Bio-degreasing

Degreasing means lifting a nonpolar film off a surface into water, which wets it badly. Two mechanisms exist. A surfactant lowers the interfacial tension until the film rolls up into droplets; an enzyme cuts the film into pieces that no longer behave as a film. The distinction that governs everything else is chemical: animal and vegetable fats are triglycerides, an ester bond every third carbon atom, while mineral oils and petroleum greases are hydrocarbons with nothing to cut. An enzyme dismantles the first and is blind to the second.

Cutting the ester

Lipase works at the oil–water interface (the same physics as in biocatalysis on hydrophobic feedstocks — see ../biocatalysis-petrochemistry/): it hydrolyses each triglyceride into glycerol and three fatty acids. Glycerol dissolves into the wash water outright. The fatty acids are the interesting product: weak acids that ionise in a mildly alkaline bath and then behave as soap — the reaction’s own product becomes a surfactant, so the cleaning accelerates as it proceeds. Even partial hydrolysis helps, because mono- and diglycerides sit between oil and water in polarity and act as emulsifiers in their own right. The film is not dissolved, it is converted into its own dispersant; that autocatalytic structure is why enzyme degreasers keep working when dilute and lukewarm. Proteases and amylases join the blend for proteinaceous and starchy soils on the same logic — each cuts the polymer that holds its soil together.

The windows

Temperature is double-edged. The enzyme wants its usual 20–60 °C range, but interfacial catalysis also needs the fat liquid: a cold, solid grease presents a crystalline surface with almost no usable area, and warming above the melting point buys more than a higher enzyme dose. pH matters twice — most detergent proteases are alkaline subtilisins, and only an ionised fatty acid acts as soap, so the working window is mildly alkaline for both reasons at once. Outside the windows the chemistry silently degrades to ordinary surfactant cleaning, which is what the formulation is padded with anyway.

Emulsions and their end

The wash must form an emulsion; the wastewater plant must break it. That tension is sharper here than with synthetic surfactants, because the fatty-acid soaps generated on site are themselves efficient anionic emulsifiers — the spent bath resists separation. Acidification or calcium salts collapse the soap emulsion, and free oil can then be skimmed; but the de-emulsification step is part of the process, not an afterthought. The other boundary is contact time: hydrolysis is slower than solvent dissolution, so enzymatic degreasing measures minutes, and the petroleum fraction that enzymes cannot touch at all is left to living cultures in the wash fluid, which oxidise hydrocarbons over days — enzymatic catalysis for the esters, microbial metabolism for the rest, and two very different clocks in the same tank.