One-phase MICP and two-phase MISP composite cementation

Abstract

Microbial-induced carbonate precipitation (MICP) cementation of sand results in the generation of waste liquid containing ammonium ions, posing environmental pollution concerns that necessitate appropriate treatment prior to discharge. To address this issue, the addition of hydrogen phosphate (HPO42−) and magnesium (Mg2+) ions to the biocementation waste solution (BWS) enables the efficient conversion of ammonium (NH4+) ions into environmentally friendly bio-struvite (Cell-MgNH4PO4(H2O)6, MgNH4PO4·6H2O or NH4MgPO4·6H2O) through microbial-induced struvite precipitation (MISP), thereby mitigating environmental pollution risks. X-ray diffraction (XRD) patterns confirm the presence of struvite minerals, while field emission scanning electron microscopy (FESEM) images reveal the blocky or irregular blocky structure of bio-struvite, with sizes ranging from 10 to 25 μm. The bio-struvite effectively fills the pores between sand particles, resulting in reduced permeability. Following 4 cementation levels, the permeability coefficient of the bio-struvite cemented sand column measures 5.04 × 10−3 cm/s, with a bio-struvite content of 5.12 % within the sand column. The principal chemical components of the cementitious materials in MICP and MISP composite cementation sand consist of struvite (MgNH4PO4(H2O)6, MgNH4PO4·6H2O or NH4MgPO4·6H2O) and calcium carbonate (CaCO3), forming spherical or massive aggregates smaller than 10 μm. The most effective composite cementation sands exhibit an average permeability coefficient of 4.85 × 10−4 cm/s and an unconfined compressive strength (UCS) of 197.96 kPa. Consequently, MICP and MISP composite cementation sand significantly diminishes permeability and offers a viable solution for desert dust control.