*Biological Activity*

This research aims to investigate how molasses and fibers influence the unconfined compressive strength of soils. However, substantial biological activity was evidenced. SEM images showed the development of different microorganism in mixture M12 and after 7 days, microorganism grew on the external layer of the samples. To the naked eye, biological activity was not detected for the mixture with the optimum molasses content (M2). Intensity of the biological activity increases as molasses content increases, which can be used to improve the properties of soils, an area that falls in the bio-mediated soil improvement. This branch of geotechnical engineering has evolved to many methods, which includes bioclogging and biocementation. Bio-mediated methods for soil improving involves the generation of chemical reactions on soil mass that generate byproducts which change the engineering properties of the soil [52].

The use of microorganism to generate the reactions is an attractive and feasible alternative due to the number of microorganisms present in the soil and its resistance to extreme conditions. There are approximately 10 <sup>9</sup> to 10 <sup>12</sup>/Kg of organisms of a soil mass near the ground surface [53]. For soil bioclogging or biocementation, the most recommended microorganisms are anaerobic and microaerophilic bacteria [54]. Biological activity is limited by nutrients availability, water availability, and other environmental conditions; carbon and mineral components as energy sources and pores larger than 0.4 µm as environmental conditions are necessary to facilitate microorganism growth [55].

Biological activity was encouraged by conditions under which this research was performed. The molasses used had a composition of 41.2% carbon and 10.01% minerals like Mg, S, K, Ca. Due to its chemical composition, molasses is a considerable source of energy for microorganisms. On the other hand, water and 10-µm pores in the soil stimulated growth of microorganism that are naturally found in the soil.
