Biological and oxidative treatment of cotton textile dye-bath effluents by fixed and fluidized bed reactors

A treatability study for highly polluted and recalcitrant azo reactive dye-baths from cotton textile dyeing processes was conducted by using fixed and up-flow fluidized bed type reactors packed with brown coal. Ozone oxidation was carried out to assess the combination of biological and chemical oxidation. COD removal efficiencies ranged from 70% to 93%, and up to 99% color removal was attained. At a COD loading rate of 25.5 × 10−6 gCOD/m2-d, COD removal was 85%. Breakthrough of the brown coal used occurred at total organic loading of 0.090 gCOD/g coal. Biodegradable and inert COD fractions of the remazol dye-bath were assessed by BOD28 and oxygen uptake rate (OUR) measurements. 50% of total COD was initially inert. The inert fraction was reduced by adsorption and ozone oxidation by 65% and 40%, respectively. Brown coal is an inexpensive material and the system has economical and operational advantages as compared to treatment options such as advanced oxidation processes (AOPs) using UV, O3, H2O2 or electrocoagulation.