Waste-water purification through a countercurrent system driven by supercritical carbon dioxide (SC-CO₂). Part I: Experimental investigation and process evaluation

Wastewater purification has been considered to be a major cost not only for industries but also for society as a whole. Current technologies in the market are both costly and time consuming. This study proposed a supercritical CO₂ (SCCO₂)-driven countercurrent system for separating the emulsified oil from water (Case 1) and reducing the chemical oxygen demand (COD) from electroplating wastewater (Case 2). The effects of the operating parameters, including temperature, pressure and residence time/CO₂ flow rate/CO₂-to-feed ratio, were discussed. In addition, a design for recycling CO₂ was developed for the purpose of saving CO₂ costs. Taking commercialization into consideration, the process was scaled-up to 250 tonnes/day, and the recommended processing fee was $1.12/tonne for a payback period of 1.29 year, based on the process simulation and techno-economic analysis (TEA). Compared to the current process, this technology has advantages including that it is low cost, efficient, and most importantly, environmentally friendly.