Oxidative pretreatment of wastewater with organic load from ultrafiltration applied to manufacture lactose-free milk

Abstract

The main process used in obtaining lactose-free milk is ultrafiltration, which results in lactose-free milk (retentate) on one side, and lactose with water and salts (permeate) on the other. This last by-product is not used as raw material, but constitutes an effluent that contributes to the total flow of wastewater. This has caused an increase in the chemical oxygen demand (COD) of the initial effluent, affecting the treatment stages of industrial effluents, with the biological treatment stage being the most affected, since the lactose converted into lactic acid decreases the pH of the system, this leads to the microorganisms not carrying out a good degradation. The following study focused on pretreatment of the lactose-laden wastewater that was the permeate of the ultrafiltration that manages to de-lactose the milk, specifically seeking to reduce organic contamination expressed as removal of COD. The methodology used in the research was applied, quantitative approach, experimental design; where the conventional Fenton advanced oxidation and ozonation processes were used, and the objective was to select that process that allows the removal of COD at values ​​below 3,000 mg/L, so that it can be passed to the production plant activated sludge that already exists and can be supported by the microorganisms at these BOD levels. The results obtained for both tests carried out in the TECSUP No. 1 laboratories, applying the Fenton advanced oxidation method, resulted in the maximum removal of 64 % for Fenton and 39 % for ozonation, but this was not enough due to the great stability of the disaccharide at low doses and complete oxidation at high doses forming soluble intermediate products that are difficult to remove in the subsequent coagulation and flocculation process. Furthermore, the time necessary to oxidize lactose, to insoluble intermediate products, is 30 minutes with the dose of 1196 mg/L of H2O2, 2000 mg/L of FeSO4 and at pH equal to 3. This test successfully reduced much of the organic matter, down to 7,280 mg/L COD, but the target removal of reducing COD to 3,000 mg/L was not achieved. However, the reduction obtained could be mixed with a certain flow of already treated water circulating back into the reactor, allowing the biological treatment to proceed. This latter step would be a study conducted by the dairy company.