INTERNATIONAL CLEANER PRODUCTION INFORMATION CLEARINGHOUSE

Case Study #244

1. Headline: EP3 - Pollution Prevention Assessment for a

Cattle Hide Tannery

2. Background:

What is EP3?

The United States Agency for International Development

(USAID) is sponsoring the Environmental Pollution

Prevention Project (EP3) to establish sustainable programs

in developing countries, transfer urban and industrial

pollution prevention expertise and information, and

support efforts to improve environmental quality. These

objectives are achieved through technical assistance to

industry and urban institutions, development and delivery

of training and outreach programs, and operation of an

information clearinghouse.

EP3's Assessment Process

EP3 pollution prevention diagnostic assessments consist of

three phases: pre-assessment, assessment, and post-

assessment. During pre-assessment, EP3 in-country

representatives determine a facility's suitability for a

pollution prevention assessment, sign memoranda of

agreement with each facility selected, and collect

preliminary data. During assessment, a team comprised of

US and in-country experts in both pollution prevention and

the facility's industrial processes gathers more detailed

information on the sources of pollution, reducing this

pollution. Finally, the team prepares a report for the

facility's management detailing its findings and

recommendations (including cost savings, implementation

costs, and payback times). During post-assessment, the EP3

in-country representative works with the facility to

implement the actions recommended in the report.

Summary

This assessment evaluated a cattle hide tannery. The

objective of the assessment was to identify actions that

would: (1) reduce the quantity of toxics, raw materials,

and energy used in the manufacturing process, thereby

reducing pollution and worker exposure, (2) demonstrate

the environmental and economic value of pollution

prevention methods to the tanning industry, and (3)

improve operating efficiency and product quality.

The assessment was performed by an EP3 team comprised of a

US expert in hide tanning, a pollution prevention

specialist, in-country EP3 staff, and local consultants.

Facility Background

This facility is a cattle hide tannery producing chrome

tanned and vegetable tanned leather from salted cattle

hides. The wastes generated by the tannery come from the

hides and the chemicals used in the production process.

The tannery has a nominal production capacity of five

hundred hides per day. The hides average 23-24 kg, with

the total weight of hides at 12,000 kg/day.

Chrome/vegetable retan leather accounts for 10,640 kg of

hides per day, while vegetable tan leather accounts for

the remaining 1,560 kg. The hides are domestic and

imported from small slaughter house production.

3. Cleaner Production Principle: The assessment identified

various cleaner production applications including: process

modification, good housekeeping, new technology,

recycling, and material substitution.

4. Descript

ion of

Cleaner

Producti

on

Applicat

ion:

Overall, the assessment identified nine pollution

prevention opportunities at this facility. Recommendations

for pollution prevention include using fleshings for

rendering, recycling the spent chrome tanning wastes,

recycling some wash water to compatible processes,

oxidizing the sulfide containing wastes, reducing

suspended solids by physico-chemical precipitation, using

solid wastes from the waste stream as fertilizer,

instituting secondary treatment of the waste stream, and

reducing VOC emissions by changing to water-based lacquer

finishes.

Manufacturing Process

The salted hides are inspected, resalted if needed, then

weighed into production lots. The hides are placed in a

conventional drum and soaked in cold water. Some minor

chemicals may be added to assist in the soaking. The water

use is approximately two liters of water per kg of hide.

After the desired soaking time, the hides are washed in

additional water.

The hair pulp process is carried out in the same drums as

the soak. First, the hides are treated with lime and

sulfides. Then, more lime is added and the hides are

washed in cold water in the rotating drum.

The washed, limed hides are removed from the drum, wrung,

then placed in a drum for deliming and bating.

This process involves the use of ammonium salts and

enzymes, which remove most of the lime from the hide.

The next step is chrome tanning, which is conducted in

drums. The hides are placed in a solution of salt and

acid, followed by the chrome tanning agent (chromium

sulfate). The pH of the solution is adjusted by adding

magnesium oxide. When the chrome tannage is complete, the

leather is washed with running water and the surface is

then cleaned by adding a small quantity of acid. The

tanned leather is then removed from the drum and wrung.

The hides to be vegetable tanned are separated from the

other hides after liming. These hides are cut into section

for bellies, shoulders, and bends in order to assure the

most efficient use of the expensive vegetable tanning

materials. The vegetable tanning is done without the use

of chromium. Because the retan system for the chrome

tanned leather is also a vegetable tannage, in most cases

the effluent from the vegetable tannages is combined with

the other effluents from the retan step.

The chrome tanned leather, after wringing, is split to the

desired thickness. This results in two layers of leather:

the grain and the split. The grain layer is the larger and

more valuable layer. The split is trimmed and further

processed in the same manner as the grain leather.

Following splitting, the leather is precision to the

desired thickness by shaving, which involves a high speed

rotating blade that removes leather in small shavings (1 X

3 mm). These shavings are sold to be used in reconstituted

leather products.

The chrome tanned leather is retanned in small batches to

color and oil the leather as desired. The retan

formulations vary widely depending on the leather desired.

In most of the leather made in this tannery, vegetable

tanning materials are used. In addition, dyes, specialty

chemicals, and leather lubricating oils are applied. The

retanning process produces large quantities of effluent

with relatively low pollutant concentrations.

