Membrane treatment options for wastewater from cellulosic ethanol biorefineries

摘要

Ethanol production from cellulose is technically feasible. However, treatment of the resultant wastewater can account for 20-33% of the total process cost and thus potentially hold back commercialisation. Wastewater from dilute acid processes has high levels of organic material, colour, sulphate and ammonium. Two approaches were considered to reduce treatment costs by selectively separating the ammonium and sulphate from the remaining organics in the wastewater. Using ultrafiltration, ammonium and sulphate retentions (68 and 57%, respectively) were similar to COD retention (67%). The second approach used was electrodialysis. This proved far more selective and was able to regenerate solutions of sulphuric acid and ammonium hydroxide with little evidence of sugar, COD or colour migrating across the ion-exchange membranes. These preliminary results thus confirm previous findings that sulphuric acid can be recovered from aqueous streams containing high concentrations of sugars with little sugar loss-resulting in a saving in the amount of ammonia required for neutralisation and indeed for the overall process.