A process is described for treating a by-product stream, resulting from the commercial manufacture of methylchlorosilanes, to remove residual silanes wherein the residual silanes comprise low-boiling hydrosilanes. The process comprises a first step where the by-product stream is contacted with hydrogen chloride in the presence of a chlorination catalyst to convert the low-boiling hydrosilanes to chlorosilanes. In a second step, the modified by-product stream comprising the chlorosilanes is contacted with activated carbon which adsorbs higher-boiling silanes including chlorosilanes, thereby forming a final by-product stream reduced in lower-boiling hydrosilanes and in total silanes. The present process is especially useful for removing silanes from by-product streams intended for incineration, thus reducing silica during combustion of the by-product stream in the incinerator.