What a Waste! - By Amanda Michel of Leather Wise

Raw Materials
To make leather we need some basic raw materials: hides and skins, chemicals and water. Interestingly enough, our hides and skins are in fact a waste material from the meat and dairy industry, so we must score some points there for recycling and making a useable product from a waste material. But wastage can still occur; if hides and skins are not properly flayed at the abattoir they may be rendered useless for leather manufacture as Sam Setter (Limeblast) has reminded us on previous occasions in this publication1. Similarly, if they are not processed quickly, either by going straight into the tannery or by salting for storage, they can putrefy. Proper handling of raw materials is vital in the quest of waste minimisation.
A huge variety of different chemicals are used in the manufacture of leather and there is no doubt that there is potential for minimising waste here. The recycling of chrome liquors is common practice and has been done very successfully for many years. However, sometimes the reuse of chemicals is not desirable, eg the recycling of salt used to cure hides as this could result in build up of potentially damaging halophilic bacteria.
Apart from recycling/reusing chemicals, chemical wastage can be minimised by not using too much in the first place. In order to achieve this, careful examination of the process may reveal that it is possible to slightly reduce the offer of some chemicals without detrimental effects on the leather properties. Very often tanners introduce a chemical to overcome a particular problem or alter a certain property of the leather, but rarely do they consider taking a chemical out of the process. For example, in order to produce a softer leather a new fatliquor is introduced. But often this is in addition to the existing fatliquors rather than replacing the existing. Fixing problems can be another waste of chemicals – a filler may be added to help alleviate a looseness problem, but wouldn’t it be better to address the cause of the looseness and prevent its occurrence in the first place? It may be that something as simple as reducing the drum speed could stop the looseness occurring. Quite apart from the wastage, if too many chemicals are introduced, the process becomes too complicated and difficult to control.
In some countries water is a rare resource and is to be conserved wherever possible. The cleansing of wastewater can enable reuse and need not cost a fortune. Where financial or power constraints exist, it is possible to utilise the highly cost effective reed bed technology to produce ‘grey’ water that is quite acceptable for reuse in some parts of the process. Other technologies such as rainwater harvesting can also be considered to top up ground or mains water supplies.

Solid Waste
It is thought that for every unit of leather that is made, there is 3 times as much solid waste produced. But let us not forget the saying ‘one man’s waste is another man’s treasure’. The leather industry is very good at finding uses for much of its solid waste. Shavings can be reformed into leatherboard and similar products, fleshings can produce tallow and other solid wastes such as hair can be used as compost. Much of the solid waste produced in the tannery can have fuel value, which leads us on to the next subject – energy.

Energy
Everyone these days should be aware of the need to prevent energy wastage. In the domestic environment we are all requested to switch appliances off when not in use. Obviously the same principles should apply in the industrial situation, if not more so. Drums etc should not be run any longer and water not heated any higher than is necessary to facilitate proper processing.
Apart from conserving energy, it is possible for tanneries to produce their own energy and the Scandinavians have taken this very seriously. Borge Garveri in Norway have invested in gasification technology which converts tannery waste matter into useable energy2. The waste, which has half the calorific value of coal, undergoes a specialised incineration process that does not produce the toxic gases that normal incineration can do. The process produces energy with which to run the plant and chromium metal can be recovered for reuse. Only a small amount of relative inert slag remains after the process. Also in Norway, Aarenes are currently investing in hydroelectric technology to harness the power of water from the fjord adjacent to their tannery3. It is envisaged that this will produce not only enough energy to run their factory, but will have some surplus that can be sold on. Pilot scale studies have also investigated the possibility of using bacteria to convert wastewater into gases that have some fuel value4.
So far we have discussed what are the most commonly thought of wastes in the tannery, but there are other forms of waste that are less obvious but probably more damaging to the economy.

Time
Let us not forget that old saying ‘time is money’. One of the key elements of just-in-time manufacturing is the elimination of any operation that does not add value; anything that adds cost but not value is a waste. For example, the unnecessary movement of goods around the tannery. This can be eliminated by careful factory layout such as reducing the distance between the chemical store and the process vessels.
Good housekeeping also cuts wasted time; machinery must be regularly inspected and well maintained to prevent breakdowns. It need not be hard work to perform such inspection; it can be done by the operator whilst cleaning down the machine at the end of the day. Ensuring that equipment and chemicals are stored properly makes sure that they can be quickly and easily accessed and are less likely to get damaged and therefore work effectively. Even really simple things can have a big impact – hang the broom back up when it is finished with so that next time it is needed it can be found easily. Hang it by the head and not the handle – it is quicker to take down that way. Paint an outline of it on the wall where it hangs so that it is obvious when missing. Applying this very simple principle around the factory costs nothing and can save a lot of time.
Stock
It is a waste to carry too much stock; unnecessary stock and a warehouse full of leather without a customer is an expensive luxury, it is money sitting on the shelf. It is a false economy to keep large buffer stocks; storage space is a cost and some products may go out of date before use. Careful calculation of reorder dates keeps stocks adequately low. Unnecessary stock and work in progress (inventory) also hides problems in the process. A useful analogy is to view the production of leather in the tannery as a flowing river. The river bed is the factory through which the production flows and the water flowing along it is the inventory. If the water (stock and work in progress) is too deep, the river bed cannot be seen clearly through the water. If the water level is reduced, any boulders that impede the water flow (bottlenecks) can be seen more clearly and removed. The flow of water is consequently improved, ie production flows more easily through the factory thus reducing time (and money!).

Mistakes
Getting it wrong can be a huge waste; not only have you wasted raw materials, time and energy, you may also have failed to get the leather to your customer on time – loss of customer loyalty is a waste indeed! The development of a simple, failsafe process and tight process control are needed to prevent mistakes happening. Keep good records and have reporting procedures in place. Then, if and when something does go wrong, it should be easy to identify and prevent a repeat occurrence.
I recall observing the night shift in the wet end of a tannery some years ago and a drain port popped open on a drum and proceeded to drain away the float an hour before that part of the process was due to finish. The operative reported that this was a common occurrence and the lock on the port needed tightening up. Had he reported it to the maintenance department (who only worked days)? – No, because he had gone home before they started in the morning. A simple reporting procedure was all that was needed to ensure that the process was completed properly and produced a quality product with fewer down grades and rejects.
So when looking for ways to minimise waste, think about the less obvious wastages too. Usually, they are the most simple to deal with and can have a big impact on the effectiveness of your business.

References:

1. Static Flaying Frame Improves Leather Quality, Leather International, August 2003
2. Leather International April 2000
3. Tanning Among the Fjords, Leather International, September 2007
4. Industrial Waste Reduction; The Process Problem, Valentino & Walmet, Environment, 28 September 1986