An LCA is an in-depth study of environmental data. Per H. Nielsen is an LCA specialist at Novozymes who has conducted an assessment at a Chinese tannery.
Enzymes have been used in the tanning industry for centuries because they are efficient at degrading protein and fat. In early times, the enzymes were derived from animal excrement, and later on from the pancreas of cattle. Nowadays, many of the enzymes are produced using microbial fermentation, and Novozymes is a major supplier of this type of enzyme.
One of the applications of microbial enzymes in the tanning industry is in soaking and unhairing processes. Enzymes can replace chemicals and shorten processing times, thereby reducing production costs. Other benefits can include increased area yield and improved quality of the final product.
As part of Novozymes’ work with Life Cycle Assessment (LCA), the company collaborated with a Chinese tannery to assess the environmental implications of the application of enzymes in the soaking and unhairing of bovine hides.
True production data
The assessment is basically a comparison between two different ways of soaking and unhairing/liming bovine hides. An entirely chemical method was compared to an enzymatic method with reduced chemical consumption.
Life Cycle Assessment has been used as an environmental analytical tool to evaluate the changes in enzyme and chemical consumption that occur when switching from the chemical method to the enzyme-assisted method. The information has been derived from a major Chinese tannery that applies chemical as well as enzyme-assisted production methods.
The study was based as far as possible on true production records and refers to an enzymatic hair-saving process - where the hairs on the hides are not dissolved by the chemicals but removed intact.
The enzymes Greasex® 50 L and NovoCor® SG were used by the tannery for soaking to degrade fat and proteins. They reduced the soaking time, which leads to electricity savings in turning the drum. There were also savings in the tenside and soda requirements for the process.
The unhairing enzyme NUE 0.6 MPX was used to degrade proteins. It reduced the sulphide requirements for the process but did not influence processing time or temperature. The lower level of sulphides required reduc es the sulphide content of the wastewater and some manganese sulphide can be saved.
Savings in chemicals
Savings in chemicals as a result of the enzyme application are shown in Figure 1. As can be seen, a relatively small quantity of enzymes replaces quite a large quantity of chemicals.
The environmental impacts of producing and delivering the enzymes to the tannery on the one hand and savings in chemicals and electricity on the other hand have been evaluated and the results in terms of energy consumption and contribution to global warming are shown in Figure 2.
Figure 2 shows that a small ‘investment’ in energy and carbon dioxide emissions in enzyme production results in considerable savings when these enzyme products are used to replace chemicals and electricity in the soaking and unhairing/liming processes. A small amount of enzyme products made from a biological production process replaces a relatively large amount of harsh chemicals made using a relatively large amount of energy derived mainly from coal.
Contributions to other environmental impacts (acidification, nutrient enrichment and smog formation) are also reduced. In fact, the environmental impacts resulting from enzyme production are at least 20 times lower than the impacts that are avoided by the savings in chemical and electricity consumption.
Sulphide savings in the unhairing/liming process are considerable compared with other chemicals. Since a large quantity of coal is used to produce sulphides and a large quantity of carbon dioxide is emitted during production, the savings in sulphides turn out to be the most important environmental effect of enzyme use (see Table 1).
A comparison of conventional and enzyme-assisted bovine soaking and unhairing/liming processes indicates that the application of enzymes in the tanning industry results in considerable reductions in the contribution to global warming. The environmental advantages of enzyme application are primarily due to savings in sulphides in the unhairing/liming process because a small quantity of enzyme replaces a considerable amount of sulphides, which have a relatively high environmental load.
Novozymes is continuously developing enzymatic solutions. In future, the company envisages that new, more efficient enzymes will be able to virtually replace conventional chemicals in the soaking and unhairing processes.
Global impact
The global supply of bovine hides for leather production was about 8.8 million tons in 2005. Today, less than 10% of bovine hides are soaked and unhaired in enzyme-assisted processes. Assuming that the environmental improvements observed in this study by switching from conventional to enzyme-assisted soaking and unhairing/liming are applicable worldwide, the global potential saving is in the order of 8 million GJ of energy and 0.7 million tons of carbon dioxide per year. The saved carbon dioxide emissions are equivalent to the annual load from 75,000 average world citizens or 170,000 cars.
Fig. 1. A relatively small quantity of enzyme products (left) serves the same function in the tannery as a relatively large quantity of chemicals (right). The saved electricity is equivalent to using a 60 W light bulb for 35 hours. The volume of the columns provides an indication of quantity in terms of weight. All figures are per ton of hide.
Fig. 2. Use of energy and contribution to global warming from enzymes and from saved chemicals and electricity when enzymes are introduced in soaking and unhairing/liming.