Permeable reaction barrier system for the treatment of textile wastewater using cobalt oxide

Abstract

Advanced oxidation processes (AOPs) have gained considerable interest in the wastewater treatment industry. Low selectivity to organic pollutants and the high oxidation potentials provided by the free radicals produced from these processes are the root of this interest. Hydroxyl radical based AOPs seemed to dominate the field but recently sulphate radical based AOPs started to become more popular due to their even higher oxidation potential. The textile industry is known to be a considerable contributor to wastewater production. Many pollutants in this wastewater are organic pollutants which are very persistent to the more traditional treatment processes such as biological treatment and membrane filtration. Numerous studies have shown the potential and success of catalytic AOPs for the degradation of organic pollutants in wastewater. One such process is the use of a cobalt oxide nano-catalyst in conjunction with a peroxymonosulfate (PMS) oxidizer (Co3O4/PMS). The shortcoming with nano-catalysts however are the difficulty of recovering the catalyst in a slurry system or the effective immobilization of the catalyst in a continuous system. To address the issue of nano-catalyst immobilization, two different methods were used in the study to effectively immobilize the catalyst in a substrate. The methods were compared by utilizing the permeable reaction barriers in a continuous flow reactor. A bench scale reactor of 2.4 L/hr was designed and used to study the effect of PMS, catalyst mass and flow rate on the degradation efficiency and to determine the residence time and catalyst per PRB cross-sectional area ratio. A scale up rationale was formulated based on a constant residence time and the catalyst mass per PRB cross-sectional area ratio. Two design correlations were developed to predict the size of the permeable barrier and the catalyst mass required for the scale up PRB system. These parameters were used to design a reactor 30 times that of the bench scale reactor. In both reactors the optimum degradation occurred within 2 minutes indicating the success for catalyst immobilization and the development of a continuous reactor utilizing the Co3O4/PMS advanced oxidation technology.