Environmental prevention and the minimisation of waste and emissions are based on the knowledge and understanding of the waste flows that are generated in the company's industrial processes and activities. The fact of having information on its waste flows and the cause of each one provides the enterprise with tools to carry out actions aimed at minimisation and cost saving

Lack of knowledge is very often the main obstacle why enterprises fail to carry out actions in the area of pollution prevention.

The purpose of this diagnosis is to establish potential opportunities for preventing pollution at source (reduction and recycling at source) and actions to be carried out that guide corporate policy in the direction of practices and technologies that make this viable.

The raw materials basically used by the PELLNETA company in the process of leather tanning are: lambskin, salts, acids and tanning substances. Aspects that may be relevant concerning alternatives have been identified for each of these as well as for the auxiliary materials.

The main raw materials used appear in the following tables.

This includes electrical energy consumption and other type of fuel and uses.

The data for energy consumption by the PELLNETA company were not available.

The different sections in the company are as follows:

- Loading and unloading depot o Beam house section

- Dyeing section o Machining section

- Suede section

- Finishing section o Dispatch depot

- Administration and offices

- Laboratory

THE PELLNETA Company is a leather tanning company that specialises in the manufacture of hides for the manufacture of leather goods using lambskin and goatskin originating from Spain and abroad.

There are four well-defined stages in the process of tanning hide. The first is receiving and preparing the hides, then tanning itself, then the dyeing of the hide in order to colour it and finally the finishing treatment. Each of these areas is subdivided into different individual operations, each with its own particular characteristics.

Purchase of hides

The first step is the purchase of the hides, either as unworked raw leather or Wet Blue, by the company's specialist personnel.

Transportation of the hides from the place of origin to the factory

The next step is the transportation of the hides from the place of origin to the production facilities. In general, hides are usually delivered by lorries on wooden pallets, which provides for ease of unloading.

Delivery and storage

When the lorry loaded with hides arrives at the factory, the merchandise and papers are first cross-checked and the hides are then unloaded either into the unworked raw hide or Wet Blue storage location, according to the state of the hides being delivered.

The hides are adequately preserved here prior to beam house processing.

Test sampling

A test sample is made of a random number of hides in each batch that arrives in order to check that the conditions on arrival tally with the characteristics agreed to at the time of purchase.

Unusable parts removed

Once the test sample has been completed, the unusable parts of the hide are removed, such as heads, tails and rough hair. With hides that have been salted, this operation is done with a knife whereas an electric saw is used for dry hides.

Recounting and hides placed on the travelling carriage

Once the unusable parts are removed, the hides are counted and placed on the travelling carriage.

From here, they can either be returned to the storage location or directly enter the beam house according to the demand for manufacturing.

Beam house is the initial stage that hides are subjected to on arriving at a factory where the complete tanning process is undertaken, as is the case of this company.

Each different step in the overall beam house stage is described below.

Soaking

This consists of a series of successive paddle vat rinses with water and biocides to prevent any breakdown of the hide due to microorganisms.

The objectives of this process are:

- To moisten the hide and restore it to a natural hydrated condition to prepare it for subsequent processes (dissolving soluble proteins with water and neutral salts, albumins and globulins).
- Eliminate unwanted compounds, excreta, earth, blood, fleshings, urine, sweat, dust, micro-organisms and chemical products used for preservation.
- To eliminate salt. Salt on the inside of the hide is forced out due to the difference in saline concentration and the mechanical action.

The change of soaking water is very important to eliminate salt in the fibres as water enters them as the salt dissolves.

The equipment consists of three fixed brick-set paddle vats that carry out one soaking operation per day, which enables an average of 1050 hides a day to be treated. Water consumption is 10 m³ per operation.

Removal of wool (or Painting)

There is still wool on the hides when they are removed from the paddle vat after the soaking operation. The following process is the removal of the wool, whereby a paint-like solution containing sulphur is applied on the flesh side of the hides and after a specified time the hide and wool can be separated.

The purpose of the wool-removal operation is to loosen the roots of the wool so that it can be extracted mechanically without damaging the hide.

The chemical attack that occurs is effective because the reducing agent loosens the roots of the wool. This chemical effect is usually combined with the physical effect of the machine that separates the wool and the hide; in the case of this company, however, the hides are painted and left. They are then put back onto the travelling carriage with a mild lime liquor.

