Treatment of Prehydrolysis Liquor from Pulp Mill using a Biological Route Followed by Reverse Osmosis

Chemical Engineering & Technology - 2005-09-29Rath RL, Bhattacharjee C, Goodwin SJ, Bhattacharya PK10.1002/ceat.200500249
A new method, comprised of a biological treatment followed by membrane separation, has been suggested for the treatment of spent prehydrolysis liquor (PHL) from a rayon grade pulp mill. First, the PHL was treated biologically using the torula utilis strain for the conversion of sugar into yeast. Reductions of 57 % in the amount of total reducing sugar (TRS) and about 46 % in COD were achieved in the biological treatment step. A "shifting order type" rate equation, where the order shifts from (m-n) at high concentrations to m at lower concentrations, was found to predict the total reducing sugar with high accuracy. An ultracentrifuge was used to separate out the yeast formed during the biological treatment. The clarified biologically treated liquor was subjected to reverse osmosis (RO) to remove all the remaining solutes. The permeate obtained was observed to be of disposable/reusable grade (negligible COD and less than 0.9 mg/L sugar). An attempt was made to predict the permeate flux during reverse osmosis (RO) using an osmotic pressure model. Modified osmotic pressure and concentration polarization models were utilized for the estimation of the osmotic pressure of different concentrations of the PHL's solute constituents. Three different concentration parameters (TRS, COD, and Brix) were chosen to estimate the osmotic pressures. The prediction of the permeate flux by the combination of these models was found to be in good agreement with experimental flux values.