Bioreactor Characteristics Simple, open Complex, sealed Cost Operation cost is high Investment cost is high Gas circulation Scale-up

Oxygen supply and heat removal Hard

Oxygen supply Easy

Product Concentration High Low Yield High Low Wastewater Seldom Large Extraction Complicated Easy

3. Aeration is much easier and the aeration efciency is higher in SSF, which is benecial for those fermentation processes demanding high levels of oxygen (Nagao et al. 2003).

4. Diversity in products, especially for anaerobic mixed SSF (Sindhu et al. 2006). 5. Lower demand on sterility due to the low water activity used in SSF (Hölker et al. 2004). 6. Less water is needed in SSF.