Textile sludge disposal using incineration technique

Abstract

The rapid growth of textile industry in Bangladesh plays an important role in economic development as well as employment generation. The sludge from the wastewater treatment plant in textile units is considered hazardous as it is often contaminated with heavy metals of dyestuffs and chemicals. Currently, land filling is the most common practice for textile sludge disposal. Leaching of heavy metals from textile sludge is a growing concern in Bangladesh. This study attempts to find out an environment-friendly solution for the management of the textile sludge. The present study focuses on the characterization, thermal treatment of textile sludge and the possibility of making value added products from the ash obtained from the incinerated sludge. In this study, sludge samples were collected from treatment plants of various textile units located at Savar, Gazipur, Tejgaon and Norsingdi. Sludge samples were oven dried for 24 hours at 1050C and the dried sludge samples were analyzed for various physical properties including pH, Acidity, Alkalinity, Sulfate, Nitrate, Chlorides etc and the heavy metals like Chromium, Cadmium, Lead, Mercury, Arsenic, Nickel, and Zinc. Characteristics of the textile sludge vary from industry to industry due to the involvement of different processes. The Toxicity Characteristics Leaching Procedure test (USEPA method 1311) was performed for the raw sludge for analyzing the long term leaching potential of heavy metals. An electric incinerator was designed, fabricated and installed for the incineration of textile sludge. The sludge samples were incinerated at 5000C, 7000C and finally at 8000C for different time intervals. The volume reduction of the sludge samples was nearly 80% at 8000 The pH of the raw sludge varied from 6.1 to 8.3, chloride concentrations 82.8-309.8 mg/kg, sulfate concentration 3276 to 6218 mg/kg and nitrate 133-300 mg/kg. The TCLP leachate from the raw sludge showed significant concentrations of Cr, Pb, Cd, Ni, Zn. Chromium 0.2-1.7mg/l, Lead 0.02-2mg/l, Cadmium 0.01-0.177 mg/l, Nickel 4-0.5 mg/l and Zinc 11-3.2 mg/l. Except for Nickel, leachate concentrations are higher C. The incineration techniques were used for volume reduction and destruction of the hazardous elements. The oven dried samples were powdered and mixed at various proportions (0%, 10%, 20%, and 30%) with clay for making the ceramic products and also mixed with sand, cement and aggregates for making blocks for the stabilization of heavy metals in sludge. The properties of ceramic products such as percent water absorption, firing shrinkage, bulk density, loss on ignition and the compressive strengths were evaluated. Incinerated ash samples were also used for ceramic tiles and block preparations. The characteristics of the sludge ash samples were analyzed using Atomic Absorption Spectroscopy and X-RD. Micro structural examinations of the solidified samples were also performed using Scanning Electron Microscopy (SEM). The heavy metal concentration of the leachate of the ceramics and blocks were analyzed using the Toxicity Characteristics Leaching Procedure (TCLP) test. than the LDR limit. But heavy metal concentrations in leachate from the Sludge Ash samples were lower than the LDR limit. The concentrations of heavy metal in leachate from the stabilized sludge samples were very low. The compressive strength, bulk density, water absorption of the stabilized sludge and ash samples were examined and the results showed that up to 10% of the raw sludge and 10-20% ash samples could be used for stabilization and/or solidification and additionally, 80% volume reduction of the raw sludge could be obtained.