INTERNATIONAL CLEANER PRODUCTION INFORMATION CLEARINGHOUSE

CASE STUDY #235

1. Headline: Pollution Prevention Assessment for a Goatskin

Tannery

2. Background:

What is EP3?

The amount of pollutants and waste generated by industrial

facilities has become an increasingly costly problem for

manufacturers and a significant stress on the

environment. Companies, therefore, are looking for ways to

reduce pollution at the source as a way of avoiding costly

treatment and reducing environmental liability and

compliance costs.

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.

Objectives of this Assessment

This assessment evaluated a facility that tans goatskin.

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 battery industry, and

(3) improve operating efficiency and product quality.

The assessment was performed by an EP3 team comprised of

an expert in hide tanning and a pollution prevention

specialist.

Facility Background

This facility is a goatskin tannery producing chrome

tanned suede and grain shoe, garment, and fancy leathers.

Dry and green salted skins, as well as wet blue goatskins

are used. The tannery produces leather from approximately

1,000 kg of dried goatskins per day.

The wastes generated by the tannery come from the hides

and the chemicals used in the production process. Tannery

wastes are discharged in a number of batches during the

production day.

3. Description of Cleaner Production Application: The

assessment identified various cleaner production

applications including: process modification, good

housekeeping, new technology, recycling, and material

substitution.

Overall, the assessment identified eight pollution

prevention opportunities at this facility. Recommendations

for pollution prevention include recycling of the spent

chrome tanning wastes, oxidation of the sulfide containing

wastes, decreasing the volatile organic discharge by

changing finishing materials, decrease of water use by

batch washing, and use of solid wastes from the waste

stream as fertilizer.

Manufacturing Process

In the production of leather from dry goatskins, the dry

skins must be thoroughly re-wet and the dirt, salt and

undesirable hide substances removed. Soaking and washing

the skins is done in three steps. The first step removes

dirt, salt, and some organic matter, while the other two

are rinses. The waste water is nearly neutral, and

contains salt and some suspended solids.

Next, the skins are unhaired by treatment with lime and

sulfides. The waste water is very alkaline, contains toxic

sulfides, and is the main cause of the high BOD and

suspended solids in the total waste stream.

The next step is de-liming and bating to remove the lime

in the skins and soften them by enzymatic action. The

first dump of this process contains ammonium sulfate,

enzymes, and some protein. The subsequent washes are very

dilute, nearly neutral pH solutions.

The skins are then tanned. The chrome tanning process is

standard for the industry: the solutions contain chromium

as chromium sulfate salt and some free acid. About 75

percent of the chromium present combines with the hide.

Finally, the retan, color, and fat liquor steps are

employed to color and oil the leather to make it as soft

or firm as desired. A number of chemicals are sued in

these steps, and about 90 percent of the load is fixed to

the leather. The spent solutions are mildly acidic with a

pH of between 4 and 6. BOD and suspended solids are

relatively low.

Existing Pollution Problems

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

pollution problems at the facility, including (1)

excessive chromium discharge, (2) excessive VOC discharge,

(3) excessive water usage, (4) excessive leather waste,

(5) excessive sulfide waste, (6) excessive suspended

solids in effluent, and (8) excessive BOD of effluent.

Normally, the unhairing wastes are dumped during the

morning, while the balance of wastes from the washes of

the untanned skins and the retan come as a fluctuating

flow of mildly acidic wastes. The variation in the flow

and the changing acidity or alkalinity of the combined

waste stream is a problem for treatment of the pollution.

Pollution Prevention Opportunities

The assessment identified eight pollution prevention

opportunities that could address the problems identified,

with significant environmental and economic benefits to

the facility. Below are listed the opportunities for

pollution prevention recommended for the facility, and the

environmental benefits and implementation costs for each.

Two of the recommendations can be implemented with no

capital investment.

--Chromium tanning--Recycle chrome tanning - decreases

Chromium to less than 3 mg/l. At the time of the

assessment the costs had not been calculated. Financial

benefits were estimated at $5,000 (US) from savings in

chemicals.

--Solvent discharge-- Change to water-based lacquer finish

- decreases VOC discharge by 60-90 percent. No costs are

involved.

--Water use-- Change to batch washes - decreases water

usage by 20-40 percent. No costs involved.

--Solid waste-- Save leather trimmings for reconstituted

leather - decreases leather waste by 60 - 80 percent.

Costs were estimated at $5,000 (US).

--Sulphide waste-- Destroy sulfides by air oxidation -

decreases sulphide waste by 95-98 percent. Cost were

estimated at $20,000 (US).