This operation is mechanical yet discontinuous and the machinery is very simple in that it merely consists of a belt which carries the hides and a sprinkler system from above from which sends out a spray of liquid sulphur and lime with a density of 15ºBe. All excess quantity falls on the tray where it drains into a tank and is recycled.

The hides are placed with the flesh side facing upwards and the operation takes ten seconds. The line worker who is behind the machine folds the hides flesh to flesh and leaves them for 5-6 hours so that the reducing agent can take effect and attack the base of the hair follicles. The line worker then returns the hides to the paddle vat and as a result of the sulphur having attacked the base of the wool, it can be more easily removed in the following liming treatment.

Sulphur paste is prepared in an appropriate container for this purpose. Two people are necessary for the painting operation, one to put the hides on the belt and the other to take them off and fold them flesh to flesh.

Liming

With the wool removed, the hides are loaded into the paddle vats for the liming operation.

This involves immersing the hides in a bath of sodium sulphide for a specified period of time. The main objectives of liming are:

- To loosen the fibrous structure of the hide.
- Eliminate the epidermis with remains of hair and wool from the corium.

4 wooden drums with a 1:1 bath ratio (1 litre of water for each kilo of hide) are used for this.

Fleshing

Fleshing (or scudding) is a mechanical process that cleans the hide by eliminating subcutaneous tissue and adipose, which is where most of the fatty material in the hide is contained. Removing these in the initial stages of manufacture prepares the hide and enhances the penetration of chemical products applied in subsequent processes.

It is important for the hides not to be scored or marked; for this reason great care is needed when adjusting the machine.

Deliming

After the hides have been cleaned and most of the sulphur from the bath has been removed, they are delimed. The purpose of this is to achieve the right alkaline pH of the hide and prepare it for subsequent treatment by cleaning the pores of the hide and eliminating any alkaline remains mixed with collagen that can lead to swelling of the limed hide.

The equipment used for deliming is the same as that for liming, i.e., 4 wooden drums with a 100% bath ratio.

Bating (also known as drenching)

The hides are subjected to a bath with specific characteristics of temperature and pH and enzymes, which have the following effects, are added:
- They loosen and cause the peptisation of the structure of the collagen.
- They clean up the grain surface by eliminating remains of hair, epidermis, glands and fat.
- The hydrolysis of interfibrillar proteins.
- The breakdown of the elastin, reticulin, collagen and fats.

Temperature conditions of 38-40ºC and a pH of 8.5 are essential in bating for maximum effectiveness of the pancreatic enzymes.

Once the specified bating time is completed, the hides are checked and then put through a continuous cleaning process using cold water, the purpose being to cool the hides the hides and the bath and stop the enzymatic reaction.

The cooling process is normally completed when the outflowing water temperature is similar to that of the inflowing water.

Pickling

The pickling process, which follows the bating operation, is also applied in the same drum.

The pickling process has various purposes. It is complementary to deliming in that it further reduces the alkalinity of the hides and brings them to the proper acid pH for tanning.

- It also definitively inhibits the bating effect due to the presence of salt and acid.
If a preservation pickle is applied and the hides left for a specified time, the protoplasmal membrane of the fat deposits is attacked by the acid hydrolysis and breaks, forcing out the fat. This is a good time to carry out degreasing if this is necessary for the article.
- It also produces dehydration of the hide due to the combined action of the acid and salt.
- The acidification process prepares the hide for the subsequent mineral tanning process, leaving it positively charged, with counter ions in the corners and an overall neutral charge, which helps penetration.
- If pickling is not carried out, overtanning of the hide would occur in the following mineral tanning process due to the basicity of the tanning salt; given that the hide is anionic and the chrome cationic, the chrome would fix to the hide too quickly and in excess as a result of the charging.

The equipment used for pickling is a polyester tipper paddle vat where two operations are carried out per day and an average of 1,650 hides treated in each rinse. The bath ratio is 1 to 5, i.e. five quantities of water to one of hides.

- Dark stains
- Fat efflorescence
- Difficulty in achieving good distribution and penetration of the products
- Uneven dyeing
- Reduced dye fastness
- Non-adherent finishes.

For maximum efficiency, the degreasing process is carried out at between 30 to 35ºC temperature. An oxyethylenate nonylic-phenyl-based surfactant is used to emulsify the fat in the hide.

Salt water at 7ºBe is used for the bath to prevent swelling of the hides (following pickling). For this reason, sodium chloride is added.

