In situ microbially induced Ca-alginate polymeric sealant in calcareous sand and potential engineering applications

This study presents a novel method for seepage control in calcareous sand using microbially induced Ca-Alginate polymeric sealant, which was achieved by the reaction between supplied alginate and microbially induced Ca²⁺ ions directly derived from calcareous sand. This approach includes two steps: (i) microbially induced soluble Ca²⁺ generated inside the pores of calcareous sand through a bio-acidification process using activated sludge and (ii) reacting with supplied alginate to form Ca-alginate polymeric sealant via the in situ gelation. With the effect of Ca-alginate polymeric sealant, the seepage rate of the calcareous sand was intensely decreased to the level of 10^–9 m/s from an initial 10^–4 m/s when 5 g/L of alginate was applied. In this way, a low seepage rate of calcareous sand was achieved which was able to remove heavy metal ions and suspended solids from the wastewater sludge. A model test was also carried out to assess the erosion resistance of Ca-alginate treated calcareous sand dam subjected to wave attack. Built on the current research, the proposed polymeric sealant is a promising method for the reduction of seepage, formation barriers for coastal construction on the island, and remediation of specific contaminants.