Study On Volatile Pollutants During Textile Dyeing Sludge Drying

Sludge treatment is difficult for high water conten. Low water content results in sludge reduction. Nowadays, there are many practical dryer for drying sludge. However, many volatile pollutants release during sludge drying. So, environmental risk exists in sludge drying process and it is necessary to control the emission of pollutants from sludge and treat the tail gas during sludge drying.More and more textile dyeing sludge produces and this problem has constrained development of dyeing and printing enterprises. In this study, the textile dyeing fresh dewatered sludge from two dyeing and printing enterprises were selected to study the release characteristic of volatile pollutants during sludge drying under different drying condition, one in Guangzhou(No.1) and the other in Doguang(No.2). The conclusions were provided an important theoretical basis for controlling the emission of pollutants. Then, the drying technology would be applicated widely in sludge treatment and relieve the pressure of sludge treatment in dyeing and printing enterprises.The results showed that ammonia, hydrogen sulfide and BTEX (benzene, toluene, ethylbenzene and xylenes) were typical volatile pollutants during the textile dyeing fresh dewatered sludge drying. The main source of ammonia might be the ammonia in the sludge,the decomposition of ammonium bicarbonate and fatty acid ammonium salt and the hydrolysis on proteins. Hydrogen sulfide mainly came from the emission of hydrogen sulfide in the sludge and the decomposition of sulfur compounds. BTEX is the important raw material of dye, serosity and auxiliaries and these compounds might exist in the sludge during the wastewater treatment. Origin of sludge, drying temperature and drying time could influence the emission of the volatile pollutants during the sludge drying.During the sludge (No.1 and No.2) drying, the emission of ammonia, hydrogen sulfide and BTEX was much more than that in room temperature. With the temperature increasing or the sludge water conten decreasing, the emission of ammonia, hydrogen sulfide and BTEX increased accordingly. Under the same drying temperature, the emission of ammonia and hydrogen sulfide from No.2 sludge was much more than that from No.1 sludge within 3 hours, and the BTEX from No.2 sludge less than that from No.1 sludge within 3 hours. The emission characteristics of ammonia, hydrogen sulfide and BTEX were different. Ammonia released more easily than hydrogen sulfide and BTEX, but hydrogen sulfide and BTEX sharply increased when the drying temperature was more than 160 oC and the sludge water conten less than 30 %. Therefore, the emission of the volatile pollutants could be controlled by adjusting drying temperature and drying time.The condensate during the sludge drying (No.1 and No.2) showed neutral, which contributed to the condensate treatment. COD and NH3-N in the condensate increased as the drying temperature increased, especially the increase is the most significant between 140 oC and 160 oC, and it must be treated before being discharged.As a result of the conclusion in laboratory, a pilot-scale textile dyeing fresh dewatered sludge drying system was set up for drying the textile dyeing sludge (No.1). The system mainly contained a continuous plate dryer with multiple heat source, which contained the steam and the tail gas from the boiler. During the system operation, the water conten of the sludge after drying was 20 %~30 % and the concentration of sulfur dioxide in tail gas reduced during sludge drying. The other pollutants in exhaust after treatment and the indoor odor could meet national environmental legislations.