INTERNATIONAL CLEANER PRODUCTION INFORMATION CLEARINGHOUSE

CASE STUDY #25 1. Headline: Zero wastewater emission in the wiredrawing process 2. Background: The wiredrawing process includes the following steps: - pickling treatment by dipping in hot aqueous solution of sulfuric acid - pre-phosphatizing and phosphatizing treatments by dipping in phosphoric acid solutions containing NO3 and NO2 salts and heavy metals (Fe, Zn) - wiredrawing and annealing treatments Waste rinse waters contaminated with sulphate and nitrate salts account for the largest amount of pollution resulting from the wiredrawing process. The first effort made by the company to reduce the environmental impact was the installation of a chemical precipitation plant. Since the early 1980s, full water reuse has been introduced, which enables a partial drag-out recovery; ferrous sulphate from spent pickling solutions is recovered as a chemical coagulation agent in biological treatment plants. The present process management solves the problem of wastewater pollution. but some critical aspects still remain: - a considerable loss of chemicals - and consequently a significant amount of sludge - has to be disposed of as hazardous waste - high energy consumption due to the heating system of the pickling baths (steam in open circuit) - an increase in salinity of recycled rinsing water due to accumulation of sulfates and nitrates, which results in difficult control of the rinsing quality. Company: Trafilerie S. Paolo Idropan-Dell'Orto 3. Cleaner Production Principle: Process modification 4. Description of Cleaner Production Application: The previous heating system was substituted with a closed- loop heat exchange. The main objective of this modification was to reduce the amount of water injected into the pickling baths as steam; as a result, the evaporation rate in the pickling solutions has been greatly improved, enabling the introduction of a counter- current rinsing system. Enabling technology: - Introduction of a closed-cycle heating system. - The introduction of multiple cascade rinsing after both pickling and phosphatizing treatments. In both processes, final rinses are carried out by recirculating water regenerated through ion exchange and reverse osmosis, respectively. 5. Economics: Cost savings Lit/year (millions) Raw material 182 Energy and water 12 Sludge disposal 82 Treatment plant maintenance 50 Labor 20 Others 10 TOTAL 356 Capital investment 318 Payback period 11 months 6. Advantages: - A 95 per cent reduction of sludge produced by the treatment plant and 90 per cent reduction in chemical consumption due to the almost complete recovery of the dragout. - Savings in consumption of water (10%) and energy (3%). - Savings in labor costs due to improved automation of the production and water treatment operations. 7. Constraints: N/A 8. Contacts:Mr Tiberio Roda Trafilerie S. Paolo Via C.F. Borromeo 22030 Arcellasco d'Erba (co) Italy Tel: +39 31 610 767 Fax: +39 31 641 887 Equipment supplier Mr Tullio Dell'Orto Idropan-Dell'Orto Via Valassina, 19 20161 Milano Italy Tel: +39 2 6680 0267 Fax: +39 2 6680 0754 9. Keywords:Italy, metal, metal finishing, process modification, heat treatment, ion exchange, reverse osmosis, raw material saving, wiredrawing 10. Reviewer comments: This case study was originally published in the UNEP IE document "Cleaner Production Worldwide", Volume II. In the process of preparing the document the case study underwent a technical review.