Simultaneous Eco-friendly Bleaching and Retting Wastewater Treatment of Hemp Fiber with Ozone Application

The main aim of this study was to reduce the biological load in the retting effluents by eliminating the microorganism and at the same time, to bleach hemp fibers in the retting liquor, with ozone treatment. In addition to prevention of the environmental pollution, time, energy, water and chemical consumption decrease were targeted by the ozone bleaching of hemp fiber in the retting liquor. For this purpose, retting liquor was treated with ozone gas in different concentrations (5–25 g/h) and durations (5–90 min) while hemp stems were still in it. The environmental impact was investigated by TOC (Total Organic Carbon), BOD (Biochemical Oxygen Demand) and COD (Chemical Oxygen Demand) measurements. Ozone application resulted in dramatic reductions on BOD and TOC values. Total bacteria count in the untreated retting liquor and ozone-treated samples was determined, up to 100% sanitation effect was achieved by ozone application. Whiteness degrees of the hemp fibers increased up to 72% with ozone application compared with the retted sample. The chemical compositions of the fibers were stated by chemical tests and oxidative damage related to ozone treatment was investigated. The lignin ratio was significantly reduced after ozone application. The results of the chemical tests were supported by FTIR measurements. The mechanical properties such as tenacity and elongation were analyzed with tensile tests. The crystallographic characteristics were investigated with XRD, the crystallinity index was increased with ozone treatment.