Tanning

The main objective of tanning is to covert the hide into a stable material which will not decay and make it resistant to hot water and the action of enzymes and micro-organisms.

The tanning process also gives the necessary feel and physical characteristics of leather and provides it with certain properties, such as homogeneity, feel, elasticity, grain, which are all achieved through one type of tanning or another and through the appropriate use of the different factors (temperature, pH, basicity, masking).

When the hides have been degreased, cleaned and drained, the tanning bath is prepared. Given that the chrome salts are acid, salt water at a 7ºBe concentration is used for the bath.

Formic acid is used to adjust the pH to 3.5 to improve penetration of the chrome salts, which are then added (in the form of chrome liquor). Sodium bicarbonate is used for basification to complete the fixing of the chrome salts.

Once sufficient time has passed for the hide to stabilise, check are made of the bath to verify correct exhaustion and of the contraction temperature of the hide (over 100ºC). The hides are finally rinsed so that they cool them and they are then loaded in wagons.

Roller pressing / Classification

Once the hide has been tanned and left for a specified time, it is passed through hydraulic machinery to remove the moisture (moisture content to 60-65%) and it is then taken to chrome storage and classified according to size, thickness and class. It is then stored prior to manufacture.

The hides are carefully covered with plastic sheeting to prevent them from drying out during storage.

Skiving / Neutralisation

The hides are shaved by machine to make any further correction of the thickness of the hide and make it uniform.

Once this mechanised operation is completed, the hide is then neutralised to correct the pH and prepare it for following operations.

If a hide is not neutralised, the residual acidity of the hide, together with the presence of salts, specially sodium chloride, creates adverse conditions for the use of the leather and leads to the wear of seams and irritation when in contact with human skin.

The products usually used for neutralisation are sodium bicarbonate, sodium formate and sodium carbonate. The use and proportions of these products varies according to the required article and the quality of hide.

Following neutralisation, the hide is then rinsed to eliminate any remains of neutral salts.

Retanning

A second tanning process is carried out to achieve optimum characteristics of homogenisation and porosity and to compact the structure. Synthetic chrome and phenol-based tanning products as well as vegetable tanning extracts are used in retanning, either individually or in combination. The treatment is carried out at a temperature of between 35-45ºC. No salt is used.

Fat-liquoring

The next process is fat-liquoring which gives the final softness and protection to the tanned hide which have been impaired during the previous processes. Through the use of fats and oils in appropriate mixes to lubricate and soften the fibre structure of the leather at a temperature of 55 to 60ºC, fat-liquoring gives it the required softness for the eventual end use.

The use of fats and oils on the hide maintains the fibres separate and lubricates them so that these slide smoothly against each other.

Both synthetic and natural fats and oils are used in an aqueous solution which is then pumped or applied manually to the drum.

Dyeing

Dyeing involves colouring the hide according to eventual end use.

Once the colouring has penetrated the hide, formic acid is added to pH 4 to fix and exhaust the bath dye stuff.

The colour of the hide is then checked through comparison with the sample requested by the client and, if correct, it is washed in cold water to reduce the temperature of the bath and the hides. When the hides have cooled, they are loaded onto wagons and left for no longer than 24 hours.

The equipment consists of 5 manually-loaded polyester and wood drums.

Finishing involves the final operations to the hides that give the end characteristics to the article. There are two subprocesses in the finishing stage:

The first subprocess includes various different separate operations from when the dyed hides are unloaded to when they are pigmented. The second subprocess includes the operations following pigmentation through to dispatch.

Once the hide has been dyed and left to rest, it is put through a rolling process in a hydraulic machine. This operation mechanically reduces the moisture content of the hide and reduces the energy consumption involved with drying.

When the hides have been roller pressed, a check is made so that the hides are stretched to the maximum before being dried.

Drying reduces the moisture content of the hide and is carried out with a vacuum machine.

The principle of vacuum drying consists of reducing the external pressure on the hide, which is enclosed in a hermetic container. A partial vacuum is created so that the water can evaporate faster and more easily at a temperature below 100ºC.

Vacuum drying is applied so that hides do not sag.

Once the hides are dried, they have to be conditioned prior to being staked. The fibres in the hide join together during the drying process, which produces a hard, compact hide.

The dried hide cannot be directly staked because this would cause the fibres to break and produce a spongy hide. In order to avoid this, the hide is conditioned until there is a homogenous humidity content of 20-22% throughout the entire thickness of the hide.

