Avaliação do emprego de processos de separação por membranas em uma central de tratamento de efluentes galvânicos

Abstract

The galvanotechnical industry is responsible for generating effluents containing heavy metals and recalcitrant substances. The restrictions on the quality of effluent discharge have intensified. An alternative to this problem are membrane separation processes, such as reverse osmosis. The present study had the objective of analyzing two strategies to improve the performance of a galvanic treatment center, composed of its current stages of treatment as: physico-chemical treatment, advanced oxidation, simple filtration and ion exchange. Then, it was studied the possibility of insertion of the reverse osmosis in the existing process (strategy 1) or the replacement of the ion exchanger by the reverse osmosis membrane (strategy 2). For this purpose, a polyamide membrane with a selective polysulfone layer was used, where the efficiency of the proposed strategies was observed for the environmental parameter. Using strategy 1, the results were observed above 92% of total nickel, 90% of total copper, 81% of zinc, 93% of total phosphorus, 87% of chemical oxygen demand (COD), 87% of ammonia nitrogen and 100% of total suspended s’olids. The Hermia methodology and the membrane resistance, using the galvanic effluent, were also analyzed by the blocking models. The results showed that the membrane presented 80% resistance per concentration for strategy 1 and 40% of fouling for strategy 2. In both strategies, the Hermia model presented a higher index for irreversible and standard block. For strategy 1, the process occurred over 180 minutes and a permeate flux reduction of 63% was observed. After the chemical cleaning, a recovery flow superior to 93% was observed, and 7% that could not be recovered correspond to irreversible fouling. For strategy 2, the process occurred over 90 minutes with a 94% of flow reduction. After cleaning, a flow recovery of 71% was observed, also showing the presence of irreversible fouling. The Rosa 9.1 DOW software showed that for a demand of 10m³ / h it would take 3 reverse osmosis modules with 24 membranes, filtration area of 891,84 m², working pressure of 6 bar pressure and a pump power of 3.48 kWh. The mentioned software detected problems of CaSO4, due to the effluent characteristics to increase the useful life of the membranes. This would imply a slowing system before being subjected to reverse osmosis. The simplified economic evaluation compared to the current treatment model and the insertion of a new technology, would entail the installation of a moving equipment that would triple the current costs of the effluent treatment plant. Considering that the release standards are at the limit of the legislation, the new equipment would treat security in compliance the legislation without being in the eminence of notices before the environmental agency. Even with strategy 2 meeting the launching standards and allowing the substitution of a process, strategy 1 has been shown to be more effective, since it presents lower final concentrations, resulting operating bigger life of the membrane, with lower stops for chemical clean-ups and operating costs.