The Influence of Cyclohexanone/Cyclohexanol on the Growth and Nitrogen Removal of Arthrospira platensis and the Cyclohexanone/Cyclohexanol Biotransformation

Arthrospira platensis is a candidate for removing nitrogen from caprolactam wastewater, but the concentrated cyclohexanone (CHN) and cyclohexanol (CHL) in the wastewater have an unknown effect on A. platensis growth. The aim of this study was to evaluate the feasibility of A. platensis for caprolactam wastewater treatment and obtain safe exposure concentrations of CHN and CHL. The biotransformation of CHN and CHL was investigated. Considering the changes of growth rate and pigment contents, the safe exposure concentrations of individual CHN and CHL were ≤ 800 and ≤ 400 mg L−1, respectively. For binary mixture, the safe exposure concentration was ≤ 200 + 100 mg L−1 CHN + CHL. Both chemicals induced decreased trichome length at all concentrations, but trichomes were large enough to be harvested efficiently by gravity filtration using filter membranes with a pore size of 25–40 μm under safe exposure. The nitrogen removal rate showed no difference in CHN and CHL treatment under safe exposure concentrations compared with the control, and the maximal nitrogen removal rate was 18.66 mg L−1 d−1. Besides, A. platensis catalyzed interconversion between CHN and CHL which preferred to convert CHN into CHL when chemicals coexisted. Results highlight the potential of A. platensis for the nitrogen removal from caprolactam wastewater when CHN and CHL were under the safe exposure concentrations.