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            Effluent Guidelines, Leather Tanning:, and Pollution Prevention;

                                 A Retrospective Study


       This study was undertaken to learn:

             O     in what ways and for what reasons a specific industry in the past
                    already was implementing pollution prevention in order to comply with
                    existing effluent guidelines; and

             O     to what degree the effluent guideline development document for that
                    industry had already previously projected that outcome.

The industry selected for this study was the leather tanning industry.  The leather tanning
effluent guidelines were promulgated in 1982.  This study looks at the steps taken in the past
to comply with those guidelines. Because of the confidentiality of the data obtained in this
study, this report will describe and present the findings in a general way that will not
compromise confidentiality.

       It is important to note that this study  is intended to serve as a case study within the
leather tanning  industry and  not as a study of the leather tanning industry as a whole.
       1.     Process changes and material substitutions were as important hi meeting the
             guideline requirements as end-of-pipe treatment.

             For example, in meeting chromium limitations a major step taken was to
             modify the chrome tanning process to get more of the chrome into the tanned
             leather and leave less of it in the tanning wastewater.  This was done through
             using different and more expensive chromium formulations as well as higher
             temperature, longer times, and less water in tanning baths.  Through these
             measures, the amount of chromium fixation was increased from about 50% to
             about 90%.

             As another example, carbon dioxide was being used on a pilot basis as a
             substitute for ammonium sulfate in the deliming process.  This was considered
             primarily as a cost reduction measure.  But, if the change to carbon dioxide is
             successful, it will substantially reduce discharge of ammonia and biochemical
             oxygen demand (BOD).


       As a third example, a technique was adopted whereby different agents were
       substituted for some of the sodium hydrosulfide used in the unhairing
       operation. This reduced marginally the amount of sulfide in the wastewater.

2.     Recycling was done to meet effluent guideline requirements.  Several waste
       streams were segregated so that portions of each could be recycled.

       For example, there was recycling of some of the spent chrome tanning liquor.
       It was collected, screened, and filtered, then recirculated back to provide acidity
       and some initial chromium hi the pickling process.

       As another example, there was recycling of the spent unhairing liquor.  After
       being screened, settled, and skimmed for removal of solids and grease, about
       20% of the spent liquor is then withdrawn from the middle of the settling tank
       and recirculated back to the unhairing process.  This reduced by somewhat less
       than about 20% the amount of sulfide and other compounds needed for

3.     Measures were adopted to reduce water use by about 50%.  These measures

                     adoption of "closed-door" batch washing of skins rather than
                     constant flow washing;

                     changing the drums used for unhairing and tanning from
                     manually operated to automated;

                     recycling some of the wastewater from the final treatment plant
                     to various points in the production process;

                     recovery of waters from pasting and vacuum drying for reuse;

                     recycling of cooling water used in refrigeration and air

4.     Pollution prevention was adopted and implemented primarily because of the
       effluent limitation requirements, even though there were  other benefits as well
       such as improved product quality, improved process efficiency, and reduced
       costs of water supply, wastewater treatment, and sludge disposal.

5.     The effluent guideline development document was generally quite accurate in
       its projections. However, two major pollution prevention measures that were
       implemented (the first two in 1. above) were not referenced in the development

       1.      The industry was implementing pollution prevention in the past to meet the
              effluent guideline requirements.

       2.      The effluent guidelines were the driving force behind the implementation of
              pollution prevention, even if not the only reason.

       3.      The effluent guideline development document projections, while quite accurate
              generally hi the areas of end-of-pipe technologies, did not forecast all the
              aspects of the pollution prevention creativity that was exercised by the industry.