Membrane distillation for algal supernatant reuse from hydrothermal carbonization aqueous product

ABSTRACT With growing demand for more sustainable dairy manure management methods, a system involving hydrothermal carbonization (HTC), membrane distillation (MD), and algae cultivation for resource recovery from dairy manure was partially investigated in this study. Two algal species, Arthrospira maxima and Chlamydomonas reinhardtii, were cultivated on the hydrothermal aqueous product (HAP) of dairy manure, but the former requires a carbonate buffer for successful cultivation. The spent HAP after algae cultivation was treated using MD where the operational efficacy and distillate quality were assessed. Comparing the MD performance of the buffered HAP to the unbuffered HAP revealed the addition of the buffer decreased water flux and distillate quality, but cultivation with A. maxima reversed these effects and produced distillates with reduced COD, TN, and NH3 concentrations. C. reinhardtii cultivation resulted in increased distillate COD and NH3 concentrations compared to the unbuffered HAP. Fluorescence was used to broadly characterize the organic components of the feed and distillate streams. Regrowth experiments with A. maxima revealed the spent buffer can successfully be recycled, but fresh nutrients are required.