Final Report: Electrochemical Treatment of Textile Effluents with Simultaneous Recovery of Toxic MetalsEPA Contract Number: 68D98114
Title: Electrochemical Treatment of Textile Effluents with Simultaneous Recovery of Toxic Metals
Project Period: September 1, 1998 through March 1, 1999
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (1998) RFA Text | Recipients Lists
Research Category: Water and Watersheds , SBIR - Water and Wastewater , Small Business Innovation Research (SBIR)
Summary/Accomplishments (Outputs/Outcomes):Currently, the textile dyeing industry is under considerable pressure to reduce the color of process waters directly discharged to municipal water treatment facilities. While the color issue has received considerable attention, more recently heavy metals (copper and chromium in particular) found in some dyes, and the toxicity of organics formed by the degradation of dyes and dye auxiliaries are being considered within the framework of pretreatment regulations. Furthermore, the Environmental Protection Agency (EPA) is attempting to reduce the hazards associated with waste sludges disposed of in landfill sites through the requirements of the Toxicity Characteristics Leachate Procedure (TCLP). Metals such as chromium and selected organics, including some acknowledged dye breakdown products, e.g., aromatic amines, are the focus of concern. Additionally, under federal mandate, states are establishing stream water quality standards which will tighten National Pollution Discharge Elimination System (NPDES) permits.
In this Phase I effort, two approaches were investigated to treat textile effluents. The electrochemical treatment by anodic oxidation using anodes with catalytic coatings effectively oxidized the dye wastes. However, three industrial effluents tested generated chlorine gas during anodic oxidation making the process, limited in it?s applicability due to the possibility of forming chlorinated byproducts. Cathodic treatment using electrochemically assisted Fenton?s reagent also effectively oxidized the dye solutions. However, this method required initial pH adjustment to between 2 and 4, before the electrochemical step, making the process unattractive.
The other method tested using ion-exchanged zeolites together with hydrogen peroxide, was a very attractive process. Several synthetic zeolites and a natural zeolite were ion-exchanged with different cations, e.g., Fe(II), Fe(III), Cu(II), Zn(II), Mn(II) and Ni(II). Out of the synthetic zeolites, Fe(II) exchanged ZSM-5 was superior. Clinoptilolite, a natural zeolite, ion-exchanged with Fe(II) was found to be even more effective than Fe(II)-exchanged ZSM-5. Since the catalytic Fe(II) sites are bound to the zeolite structure, no sludges are formed and the cations released to the solution during organometallic dye degradation were found to absorbed by the zeolites. Thus, toxic metals like copper or cobalt released during dye degradation can be easily recovered using this process. Similarly, the process is amenable to scale-up as packed columns of Fe(II)-exchanged zeolites can be used for waste oxidation. Similarly, the toxic metals ion-exchanged onto zeolites can be easily leached out using dilute acids. In addition, it was also found that spent zeolite columns loaded with organic dyes can be regenerated by using 30% hydrogen peroxide solutions. This allows the effective regeneration of the columns.
The hydrogen peroxide decays to oxygen and water, so the entire system is environmentally friendly. Zeolites are non-toxic aluminosilicates and pose no disposal problems. Natural zeolites and the chemicals required (hydrogen peroxide and ferrous sulfate) are inexpensive making the process economical. All these advantages makes this advanced non-photoassisted catalytic oxidation process using Fe(II)-exchanged natural zeolites, a very attractive process for a variety of applications in environmental remediation. The feasibility of this process has been amply demonstrated to recommend further studies under a possible follow-on Phase II project.