The system used for conditioning the hides is very simple in that they are placed on a conveyor belt that passes beneath a series of sprinklers whereby they get covered by the spray of water. The moistened hide is put on the travelling carriage and left for some time under plastic sheeting in order for the moisture to spread in a uniform way.

Staking is a mechanical operation that makes the hide flexible. The type of staking is done with a pivot machine.

This machine transports the hide on two rubber belts that pass through parts with vibrating pivots. The level of percussion can be regulated independently for each hide, which enables the intensity of staking to be achieved for each area of the hide.

Toggling is done after the mechanical process of staking because the hides need to be dried while they are kept flat until the final moisture content is reduced to approximately 10-12%.

Unusable parts for manufacture are then trimmed using scissors, including marks from drying pegs, areas with defects or cuts, etc., the purpose being to improve the class of the hide and to improve its machineability.

The following operations are also carried out on certain types of hide:

Buffing is used to produce suede articles, to clean the edges of the leather on articles, to manufacture nubuck, etc.
The buffing machine consists of an emery wheel that makes two simultaneous movements, one circular movement on the axle and the other, an axial type movement, that prevents the formation of scratches or striations on the hide.

A large amount of dust is produced during the buffing operation, part of which adheres to the hide due to electrostatic load. Given that the dust has to be totally eliminated in order to finish the hides (irregularities would develop in the finish if not), the dust is removed (dusting).

The company has a brush-type dusting machine, the workings of which are very simple. It consists of two cylinders with brushes that rotate in opposite directions and the hide is placed between the two.

The purpose of product application is to give the surface of the hide the appropriate colour and glossy finish.

The products are applied in this company using rotary air-brushes.

Products used for finishing include pigments, dye and colouring matter, resins, wax, lacquer and casein.

Spray-applied pigments are used to obtain very light, uniform coatings that do not overload the grain while highlighting the quality of the hide.

The main purpose of drying is to evaporate the water, solvents and diluents used to prepare and apply the finishing.

The drier consists of different independent elements assembled consecutively along the conveyor, with a total drying capacity in line with the application system.

The hides are stacked when they come from the pigment coating machines and drying line prior to polishing and glazing.

Polishing and glazing are applied according to the type of hide and the article required.

Glazing is exclusively for finishes with proteinic bonds and gives a very characteristic aspect that even today is irreplaceable. The glazing operation is done using a machine with an arm that has a glass cylinder on the carriage that quickly slides under pressure to produce a shine and feel that is totally different from that achieved with other machines.
Others types of hide are polished. This is achieved by fairly vigorous friction of the hide surface as it passes between cylinders that are under a certain pressure.

Ironing is to ensure the correct fixing of the different products that have been applied.

The hide is placed in an ironing machine which has two cylinders that compress the hide as they turn in the same direction. One of the cylinders is metallic and incorporates a heating system whereby the hide is pressurised and heated along the line of contact with the cylinder as the machine turns.

The finished hides are merchandised according to surface area and therefore need to be measured. This process is carried out with an electronic machine consisting of:
- Conveyor belt.
- Measurement header.
- Automatic foot measurement marker.
- Foot measurement indicator and adder.

The hide is placed as flat as possible on a frame-type conveyor belt that passes beneath the measurement header in the middle. A system of photoelectric cells reads the surface of the hide, which is then automatically marked on the back-side of the hide.

Once the hides have been measured, they are classified according to the characteristics requested by clients and the different classes of hide are then stored in the dispatch storage location.

When an order comes in, the hides are packed in different sized cardboard boxes. These boxes are folded and printed on arrival and the only operation required is manually opening them out, packing the hides and sealing the boxes.

This physiochemical treatment consists of the following stages:

Mechanical barscreen:

Water from the factory (from both the drums and paddle vats) flows into an outside channel approximately 50 cm wide, at the end of which there is a fixed rough-dressing grate with a 2 cm mesh. Particles larger than this size are retained by the grate and are periodically removed manually and managed as solid waste. Once the water has passed through the grate and prior to reaching the pump well, it passes through a tank (width 2m, height 3m and depth 2m), where the heavier colloidal particles separate out to the bottom, while that which floats goes into the pump well. This tank is cleaned periodically by a tank wagon.

Pump well:

Water from the mechanical barscreen and the separating tank falls by gravity into the pump well, which has an air activated agitator system although its sole function is to receive water which is then sent by mechanical pumping to the purification treatment process. The pump well has an approximate capacity of 50m³ and the surface is square-shaped although the lower part slopes down.

