Investigation of treatability and recycling of landfill leachate by electrodialysis process

Beside the treatment of wastewaters, it is very important to make use of treatment byproducts. Electrodialysis process could produce high quality waters. Simultaneously, it is very beneficial that the byproducts of the process, the concentrate which is considered the origin of problems for membrane processes, could be used. Thus, these processes need to be evaluated in detail as those with no byproducts.This study focuses on the treatment of three leachates of various ages (with differing characteristics) by electrodialysis process to evaluate the process performance. Before applying electrodialysis, a proper pretreatment method was applied to the leachates to prepare them for the electrodialysis process. Three leachates of various ages were then treated by the bipolar-membrane elecrodialysis process under different operational conditions to evaluate the process? deionization performance. Further, the use of anolite and catholide solutions were investigated based on their acidic/alkaline properties.In the study, an ultrafiltration unit was installed as a preliminary treatment unit to prevent fouling of electrodialysis membranes. The ultrafiltration unit was followed by a five-stage cationic exchanger to remove primarily divalent cations such as calcium and magnesium. Calcium removal efficiencies of preliminary treatment were 94.1%, 93.6%, and 88.2% for young, medium-aged, and old leachates, respectively. Magnesium removal efficiencies were 97.1%, 99.5%, and 88.7%, respectively.In the deionization process after the preliminary treatment, an optimization work was done on operational parameters such as membrane order and voltage. Best performances were obtained for young leachate for which four bioplar membranes were used at a voltage of 25 V. The conductivity of leaches after a runtime of 190 minutes were reduced from 22 mS.cm-1 to 2 mS.cm-1. For medium-aged leachate, the best performance was observed in the case of single membrane operated at a voltage of 25 V, with a reduction of leachate conductivity from 14.6 mS.cm-1 to 2 mS.cm-1. For this case, removal efficiencies of 96.15%, 92.8%, and 86.7% were obtained for NH4-N, TKN, and COD, respectively. The best treatment performance for old leachate was obtained in the case of four membranes operated at a voltage of 25 V, with a reduction in leachate conductivity at the end of 300 minutes from 26.4 mS.cm-1 to less than 2 mS.cm-1.Anolite and catholite solutions were continously monitored for pH. For young leachate, the hydrogen and hydroxide ion concentrations were measured as 0.024M and 0.042M, respectively. For medium-aged leachate, the concentrations rised up to 0.095M and 0.048M, respectively. Highest concentrations for old leachate were observed as 0.022M and 0.026M, respectively. All of these results were obtained for 1 L each of anolite and catholite solutions per 1 L of wastewater. Therefore, volumes of anolite and catholite solutions lower than that of wastewater were taken to concentrate the anolite and catholite solutions. At the end of concentration studies in which the volumes were reduced by a factor of four, hydrogen ion concentrations increased, by a factor of 3.8, from 0.019M to 0.076M, while hydroxide ion concentrations increased, by a factor of 3.98, from 0.023M to 0.0933M. It is evident that the concentrations of hydrogen and hydroxide ions may be increased to higher levels by reducing the volumes, through which more concentrated acidic and alkaline solutions may be obtained.This study shows that wastewaters of various characteristics can be treated by electrodialysis process with high removal efficiencies especially in the aspect of ionic pollutants. Besides, the byproducts of the process could be of great value since they can be obtained as concentrated acids and bases. In conclusion, both treatment and use of byproducts can be accomplished in a single process.