Existing Pollution Problems

At the time of the assessment, there were a number of

pollution problems at the facility, including excessive:

(1) solid waste, (2) chromium discharge, (3) VOC

discharge, (4) water usage, (5) sulfide waste, (6)

suspended solids in effluent, and (7) BOD of effluent.

Pollution Prevention Opportunities

The assessment identified nine pollution prevention

opportunities that could address the problems identified,

with significant environmental and economic benefits to

the facility. Below are listed the opportunities

recommended for the facility, along with the environmental

benefits and implementation costs for each. Two of the

recommendations can be implemented with no capital

investment.

Summary of Recommended Pollution Prevention Opportunities

Fleshings from soaked hides--use fleshings for rendering--

decreases solid waste by 1000-1500 kg per day. Cost is

about $3000 (US).

Chromium tanning--recycle chrome tanning decreases

Chromium to less than 3 mg/l. Costs estimated at $20,000

(US) with a savings of $60,000 (US) per year.

Solvent discharge-change to water-based lacquer finish -

decreases VOC discharge by 60 to 90 percent.

Water use--recycle some wash and cooling water to

compatible processes decreases water usage by 130 -150

cubic meters per day. Costs estimates of $20,000 (US) for

pumps pipes and tanks.

Sulfide waste- destroy sulfide by air oxidation -

decreases sulfides in effluent to less than 3 mg/l. Costs

estimated at $30,000 (US) for pumps pipes and tanks.

Primary treatment--Physico-chemical precipitation with

spent unhairing waste- decreases suspended solids by 60 -

80 percent; decreases BOD by 40 - 60 percent. Estimated

costs of $100,000 (US) for pumps pipes and tanks.

Sludge from primary treatment-dry sludge for land

application- disposes of sludge as fertilizer. Cost

estimates of $20,000 for sand filters.

Secondary treatment- treat primary waste - decreases BOD

by 60 - 80 percent. The cost is for $50,000 (US)

(trickling filters)

Total estimated costs for implementation $240,000 (US)

capital with $60,000 (US) savings.

The largest sources of pollutants at the plant are from

the soaking and hair pulp systems, which have very high

concentrations of suspended solids and high BOD. The hair

pulp system also contains sulfides and strong alkali as

calcium hydroxide. Sulfides are deadly toxic materials and

must be destroyed chemically. The normal treatment system

in the industry is to collect all the sulfide containing

wastes, then oxidize the sulfides with air with a

manganese sulfate catalyst. The lime solution, free of

sulfide, can be used to neutralize the acid wastes to

adjust the pH to the acceptable range.

The mixing of the acid and alkaline wastes at a controlled

pH will result in a coagulation of the suspended solids.

The removal of the coagulated materials by primary

treatment will result in a decrease of suspended solids by

about 80 percent. The primary treatment of tannery wastes

by coagulation and settling will also decrease the BOD by

50-70 percent. This approach has been successfully used in

at many tanneries.

The chrome tanning wastes contain valuable chrome tanning

materials. These spent solutions should be recycled to

remove the chromium from the effluent and also reduce

processing costs.

It is recommended that several steps be taken by the

tannery:

- The hides, after washing, should be fleshed before the

hair pulp step, improving the quality of the production

and allowing the sale of 1000-1500 kg of fleshings per day

to a rendering facility.

- Recycling spent chrome tanning solutions will produce

economic benefits for the tannery, decrease water use and

prevent pollution of the effluent by chromium.

- Recycling some water washes that are only slightly

contaminated with process chemicals, where compatible with

production processes, will result in water use reduction.

- Removing toxic sulfides from the waste stream by oxidation

will effectively decrease the sulfide in the waste stream

to less than 3 mg/l.

- Mixing the separated waste streams with pH control, after

sulfide and chromium removal, will co-precipitate the

suspended solids and decrease the BOD.

- Implementing secondary treatment, which will lower BOD,

should be delayed until the primary system has been

optimized. At that time, the most cost effective method

for BOD reduction can be determined.

Implementation of the Recommendations

The implementation of the recommendations will be required

to meet regulatory pollution abatement requirements.

Wash Water. The change in hide washing practices to

produce better hair pulping and cleaner flesh is a

relatively simple matter. There is no quality risk in this

change and it should be taken as soon as possible.

Chrome Recovery. In addition to pollution prevention

benefits, recycling chrome tanning solutions has technical

benefits for the tanner. This step is not simple, however,

and will require some process adjustments. Required

personnel should be hired and the project started as soon

as possible.

Sulfide Oxidation. The pollution control regulations

require sulfide oxidation; this step can not be avoided.

The engineering of the sulfide oxidation system should be

started and the project implemented as soon as possible.

Primary Treatment. The primary treatment system is the

most extensive project recommended in this report. The

suspended solids requirements make the primary treatment

system essential. The design of the system should begin

immediately and construction should start when planning is

complete.

5. Economics: See above.

6. Advantages: See above.

7. Constraints: See above.

8. Contacts:

EP3 Clearinghouse (UNITED STATES)

TEL: 1 (703) 351-4004

FAX: 1 (703) 351 6166

Internet: apenderg@habaco.com

9. Keywords: leather, tanning, recycling, United States,

USAID, EP3, hide, chrome, sulfide, salt, biotechnology,

enzyme, VOC, BOD, solvent, water saving, sulfur

10. Reviewer's comments: This case study was carried out in a

developing country in which EP3 has an established

programme. It was submitted to UNEP IE and edited for the

ICPIC diskette in August 1995. It has not undergone a

formal technical review.