Grit Trap:

Water from the pump well is rough-dressed until particles larger than < 0,5 mm are separated out. The filter has two discs that turn and cause the filth to accumulate, which is very important for solids that it are difficult to eliminate using other filters, such as dust from buffing and reduced agents that are sometimes still present in the water. Solids that are removed are managed as solid waste whereas the filtered water falls by gravity to the homogeniser. If the filter cannot absorb all of the water forced through the pumps from the pump well, there is an overflow system that returns the water to the beginning again so that non-filtered water never enters the homogenisation tank.

Homogenisation:

The rough-dressed water enters the civil works circular homogenisation tank located outside of the separating tank. This tank is aired by way of a submerged current-type ventilator that is in constant operation and it also has a turbine that works intermittently, according to a timer.

The characteristics of the tank are as follows:

Coagulation-flocculation chamber:

The coagulation-flocculation chamber is located next to the homogenisation tank and the water to be treated is pumped in at a constant rate. The quantity of water entering the separating tank is regulated and any water exceeding the set amount is returned to the homogeniser. The first product to be added is the coagulant, which is mixed in by the movement of the water whereas the flocculent, which is added straight after, needs to be mixed with a mechanical agitator that is located in the chamber itself.

The systems used to prepare both the coagulant and the flocculent are described below.

Separation:

Once the chemical reaction has taken place, the water has to be separated from the flocculated material, and this operation is carried out in a brick-built separating tank with an inclined bottom that has a bridge scraper for the sludge. The separating tank covers an area of approximately 28m2.

The flushed water goes to the sewer system which leads to the municipal treatment plant while the sludge is pumped to the sludge thickener.

Sludge thickener and sludge preparation:

Sludge from the separating tank passes through a sludge thickener which increases the dry material content in the sludge and makes dehydration easier. The sludge thickener is located next to the homogeniser and a series of thin plates in installed to increase the separating capacity. The sludge passes through channels into an attached tank Ferric chloride is added according to the reading on a pH-metre and it finally goes into another tank where it is lime-adjusted. The quantity of lime added depends on the parameters entered in another pH-metre. It can occur that sludge is pumped from the separating tank and yet is not totally absorbed by the sludge thickener. In this case, it gets returned by an overflow and enters from the beginning again.

The ferric chloride is pumped by a 0'5" pneumatic pump and is taken from the tanks. Liming is prepared as follows:

Sludge dehydration:

Once the sludge has passed through the sludge thickener, it needs to be dehydrated because it is still very liquid. It is then pumped from the preparation chamber into the filter press.

The dehydration system is described below:

Steam boilers Pigment coating machines and pigmentation driers

* Not assessed individually
** Estimated data

Definition of the most important waste flows will depend on the cost of their management and improvements of any type often have a direct effect on this.

Waste that is recovered (either internally or externally) is not a cost for the company and in certain cases can even lead to income if the waste is sold to another company.

In this particular case, the only cost is that of non-selectively collected waste and the effluent treatment sludge. Costs are accounted for by the transportation and disposal on the corresponding controlled landfill site.

In this case, there are two types of source:

• Steam boilers: Used to generate energy for different uses.

• Pigment coating machines and pigment dryers used in processing.

Waste water is often one of the most important waste flows. This company channels all waste water from the different separate processes (beam house, tanning, dyeing, finishing and domestic and sanitary use) into a physiochemical purification system located next to the factory, within the grounds of the company. The water ends up in the municipal sewerage system whereby the water enters the municipal treatment plant.

The main forms of solid waste generated by this company are plastic containers, hide offcuts and shavings, fleshings, non-selective collection waste, effluent treatment sludge, which are sent to landfill on a controlled site.

(1) Although the volume of water generated in this operation is not so high as in beam house processes (approximately 30m³/day), its pollution load is very important. The water is highly alkaline, there are remains of proteins and small quantities of fatty material that are sent to the company's own treatment plant.
*Estimated data

* Estimated data
(1) Waste water has a high sodium chloride (8 to 10ºBe) and acid content and is therefore highly acid (pH 3 - 3.5 UpH).

* Estimated data
(1) Waste water from the rinsing of chrome tanning, calculated as being 7m³/rinse, has a high concentration of chemical products with a pH of 3-4, high salinity, large amounts of chrome salts and leather fibres in suspension, and emulsified fat. This water is also given physiochemical treatment.

