Two-Stage Chemical Absorption–Biological Reduction System for NO Removal: System Start-up and Optimal Operation Mode

A novel chemical absorption-biological reduction (CABR) integrated process, employing Fe(II)EDTA as an enhanced absorbent, is a promising technology for nitrogen oxides removal. In this work, we developed a new two-stage CABR system applying a mixed cultivation model of denitrifying bacteria and iron-reducing bacteria, which consists of a sieve-plate tower and a bioreduction tower to separate the absorption and reduction processes. The start-up period of the two-stage system was shortened to 19 days, while that of the one-stage CABR system was 46 days. In addition, the two-stage CABR system featured a better oxygen-resistance ability and a higher NO removal loading. In effort to optimize system operation, we compared different modes of system operation and found that (1) continuous addition of glucose was better than the batch type addition and that (2) the NO removal efficiency could be maintained at >90% while the FeEDTA concentration was higher than 4 mmol/L; however, reducing the initial concentration of ferric iron complex could inhibit the loss rate of Na(2)EDTA. Furthermore, the optimized operating mode parameters were 4 mmol/L initial Fe(III)EDTA, 0.6 mg/min NaEDTA, and 5 mg/min glucose with a 2 L/min gas flow rate under a 400 ppm of NO condition, while the NO removal efficiency was kept >90%; the corresponding operating cost in terms of glucose was 8.4 g of glucose/g of NO. The purpose of this work was to provide preliminary data to support future industrial application for NOx removal, as well as sufficient technological insights on the process configuration and reactor operation of the two-stage CABR system.