Russian researchers, specialists of the Open Joint-Stock Company State Research Institute of Albumen Biosynthesis and the All-Russian Institute of Medical and Aromatic Herbs have analyzed opportunities for biological recycling of glycerin-containing industrial waste. In the researchersĺ opinion, such recycling should use not special genetically modified cultures but natural microbe associations. Only such technology will make glycerin-containing waste recycling economically effective. The researchers based their proposals on analysis of scientific publications.
The wastes containing glycerin are formed in production of biofuel, foodstuffs and makeup preparations, industrial spirits distillation in fracking fractionator and obtaining bioethanol from plant stuff, and in biodiesel production. The latter production discharge, which is customary called unpurified glycerin, is generally a mixture of glycerin, methanol, water, catalyst traces, free fatty acids, methyl ether and other compounds. Glycerin can be purified by physicochemical methods, and then used in various industry branches. However, biofuel production is developing so impetuously that glycerin is produced in too big amounts, at present a lot of enterprises incur expenses on its storage.
However, it is possible to process glycerin-containing discharge by microorganisms so that they could produce something useful from glycerin. The convenience is that glycerin does not require purification for microbe recycling. Glycerin biotransformation process can take place both under anaerobic and aerobic conditions. Entereobacteria, clostridia, cytobacteria and other groups of microorganisms are able to oxidize and ferment glycerin.
Under anaerobic conditions, 1,3-propanediol is obtained from glycerin to be used in composite materials, glues, laminated plastics, dissolvents and other chemical synthesis products. At present, 1,3-propanediol with utilization of genetically modified bacteria is produced by Dupont Tate, Lyle and Shell. Biogas, which produces methanogenic bacteria, can also be obtained out of glycerin. Glycerin transformation into biogas is a new task, and the process has still been studied rather weakly.
Glycerin aerobic fermentation enables to get a wider set of useful products, including low-cost citric acid and polyhydroxyalkanoates (PHA). In terms of physicochemical properties, they are similar to thermoplastics obtained from mineral oil, but in contrast to them, they are synthesized from renewable raw materials, easily undergo biodegradation and are promising as materials that are able to replace ordinary plastics. PHAs are currently applied in medicine, food industry and agriculture.
Production of useful products, especially PHAs, from glycerin-containing wastes could be economically sound if it were slightly less expensive. According to the Russian researchersĺ opinion, savings can be achieved if natural microorganism associations are used instead of pure laboratory cultures. Special cultures require sterile manufacturing environment, which is very expensive to maintain. Natural mixed cultures do not require sterility, and their productivity is the same as that of pure cultures of genetically modified microorganisms. The researchers have even suggested the scheme for recycling biodiesel production wastes into PHAs with utilization of natural microorganism associations under the non-sterile fermentation conditions. The suggested recycling technology will enable to get about 270 kilograms of biodiesel and 10 kilograms of PHAs, and about 700 kilograms of protein-vitaminous fodder additives out of 1 ton of rape. At that, production of 1 kilogram of PHA will cost about 6 euros, this being quite acceptable price.