The dyeing stage consists of the following operations: neutralisation; retanning; dyeing; and fat-liquoring.

Solid waste that is generated consists of plastic bags that contain the neutralisation salts, damaged wooden pallets and the plastic containers for the dyes/colouring matter, retanning agents and fat-liquors. There is also an aqueous waste flow from rinsing following neutralisation, fat-liquoring and dyeing.

* Estimated data
(1) Rinsing water from neutralisation, fat-liquoring and dyeing is slightly acid (pH 4-5) and mainly contains surfactants and, in some cases, emulsified surfactants, colouring matter/dyes, neutral salts and retanning agents. The volume of water from these operations varies considerably according to the article being manufactured.

• RECYCLING THE LAST RINSE OF THE SOAKING OPERATIONS
•HOT CHROME TANNING
• USE OF CHROME LIQUOR
• RECIRCULATION OF THE PICKLING BATH

In the soaking operation, a large volume of water is generated which has a neutral pH and contains soluble proteins, remains of blood, excreta, sodium chloride, naphthalene and other preservatives, according to the type of hide being worked.

Prior to soaking as such, the hide is rinsed twice and then soaked in a final rinse. These rinses consist of filling the paddle vat, mechanically stirring the hides and then emptying the vat.
Given the characteristics of the paddle vats and the bath ratios used in the production process, the volume of water used in beam house processes represents a significant proportion of the total amount of water consumed by the company.

The water from the last rinse in the soaking operation has a low salinity (0.3ºBe), which means that it can be reused.

Chrome tanning is usually one of the most inefficient operations and, depending on the method, the theoretical use of the chrome used is from 15% to 70%.

A large amount of the chrome salts added to the bath are therefore lost, which represents an unnecessary cost, as well as large quantities of chrome salts being transferred to the waste water (3,085 kg of commercial chrome salt per ton of pelt).

As well as the cost of these kilos of unused chrome salts, there is also the cost of recovery, if this is done in the facilities, or purification treatment of the sludge that is produced.

The parameters that condition the efficiency of tanning by modifying the capacity and/or rate of reaction between the hide and the chrome salt have been known for a long time. Some are due to the hide itself and the pretreatment processes such as compactness, thickness, intensity and duration of the liming process, bating and pickling, as well as the types of acid used.

Others factors play a role during the tanning process: pH and acidity, quantity and type of neutral salt, quantity and basicity of chrome salt, the degree of masking and fat-liquoring, the bath volume and chrome concentration, the mechanical effect, temperature, the length of time, etc..

Of all of the factors mentioned above, the influence of temperature is one of the most important. For example, for a set period of time, chrome fixation in the hide will vary according to the temperature. Furthermore, the fixed chrome is more stable, resulting in a reduced need for rinsing in subsequent operations.

The temperature also considerably increases the speed of the tanning process, in that:

The best available techniques have been determined on the basis of the experience of the workers in the company themselves and observations of the work method used in the company. The grounds for applying this alternative are as follows:
• Tanning with preprepared chrome liquor results in greater penetration with a better fineness of grain.
• Improved workmanship. The worker does not have to handle 25-50 kg. bags.
• Improved environmental conditions. It is no longer necessary to handle chrome in powder form, which penetrates very rapidly into the respiratory tract due to the small size of particles. When the chromium salts are being prepared, a considerable quantity of green powder is found to frequently accumulate on the mucous membranes of the respiratory system, which is trivalent chromium salt.
• The adding of chrome salt to the drum by means of a pump connected to the input tank stops the flow of the carriage that runs on gas-oil and the fumes in the air build up considerably over a period of a few hours.

The picking operation, which follows the bating process, has several purposes:

- It completes the deliming process as it continues to eliminate the alkaline state of the hide to the point where it becomes acid.
- It definitively stops the effect of bating.
- If a preservation pickle is done and the hide is then left for a time, the protoplasmic membrane of cells containing fatty material gets attacked by the acidic hydrolysis and breaks. This forces the fatty material out and facilitates the degreasing process.
- The hide also dehydrates.
- The hide is prepared for the following mineral tanning process.

The pollutants generated in pickling are the salt and acid added for the process and that remain in residual form in the water.

The used pickling baths have a high concentration of sodium chloride, which is normally 8-10ºBe in the case of preservation pickles and 3-4ºBe in the case of conventional pickles.

pH at the end of a preservation pickle should be between 1-1.5.