Enhancing hexavalent chromium removal from textile effluent with low-cost adsorbent: simulation and a techno-economic study

Abstract

This paper simulated hexavalent chromium (Cr(VI)) adsorption using cocoa pod husk biosorbent in a fixed bed column using Aspen Adsorption. This study was designed to show the effectiveness of computational methods in designing, optimising and evaluating the scaled-up adsorption process using low-cost adsorbents. To the best of our knowledge, the economic analysis of Cr(VI) removal using biosorbent adsorption columns with the assistance of Aspen Adsorption and response-surface methodology (RSM) has not been performed previously. Design Expert and RSM were used to optimise and describe the effect of flow rate and initial concentration on breakthrough and saturation times. The breakthrough time was improved by a higher bed height (2.0 m), a wider diameter (2.0 m), and lowering the flow rate (0.010 L/s). The initial concentration had no effect (1.00 mol/L). The predicted breakthrough and saturation time were 29,360 s and 313,351 s, respectively. Two scenarios were economically compared over 20 years. Scenario 1 (1-day breakthrough time) costs $746,585 and Scenario 2 (4-week breakthrough time) costs $1,538,319. This is because Scenario 2 used a taller, wider column which required a greater amount of adsorbent, and 387,873 m³ of water were processed, respectively. Processed water was dependent on the flow rate and breakthrough time. It was concluded that cocoa pod husk could be an efficient adsorbent and the adsorption process can be successfully simulated and optimised. The use of alternative low-cost adsorbents should be encouraged. The economic study showed that simulation and RSM data could successfully be used for economic analysis.

Graphical abstract