The selection of nanofiltration membrane characteristics to purify landfill leachate and reduce concentrate
Alexei Pervov1*, Vyacheslav Dzubenko2, Tatiana Shirkova1
1Moscow State University of Civil Engineering, 26, Yaroslavskoye Shosse, Moscow, Russia
2JSC RM Nanotech, 224d, Dobroselskaya str., Vladimir, Russia
*Corresponding author
https://doi.org/10.5004/po2024102
ABSRACT
State of the art of landfill leachate treatment using reverse osmosis is presented. When we prepared the review, we were surprised by the widespread use of seawater membranes, which is striking. This can be explained by high osmotic pressure values of leachate that requires high working pressures. A serious disadvantage of this approach is the use of reverse osmosis high pressure membranes which leads to losses of membrane permeability and necessity of the additional treatment of the concentrate. This approach is used in seawater desalination technologies to reduce concentrate and is known as "membrane brine concentration" (MEC) technology. Not only operational costs (such as energy and membrane replacement) are compared in the research. The value of operational costs is influenced by calcium carbonate precipitation rate, as well as fouling rates of other organic and inorganic deposits that create the hydraulic resistance increase of membrane channel. Results of investigation are presented that demonstrate that the formation of calcium carbonate is excluded when using nanofiltration membranes. The increase and growth of hydraulic resistance of membrane channel is easily avoided by the use of modified spacer that provides an increase of area of the live section of the stream and improves its hydrodynamic characteristics flow when suspended solids and organic fouling occur in the channel. This measure also improves the efficiency of hydraulic flushing procedures applied to destroy and remove fouling layers. Results of determination of scaling and organic fouling rates are presented and illustrated by the SEM photos of fouling layers and their spectral analysis performed after membrane element autopsies. Contrary the fears of experts, the main obstacle in membrane safe operation is attributed not to organic fouling and not to high COD values of feed water but to calcium carbonate “hidden” in the organic fouling layer and formed due to supersaturation conditions provided by high pressures and high membrane rejection of "seawater" membranes. Results of economical calculations are presented that demonstrate advantages of the new proposed technology based on the use of low rejection membranes to reduce concentrate flow as compared to conventional high pressure (“seawater”) membrane application.
Keywords: Reverse osmosis; Nanofiltration; Membrane rejection; Scaling; Organic fouling of membranes; Increase of hydraulic resistance of membrane channel; Membrane spacer; Improvement of membrane spacer
