Abstract
The effects of membrane pretreatment on the ozonation and ozone-biotreatment of the wastewater from the alkaline bleach plant of Kraft pulp mills were investigated. Membrane pretreatment involved using a ceramic membrane with nominal cutoff of 1,000 g/mol, that separated organics based on their molar mass and structure. The retentate stream, consisting of concentrated high molar mass organics, was treated in an ozonation bubble column contactor. Different parameters including chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total carbon (TC), pH, color, and ozone concentrations in the gas and liquid phases were monitored. The pretreatment process separated the low molar mass and more biodegradable constituents of the alkaline bleach plant wastewater. Hence, more effective removal of high molar mass and recalcitrant organics was achieved in the subsequent ozonation stage. Also, the biodegradability of the wastewater during the ozone oxidation increased significantly (by up to 200%) with the implementation of membrane pretreatment. The ozone demand and consumption for improving the quality of wastewater (i.e., BOD5 enhancement and TC, COD, and color removal) increased by up to about 10-fold compared to the control process involving standalone ozonation. Furthermore, membrane pretreatment reduced the consumption of ozone per unit COD removal from the alkaline effluent.
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