Study on anti-scaling of landfill leachate treated by evaporation method

Abstract

In the mechanical vapor recompression (MVR) treatment of landfill leachate, scaling in the evaporator and heat exchanger poses a serious problem. This study explored the reasons for such scaling and proposed acid or ion-exchange pre-treatments to reduce the alkalinity of the landfill leachate nanofiltration concentrate (LLNC) to prevent scaling. The feasibility of these two methods was evaluated and the technical and economic parameters for application were obtained via experiments. A large amount of HCO3- in the LLNC was the main cause of scaling. The acid addition experiment and field application demonstrated that this method could prevent fouling problems. The cost of acid addition was USD 0.18/t. LLNC pre-treatment by ion-exchange showed that a weakly acidic cation-exchange resin performed better than a strongly acidic cation-exchange resin did. The amount of solid residue under an alkalinity of 0 mg/L could be decreased by 92.9% compared with that of raw LLNC during evaporation. Both methods could alleviate scaling and enable the wide application of the MVR evaporation process in landfill leachate treatment. Highlights The key cause for fouling of MVR is the presence of a mass of bicarbonate in the LLNC.; After treatment, the residual solids generated during evaporation will reduce by 92.9%.; Hydrochloric acid pre-treatment is a cost-effective way to prevent scale.; Weak acid ion-exchange pre-treatment can prevent scale without introducing other ions.;

Keywords

• acid pre-treatment
• anti-scaling
• ion-exchange pre-treatment
• landfill leachate
• mvr evaporation process
• nanofiltration concentrate