With the site application in mind, we isolated microorganisms from the railway embankment site, where the field demonstation of the technique would take place. We screened these microorganisms in terms of their ability to produce a specific enzyme, carbonic anhydrase, which helps catalysing chemical reactions involving CO2. For the proposed techniques, the enzymes produced by the micoorganisms can be harvested and used on their own (free enzymes) or the microorganisms will be producing the enzyme while in the soil, at the site that requires ground improvement. Either method has advantages and limitations, therefore we researched both options. Regarding the first option, for the first time, we bound the enzyme on some synthesised carriers in the form of nano-flowers, so that the enzyme does not degrade while in the environment, and also as a method of recovering and reusing the enzyme, hence reducing the costs of the technique. For the latter method, using the microorganisms to produce the enzyme on site, while in the soil, we used 2 different ways of doing this, with the native bacteria in the soil: a) we inceased the population of the microorganisms favourable for the process and introduced them back into the soil (bioaugmentation) and b) we stimulated instead the microorganisms already in the soil to produce the carbonic anhydrase enzyme (biostimulation); we performed modelling of the biocementation process using experimental data, as modelling validated by experimental data can help generalise future predictions without the need to repeat many lengthy tests. To grow the microorganisms for the bioaugmentation process we used successfully food waste from our university canteen, thus considerably reducing the costs of the process, with the industrial upscaling in mind. Considering the field application, we had to think of a practical way to implement the treatments into soils under existing infrastructure, where it is critical not to disturb the structural health of the infrastructure works. Treatments in this context refer to nutrients for the microorganisms (including the microorganisms, when bioaugmenting) and the required salt solutions that help us producing the cements naturally. As a large part of the materials we dealth with were of very low permeability, we decided to send the treatments to the soil using low DC voltage (electrokinetic treatment); this way the treatments can be conveyed under the existing structure many times faster than without the application of the electric current, and without building up high fluid pressures inside the soil. We performed site visits, consulted Ground Investigation reports and existing literature with some own modelling, to understand the causes of movement of the railway earthworks that needed to be treated with our proposed techniques (biocements combined with the electrokinetic method). We proposed a site treatment set up for the pilot field testing, and assessed the environmental impact and sustainability of the proposed techniques, towards further optimisation of the processes in the future.
