Anaerobic digestion of high sulphate cane juice stillage in a tower fermenter

Summary

The use of a continuous tower fermenter for the anaerobic digestion of cane juice stillage, with chemical flocculant addition to accumulate biomass, is reported. While stable and efficient treatment was achieved at relatively high loading rates (>5kg COD m⁻³ day⁻¹) an operational limit was reached which restricted the maximum loading rate attainable. This was due to the composition of the cane juice stillage (predominantly high sulphate levels). Following nutrient assessment, continuous iron addition improved digester performance substantially. However, in the long term, this solution was not commercially practical due to excessive FeS precipitation which increased flocculant requirement. It is concluded that significant improvements in the loading rates achievable in this system would likely result from the digestion of (normal) low sulphur stillage.