Bolivian tanning industries are an important part of a productive Chain which has been considered as a priority by the Bolivian System of Productivity and Competitiveness, because of its important role in the manufacturing sector and its great export potential. It constitutes a traditional industry, intensive in consumption of fresh water and chemicals, which generates negative environmental impacts that are subject to increasingly controlled strict regulations. For this reason, the established firms have committed themselves to gradual adjustments within a scope of severe financial and technological constraints.

One of the principal problems faced by tanning industries is the emission of wastewater contaminated with chrome and neutral salts. Chrome is the most widely used tanning chemical of which significant quantities are wasted in conventional processes (20 – 40 %). Although this versatile heavy metal plays an important role in metabolic processes occurring in animals and plants in low concentrations, its oxidized derivatives (Cr6+) are extremely toxic. On the other hand, residual tanning liquors also contain very large concentrations of sodium chloride, which provides excess salinity to soils, lowering crops growth.

In order to reduce total loadings of these chemicals to environment, the ecologically sustainable industrial development approach has been adopted, through the utilization of Cleaner Production techniques. Among these, direct recycling of pickling-tanning liquors has been chosen to be studied as the most appropriate to present conditions and financial possibilities of a small tannery of Cochabamba. This approach is successfully applied in America and Australia since 1970’s. Nevertheless, its use in local and national industries is quite incipient, because of several reasons, one of which is the need of a close control of concentrations of chemicals in waste liquors that require rapid, exact and precise measurements that are not manageable by the numerous small tanneries located in Bolivia. The present work also addresses this problem.

Experimental work consisting in the analytical determination of composition of spent liquors has been done applying direct recycling up to ten cycles, both at laboratory and factory levels, achieving wet-blue and finished leathers of comparable quality to those produced by the conventional tannery process. No build-up or depletion of important components was observed. These results confirm the technical feasibility of this Cleaner Production technique.

Three essential indicators were defined for process control: pH level, ionic strength/specific gravity and chrome depletion. A very simple, practical and liable measuring technique has been developed for the quantification and reposition of the chrome absorbed between consecutive cycles. This non-destructive colorimetric method was based on the validation of another spectrophotometric one, also developed during this study, which uses the same tanning liquors utilized in the factory as standards.

A simple design was carried out for sedimentation of suspended solids contained in recycling liquors and for the chemical precipitation of chrome in excess liquors.

The approach is economically feasible, where small investments for the construction of necessary equipment are recovered, through savings in water and chemicals consumption, in less than four months.

Analysis of environmental impact made for pickling-tanning steps shows that applying direct recycling of pickling-tanning chrome liquors will allow the company to pass from Category II, where it is compulsory to adopt mitigation measures, to Category III, where only an appropriate control of the process is mandatory.

Report-CIPI-1: MINIMIZACIÓN DE RESÍDUOS DE CROMO MEDIANTE LA APLICACIÓN DE UNA TÉCNICA DE RECICLADO DIRECTO EN LA EMPRESA “CURTIEMBRE VALENZUELA”.