## 2 Materials and Methods  
### Materials Used in the Research  
Eurodiesel (MDO) manufactured by Lotos was used for this study. The tested fuel was characterised using selected parameters, which are summarised in Table 1[44]. Before starting the research, effective microorganisms (EM) were added to each tank in the form of liquid and ceramic tubes, as well as silver in the form of its solution and colloidal silver. Effective microorganisms are specially selected from the smallest organisms on Earth, which consist of various strains of aerobic and anaerobic microorganisms including lactic bacteria, yeast, photosynthetic bacteria, moulds and actinomycetes [45]. EMs are not genetically modified and are completely environmentally friendly. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**No.** & **Parameters** & **Value** & **Unit** \\ \hline
1 & Flash point & 62 & \({}^{\circ}\)C \\
2 & Water content met. [PERSON] & 51 & mg/kg \\
3 & Solids content & 6 & mg/kg \\
4 & Sulphur content & 9.4 & mg/kg \\
5 & Cold filter blocking temperature & \(-\)15 & \({}^{\circ}\)C \\
6 & Density at 15 \({}^{\circ}\)C & 0.8248 & g/cm\({}^{3}\) \\
7 & Kinematic viscosity at 40 \({}^{\circ}\)C & 2.588 & mm\({}^{2}\)/s \\
8 & Cetane number & 55.4 & \(-\) \\
9 & Lubricity (WSD) & 215 & \(\mu\)m \\
10 & Fatty acid ester content & 6.8 & \% [\(v/v\)] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Eurodiesel oil specification [44]. Effective microorganisms in the form of ceramic tubes are a special type of fermented clay inoculated with beneficial microflora. The clay is fired at high temperatures under anaerobic conditions. Ceramic is an inorganic material and does not contain metals. It is shaped and then hardened by firing at high temperatures of 1200-1300 \({}^{\circ}\)C. Ceramic tubes do not react chemically, are non-flammable and harder than steel. The content of effective microorganisms was 3% in each ceramic tube [46; 47]. Effective microorganisms in the form of ceramic tubes in a designated amount (based on previous studies) were mixed with the fuel. As these tubes are in solid form, they do not dissolve and form an emulsion with the fuel. Due to their mass, they sink to the bottom of the tank and there the microorganism release processes begin. The fuel together with the ceramic tubes is stored for approximately 4 weeks. The effective microorganisms are released very slowly into the liquid, in this case the fuel. EM ceramics emit infrared waves, the longest rays in the light spectrum. The ceramic tubes are then removed from the fuel by filtering before the fuel is fed into the engine. EM technology has enormous potential. It offers an opportunity to use these properties to solve global problems that are troubling current generations. Diesel additives in the form of effective microorganisms are widely available and used, among other things, in the following [47]:  
* Agriculture for soil fertilization, animal husbandry and in the processing of organic waste;
* Environmental protection, including water treatment processes and treatment of domestic, municipal and industrial wastewater, as well as for treatment of contaminated water reservoirs;
* Other industries. Since their use in the above-mentioned area has the expected results, it is therefore necessary to study the effect of using effective microorganisms on petroleum products, which, when stored in tanks, undergo microbial decomposition to form sludge, among other things, and also contribute to tank corrosion. Solving this problem is very important because microbial contamination of diesel fuel occurs even in properly operated and maintained tanks where oils are stored. The tanks experience uncontrolled microflora growth and changes in the properties of the fuel to such an extent that they are often unsuitable for use in the engine and cause excessive wear on its components.