Solvent extraction of wastewater - 2
Let's seek ways around the restraints for solvent extraction of wastewaters. We need an organic solvent that is so inexpensive that there is no need to use heat for its recovery. There just happens to be something that should work. The grease and fats that get into sewers are removed in the initial sedimentation step. They form a scum that is skimmed off at the top. This is very gunky stuff with little value; often it is burned. If recycled as a solvent for extraction, losses to the spent aqueous phase would not matter. These would be about the same as present losses, and the steps for biological waste treatment would handle this tiny load easily.
This awful stuff skimmed from the sewer water is not likely to be suitable for solvent extraction without some clean up. The initial step should be filtration to rid of dirt. There has been some microbial degredation of the fats and some hydrolysis by lipases excreted by microorganisms. Fatty acids must be present, and they probably lower distribution coefficients for highly non-polar target compounds such as pesticide residues. In any event, fatty acids will promote the formation of emulsions. They can be removed by extraction with water at high pH. The remaining organic phase should be mostly fats that would be excellent solvents. The process summary is :
while on sabbatical leave, ESB, Porto, Portugal July 1996