Adsorbent treatment process, drawbacks

There are basically two options in the purification, that is, the water washing process and adsorbent treatment process (water-free process). In the water washing process the main drawbacks are the amount of wastewater produced and the energy costs to evaporate and recover water for re-use. In the adsorbent treatment process the problems are the high cost of adsorbent (e.g., Mg-silicate) and the disposal of the spent adsorbents. A potential cleaner process should thus eliminate the catalyst cleanup step and simplify biodiesel and glycerol purification. The options are (i) the use of heterogeneous solid catalysts, (ii) the use of an enzymatic transesterification processes and (iii) a catalyst-free process, using, for example, supercritical methanol. 

After treatment has proceeded for a period of time, either the coating reaches its maximum capacity to remove metals or the filter requires backwashing. At this time, the column can be backwashed to recover particulate metals from the column, and an acidic solution can be used to recover the adsorbed metals, thereby regenerating the column. Because the ferrihydrite is trapped on the sand particles, only the contaminant metals and nonferrihydrite are released. Thus the need to dispose of large amounts of iron oxide with the metal sludge, one of the main drawbacks of a conventional treatment process, is eliminated. 

Each has advantages and drawbacks. However, at the present time, there is no single adsorbent capable of satisfying the above reqniranents. Thns, there is a need for new systems to be developed. In addition, the adsorption process provides an attractive alternative treatment, especially if the adsorbent is selective and effective for removal of anionic, cationic, and nonionic dyes. 

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