# Microbially Induced Desaturation and Carbonate Precipitation through Denitrification: A Review
## 6 Suggestions for Future Work  
The findings evaluated in this paper demonstrate that microbial induced desaturation and/or precipitation through denitrification possesses a great potential to solve a wide range of environmental, geotechnical, architectural and structural problems under anoxic conditions in a sustainable, environmentally friendly, and cost-effective manner. Promising MICP-driven applications include microbial self-healing concrete with a corrosion inhibition property, bioremediation of artwork and monuments, treatment of high strength industrial wastewater and soil reinforcement. Most importantly, liquefaction mitigation is a novel and unique MIDP-driven application specific to denitrification pathway. Along with other microbiological processes, such as urea hydrolysis, aerobic respiration and sulfate reduction, denitrification-based MICP has initiated a revolution in various civil engineering applications. However, there are still many challenges that are needed to be addressed before this biotechnology can be commercialized. Further exploratory studies should be conducted to enhance the efficacy of the in-situ biogas and biomineral production at the microbial level and at the field scale (Table 5). Ureolytic bacteria (_Sporosarcina pastevii_) is recognized as the most suitable microbe for MICP via ureolysis, but no specific denittifying bacteria is widely accepted to be the most useful for denitrification-based MICP. Therefore, initial efforts should be made to isolate and select a model organism or develop a microbiome with superior carbonate precipitation yield (i.e., denitrification abilities). Furthermore, more tightly controlled experiments focusing on the key factors would be useful for understanding, optimizing, and successfully developing denitrification technologies. One key factor is the substrate concentration, namely, of the electron acceptor (nitrate) and the organic carbon donor (e.g., formate, acetate, methanol, and ethanol), which affect the conversion rate of the denitrification reactions and the production of the intermediates. Other key factors include, but are not limited to, temperature, pH, pressure, grain size distribution, and salinity. Considering the complexity of natural soils and groundwater, a novel method, which may be helpful in future research, is a combination of metabolic pathways in a way that one process dominates the conditions in which nitrate and carbon source are present under anoxic conditions, and the latter process dominates when the environment is oxic. In addition, special efforts should be made to evaluate the long-term efficacy of denitrification-based MICP and MIDP in different applications. Currently, many studies are working on adding some environmentally friendly additives like nanoparticles and mainly iron nanoparticles for the removal of wastewater contamination [92; 93; 94]. The results are proving that these nanoparticles have a positive effect on the anaerobic digestion process and the bacterial growth [92], which in turn could have a positive effect on the denitrification process, thereby, efforts could be made to test the efficiency of MICP as well as MIDP by adding iron nanoparticles to the reaction systems. Finally, although a biogeochemical model (no-flow condition), has been developed to simulate the process of MIDP via denitrification by [PERSON] et al. [95], which is an upgraded version of the model created by [PERSON] et al. [20], mathematical models should be further studied to account for continuous flow. The successful development and implementation of the denitrification-based MICP and MIDP processes described in this paper could also be used for other applications. Owing to their abundance in subsurface soils and groundwater, denittifying bacteria and denitrification based MICP can be exploited for co-precipitation of minerals and metals enabling in-situ remediation of metal contaminants and radionuclides in anoxic conditions.