Economic aspects of landfill leachate treatment using reverse osmosis membranes

Introduction. Landfill leachates contain highly concentrated organic products of waste degradation and mineral salts. Concentrations of organic matter demonstrate high COD values up to 5,000 mg/l, concentrations of ammonium ions reach 2,500 mg/l, while the total salt content may reach 15,000 mg/l. Two to three reverse osmosis treatment stages may be nee­ded to produce the water that meets effective regulations governing the composition of water discharged into the environment. Also, high salt content and COD values dramatically reduce the membrane capacity. The co-authors explored the use of nanofiltration membranes at the first stage of the leachate treatment in an effort to reduce membrane operation costs. Materials and methods. The experiments, conducted within the framework of this research undertaking, allowed to identify a change in the concentrations of contaminants, dissolved in the leachates of reverse osmosis and nanofiltration membranes, as well as the reduced capacity of membranes at each stage of treatment. The co-authors have studied the alternative methods that may ensure maximal reduction of the concentrate consumption in the process of leachate treatment. Principal dependencies, derived as a result of the research, enabled the co-authors to identify the concentrate consumption rates depending on the extent of treatment focused on ammonium ions. The co-authors describe the methodology employed to identify the area of membranes at each treatment stage depending on the leachate composition. Results. Calculations of operating costs are provided for three compositions of leachates, typical for the Moscow region, depending on the treatment methodology and further recovery of membrane concentrates. Conclusions. Nanofiltration membranes can be used at the first stage of the landfill leachate treatment in the case of high COD and salt content. The application of nanofiltration membranes allows to reduce the concentrate consumption rate and cut operating costs. A new technology is developed to split the concentrate into two flows: the flow that has a high organic matter content, and the flow that has a high content of mineral salts, sodium and ammonium chlorides in order to facilitate the recovery of the concentrate.