Microbially induced carbonate precipitation (MICP) using ureolytic bacteria shows promise in the field of geotechnical engineering for several different applications, such as ground improvement and groundwater control. This study examined optimal use and efficient control of Sporosarcina pasteurii to induce the precipitation of ${\mathrm{CaCO}}_3$ in open environments. Laboratory tests were conducted to investigate the effect of changing treatment factors, such as chemical concentrations, retention times, and effective input rates ($\mathrm{mol}/\mathrm{L}/\mathrm{h}$ ) on chemical efficiency. Chemical efficiency was measured based on weight measurements of ${\mathrm{CaCO}}_3$ precipitation compared with the amount of chemical reactants injected to samples. Based on the experimental results, the optimal time required for the precipitation process to take place in porous media for a specific range of bacterial optical density was determined. Results show that, below a certain urea and ${\mathrm{CaCl}}_2$ input rate ($0.042\mathrm{mol}/\mathrm{L}/\mathrm{h}$ ) and for a bacterial optical density (${\mathrm{OD}}_{600}$ ) between 0.8 and 1.2, the reaction efficiency remained high and the amount of precipitation was not affected by the liquid medium concentration (for input concentrations up to 1 M). However, the precipitation pattern at the pore scale was found to be affected by the injected concentration. Scanning electron microscopy images taken of different samples at different levels of cementation showed that, for the same amount of precipitation, the use of lower chemical concentrations in injections resulted in better distribution of calcite precipitation, especially at lower cementation levels. This variation in precipitation pattern is expected to affect the use of MICP for different applications.

Coupled human and natural systems (CHANS) represent dialectic interaction between human and nature subsystems. This dynamic interaction involves a prominent level of complexity stemming from the uncertain interrelation between the systems and the incorporated subsystems. The complexity within CHANS includes reciprocal effects, nonlinearity, uncertainties, and heterogeneity. Although many researchers have highlighted the significance of understanding the nature of the coupling effect, most of the prevailing literature emphasises either human or natural systems separately, while considering the other as exogenous, despite evaluating the reciprocal and complex interrelations. The current review utilises the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA). It focuses on synthesising the prevailing literature on the CHANS framework in several disciplines, focusing on the approach, findings, limitations, and implications. The review comprises 56 relevant articles, found through Endnote and Covidence database searches. The findings identify the dominant complexity character as reciprocal effects and feedback loops, confirming the complex interactions between human and natural systems. Furthermore, the review provides evidence surrounding the significance of developing an analytical framework that can better explain the complex connections between humans and nature, as it provides a comprehensive understanding of CHANS and their potential impacts.

Recent sampling projects in greater Cairo, Egypt have indicated the presence of trihalomethanes and other chlorine disinfection by-products (DBPs) in the public water supply at levels that are periodically in excess of regulatory limits. Therefore, hydrophobic-hydrophilic fractionation of natural organic matter (NOM) was performed for raw Nile River water samples in order to identify the organic fractions that most readily react with chlorine to produce DBPs. Averages of five events over a 13-month period revealed that the hydrophilic neutral fraction made the highest contribution (35%) to the dissolved organic carbon (DOC), followed by hydrophobic (29%), transphilic (23%), and hydrophilic charged (13%) fractions. Relative contribution of NOM fractions to DBP formation was measured according to the trihalomethane formation potential (THMFP) test. Although the transphilic fraction was only the third highest contributor to DOC, on average it constituted the major contribution to THMFP (38%) followed by the hydrophobic fraction (31%). This finding was corroborated by the results of two events in which samples were collected in both Cairo and Luxor (750 km upstream). The transphilic fraction also yielded the best correlation between percent contributions to THMFP versus DOC.