biomass liquid stream during the pretreatment step other organic compounds are usually formed or extracted from the biomass these compounds usually derive from the cellulose or from the hemicellulose or from the lignin portions in some cases other organic compounds are present in the pretreated biomass stream due to organic compounds like starch or extractives in the inlet biomass feedstock to the pretreated process these organic compounds such as furfural formic acid and acetic acid or at least a portion of them can be separated and collected in the pretreated biomass liquid stream the process described below has been able to remove one or more organic compounds of interest like the acetic acid from the pretreated liquid biomass stream one pre treated stream of interest is the liquid stream obtained by water soaking the ligno cellulosic biomass stream and removing the liquid this stream will comprise water some solids acetic acid and water soluble c5 39 s as described above the pre treated liquid ligno cellulosic biomass stream comprising water solids acetic acid and c5 39 s first undergoes a solids separation step while any solid separation step is believed to work it must be efficient enough to remove the solids that would otherwise destroy the membrane filtration process downstream the preferred separation was done by centrifugation after centrifugation the liquid stream is nano filtered the centrifugation was done on an alfa laval model lab102b with an operating velocity of 8800.