as well as clay dispersion and filtration, are analysed; clay dispersion is indicated as the probable main cause of the observed behaviour. Furthermore, particle dispersion seems to be dependent on the changes in soil porosimetry (lower fraction of macropores), which is caused by higher compaction energy. Breakthrough curves obtained for magnesium (Mg) and calcium (Ca) suggest that bivalent cations were replaced by sodium (Na) cations during the tests. Furthermore, for longer test times, a noticeable amount of solid-particle sediment was observed at the bottom of the fluid collection jars. The authors confirmed that bioclogging did not significantly influence the reduction in soil hydraulic conductivity, as this reduction occurred before the start of any microbial activity.