--Primary treatment--decreases suspended solids by 70-85

percent. Costs were estimated at $50,000.

--Sludge from effluent-- Dry sludge for land application -

allows for disposal of sludge as fertilizer. Costs were

estimated at $10,000.

--Secondary treatment-- Treat primary waste decreases BOD

by 60-80 percent. Tickling filters were estimated at

$50,000.

The total costs for the actions were estimated at $135,000

(US) in capital costs. The total financial benefits were

estimated at $5,000 (US) plus 7 unquantified

opportunities.

Effect on the Environment

The recommended actions are based on cost effective

methods that have been proven in commercial applications.

These actions will have a number of positive environmental

impacts.

1) Chromium recycling will decrease the chromium in the

discharge by 80-90 percent. The spent chromium solutions

contain about 25 percent of the total chromium used in the

tannage. The loss of this valuable material can be

decreased and the chromium concentration lowered by

recycling. Some of the spent chromium solution can be

directly used to make the pickle solution without

affecting the quality of the leather. The remainder can be

saved, and the chromium precipitated with the addition of

an alkali. The recovered chromium can be dissolved in acid

for use in the tannage.

2) The suppliers of finishing products have developed

water-based lacquers with significantly lower volatile

solvent contents. The reduction of volatile solvents will

decrease VOC releases to the atmosphere by 60-75 percent.

3) In some hide wetting processes there is an opportunity

to recycle the final rinses. In the goatskin process,

extensive washing of the bated skin is common. The water

from this wash could be used for rinse water in the

original soaking, as the final rinse wastewater is

compatible with fluids used for the first wetting of

hides. The judicious recycling of rinse waters and

automated systems in a tannery could result in savings of

up to 50 percent of water consumed.

4) Elimination of solid leather waste discharges by using

trimmings to make reconstituted leather will ease the

burden on landfills.

5) Eliminating sulfide discharges is very important as

sulfides can corrode pipes, cause objectionable odors, and

cause fatal accidents. The sulfide-lime solution, and

washes from this process can be easily collected, placed

in a tank, and the sulfides oxidized by air with a

manganese sulfate catalyst. This method is effective and

can destroy the sulfide in 4-8 hours. The oxidized wastes

are kept for use in controlling the pH of the effluent

stream.

6) Decreasing by 80 percent the suspended solids

discharged, and instituting secondary treatment will serve

to decrease BOD. With primary and secondary treatment, the

BOD can be reduced by 75 percent. In addition, the

reduction of suspended solids creates a useable by-product

in the form of an organic fertilizer, thus eliminating

possible high disposal costs.

Implementation Plan

The schedule and timing of implementation of the

recommendations will depend on the relative costs and

benefits and the availability of personnel and capital.

The recycling of the chrome tanning solutions is the most

cost effective recommendation in that the company will

have a large saving in material costs in addition to

significant pollution prevention.

Chrome Recycling. The value of chrome recycling to the

tannery and its low capital costs should make it an

attractive option. Implementation may be accomplished in 2-

6 months.

Solvents. The shift to low VOC finishes should occur

between 6-12 months as the system is accepted by the

company for each of the leathers it makes.

Process Water. The decrease in the volume of process water

used can be accomplished without a capital investment. The

batch washing of coloring and fat liquoring batches could

result in savings of about 50 percent in these operations.

With the recommended pretreatment system, a decrease in

flow would decrease the capital and operating costs of the

treatment system. The shift to lower water use should come

gradually over the next 12 months.

Solid Wastes. At present, the tannery has useful disposal

of most of its solid wastes in the form of fleshings,

trimmings, and leather shavings. With the introduction of

the pretreatment system, a new source of solid waste --

about 1000 kg of solid sludge containing 120-150 kg of

nitrogen-- will be generated. This organic nitrogen and

the other materials in the sludge have been proven to be

very valuable as fertilizers and soil conditioners. The

implementation of the primary treatment system over the

next 6-18 months will not only clean the liquid tannery's

wastes, but result in an environmental benefit to the

community.

Pretreatment. The implementation of the pretreatment

system will require design data and engineering and

construction of the system. Total time to completion

should be 12-15 months.

5. Economics: See above

6. Advantages: See above.

7. Constraints: No information provided.

8. Contact:

EP3 Clearinghouse (UNITED STATES)

TEL: 1 (703) 351-4004

FAX: 1 (703) 351 6166

Internet: apenderg@habaco.com

9. Keywords: tanning, leather, goatskin, recycling, leather

tanning, EP3, chrome, solvent, raw material saving, water

saving, sulfur, BOD, nitrogen, good housekeeping, process

modification, material substitution, USAID

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.