An in-depth study of the serious problems caused by the proliferation of various microorganisms in the emulsions affecting the efficiency of the fluids and the working environment
Micro-organisms – or microbes – can be defined as living organisms visible only thanks to a microscope and their world is extremely varied: they are divided into unicellular organisms, which are less evolved and therefore more simple on a structural level, and multicellular. Bacteria and Fungi (intended as micromycetes) hold a main relevance into the world of Metalworking.
Fungi, yeasts and molds
The most highly evolved unicellular and multicellular organisms are defined as eukaryotes and among them there are fungi and yeasts as well. The organisms that fall under the generic definition of fungi are divided into macromycetes, the classic mushrooms of the undergrowth which are visible to naked eye and among which there are also edible species, and micromycetes, which are only visible with the microscope. The latter are commonly referred to as molds and are responsible for contamination in the coolants tanks used in metalworking operations.
Micromycetes are larger and more evolved organisms than bacteria (>2цm) and consist of several cells organised into characteristic structures known as “hyphae”. The hyphae are then organised into a superstructure known as “mycelium”.
The apical growth of the hyphae and their organisation into a branching system as complex as the mycelium allows the organism to spread in a capillary way and targeted towards the sites where the greatest amount of nutrients lies. This uncontrolled growth is therefore often a serious and relevant problem because it constitutes a significant-sized mass.
In addition, molds are capable of producing bacteriostatic or even toxic substances such as mycotoxins, molecules which are also dangerous to human health, and they proliferate easily thanks to various sources of nutrients which are often available from mains water, the most important of which is phosphorous. For this reason, demineralised water should be used for the preparation of emulsions in Metalworking systems.
These micro-organisms are particularly difficult to eliminate for two reasons: firstly, because the hyphae, as well as being organised structures, are also equipped with walls which make them very resistant; secondly, because they have an extraordinary capacity for propagation through spores or with even small parts of the mycelium.
The fungal cell wall
It is just because of this thick cell wall, which is incredibly resistant to normal biocides, that the most damage in industrial systems happen. Specific fungicides must therefore be used to ensure that the contamination is effectively eliminated, in addition to the manual removal of these anomalous masses.
The fungal cell wall is the barrier and interface between the micro-organism and the external environment. It performs numerous functions such as giving rigidity and shape to the cells and hyphal system, protecting the micro-organism from external hazards, and last but not least, acting as a filter by controlling both the exit and entry of molecules into the cell.
Mold genera relevant to Metalworking systems include Aspergillus sp, which is ubiquitous and capable of generating mycotoxins, Acremonium sp, a fungus of the Hypocreaceae family, which is harmful to humans while cephalosporin family of antibiotics are obtained from it, and Trichoderma sp, also of the Hypocreaceae family, which is present in soils and not dangerous to humans.
Yeasts
Among the most highly evolved single-celled organisms there are yeasts, which are larger single-celled organisms than bacteria. Yeasts are unicellular eukaryotes, which, unlike moulds and bacteria, have no wall and prefer neutral or slightly acidic pH environments in which to proliferate; they appear elliptical or spherical under the microscope.
Some yeasts use only aerobic respiration to obtain energy, others, in the absence of oxygen, can also use a different process called fermentation. Fermenting yeasts produce energy by converting sugars into carbon dioxide and ethanol and therefore play a key role in many production processes in the food industry, such as in alcoholic beverages like wine and beer or in baking.
The most important yeast species include Candida albicans, a type of yeast that plays a significant role in fermentation processes in the food industry and it’s also naturally present in the human microbiome, and Saccharomyces cerevisiae, better known as brewer’s yeast, which can be found in a wide variety of surfaces and environments including cooling lubricants.
In conclusion, therefore, the fungi which cause contaminations in Metalworking environment are mainly eukaryotes belonging largely to the category of micromycetes, due to their strong environmental presence in the soil and air and their resistance, and to a lesser extent yeasts, which proliferate mainly through human contamination, given their poor ability to resist in a hostile environment.
