The growing concern over the long-term persistence of plastic waste has driven research into biological methods of breaking down polymers. This study investigated a process that combines physicochemical pretreatment and biodegradation of low-density polyethylene (LDPE) using bacterial strains isolated from commercial compost. Four bacterial strains were genetically identified and classified as Actinomycetes. Exposure of LDPE to these selected strains resulted in a measurable reduction in polymer sample weight, accompanied by alterations in surface hydrophobicity. Furthermore, the chemical modifications at the films’ surfaces were confirmed by the spectra obtained by Fourier transform infrared spectroscopy (FTIR). The microbial colonisation of plastic surfaces plays a key role in the overall biodegradation process. The formation of a biofilm and the subsequent morphological changes on the LDPE surface were revealed by scanning electron microscopy (SEM). The modification of the polyethylene surface by nitric acid treatment was found to be a promising strategy for enhancing the LDPE degradation. The acid-treated films exhibited the greatest weight loss, the greatest increase in carbonyl index values, and the greatest change in hydrophobicity following microbial exposure. Moreover, it was found that biodegradation under these conditions resulted in the lowest levels of phytotoxic byproducts. The transformation of polyethylene surface properties—from hydrophobic to hydrophilic—combined with the presence of oxidized functional groups made it easier for microorganisms to degrade LDPE.

A novel, cost-effective, partially purified biosurfactant in the form of a rhamnolipid biocomplex (RLBC) was investigated for its emulsifying properties. The RLBC was obtained through the cultivation of Pseudomonas sp. SP-17 on glycerol, followed by acidic precipitation, without the use of organic solvents for isolation or purification. Composed of rhamnolipids (RLs) and the exopolysaccharide alginate, RLBC exhibited emulsifying properties towards rapeseed oil comparable to those of purified RLs at concentrations as low as 0.15% (w/w), sufficient for the effective stabilisation of oil-in-water (o/w) high internal phase emulsions (HIPEs, 80% oil). Dynamic light scattering analysis revealed similar droplet sizes (9.54 ± 0.96 µm for RLBC vs. 8.93 ± 0.58 µm for RLs), while multiple light scattering confirmed high emulsion stability over 120 days. The emulsions displayed shear-thinning behaviour, with yield stresses of approximately 11.5 Pa and 7.7 Pa for systems prepared with RLBC and RLs, respectively, after seven days of pre-storage. Although increasing the RLBC concentration from 0.15% to 1% (w/w) slightly improved the degree of emulsion dispersion, it did not substantially impact the long-term stability observed at the lowest concentration. Biodegradation tests demonstrated that the RLBC preparations are environmentally friendly alternatives to synthetic surfactants, achieving 60% biodegradation within 2.5 days and complete biodegradation within 14 days, which outperformed synthetic emulsifiers. The RLBC offers both environmental and economic advantages over purified RLs, including reduced production costs and the elimination of organic solvents. Our findings highlight the potential of RLBC for stabilising HIPEs in applications requiring sustainable and biodegradable formulations, such as cosmetics, lubricants, and industrial fluids widely manufactured and utilised today.

Background. Important problems of technologies of biosurfactants production are the search for active strain-producers, optimization of their biosynthesis, as well as elaboration of effective methods of biosurfactants isolation from cultural liquid after fermentation. Objective. The influence of extractants to release surfactant lipids from the supernatant of cultural liquid of the strain P. aureofaciens NB-1 and investigation of their ability to use for protection of the steel against corrosion. Methods. Surfactants were isolated by extraction of various solvents and their mixtures, their composition and weight were analyzed. The effectiveness of corrosion inhibition was analyzed by corrosion rate of steel plates. Results. Microorganisms of strain P. aureofaciens NB-1 synthesize extracellular biosurfactants of rhamnolipid and lipopeptid nature. It was shown that at pH 11, biosurfactants yield using ethylacetate and isopropanol (2:1) was 3.71 g/L, exceeding their output at pH 3 to 54 %. The efficacy of using the supernatant of cultural liquid P. aureofaciens NB-1 (dilution 1:10) for corrosion protection of St3 steel in aggressive medium was shown. Conclusions. The methods of optimal isolation of surfactant of P. aureofaciens NB-1by the selection solvents and control of pH indicators were elaborated. As a result the synthesis parameters were significantly increased. It was shown that obtained product is perspective as inhibitor of metal corrosion.