Experimental Research On Saltwater Intrusion Prevention And Its Biological Treatment

Intrusion of salt water is a recurrent problem in coastal areas over the world andin China. This phenomenon is often caused by over extraction of fresh water incoastal aquifers and has important consequences on environment, economy andhuman health. The purpose of this study is to find a new solution to salt waterintrusion by using biological treatment methods.This Biological treatment consists in the injection of bacteria and nutrients insoil in order to delay transport of salt in sand porous media. Biological treatment is aninteresting technique, mostly because of its limited cost, effectiveness and low impacton the environment. Our purpose is to test this treatment in salty environment, to seeif the microorganisms can survive harsh salty conditions and if dispersion of salt canbe delayed.Initial calculations have been made to determine the initial increase of saltconcentration in test columns filled with Tangshan sand. On this basis, experimentalcolumns have been designed and treated with the bacillus Sporosarcina pasteurii. Thebioclogging of the columns has been achieved by injection of urea and calciumchloride into the columns. The creation of calcium carbonate by a carbonationprocess is induced by the bacillus sporosarcina pasteurii, causing a decrease inpermeability in each column. Four test columns have been used during the first batchof experiments and three test columns have been used in the second batch.Falling water head and constant water head methods have been used todetermine permeability in the columns at each step, whereas dispersion coefficient inthe columns has been calculated by regression of the results obtained during saltwatertransport experiments, before and after biological treatment. In2weeks, thepermeability has been reduced by10times in the most clogged column, proving therelative efficiency of such a biological treatment, even in very salty conditions. Theafter treatment saltwater transport experiment proved also that there is a delay of thesalt concentration propagation due to the biological treatment. At the end of the column experiments, some biological, chemical and physicalexperiments have been done to observe the clogged sand material and the results ofthe biological treatment. A chemical analysis of solid and liquid samples showed ahigh content of dissolved salt and calcium in the treated columns. Environmentalscanning electron microscopy (ESEM) was then used to observe the microstructuralchanges in the sand after the treatment. This study showed that bioclogging of sandusing bacillus sporosarcina pasteurii and carbonation process was possible in high saltconditions.This study has an important value for the future development of biologicaltreatment methods in salt environments, which has been shown possible.