Removal of ammonium by‐products produced during biocementation soil improvement using rinse injection strategies

Abstract

AbstractBio‐mediated soil improvement technologies leverage microbial enzymatic and metabolic processes to generate minerals, gases and biopolymers that can improve soil engineering behaviours with the potential to reduce detrimental environmental impacts when compared with conventional methods. Ureolytic biocementation is perhaps the most widely researched of these processes and relies on urea hydrolysis in the presence of calcium to initiate the precipitation of calcium carbonate minerals on soil particle surfaces and contacts, thereby improving soil behaviours. Although effective, urea hydrolysis generates aqueous ammonium by‐products that may result in undesirable environmental and human health impacts, if left unaddressed. Recent studies have shown the potential of rinse solution injections to effectively remove generated ammonium following biocementation through both advective flow and the removal of sorbed ammonium from soil surfaces; however, critical gaps remain in our understanding of the effect of rinse solution composition and injection strategies on ammonium removal efficacy. In this study, 16 soil column experiments were performed to investigate the effect of rinse solution cation types, cation concentrations, applied injection sequences and biocementation treatment variations on the removal of ammonium from a biocemented poorly graded sand. All columns receiving cation‐enriched rinse solutions achieved greater than 98% aqueous, 65% sorbed and 95% total ammonium removal after injecting 12 pore volumes, with no detectable impacts on cementation integrity. Cation‐enriched solutions specifically enhanced sorbed ammonium removal and achieved sorbed ammonium concentrations up to 2 orders of magnitude less than those observed in columns rinsed with deionized water alone. Columns receiving K+‐based rinse solutions and 12 daily 1‐PV rinse injections also achieved greater total ammonium removal when compared with comparable columns receiving rinse solutions containing other cations and continuous 12‐PV rinse injections.